STRUCTURE magazine | April 2016

April 2016 Concrete

A Joint Publication of NCSEA | CASE | SEI

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April 2016 34

FEATURE

34 EDITORIAL

7 Swing Batter, Batter!

By David W. Mykins, P.E. CODES AND STANDARDS

10 Navigating New Concrete Repair Standards

By Jay H. Paul, S.E. STRUCTURAL REHABILITATION

12 Life before the International Concrete Repair Institute (ICRI)

By Craig E. Barnes, P.E., SECB

San Marcos High School

By Hossain Ghaffari, Ph.D., P.E. The San Marcos High School project transformed the existing single-story complex to a state of the art multi-story high school complex. The new Campus features several separate structure that utilized tilt-up and cast-in-place concrete, and structural steel construction.

Tilt-up construction offered solutions to two critical concepts where a concrete façade was used.

PRACTICAL SOLUTIONS

32 Solving Interior Water Leakage Problems Below-Grade

By Brent Anderson, P.E. BUILDING BLOCKS

42 A Deep Dive into Conformity Assessment

By William Gould, P.E. GUEST COLUMN

46 Design Considerations

By Gary Cudney, P.E.

STRUCTURAL TESTING

17 Understanding the Rates of Corrosion in Concrete Structures

INSIGHTS

50 Smart Structures

By Dilip Khatri, Ph.D., S.E.

By Gina Crevello, Irene Matteini and Paul Noyce STRUCTURAL DESIGN

22 A Structural Engineer’s Survival Guide for Waterproofed Appendages

By P. Travis Sanders, P.E., S.E., Geoff A. Laurin and Achim A. Groess

CODE UPDATES

53 Significant Changes between ACI 318-11 and ACI 318-14 – Part 1

28 Fairmount Bridge across the Schuylkill River

FEATURE

Houston’s Hobby Airport Gets New International Upgrade

By David W. Hillery, P.E., Matt Henderson, P.E. and Raxit Patel, P.E. In 2015, Houston’s William P. Hobby Airport added its first international terminal with 280,000 square feet of new space and five new boarding gates. Additional features included renovations to existing spaces, 16,000 square feet of additional concession space and space to allow 800 arriving passengers to be processed through 16 passport inspection stations. While new structures were constructed and connections from the older to the newer features were being made, all airport-related traffic, concessions and other businesses had to be maintained without interruption.

By S. K. Ghosh, Ph.D. SPOTLIGHT

59 Columbia Medical Center’s Vertical Campus

By Daniel Sesil, P.E., S.E.,

HISTORIC STRUCTURES

37

Matthew Melrose, P.E., Michael Hopper, P.E. and Andrew Polimeni, P.E.

IN EVERY ISSUE 8 Advertiser Index 57 Resource Guide (Engineered Wood Products) 60 NCSEA News 62 SEI Structural Columns 64 CASE in Point

By Frank Griggs, Jr., D.Eng., P.E. STRUCTURAL FORUM

66 Who Hijacked My Building Code?

By David Pierson, S.E., SECB Publication of any article, image, or advertisement in STRUCTURE® magazine does not constitute endorsement by NCSEA, CASE, SEI, C 3 Ink, or the Editorial Board. Authors, contributors, and advertisers retain sole responsibility for the content of their submissions.

STRUCTURE magazine

5

On the cover The Columbia University Medical and Graduate Education Building utilizes state-of-the-art concrete construction technologies, including bonded post-tensioning, slab void formers, and high strength materials to create a world-class medical education facility in New York City. Photo

by Matthew Melrose/Leslie E. Robertson Associates. See Spotlight article on page 59.

April 2016

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Editorial

Swing new trends, new Batter, techniques Batter! and current industry issues

By David W. Mykins, P.E., Chair CASE Executive Committee

I

magine that, one day, you and some of your friends decide to go out and play a game of softball. You don’t have enough players, so you go to the local park and find a friendly group and ask them if they’d like to play. They have never played before, but you assure them it’s a lot of fun. After a cursory explanation, they agree and you take the field to start the game.

The first batter comes up and, after the third strike, your team declares her ‘out’ and calls for the next batter. But the other team protests saying, “That’s not fair. You didn’t tell us we only got three strikes.” And an argument begins before the game is even through the first inning.

Playing a game without everyone understanding the rules is just like running a business without an employee handbook. An employee handbook is an important foundation for any business, whether it is an emerging small business or an international mega firm. The handbook sets forth the expectations between the employer and the employee, and thus provides an important risk management tool.

By that I mean, it helps businesses avoid litigation and also puts staff members at ease by spelling out the company’s policies and minimizing misunderstandings.

Another benefit of having an employee handbook is that it saves time for both your management team and your HR staff. Having documented rules and procedures saves them from explaining the same policies over and over to current or new employees. These written policies also help managers apply the rules consistently across the board.

Additionally, a properly written handbook will help your firm comply with federal and state employment laws, and can be a beneficial legal defense in the event of a lawsuit.

So what are some of the do’s and don’ts of an effective employee handbook?

Do use simple language – Most experts agree that it is very important to have a handbook that is written in plain, easy to understand language. Avoid legal jargon that will confuse employees and describe the policies in clear, positive terms that reflect the company’s culture.

Don’t go alone – Labor laws can vary significantly from state to state and it is important that the policies in the employee handbook do not contradict any Federal or State laws. Therefore, it is recommended that an attorney be consulted before finalizing and distributing the handbook.

Do get sign off – Include an employee acknowledgement page.

This ensures that every employee understands and agrees that it is their responsibility to read and follow the policies set forth in the handbook. These acknowledgement pages usually are required to be signed and then are kept in the employee’s personnel file.

Don’t set it and forget it – The employee handbook is a living document. Regular reviews of the handbook should be made to be sure that it is up to date, not only with current labor laws, but with ever-changing living and working environments. Who would have thought 25 or even 10 years ago that we would need to address these issues:

STRUCTURE magazine

• Concealed weapons at work • Benefits for domestic partners • Transgender equality • Social media • Political information in the workplace These are just the start. The extent to which a handbook covers these issues and others will vary widely from firm to firm depending on many factors such as firm size, location and corporate culture.

The employee handbook is very unique to the firm that produces it.

Do tell the back story – Since the employee handbook is usually the first introduction a new employee has to the company, many firms begin the handbook with a company history. This is an opportunity to familiarize the employees with the mission of the firm, why it exists, who its clients are and what its core values are. Such a statement defines the corporate culture and sets the tone for the rest of the handbook.

Don’t re-invent the wheel – There are lots of great references and examples available to help you with creating a new document or updating an existing handbook. The CASE Toolkit Committee is just finishing work on a Sample Policy Manual that provides a great outline and some sample policies that can be adapted for an employee handbook. This document is set to be published in June 2016.

Hopefully this has helped you understand why the rule book is so important and spurred you to think about ways to create, enhance or improve your own. In any case, let’s make sure everyone knows the rules, then step up to the plate and swing for the fences.▪ David W. Mykins is the President and CEO of Stroud, Pence & Associates, a regional structural engineering firm headquartered in Virginia Beach, VA. He is the current chair of the CASE Executive Committee. He can be reached at dmykins@stroudpence.com.

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April 2016

ADVERTISER INDEX

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American Concrete Institute ............. 2, 16 Anthony Forest Products Co. ................ 31 Applied Science International, LLC....... 67 ASDIP Structural Software .................... 26 Canadian Wood Council ....................... 56 Concrete Reinforcing Steel Institute ...... 40 Construction Specialties ........................ 25 Dayton Superior Corporation ............... 29 Dlubal Software, Inc. ............................ 51 Expanded Shale, Clay and Slate Inst. ..... 47 Halfen USA, Inc. .................................. 52 ICC – Evaluation Service ...................... 43 Inspection Instruments, Inc................... 23 Integrity Software, Inc. ............................ 8

Integrated Engineering Software, Inc..... 55 JMC Steel Group .................................. 36 KPFF Consulting Engineers .................. 45 Legacy Building Solutions ..................... 39 MAPEI Corp......................................... 49 NCSEA ................................................... 9 RISA Technologies ................................ 68 S-Frame Software, Inc. ............................ 4 Simpson Strong-Tie......................... 13, 21 Structural Technologies ......................... 15 StructurePoint ....................................... 58 Struware, Inc. ........................................ 19 Trimble ................................................... 3 USG Corporation ................................... 6

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Visit the STRUCTURE website (www.STRUCTUREmag.org), click the “For Authors” tab in the navigation bar, and download the Author’s Handbook. Then write a short abstract explaining your article idea and send it to publisher@STRUCTUREmag.org.

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April 2016

Evans Mountzouris, P.E. The DiSalvo Engineering Group, Ridgefield, CT Greg Schindler, P.E., S.E. KPFF Consulting Engineers, Seattle, WA Stephen P. Schneider, Ph.D., P.E., S.E. BergerABAM, Vancouver, WA John “Buddy” Showalter, P.E. American Wood Council, Leesburg, VA C3 Ink, Publishers A Division of Copper Creek Companies, Inc. 148 Vine St., Reedsburg WI 53959 Phone 608-524-1397 Fax 608-524-4432 publisher@structuremag.org April 2016, Volume 23, Number 4 ISSN 1536-4283. Publications Agreement No. 40675118.

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CODES AND STANDARDS updates and discussions related to codes and standards

I

n 2013, the American Concrete Institute (ACI) published the first U.S. code requirements specifically for the repair of reinforced concrete, Code Requirements for Evaluation, Repair and Rehabilitation of Concrete Buildings (ACI 562-13), having recognized the need for consistent practices and longer-lasting concrete structures.

This was also ACI’s first performance-based code. The distinction between prescriptive and performance requirements is an important one for concrete repair, as project conditions such as a structure’s age, materials used, and strength requirements can vary widely. Thus, ACI 562 is structured to afford licensed design professionals significant flexibility in selecting materials and devising customized repair strategies, while following a minimum baseline of code requirements.

ACI and the International Concrete Repair Institute (ICRI) have now published the Guide to the Code for Evaluation, Repair, and Rehabilitation of Concrete Buildings (referred to herein as the Guide) as a companion to the code, which will help designers clearly and quickly interpret new, performance-based provisions of ACI 562 that directly impact the way they approach concrete repair.

Navigating New Concrete Repair Standards

By Jay H. Paul, S.E., FACI

How the Guide Works Jay H. Paul is a Senior Principal of Klein and Hoffman, Inc. in Chicago, Illinois and has served the industry through numerous professional organizations including the Structural Engineers Association of Illinois (past President) and the American Concrete Institute (ACI, past Chair of ACI Committee 546 – Concrete Repair).

Jay is currently a member of the International Concrete Repair Institute and ACI Committee 562 – Evaluation, Repair, and Rehabilitation of Concrete Buildings. Recently he served as chair of the review committee for the development of the Guide to the Code for Evaluation, Repair, and Rehabilitation of Concrete Buildings.

He can be reached at jayhpaul@comcast.net.

The online version of this article contains detailed references. Please visit www.STRUCTUREmag.org.

While ACI 562 offers many alternative ways to repair concrete, solutions for specific projects are ultimately up to the designer’s interpretation and professional judgment. The Guide addresses

users’ most fundamental concerns in a straightforward format, with Chapter Guides and Project Examples that provide resources to help identify the most effective repair strategies.

Chapter Guides mirror each section of ACI 562, providing insight into how each chapter and section of the code applies to different aspects of concrete repair, including: • Notation and Definitions • Referenced Standards • Basis for Compliance • Loads, Load Combinations, and Strength Reduction Factors • Evaluation and Analysis • Design of Structural Repairs • Durability • Construction, and • Quality Assurance The Guide provides flowcharts illustrating how to navigate key decisions, such as determining material properties at the jobsite (Figure 1). In this example, an engineer can use the visual reference to quickly identify which sections of ACI 562 to reference when conducting a visual inspection, reviewing available documentation, and performing physical testing.

Highlighted call-out boxes in each chapter explain scenarios that may require more interpretation or unusual circumstances that are not directly referenced in the code, including “Unique Analysis Considerations” designers might encounter during a concrete repair project (see sidebar).

Call-out boxes also list additional references for specific repair topics, such as other standards and guides for evaluating and repairing reinforcement in concrete structures.

Figure 1. Summary of process to determine material properties in accordance with ACI 562, Section 6.3.

10 April 2016

Unique Analysis Considerations

Figure 2. Concrete spall with exposed reinforcing bars and delaminated loose concrete at slab edge.

To reinforce the material covered in the Chapter Guides, several Project Examples illustrate how ACI 562 applies to actual concrete repair scenarios: • Typical parking garage repairs, • Typical façade repairs, • Repair of a historic structure for adaptive reuse, • Strengthening of a two-way flat slab, and • Strengthening of double-tee stems for shear.

Although the code was not in existence at the time these projects were completed, real-world examples have been adapted to demonstrate how the code could have been used. Rather than giving prescriptive formulas for concrete repair, the examples show how designers can draw on relevant sections of ACI 562 to meet unique project conditions.

The project scenarios include architectural drawings, photographs, and details to help designers become familiar and comfortable with applying the new repair code. For example, the guide walks users through a typical façade repair project, in which concrete corrosion occurred in a 1970s residential building (Figure 2).

In a column alongside the project description, designers can see which sections of ACI 562 would apply to each step, beginning with evaluating the structure and selecting the best repair approach. Drawings illustrate the structure’s existing condition and several repair options, including the approach that was ultimately selected (Figure 3).

The Guide also refers designers to ACI 562 provisions that govern the preparation of contract documents, actual construction and quality assurance processes, and communication of maintenance instructions with the project owner.

The Guide concludes with several references, including an overview of ACI 562 provisions and where they are referenced within the Guide. Designers can quickly find cross references to a specific section of the code within a chapter or Project Example, without having to review the entire guide.

Numerous situations are encountered with existing structures that require unique analysis considerations, both for the existing structure and the design of repairs. ACI 562 specifies that the licensed design professional consider the various analysis aspects of each situation. Although not intended to be comprehensive, the following scenarios present unique analysis considerations for various cases: • Spalling has occurred at the top side of a continuous girder, resulting in loss of bond at some of the top longitudinal reinforcing steel. The damage may have caused loss of development in the reinforcing steel and additional structural demand in other portions of the existing structure as a result of redistribution of the negative moments.

• Full-depth slab repair is required to address top and bottom reinforcing bar corrosion in a parking deck. During repairs, the unbraced length of the adjacent columns could significantly increase and temporary bracing of the column may be required.

• Alterations as a result of change of occupancy will include new openings in a twoway slab. The demolition for the alteration may result in redistribution of existing moments and shear forces in the remaining structure.

• Damage, deterioration, or repairs of a prestressed concrete structure that may have resulted or will result in prestressing force release (reference ACI 562, Section 7.6.4).

Repairs that affect the development of prestressing steel reinforcement may reduce member capacity.

• Concrete spalling has occurred on a column. The concrete removal during repair may result in redistribution of internal forces that are locked-in. The strength of such columns must be considered in accordance with Section 6.5.4 of ACI 562.

Excerpted from the Guide to the Code for Evaluation, Repair, and Rehabilitation of Concrete Buildings, ACI and ICRI 2015.

The Guide in Practice As with any new code, the designer’s first challenge is recognizing when to reference ACI 562 as opposed to ACI 318, the International Existing Building Code (IEBC), or other standards. The purpose of ACI 562 is to provide a comprehensive standard for concrete repair projects from inception to completion, including provisions not addressed by previous standards.

However, where provisions do overlap, the Guide explains how the code references existing standards to specify, clarify, or expand upon new requirements. For example, Section 5.1.6 of ACI 562 requires the use of ASCE/ SEI 7-10, Minimum Design Loads for Buildings and Other Structures, for gravity and wind load requirements, but references ASCE/SEI 41-06, Seismic Rehabilitation of Existing Buildings, for the treatment of seismic loads.

Designers can also follow the code’s repair program to determine initial causes of deterioration, assess the compatibility and durability of various repair materials with the existing structure, and communicate appropriate maintenance practices with clients. The Guide’s Project Examples illustrate ways to apply these durability requirements and considerations to achieve a longer service life.

Used in conjunction with ACI 562, the Guide to the Code for Evaluation, Repair, and Rehabilitation of Concrete Buildings helps design professionals apply new code provisions that are increasingly becoming standard practices.

STRUCTURE magazine

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April 2016

Figure 3. Built-out replacement at balcony slab edge.

Although ACI 562 is compatible with the IEBC, it has not yet been adopted into the international code. However, when adopted by local jurisdictions and building authorities, ACI 562 provides a means of acceptance for the repair of reinforced concrete structures. For more information about ACI 562, see Requirements for Evaluation, Repair and Rehabilitation of Concrete Buildings, in STRUCTURE, September 2014.▪ The Guide to the Code for Evaluation, Repair, and Rehabilitation of Concrete Buildings is available as a bundle including a copy of ACI 562-13 and as a standalone document at www.concrete.org and www.icri.org.

Structural rehabilitation renovation and restoration of existing structures

T

his is the first of a two-part article on repairing aging, normally reinforced, concrete garage structures existing in aggressive weather environments. The first article is from the perspective of the engineer and the second article from that of the contractor. While the topic is the same, and the articles are complementary, they are not intended to be a point-counterpoint.

The Designer’s Perspective Although construction sophistication has improved remarkably over the years, there are many parking structures, particularly those in the northeast built forty to sixty years ago, that were constructed without much thought or understanding about how the aggressive nature of the environment and the world we live in would deteriorate these structures.

When one has been in the business of garage repair for a lengthy period, you encounter interesting situations and meet interesting people. This article is intended to be a useful tool for the younger engineer to be able to absorb some history and lots of experiences.

Parking garages come in many shapes, sizes, and structural configurations: Steel frame, pre-cast, CMU-bearing, metal-deck with concrete, post-tensioned decks (filigree-type), topped and pre-topped pre-cast, bituminous surface, free-standing garages, and garages beneath structures. This article will concentrate on normally reinforced, cast-in-place concrete parking structures.

How does concrete in a garage structure deteriorate? Well-researched over the years, deterioration is largely due to the oxidation of the structural reinforcement which in turn creates a phenomenon called rust-jacking, resulting in spalled concrete. The rust-jacking phenomenon is evidenced in bulging and/or cracked concrete, often with rust staining, and is a direct result of the pressures created as embedded reinforcement rusts within the concrete structure. Low quality concrete, lack of air-retention, and concrete carbonation are all accelerants to the deterioration process.

A project usually starts when a facility user (usually the Owner) contacts the engineer or contractor stating that pieces of concrete are unusually erupting from the floor surface, exposing reinforcing rods, or falling from overhead.

A quick inspection and a phone call advises the prospective client that water, making its way through or into the concrete, has been present around the reinforcement over a sufficient period of time to cause steel oxidation and the

Life before the International Concrete Repair Institute (ICRI)

By Craig E. Barnes, P.E., SECB

Craig E. Barnes is the Founding Principal of CBI Consulting Inc. Craig can be reached at cbarnes@cbiconsultinginc.com.

12 April 2016

rust-jacking phenomenon. When the client asks what should be done, the response is typically: “Are you buying or selling?” That simply means does the client hold a long-term position in the facility, or are they simply looking to improve life-safety conditions in order to extend the service life for a short period? This article assumes that the prospective client is in a long-term position.

The garage study begins with a determination of the extent of deterioration. Spalling concrete on travel surfaces and on missing pieces from concrete soffits is readily observable. Beneath a surface that may visually appear to be secure could be an ongoing corrosion issue. Forty (40) years ago, a reliable process called “sounding” was utilized to estimate the extent of what was called “concealed deterioration”. Concealed deterioration suggests that the surface may appear to be sound or solid, yet the corrosion process beneath the surface has reached a degree where concrete has debonded or layered as a result of the rust-jacking process.

Sounding requires nothing more sophisticated than a hammer, a steel rod, or a chain to be able to begin mapping the extent of debonding.

Through the years, technology has developed some rather exotic means for determining the extent of debonding. Many an “older” engineer has noted that it would be great if someone would invent a way to assess debonding without the need to survey a surface on hands and knees while using a hammer. Technology has answered that request in the form of ultrasound, x-ray, or a rotary percussion tool on an extension pole. The newer techniques (still undergoing development for preciseness) are good for quantity mapping and relatively quick, general overviews. This author still finds that the precision of sounding is still the most reliable.

Sounding is best done in a relatively quiet environment so that the individual doing the sounding can hear the distinction between solid concrete (a clear ring) and spalled concrete (a dull thud). In a noisy environment, it is still possible to do sounding in a localized top of slab area, with a hammer, by lightly sprinkling small pieces of aggregate over the surface before sounding. The spalled concrete will vibrate, and a vibrating sand line demarking solid and debonded concrete can be easily observed. When marking for excavation, chalk or paint may be marked directly on the concrete surface. A good practice is to extend beyond the specific spall line by several inches to allow for oxidizing steel that may not yet have generated to the point of active spalling.

A filigree concrete system consists of a relatively thin precast concrete panel that by itself is not sufficient to support full span line loads but, in composite combination with a cast-in-place topping, becomes a longer span, code load supporting structural floor or roof.

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Concrete Removal

Figure 1.

Removing oxidation corrosion from reinforcing bars using wire wheels, hammers and chisels, sand blasting, and hydro-blasting can be appropriate. The engineer should also be mindful of evaluating the required structural strength. At times, the area/quantity of steel can be reduced and still satisfy the live load demand. As an example, a specification that reads “steel with a 10% cross-section reduction is to be supplemented” might be an unnecessary regiment if the existing steel could satisfy the intended design purpose with a cross-section reduction of 25%.

Why is it often suggested to have more cover protection for the reinforcement that is to remain in the repair area than was necessary during the original construction? In a final product where a parking garage will receive an opaque elastomeric waterproof coating, a typical recommendation, the conditions that promoted the original deterioration will be largely controlled. With a system that will remain uncoated, wisdom suggests that more attention should be paid to the protection of the reinforcement. Protecting the reinforcement in the patch area reduces the corrosion potential for that steel, but forces the corrosion potential to the unprotected steel that is adjacent to or entering the patch area.

This often gives rise to a phenomenon called the “halo-effect”, where the patch appears to be working well, yet through the years the adjacent concrete begins to deteriorate.

Surrounding the perimeter of the patch area with sacrificial anodic devices will prolong the life of the original reinforcement adjacent to the patch and is a great technological advancement. There are several manufacturers who will provide devices for this particular purpose. Vector Corrosion Technologies has been responsive in assisting the author’s firm with technical support in this respect.

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Electric or pneumatic chipping guns and hydro-demolition (hydro) are the tools of first choice for removing deteriorated concrete.

Site conditions will often determine which method is the preferred technique. Hydrodemolition creates a significant amount of waste water that needs to be controlled.

Although water-recovery systems and recycling can be utilized, there is still containment and waste water to be dealt with. One feature of hydro-demolition that mechanical demolition doesn’t provide is that hydrodemolition will often prepare the exposed reinforcement by removing oxidized material.

Impact hammer is a more labor-intensive process and is a generator of airborne particles and greater airborne noise. Noise from impact tools and hydro equipment travels through a concrete frame for long distances. The hydro process overall creates less noise.

Once the sounding is done and the areas are marked out for excavation, the floor will probably look like an area of randomly located “amoebas” (Figure 1). In an ideal situation, isolated amoebas should be circular. In the case of concrete removal by pneumatic equipment, the easiest process from the contractor’s perspective, however, contains straight lines and large rectangles. Be mindful that extending well beyond the spall line removes sound concrete, where it will be more difficult to expose the encapsulated reinforcement that has not corroded. Leaving feathered excavation edges at concrete spall is a poor practice, and one that is almost guaranteed to result in lifting of the patch material at edges, even when a manufacturer of an engineered patching product permits feathering the edges.

Understanding a practical approach to concrete demolition requires an understanding of excavation equipment. If full demolition of concrete with embedded reinforcement is required, large impact equipment greater than 25 pounds could be appropriate. To retain solid concrete for patching, mid-size equipment to remove some of the most distressed concrete could be appropriate. Using smaller equipment, such as rivet busters and electric chipping hammers, for fine-tuning would be a next step. Detailed excavation utilizing hand-held hammers and cold chisels is appropriate. Removal of 2500 psi versus 6000 psi concrete will yield different experiences and require different techniques. Even though it may appear to be efficient, don’t use equipment that is larger than necessary, as there is an inherent danger of microcracking of concrete that is not intended to be removed.

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Parent Concrete to Patch Interface There are several possibilities to address the interface between new and existing concrete.

For the feather edge spall, a definite demarcation is necessary. A logical approach is to make

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Figure 2. Grinder with vacuum attachment.

a saw/grind cut, which is often restricted to a ¾-inch depth. Three-quarters of an inch is a reasonable cut depth, or estimation of the clear cover, so as to maintain intact the existing steel beyond. Confirm this dimension before production cutting. Increasing the depth beyond ¾ inch using impact power tools will result in a rough surface, which is desirable to promote bond between the existing concrete and new patch material.

Grinding/cutting will appear to polish the cut surface of the sound concrete. For bonding purposes, this is a poor surface. If using grit blasting to clean the reinforcing steel, one can utilize that same process to provide a light raised profile to the cut surface. A natural hair-line shrinkage crack is likely to form at the patch-to-parent concrete surface, resulting from concrete shrinkage while curing. It is almost impossible to eliminate this crack, but control of water content and good construction practices are very helpful in minimizing it. Again, understanding if the final product will receive an opaque coating will assist in these decisions. The meeting line of new patch material to old concrete is one of the more vulnerable locations when considering crack control. It is the location where essentially dissimilar materials come together and results in a natural shrinkage line. If the final product does not receive a topical waterproof coating, one can be assured that some level of deterioration will initiate at this location. If the patch material and the parent concrete begin to debond at this location, having a slight undercut of three to five degrees on the ground joint will provide a mechanical wedge, which will help to control the patch from lifting. The rough profile of a grit blasted joint (adequate) or a mechanically profiled surface (best) to create a friction interface can be very beneficial. A minimum ¼-inch amplitude profile on the horizontal surface of the patch area has been found by the author to work well.

Bonding the patch material to the parent concrete is the greater challenge and may be

where the success of the patch is ultimately judged. The reader may have heard statements to the effect that the process of curing concrete is never completed. The author read in one article that concrete used by the Romans is still in the process of hydrating.

Taking advantage of cement particles within the parent concrete that have been relatively dormant and can participate in the hydration process can be done by achieving a saturatedsurface-dry (SSD) surface. From the author’s perspective, this means more than simply applying a light water spray to the surface immediately before patching; it means providing a 12-hour saturation by first applying the water spray and then covering with burlap/ burlene/etc. to prevent drying. Without letting the surface dry, and immediately before applying the patch material, apply a coating of neat cement (cement mixed with water to the consistency of heavy paint) to the SSD concrete surface. Take the time to broom the neat cement into the parent concrete and a perfect surface will be readied for bonding the new to the old concrete. Do not let the neat coating dry, otherwise a surface of dry, dehydrated cement will result and the bond will be negatively impacted.

The placement of concrete is one that requires attention by both consultant/inspector and contractor. Apply the neat cement in advance of the concrete placement so that it is not permitted to dry out. A color change in the neat from a dark gray sheen to a light gray mat color is an indication that drying has taken place. Drying does not mean that the cement in the neat has cured. In drying out, it becomes a bond-break surface that may not regenerate during the hydration process. In the early stages of the drying process, if the concrete is delayed in delivery, a light spray from a hose is acceptable. The light spray should not be of a concentration that allows water pockets to accumulate.

With longer delay, applying additional neat and brooming it vigorously will break up the surface that has begun to dry, and allow it to be reestablished. One can probably get away with doing this once. Beyond that, the surface is lost and grit blast removal of the dry neat is recommended.

Generally, spalls are a rather shallow patch, which makes vibrating of the concrete for consolidation purposes difficult. The use of pencil vibrators can be very helpful, particularly where there are significant areas of reinforcement congestion. A relatively new tool called the vibrating screed, that can be operated by one person, has been found to be very beneficial for concrete consolidation as well as surface profile/finish.

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Figure 3. Remotely operated excavation hammer.

The contractor and inspector should not be the decision makers as to: (a) how aggressive the concrete removal is, (b) how much of the bar is to be exposed, (c) is there excess steel which may be removed, or (d) where and how much shoring should be placed. These are questions for the Engineer of Record.

Working the edges of a patch placement to consolidate the concrete against the parent substrate is a very important step. Finishing the concrete surface to prepare it for either vehicle traffic or for subsequent coating is an important step as well. Be familiar with the use of the garage to determine whether an aggressive or a lighter broom finish is required.

If the garage is to be coated, a magnesium float surface is perfectly acceptable.

Facilitating the curing of the patch material takes place either with the application of moist curing blankets or chemical sprayon compounds. If using a chemical and the garage is to be coated, don’t use a chemical that will not be removed with the track blasting process.

Soffit Repair Repairs on vertical surfaces and overhead repairs require different techniques altogether.

First, one needs to assess what has been the contributor to the overhead spalling and steel deterioration. Has the deterioration resulted primarily from the passage of water from above, or are other issues involved? One will probably find the largest extended deterioration results from cracks in the concrete that allow aggressive water to pass through. When a garage ages and when it has been exposed to the carbon-monoxide rich environment of a parking garage, carbonation of the concrete can take place. This process dilutes the natural passivity protection that concrete provides to the steel, thereby creating increased corrosion potential. Those practicing in New England, repairing garages along the coast, are faced with an unusual situation in garage repair.

Carbonation, chloride-laden air, and seasonal condensation cycles (Spring/Fall) initiate steel

corrosion and concrete spalls on concrete garage surfaces of the underside of decks that have no other explanation.

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Overhead work can be as demanding as deck work. Almost exclusively today, overhead patching is done with a combination of hand-patch materials, hand-patch and partial form work, or overhead pumping with engineered materials. With the exception of rare instances where traditional sand and cement dry-pack is utilized, prepackaged engineering products produced by a variety of manufacturers are used today. Those products with a cement base are ones with which the author has had the most success. With the hand-patch process, the construction crew is usually unable to proceed the placement with repeated misting of the parent surface and neat application. Here is where one faces the engineers’ conundrum. If everything noted in this discussion is necessary to achieve a good patch with long term viability, how can the engineer accept something less? The realities are quite simple. The “old fashioned” process of hand patch with cement-sand-and-water, followed by asking the facility operator to keep traffic off the surface above the patch for at least fourteen days to control vibration that would de-bond the patch, is not a dying process…it is “dead”. Here is a suggestion: knowing that overhead patches are questionable, should something go wrong and a potentially hazardous situation result from the overhead patch material dislodging, the author’s firm utilizes a combination of the existing rebar and non-corrosive pins and wires within the patch material to provide secondary securement of the new material.

Soffit forming and patch material placement by pumping has advanced substantially over the last 10 to 15 years. The need to over-pour through a pour pocket or trough to create a concrete head has been largely done away with, with flowable materials [shrinkage compensated] and pressure pumps. Creating an SSD surface is much more difficult overhead.

Young engineers should not despair. As self-consolidating concrete (SCC) has allowed the engineer to design a w/c = 0.4 concrete, water reducing admixtures have allowed that design to be placed with a 9-inch slump, a magic “goo” results that can provide confidence for long-term bond of patch material to parent concrete. Just wait and see!▪

The Concrete Authority ACI 318-14: Building Code Requirements for Structural Concrete & The Reinforced Concrete Design Handbook (Vol. 1 & 2) Organized from the designer’s perspective, the new edition of ACI 318-14 includes more tables and charts, a consistent structure for each member chapter, and fewer cross references. “The Reinforced Concrete Design Handbook” provides many design examples of various reinforced concrete members based on the design of a seven-story building.

ACI 562-13: Code Requirements for Evaluation, Repair, and Rehabilitation of Concrete Buildings & Guide to the Code for Evaluation, Repair, and Rehabilitation of Concrete Buildings The American Concrete Institute published ACI 562-13 specifically for the repair of reinforced concrete. ACI and ICRI have jointly published the new “Guide to the Code for Evaluation, Repair, and Rehabilitation of Concrete Buildings” to help users navigate the performance-focused standard while clearly and quickly interpreting code provisions.

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A

s concrete structures begin to age and deteriorate, the need to understand corrosion behavior is pertinent to determining where a structure is in its life cycle. One of the most successful methods of determining the corrosion rate of embedded steels is the Linear Polarization Resistance (LPR) method. The results of this test method provide measurements of corrosion current (Icorr,) or corrosion penetration rates. From this measurement, metal loss predictions can be made. Based on scientific formulations (Faraday’s Law), the amount of iron or steel reverting to rust at the time of testing is projected. Based on known amounts of rust gain in the deterioration process, section loss can be converted to rust accumulation at the steel. As the accumulation of rust will eventually lead to distress of the concrete, this data is vital to predicting performance for reinforced concrete structures and for use in durability modelling.

Introduction First introduced in 1957 by Milton Stern and A. L. Geary (Stern-Geary Equation), Linear Polarization Resistance (LPR) is an electrochemical technique used to measure the corrosion rate of a metal in an electrolyte. The object of a corrosion rate measurement in reinforced concrete is to determine the rate of embedded steel turning into rust. The corrosion rate measured in the field is a snapshot of the steel’s behavior at the time of measurement. The objective of the measurement is to be able to calculate, through Faraday’s Law of Metal Loss, what the average corrosion rate would be over a one year period based on the time the measurements were taken. These rates can then be utilized to determine long term performance of metals.

Prior to taking the corrosion rate measurement, the Corrosion Potential, or Ecorr, is measured and forms the baseline of the corrosion rate test.

The potential is then changed anodically (more positive) or cathodically (more negative) by 20 milliVolt (mV), where the resulting corrosion current, or Icorr, is measured maintaining the 20mV potential change. This polarizes the steel to determine the resulting current. Essentially, a controlled voltage change determines the amount of current needed to balance the corrosion reactions.

The accumulation of scale is determined from measuring the amount of steel dissolving and forming oxide (rust). This is carried out by determining the electric current generated at the anodic reaction.

The anodic reaction is where iron looses two electrons: Fe → Fe2+ +2e-

Equation 1

Structural teSting issues and advances related to structural testing

Figure 1. Michael Faraday, English Chemist and Physicist, c 1850s. Courtesy of Pictorial Collection, Science & Society Picture Library.

These electrons are then consumed at the cathodic reaction: The cathodic reaction is where hydrogen combines with oxygen and the two electrons lost at the anode are gained at the cathode site, to form hydroxyl ions: H2O + O2 + 2e- → 2OH-

Understanding the Rates of Corrosion in Concrete Structures Equation 2

The resulting data from the field testing provides the investigator with the steel potential (mV) and consequently the corrosion rate in microns per year (μm/yr). This has a direct relationship to metal loss which is calculated by Faraday’s Law.

Faraday’s Law The amount of material lost at the anode or deposited at the cathode is a function of the atomic weight of the metal or substance, the number of charges transferred, and the corrosion current (Icorr). This relationship was developed

by Michael Faraday while working at the Royal Institute in London, England in 1833 (Figure 1).

Corrosion Rate Thresholds for Steel Reinforced Concrete Structures The deterioration rate is very important, as it enables the engineer to decide when minor or more major work needs to be made to the structure.

In the use of coatings, the corrosion rate readings can identify when or how effective they are and can provide the engineer the option of applying further coatings when the corrosion rates start to increase to unacceptable levels. continued on next page

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The Use of Corrosion Rates to Predict Material Performance

By Gina Crevello, Irene Matteini and Paul Noyce Gina Crevello is material conservator and Principal of Echem Consultants. Gina is on the board of the Association for Preservation Technology International. She may be reached at gcrevello@e2chem.com.

Irene Matteini is an architect and material conservator with Echem Consultants. She can be reached at imatteini@e2chem.com.

Paul Noyce is a concrete and material durability expert. Paul is the Chairman of National Association of Corrosion Engineer’s (NACE) Standard Technical Group 01 for Reinforced Concrete. He may be reached at pnoyce@e2chem.com.

The Icorr reading has been used to identify the amount of predicted section loss that would occur at the end of a year.

It should be noted that the best and most accurate means for the determination of corrosion related material degradation of steel in concrete is through the use of Linear Polarization Resistance. The results provide the amount of section lost on the steel by measuring corrosion current (Icorr). The results of the data can be utilized in durability models, where the relationship between metal loss, the amount of expansive oxide growth on the steel surface, and the subsequent tensile forces which will lead to cracking of the concrete can be established.

Identifying when these damages or failures will occur in reinforced concrete or steel frame structures can significantly reduce future damages by developing a proactive repair process. Durability models, such as Life 52™, allow for such predictions to be made. This type of service life program provides performance models that are predictive in nature, and is based on data collected from the structure including information on the concrete, steel and environmental conditions. An analysis can project when a structure will enter corrosion initiation, corrosion propagation, and time to cracking, and can be utilized to assess the longterm performance of the structure as well as repairs based on known historical performance.

The following tables show the relationship between corrosion activity and material degradation: Table 1 indicates the amount of corrosion penetration of the steel in mils per year (mpy) based on the measured corrosion current density, or Icorr. Icorr is the loss of electrons occurring at the anodic site of the corrosion cell and is measured in microAmps per square centimeter (μA/cm2).

Table 2 provides corrosion current density values in both μA/cm2 and microamps per square inch (μA/in2) and the relationship to when anticipated damage would be expected to occur on a reinforced concrete structure.

Table 3 indicates the relationship between corrosion current density, metal (section) loss of the steel, and the accumulation of corrosion scale, i.e. rust, on the reinforcing steel’s surface, measured in mils per year (mpy).

The Use of LPR in the Field The LPR method allows the investigator to determine locations of corrosion hot spots versus corrosion potential, which is very important when assessing aged, chloride contaminated and carbonated structures. This is a

Table 1. Corrosion rates of steel in concrete.

Rate of Corrosion

Corrosion Current Density, (Icorr) μA/cm2

High

Corrosion penetration, mpy

10–100

100–1000

Medium

1–10

10–100

Low

0.1–1

1–10

Passive

<0.1

<1

Table 2 . Corrosion rate and expected damage.

Icorr (μA/cm2)

Icorr (μA/in2)

< 0.2

< 0.031

Severity of Damage

0.2 – 1.0

0.031 to 0.155

Corrosion damage possible in 10 to 15 years

1.0 – 10

0.155 to 1.55

Corrosion damage expected in 2 to 10 years

> 10

> 1.55

Corrosion damage expected in 2 years or less

No corrosion damage expected

Table 3. Typical section loss and rust accumulation.

Icorr (μA/in2)

Metal Loss (mpy)

Rust Accumulation

< 0.0155

0.046

0.13 mpy Rust Growth

0.0775

0.229

0.67 mpy Rust Growth

0.155

0.457

1.37 mpy Rust Growth

1.55

4.570

13.7 mpy Rust Growth

Note: The expansive iron oxide (rust) growth between 0.394 mpy (10 μm) and 3.94 mpy (100 μm) (0.01 to 0.1 mm) will cause cracking of the concrete cover.

Also note: Some values between the tables may not correlate exactly.

Figure 2. Team getting ready to perform LPR test at location in New York City, May 2015.

key differentiator for condition assessments, as the half-cell potential is largely influenced by conditions which impact the steel’s electromotive force, EMF. The interpretation of half-cell potential data (in accordance with ASTM C876, Standard Test Method for Corrosion Potential of Uncoated Reinforcing Steel in Concrete), alone, can be very misleading

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when assessing aged concrete. Since the LPR method establishes the potential prior to obtaining the corrosion rate, the value of the data can allow a more accurate picture of corrosion behavior of the embedded steel.

The corrosion rate data can be used in a number of ways to assist the investigation and the design team (Figure 2). The data can

Figure 3. View of the east elevation.

Figure 4. Efflorescence and water infiltration is visible on the south soffit of the cantilever.

STRUCTURE magazine

2002 Concrete Structure with Epoxy Coated Reinforcing A memorial, located on a 0.5-acre site in New York City, was completed in 2002 and assessed in 2015 (Figure 3). The Memorial was designed to resemble a hill in the Irish countryside, and thus the structure was built at an incline. The edges of the inclined structure resemble cantilevered soffits when viewed from below. An area on the south cantilevered soffit was exhibiting cracking, one spall, efflorescence, water infiltration, and corrosion of the construction support chairs, which were visible from below. There was concern that the conditions could be impacting the performance and longterm durability of the embedded reinforcing bars at this location. The scope of the project was to determine the corrosion condition of the embedded reinforcing steel where moisture staining and efflorescence was visible.

Construction The structure is a gently sloping platform with support walls. The concrete platform has both precast concrete beams and reinforcing steel. The reinforcing steel is epoxy coated and the structural steel was presumed to be uncoated. continued on next page

19

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visually illustrate corrosion activity by contouring the results alongside the corrosion potential. This provides a graphic depiction of where activity is occurring. This can allow the team to make more targeted openings and to further assess material properties that would impact corrosion. When the data is used in deterioration models, it can provide critical threshold limit states for section loss, rate of cracking, and service life performance and repair performance models.

A limitation of the testing method is that the results do not differentiate between chloride induced pitting corrosion or general corrosion.

Pitting corrosion is a concentration cell and, therefore, the corrosion current is coming from one location versus general corrosion which can be assumed to occur across the entire surface area of the steel that is being tested. The standard surface area calculated in the LPR instrumentation is typically 100 cm2 (15.5 in2). When the steel surface area is greater than or less than this presumed area, adjustment factors in the corrosion rate need to be applied to the field data. Like chloride induced corrosion, if epoxy coated reinforcing (ECR) is tested for corrosion rate, the data collected can be less than 100 times the actual corrosion rates.

When assessing corrosion condition and material degradation where corrosion is present, LPR testing provides the foundation of the analysis. This data is extremely valuable in assessing remaining service life and predicting the durability of extant structures. Additionally, the understanding of general environments and macro and micro climates are required. The relative humidity (RH) and temperature of the concrete will influence the readings. Annual weather cycles, climatic conditions and atmospheric contaminants should be considered when carrying out the assessment. The authors have applied this test method and subsequent analyses in virtually all structure types ranging from historic landmark buildings, aging infrastructures, marine structures, industrial plants, and, more recently, relatively new construction.

The method can be applied to any embedded reinforcing steel where corrosion initiation has begun. Recent advances in technology are even allowing for polarization resistance to be measured in discontinuous steel elements, such as anchors and isolated ECR. An interesting case study of the Irish Hunger Memorial, located in New York City, provides an illustration of the method employed in a corrosion assessment of a fairly new structure.

Figure 5. Corrosion rates with four variations of surface exposed steel area.

Summary of the Corrosion Evaluation The condition of the south cantilever soffit exhibited visible signs of continuous water infiltration, possibly from a waterproofing membrane failure above the concrete soffit.

A considerable amount of efflorescence was present as well as small stalactites with dripping water hanging from the same area, as shown in Figure 4 (page 19). In addition, horizontal cracking was observed on the lateral surface of the cantilever soffit.

Three different reinforcing bars were located to verify continuity of the steel within the structure and these bars were exposed using a hammer drill. After the reinforcing bars were exposed, it was observed that the bars were coated with green epoxy as indicated in the original drawings. The surfaces of the reinforcing bars were then ground to expose clean (near white) metal, is a requirement for continuity testing. The exposed reinforcing bars were then tested for electrical continuity. This is done by measuring the electrical resistance between each area of exposed reinforcing bar.

Each reading showed a resistance below 1 ohm, suggesting that the reinforcing steel was continuous. The purpose of the continuity test was to ensure that the bars were continuous, especially for epoxy coated reinforcing bars which are often discontinuous. Discontinuous steel cannot be easily tested, as a connection would be required at each piece of steel.

Concrete cover, half-cell potential, corrosion rates and resistivity were carried out and analyzed to assess the impact of the epoxy

coating on macro cell corrosion behavior. As half-cell and corrosion rates were detected, these indicated that “holidays” (which are holes in “coating language”) in the coatings were present. It is quite unusual to detect active corrosion rates in fairly new ECR unless degradation of the coating is present.

Due to the use of epoxy coated reinforcing, macro-cell corrosion will exist where there are holidays in the coatings. The data was analyzed with four variations of ‘exposed steel’ surface area. The instrumentation used for corrosion rate testing assesses the data as if the steel is uncoated and the readings account for a surface area of 100 cm2 (15.5 in2) of exposed steel. Since the steel is epoxy coated, the values measured would be an underestimation of the actual corrosion activity on the structure. Therefore, the data values were increased to represent 50%, 25% and 5% of the collected values. The calculations, which provided a decrease in surface area, were performed to illustrate the increases of corrosion activity which occur with ECR corrosion concentration cells. This is referred to as a macro-cell effect, found to be a common issue with epoxy coatings. This type of corrosion occurs in a similar manner to chloride induced pitting corrosion (Figure 5).

Results Analysis Life 52 durability models were used on various readings to help the client understand the damages which would occur on their structure in the future. The cracking models that were used are applied to existing structures to determine two parameters: 1) when the structure may

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exhibit damages in relatively sound material based on current corrosion activity, and/or 2) when the structure may exhibit damages after a traditional repair is performed in which corrosion is not addressed as part of the repair.

This model is a function of steel size (geometry and surface), concrete cover, and the compressive strength of the concrete cover.

This calculation determines the time frame from which tensile forces created by the formation of iron oxide or rust (based on actual corrosion current) will cause cracking and damages to the concrete cover. Variations occur in reactions based on all factors. For this model, a 0.5 mm (0.02 inches) crack was used in the calculation. This value, 0.5 mm (0.02 inches), is considered by the corrosion industry to be a crack width that is sufficient in size to support corrosion activity. Cracks which are greater than 0.5 mm (0.02 inches) will allow oxygen, moisture and atmospheric solids into the concrete electrolyte.

At present, the models for the Memorial indicate that, based on the intensity of the corrosion activity, there may be corrosion related damages occurring from the present time through the next 40 years in the best case scenario. As macro-cell corrosion is more intense than general corrosion, it would be presumed that corrosion related deterioration could occur between 4 and 10 years.

Conclusions From the results of the field testing, it can be illustrated that the use of Linear Polarization Resistance as a supplementary test method to a condition survey can assist the team in determining actual corrosion activity. The case study presented a unique structure type where LPR testing was utilized for a more novel purpose than it would have been typically employed.

For the Memorial project, the corrosion rate data provided significant insight into the active rates of corrosion for new structures. From the testing, the team was able to provide the owner with a forecast of the structure’s future condition, and a methodology for utilizing future testing methods after the structure is repaired.

In all instances where the authors have performed LPR testing, the results, utilized with durability and service life models, have allowed the team to assist the client in understanding the urgency and necessity of repairs required to their structures. Additionally, with advances in corrosion testing instrumentation, this method can be applied to reinforced concrete structures, epoxy coated reinforcing steel, steel frame structures and buildings, and even discontinuous elements such as masonry anchors and steel plates.▪

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Structural DeSign design issues for structural engineers

R

ecent fatalities associated with failed structural building elements have generated discussion about actual causation and whether building code changes are required. These failures have also increased the demand for architectural and structural inspections on similar existing elements.

The authors are consultants who frequently forensically diagnose alleged construction defect claims. Clients are typically developers, designers, contractors, insurance agencies, attorneys, manufacturers or building owners. This background provides a unique perspective on the relative risk to the structural engineer.

Although the structural engineer usually does not specify the exterior envelope, the potential for alleged liability remains at locations where structural elements interface with and/or penetrate the exterior building envelope. Engineers have a primary responsibility to protect public safety, so understanding the goals, methods, and potential problems with the building envelope at decks and other structural appendages can allow them to be part of the solution and perhaps limit their liability exposure.

This article will primarily discuss balconies, decks, and stairways, but the issues are similar for other structural and non-structural appendages as well.

A Structural Engineer’s Survival Guide for Waterproofed Appendages

By P. Travis Sanders, P.E., S.E., Geoff A. Laurin, GC, NACHI and Achim A. Groess

Recent Failures

P. Travis Sanders is a Senior Structural Engineer at CASE Forensics in Portland, Oregon.

He can be reached at tsanders@case4n6.com.

Geoff A. Laurin is a Principal at Engineered Research Group, Inc. located near San Francisco, California. He can be reached at geoff@ergroup.org.

Achim A. Groess is a Principal at Engineered Research Group, Inc. He can be reached at achim@ergroup.org.

The two most recent structural failures involving exposed exterior elements (EEEs), both with resultant loss-of-life, involved multi-residential wood light-frame construction. The first was an exterior cantilevered balcony in Berkeley, California. The second was an exterior stairway in Folsom, California. Although the various forensic investigations (by others) into these tragic failures are ongoing, media images depict conditions associated with wood decay related to severely damaged structural components and unintended water intrusion.

The Berkeley tragedy involved a cantilevered system that had limited redundancy in the vertical load path. Obviously, material degradation to a structural member in a low redundancy system can lead to exactly these types of catastrophic failures. In response, the Structural Engineers Association of California (SEAOC) wrote to the California Building Standards Commission (CBSC) with respect to the California Building Code and the California Residential Code. In an attempt to provide improvements, the letter recommended the following multi-pronged approach:

22 April 2016

1) Review water barrier requirements.

2) Review ventilation requirements.

3) Consider introducing requirements to improve the durability of EEE’s structural members where the structural members are concealed.

The problem will not be an easy one to resolve, since it is a very complicated issue involving many disciplines with overlapping levels of responsibility.

The Decay Problem In light-frame wood structures, deterioration is primarily caused by long-term excessive moisture trapped within concealed spaces. Decay requires a food source (the wood) for fungi, and the presence of oxygen and moisture. Fungi and oxygen are always present, so moisture is the ingredient that can most easily be mitigated. The moisture sources can vary across different climate zones.

The most common condition that leads to longterm excessive moisture exposure is building envelope leakage. The author’s experience shows that structural appendages and their supports exposed to excessive moisture without drying usually, but not always, exhibit some form of visual indicator prior to a change in structural performance (i.e. failure).

A typical California wood balcony, under construction, is shown in Figure 1. Non-treated Douglas-fir lumber joists are designed to cantilever outward from the interior of the building (as extensions of the floor framing), passing through the exterior wall. Ideally, all of the wood is protected by waterproofing and any water on the surface of the deck drains away. In a perfect world, the structural engineer designs the framing, the envelope designer (usually the architect) designs the waterproofing and the contractor builds it so there is never a leak.

Fundamentals of Waterproofing Newer building envelope design embraces the “four Ds”.

Deflection – Simply means that an effective way to keep the structure dry is to deflect the water away.

Drainage – To the extent that water contacts the building, plan on a managed drainage path.

Similar to a complete load path, a proper drainage path is pivotal.

Drying – To the extent that portions of the building do get wet, allow them to dry. A key part of drying is ventilation.

Durability – In the event that prolonged periods of wetness are unavoidable, use durable materials.

The tip for the structural engineer is to be cognizant of what the envelope designer is trying to achieve. Then the engineer can evaluate if their structural design is part of the solution or part of the problem.

X" N.T.S.

2

Figure 1. Common wood balcony configuration under construction.

Leaks often occur when the four Ds are not addressed; where water is not deflected, the drainage path is interrupted and there is limited ventilation to allow for evaporation of the water that has worked its way through the building envelope.

Waterproofing on vertical walls is similar, but with a very steep slope. Cladding deflects water; a drainage plane allows water behind the cladding to drain and provides air flow for ventilation and drying.

Entry Points for Water

Figure 2. Generic detail.

The important takeaway point is that it is not just low-slope waterproofing systems that leak and cause structural damage, but that adjacent walls and fenestrations are frequent contributors to damage as well.

Requirements of the International Building Code The following are requirements in the 2012 IBC concerning waterproofing. There is no single section of the code that addresses all of the issues, and many sections default to manufacturer’s instructions.

Chapter 15 of the 2012 IBC addresses slope in the requirements for roof coverings but does not explicitly include waterproofed surfaces of decks and balconies. Balconies and decks can be covered by the requirements of Chapter 15 by applying the definition for rooftop structures of “a structure on top of

any part of a building”. Since this is critical to waterproofing performance, this is an issue worthy of a potential code change.

Chapter 14 of the 2012 IBC contains requirements for exterior wall weather protection performance, essentially that it must prevent the accumulation of water within the wall assembly and provide a means of draining water to the exterior. Section 1405.4 requires flashing to be installed in such a manner so as to prevent moisture from entering the wall or to redirect it to the exterior. This is obviously a performance-based provision. It also focuses exclusively on details at specific locations, which is consistent with what is found in forensic investigation practice.

It has been, and continues to be widely accepted that it is beyond the structural engineer’s scope to anticipate and design for defective “as-built” building envelope construction. Section CB.5 of the Commentary in the 2002 version of ASCE 7 stated this

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Building envelope leakage at EEEs can be from one or more of the following sources: a) flashing details at a horizontal waterproofing system b) flashing details at guardrail and/or handrail assemblies c) flashing details around fenestrations such as doors and windows d) flashing details around penetrations e) a combination of some or all of the above Horizontal waterproofing membranes are low-slope, or near-horizontal, systems that rely on a complete integration to perform. Think of it as a complete load path. Most membranes are either a sheet-good or fluid-applied. The membranes typically adhere to sheet metal shaped to create flashing at corners, edges, scuppers, drains, etc.

Even though these membranes are characterized as “waterproof ”, most rely on water draining away in relatively short periods of time (days rather than weeks).

Standing water on membranes can prematurely deteriorate the membrane and or “sweat through” to the substrates. This is why slope and drainage provisions are critical.

GENERIC THRESHOLD SECTION

Figure 3. Detail creates a reverse slope.

Figure 4. Failed waterproofing at elevated stairway.

understanding as, “Water infiltration through poorly constructed or maintained wall or roof cladding is considered beyond the realm of designing for damage tolerance.”

Chapter 23, Section 2304.11 of the 2012 IBC addresses the protection of wood against decay. The presence of an impermeable moisture barrier generally meets the requirements for protection against decay.

The recent failures and the potential risk to life safety warrant reevaluating and perhaps strengthening these requirements. Perhaps the inclusion of a drainage plane and/or sloping of the impermeable moisture barrier, in addition to the mere presence, are worthy of inclusion.

Proper Design and Plan Review As noted above, the design of the waterproofing system is generally in the architectural scope, not the scope of the structural engineer.

Compounding the problem, the waterproofing system gets far less attention in design, plan review and construction than it deserves,

on a relative risk basis, compared to other parts of a project.

In the author’s experience, waterproofed balconies and other appendages are treated by plan checkers as roofs with respect to applicable slope and drainage provisions, in the absence of detailed product ICC Evaluation Reports. In reality, each waterproofing system has an ICC Evaluation Report that mandates minimum slope and drainage requirements (typically 2%). Creating a consistently proper slope within the actual waterproofing systems is uncommon. The membranes typically follow the slope of the structural framing substrate.

Finally, most membrane manufacturers have requirements for what is considered an acceptable substrate. If the membrane is being placed directly on a structural element such as structural sheathing, asking the designer of the waterproofing system if he or she is specifying a product compatible with the structural material could go a long way to avoiding lawsuits or even injury to occupants resulting from the decayed structural member that can follow a failed membrane.

(a)

(b)

Figures 5a and 5b. Penetrations.

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Lessons to be Learned Slope Considerations Figure 2 (page 23) depicts a typical exterior deck-to-wall detail. The membrane is located on the top of the wood sheathing, beneath the concrete topping and turned up the vertical surface to lap beneath the metal pan flashing.

The detail graphically depicts sloped structural wood framing, the wood sheathing, and the concrete topping. The detail also refers the contractor to the structural drawings for the deck framing. These notes could be interpreted as transferring the reader’s attention to those portions of the drawings prepared by the responsible party (which is would be incorrect in almost all instances) or transferring responsibility for computing framing slopes/ elevations/clearances on the exterior deck to the structural engineer (which the structural engineer would object to). For many modern light-frame apartment complexes, the drainage design can be a complex exercise which cannot be addressed with simple notes on continued on page 26

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Figure 6. Fascia board over edge-beam.

Figure 7. Structural framing (fascia removed from assembly shown in Figure 6).

This detail could easily be constructed with level structural framing if the structural drawings don’t show the required slope and a flat or nearly flat concrete topping due to dimensional restrictions. This detail does not show the configuration of the cantilevered wood joists. However, cantilevering a level floor joist out past the exterior of the building requires specific structural detailing to produce a sloped structure on the cantilever.

A cantilevered joist system also results in no elevation change of the structure across the threshold, requiring a different solution for matching finished elevation. The bottom line is that elevations, clearances and surface slopes must all be coordinated by the building envelope (and waterproofing) designer, which is typically not the structural engineer.

In harsher climates where the freeze thaw cycle is a concern, drainage and drying become even more paramount. Water that is not drained away from the building can saturate concrete and masonry resulting in very rapid deterioration.

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the architectural drawings or hoping that the structural engineer has somehow dealt with the issue.

Note also how the concrete topping is specified as “2-inch min”; the implication being that the topping can be thicker as needed.

But the fixed dimension from the threshold to the top of the structural elements limits the ability to slope the topping by thickening the topping. Inadequate slope of the concrete topping fails to provide Deflection, the first ‘D’.

The dimension on the left is “not to scale”, resulting in a detail that makes it look much easier to achieve the minimum thickness and slope than it really is.

This detail also specifies a protection/drainage board over the membrane to protect the membrane from damage during the placement of the concrete topping and other construction activities, as well as to provide a drainage plane. Providing the slope for drainage, the second ‘D’, at the membrane is important as water will work its way beneath the concrete topping.

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Figure 3 (page 24) shows a condition where the details at the edge of the concrete topping created a reverse slope in the membrane interrupting the second ‘D’, the drainage path to the weep holes. This stairwell is exterior of the building envelope and exposed to rain, similar to a covered balcony. The buildup of layers of materials, notably the closure plate for the concrete topping, cause the membrane to change slope at the edge of the stairwell. This situation is perhaps a little more difficult for the structural engineer to anticipate and influence in design, but it is certainly something to look for during design coordination phase and during structural observation site visits.

Smooth Surfaces Figure 4 (page 24) depicts an elevated stairway exposed as part of an investigation associated with litigation. The stairs were comprised of steel stringers and pre-cast concrete treads.

The guardrails were comprised of steel pickets lag-screwed into the supporting wood framing.

The waterproofing membrane and concrete topping system was conceptually intended to emulate a “bird-bath” with perimeter weep-holes intended to drain water reaching the membrane level. It was discovered that the waterproofing design and installation fell well below the performance standard of providing positive drainage to prevent ponding and preventing moisture from penetrating the building envelope.

Issues observed within Figure 4 include: A) Inadequate slope to drain, the second ‘D’. Areas of “reverse-slope”.

B) Waterproofing traverses rough/ sharp edges.

C) Horizontal OSB notched for steel plate. Water directed behind cladding.

D) Waterproofing spans dissimilar materials.

Without adequate waterproofing, the supporting structural element was exposed to excessive amounts of moisture. The

Figure 8. Steel balconies.

Figure 9. Steel stair landing. Images are actually taken from multiple examples of this landing type.

actual waterproof design coordinator of record (The Architect) was apparently unaware of the myriad of “as-built” changes and errors.

All the details pointed out above are issues the structural engineer should be aware of and represent opportunities for the structural details to help in the waterproofing solution.

between the plies of the beam. This deck was not waterproofed, but it illustrates how multi-ply elements can trap moisture and conceal damage. Using a single, solid structural member is a more durable solution that eliminates the faying surface that traps moisture between the plies. Adding vertically oriented spacers that provide a drainage space between the fascia and the beam could have significantly improved the performance of this deck.

Penetrations Appendages are the intersection of the interior and exterior, and as such require some elements to cross the moisture barrier. Penetrations such as those shown in Figures 5a and 5b (page 24) occur in both the vertical barrier on the wall and horizontal barrier on the surface of the appendage. Penetrations may be unavoidable, but they can be reduced and located and designed strategically to better integrate with the waterproofing system. Providing Deflection and Drainage (the first and second Ds) to direct water away from penetrations is the first line of defense at penetrations. Providing Drying and Durability (the third and fourth Ds) can go a long way toward mitigating minor, intermittent water intrusions and prolong the life of the structure.

Multi-ply Members Members built up of multiple plies can trap moisture between the plies. The exterior of the member can appear in generally good condition while the interior begins to resemble a hollowed out log.

Figure 6 show a fascia board over the face of a multi-ply edge beam at the edge of a deck and Figure 7 shows the structural framing once the fascia has been removed. Further investigation revealed similar concealed deterioration

Materials Why not just use steel? Figure 8 shows steel balconies in Colorado. The setback of the exterior walls allows for a structural framing system alternate to cantilevering of the interior floor joists. The choice of material is the fourth ‘D’, durability.

However, to highlight that steel is not a panacea and the difficulty of integrating structural appendages, Figure 9 depicts a pre-fabricated steel stair tower bolted to a wood-frame building. The project requirements featured mock-ups, quality-control inspections, coordinated design and a specialty waterproofing consultant, yet this element failed to perform. The openings created by coped structural connections provided a path for water to access the interiors of the elements. The structural engineer can’t blame that on the architect.

So if steel isn’t necessarily the solution in and of itself, should the industry stay with wood?

Durability of wood is an important consideration for appendages. Perhaps evaluating the project specific conditions that may create challenges to achieving a well performing moisture barrier warrants considering the use

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of preservative treated members. However, the use of preservative treated lumber also requires consideration of corrosion of fasteners and hardware. As noted above, this is a complicated issue, with no simple solution.

Summary In summary, the structural engineer should become versed in the issues involved in waterproofing design, for no other reason than as a means for risk reduction. The structural engineer can do the following to improve the current situation: 1) Confirm that the project actually has a building envelope and waterproofing designer.

2) Enhance coordination between the structural and architectural details, particularly at appendages and structural interfaces (stair stringers, guardrail anchorage, ledger attachments, cantilevered members, etc.).

3) Recognize the importance of drainage and slope for the performance of all waterproofing systems.

4) Use more durable materials such as pressure preservative treated lumber and steel but recognize that they have their own design challenges such as corrosion.

5) Know the 4 Ds.

Acknowledgements Several prominent structural engineers provided steering and technical review. The authors sincerely thank them.▪

Historic structures significant structures of the past

I

n 1838, an arsonist burned Lewis Wernwag’s Colossus Bridge (STRUCTURE, June 2014) over the Schuylkill River near Philadelphia. Its 340-foot main span was, at the time, the longest single span bridge in the United States. Charles Ellet, Jr. (STRUCTURE, October 2006) immediately proposed replacing it with a wire cable suspension bridge. By this time, several Finley Chain Bridges were built in the Philadelphia area as well as a short lived, long-butextremely-narrow, pedestrian wire bridge across the Schuylkill River built by Josiah White and Erskine Hazard.

Since it was the first wire cable bridge in the world, reference is made to an article in the Port Folio of June 1816 that indicated, “It is supported by six wires, each three eighths of an inch in diameter – three on each side of the bridge.

These wires extend, forming a curve, from the garret windows of the wire factory to a tree on the opposite shore, which is braced by wires in three directions. The floor timbers are two feet long, one inch by three, suspended in a horizontal line by stirrups of No. 6 wire at the ends of the bridge and No. 9 in the center, from the curved wires. The floor is eighteen inches wide, of inch board secured to the floor timbers by nails, except where the ends of two boards meet; here, in addition to the nails, the boards are kept from separating by wire ties. There is a board six inches wide, on its edge, on each side of the bridge to which the floor timbers are likewise secured by wires. Three wires stretched on each side of the bridge along the stirrups form a barrier to prevent persons from falling off. The floor is sixteen feet from the water, and four hundred feet in length.” It was only in use for a short time, until a wooden covered bridge by Lewis Wernwag replaced Finley’s bridge.

On March 16, 1839, the Commonwealth of Pennsylvania passed an Act, commonly known as the Free Bridge Act, to “authorize the erection of free bridges over the River Schuylkill at or near Philadelphia.” Commissioners were authorized to solicit designs for a bridge at Arch Street and one at Callowhill Street.

To promote his design, Ellet wrote A Popular Notice of Wire Suspension Bridges in a 12-page pamphlet on April 15, 1839 that was later reprinted (June1, 1839) in the American Railroad Journal and Mechanics Magazine. The editors noted, “It is with great pleasure that we commend to the attention of our readers the following paper on Suspension Bridges – by one of our most able and enterprising young engineers. He has the merit of having been one of the foremost in drawing the notice of the profession to this most beautiful and economical mode of structure.”

Fairmount Bridge across the Schuylkill River

By Frank Griggs, Jr., Dist. M.ASCE, D.Eng., P.E., P.L.S.

Dr. Griggs specializes in the restoration of historic bridges, having restored many 19 th Century cast and wrought iron bridges. He was formerly Director of Historic Bridge Programs for Clough, Harbour & Associates LLP in Albany, NY, and is now an independent Consulting Engineer.

Dr. Griggs can be reached at fgriggsjr@verizon.net.

28 April 2016

Since his earlier proposals for a major multiple span suspension bridge across the Potomac River and the Wheeling Bridge across the Ohio River had limited distribution, this was the first major, broadly distributed, article on wire suspension bridges in the United States. Some of his main points were as follows: Particular Advantages of Wire Cables.

8. There are many reasons adduced for the preference given to wire cables, over the chains of bar iron, which they have nearly superseded. It is not possible to obtain iron free from flaws, though all reasonable precaution be observed in its manufacture; and it is not always practicable to detect the flaws by the test to which each bar is subjected prior to its employment in the structure.

16. A suspension bridge across the Schuylkill would leave the channel unobstructed, as at present. It would be secure against destruction by fire, or by flood. It would be much less expensive than a wooden bridge, constructed on permanent piers, and not more expensive than the lowest class of those bridges that could, with any show of propriety, be admitted. It would be not less firm than one of timber, and scarcely less durable than one of stone. As a contribution to the architecture of the city, and an ornament to the Schuylkill, it would be unsurpassed.

17. The lightness, grace beauty of these structures, when tastefully designed and judiciously applied, can be only adequately appreciated when witnessed in place. No drawing or description can properly represent their appearance.

And the edifice never parts with its beauty.

The form it assumes, when first thrown over the stream, is the result of natural laws which are always in action, and will preserve its position and figure forever. It may at times undergo a slight inflection – imperceptible to the eye – when heavily and unequally loaded, but immediately recovers its position on the removal of the charge.

This small pamphlet was the first to describe the wire cable suspension bridge in the United States, even though Finley’s chain bridges (STRUCTURE, March 2016) were well known through his article in the Port Folio both in America and Europe and had been mentioned in Thomas Pope’s 1811 Treatise on Bridges. He then presented two sketches, one for a bridge on Arch Street with masonry side arches and one with the towers on the Wernwag abutments with the anchorage on the west, 275 feet back from the tower, and on the east two options for cable anchorage. One had the cable anchored close to the tower and one with the cable extending back to a rock cliff for anchorage.

He wrote that his drawing of the bridge appeared to some “more like cobweb or gossamer than the

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Trautwine Bridge details.

commissioners a change of the location has caused certain modifications to be made to adapt it to the new site.

The process of awarding the contract to build the bridge was anything but clean. Ellet was traveling in the west in parts of 1839 and 1840. The interactions between Ellet, John A. Roebling and Andrew Young (STRUCTURE, November 2008, Sayenga)were extensive and sometimes bitter. The contract was awarded to Young on May 9, 1840, using Ellet’s plan. On June 11, 1841, the decision was reversed and the contract was given to Ellet who signed it on June 17, 1841. The National Gazette wrote, “The plan for the bridge is beautiful, and as this is the first wire suspension bridge in the United States, it will be an object of great interest to the whole community. Mr. Ellet is entitled to great credit for this plan, and his execution of the work will give him higher claims to the consideration of his fellow citizens.” The North American reported on June 14, 1841, “We are gratified to learn that the Bridge at Fair-Mount is to be rebuilt immediately. Mr. Charles Ellet has contracted to do the work; at a cost not to exceed $71,000…

The National Gazette says it is to be a wire suspension bridge on a beautiful plan the only one of the kind in the United States.

The work will proceed at once, if possible, be finished before the first of January.” His design for a central span of 357 feet was ultimately selected from over five competing designs, and would be the second iron wire suspension bridge in the United States and the first of any major bridge.

Ellet started work in July and progress on the bridge was kept in front of the public by another article in the American Railroad Journal on November 15, 1841 that had originally been published in the United States Gazette. It wrote, The bridge is constructed at the expense of the county, and under the superintendence

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rough stuff adapted to the wear and tear of heavy teams and droves of beef cattle, it met with no little opposition both from well meaning and from interested parties.” He then wrote another promotional five-page piece entitled, Suspension Bridges. – Plan of the Wire Suspension Bridge About to be Constructed Across the Schuylkill, at Philadelphia for the American Railroad Journal in their March 1, 1840 issue.

He wrote, in part, The wire suspension bridge represented in the annexed engraving, was designed in compliance with an invitation of the Commissioners of the city and county of Philadelphia; and is intended to succeed the Fairmount bridge, which was destroyed by fire in the summer of 1838. The plan as approved by the Board, who have since advertised for proposals for the erection of the work; and it is understood to be their intention to urge its immediate completion.

Without adverting to the merits of this plan, as a particular application of the principle of suspension; the fact that such a bridge is about to be constructed, cannot but be matter of interest to the profession, as an auspice of the introduction into this country of an improvement which has deserved and acquired the most abundant success abroad.

The engraving of the bridge intended to be constructed across the Schuylkill offers a very faint idea of the appearance presented by such a structure, when tastefully designed and viewed in place. It will, however, serve to convey an impression of the general appearance of suspension bridges, to those who have not possessed the opportunity of witnessing some of the fine specimens of the art which have of late years been erected in Europe…

The proceeding remarks apply to the plan of the bridge as it was presented and approved; but since its adoption by the

Fairmont Bridge proposal, Schuylkill River at the Arch Street Site, 1840.

of Mr. Ellet, the Engineer, who furnished the plan. We wish him success in his enterprise; though we should judge from the magnitude of the edifice, and the costliness of the materials employed, that the contract price (fifty thousand dollars) will hardly remunerate him for his exertions.

The former bridge on the same site cost about one hundred and twenty thousand dollars, though the masonry was of the coarsest description, and the superstructure of wood. We can, therefore, hardly suppose that such an edifice as is now in progress, composed of massive blocks of granite, finely cut and beautifully fashioned, and which is supported by cables of an indestructible material, can be erected on the same ground for less than one half the cost of its predecessor. At any rate if Mr. Ellet succeeds in accomplishing the work at his estimate, we speak for this sort of bridge, a degree of popularity which may eventually remunerate him for the hardness of his present bargain.

John Trautwine noted in his Civil Engineering Handbook that there were 2,816 wires in the ten strands and that “every wire was separately boiled in a preparation of linseed oil, as often as was found to be necessary to give it a suitable coat of the varnish and after the cables were in place they were thoroughly saturated with the same material, an application found to be an adequate protection against oxidation.”

There were five 3-inch diameter strands on each side that laid flat on the top of the towers and then draped down towards mid span on different arcs, giving sag to span ratios of 1/12

to 1/13. This configuration of the cables was similar to that used by the Sequin Brothers in France and was called a garland system. Since Ellet had studied in France, he used their practices when he returned to the United States in 1831. The cables converged toward mid span, with the spacing at the top of the towers being 35½ feet and at mid span 29 feet. The suspenders were ¾-inch diameter and had a spacing of 4 feet. The suspenders were hung from each cable strand alternately such that, given there were five cables, the spacing of suspenders on any one cable would be 20 feet. At the lower end of the suspenders, the wires ran through an eyebolt passing through the lower chord and adjusted with nuts. The wire suspender was then wrapped back on itself and wrapped with wire. The width of platform out-to-out was 27 feet and from inside-of-curb to inside-of-curb 25 feet. There were walkways on each side with a width of 4 feet 4 inches, giving a roadway width of 16 feet 4 inches. The railings doubled as a stiffening element. There were three longitudinal truss members, as seen on the right side of the diagram, with the bottom two bracketing the cross beams, g, in the Howe truss form. The doubled vertical rods were 7/8-inch diameter and ran from the top chord to the bottom cord with threaded ends. The wooden diagonals were 4 by 5 inches and were set into iron castings. In the upper left corner, Trautwine had a detail on how Ellet connected his suspenders to the cable strands.

The North American reported on November 29, 1841, “This novel, yet beautiful structure, is going ahead rapidly, and will be ready for use early in the spring. The bridge itself

Fairmount Bridge.

Fairmount Bridge with Wernwag’s wing walls.

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will be composed of wood suspended from wire cables. Ten cables consisting of about 300 wires each are stretched from the abutments on each side of the river. They pass over the tops of massive granite columns 30 feet high… we imagine this beautiful bridge will be the first and the only one of the kind in this country. The greatest difficulty in its erection, we should judge, is securing the ends of the cables.” It was test loaded on January 1, 1842, at which time The North American reported, “On New Year’s day the new Wire Bridge was so far completed as to enable a number of persons to cross the river upon it.

Mr. Ellet deserves credit of the rapidity with which he has pushed forward this work to completion.” The bridge opened in the spring of 1842 with a final cost of $53,000.

The bridge lasted until 1875, when Jacob Hays Linville and the Keystone Bridge Company built a double deck bridge around the suspension bridge without stopping traffic.

As the first of its kind in the United States, it was a resounding success in promoting the further use of wire cable suspension bridges. Ellet went on to design bridges across the Niagara River and across the Ohio River at Wheeling.

He also proposed many other bridges, but was unsuccessful in obtaining the contracts. Ellet died in June 1863 after his ramboat battle on the Mississippi River at Memphis during the Civil War. His main competitor in the wire cable business, John A. Roebling, built the replacement for Ellet’s bridge at Niagara.

He built a major bridge at Cincinnati across the Ohio River and prepared the preliminary design for the Brooklyn Bridge that was built by his son, Washington A. Roebling.▪

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Practical SolutionS solutions for the practicing structural engineer

I

n the design of concrete structures, where concrete slabs and walls are used as the environmental barrier, water leakage is a concern. In well consolidated, normal weight concrete, high pH components within the cement/gel paste react with iron on the steel surface and resist corrosion from actively occurring around the steel. This is called “passivation.”

However, concrete cracking, due to high stress and associated strain defects in the element, allows leakage and lateral migration of water, and effectively introduces all of the necessary components – oxygen, water, and an electrolyte – needed for uncontrolled corrosion of the steel reinforcement. Groundwater leakage through concrete continues to bring water with dissolved oxygen and enhances the electrolytic environment, and salt water exacerbates the problem dramatically.

To help control leakage into a concrete element, it is important to understand the best water control solution is generally to provide a new, exterior membrane to a structure.

However, initial cost, accessibility, public nuisance, or other circumstances, may dictate that such a solution is prohibitive.

In such cases, other methods of water control must be explored.

When solving a water leakage problem around a building foundation or civil structure (tunnels, tanks, vaults, pipes, bridges and docks), approaches can be applied either exterior (positive side) or interior (negative side). Positive side solutions are in direct contact with hydrostatic water, and therefore resist water penetration at the interface. Negative side solutions are not in direct contact with water. It is common to use a combination of solutions, or perhaps different solutions on various parts of a structure, to control water migration.

After a leakage problem has been diagnosed, five classic approaches to an acceptable resolution can be explored: 1) Crack/Joint Routing, Caulking, and/or Dry-packing 2) Crack/Joint Injection, Chemical Grouting 3) Water Management & Drainage 4) Coatings, Sealers, Reactants, Sheet Liners 5) Electro-Osmotic Pulse (EOP) Technology There is not always one right answer to the problem and there are exceptions to any water control solution, so blended approaches are very common.

Solving Interior Water Leakage Problems Below-Grade Five Classic Approaches

By Brent Anderson, P.E.

Brent Anderson is the Moisture Control Solutions Team Leader at Structural Technologies. He serves on ACI 332 Residential Concrete and previously served on ACI 515 Protective Coatings for Concrete. Brent can be reached at banderson@structuraltec.com.

Crack/Joint Routing, Caulking, and/or Dry-packing A simplistic, first attempt is to paste over a leaking crack/joint with a high viscosity compound. This paste should extend over the crack/joint one inch and the paste should be 1/8-inch thick; sometimes it is reinforced. On rare occasions, this may temporarily resolve the leakage problem in the long

32 April 2016

term, provided cracks are static. Costs vary; $5.00 per linear foot is common, plus mobilization.

A slightly more robust solution would be to grindout or rout-out the crack in a “U” or “V” shape, and fill with a high viscosity, low modulus filler.

The performance of this solution depends upon slot depth and width, use of bond breaker, and adhesion to concrete sides. Slots ranging from 3/8 x 3/8 inches, to ¾ x ¾ inches, are common. Fillers ranging from elastomeric (low modulus) sealants, to high modulus epoxies are used. Costs vary, $25.00 per linear foot is common, plus mobilization.

Similar to using polymeric compounds in sawcut or routed-out concrete slots, it is possible to fill the slot with a Portland cement based compound/mortar. The most common technique is to use a crystalline growth mortar. Similar to using high modulus epoxy fillers, the crack needs to be relatively static. Routing out slots in concrete for crystalline mortar filling generally requires a 1- x 1-inch slot, up to 1.5 x 1.5 inches; larger slots are also common. Costs vary; $45.00 per linear foot is common, plus mobilization.

Crack/Joint Injection, Chemical Grouting There are three basic approaches for sealing water leaks at concrete wall/floor defects (cracks and joints). These approaches are as follows: 1) Backside Injection (curtain grouting), whereby a grout material is deposited behind the wall/floor crack/joint or into the earth backfill (permeation grouting or soil solidification). The grout material solidifies soil and plugs leaking water points of origin.

2) Internal Injection (interception grouting), whereby a grout material is deposited into the internal concrete crack/joint at middepth. The internal injected grout fills the crack/joint from internal to external face.

3) Surface Mounted Injection, whereby a grout material is applied to the surface of the leaking crack/joint, or is partially routed and plugged with a water impedance material prior to pressure injection.

Typical resinous injection and generic grout types available in the industry include: • Epoxies • Bentonites • Hydrophobic Urethanes • Hydrophilic Urethanes • Two-Component Structural Urethanes • Acrylamides • Acrylic Resins • Rubberized Mastic or Gels • Micro-Fine Portland Cement This injection process involves placement of a resinous polymer, and/or non-reactive gel or paste, into a crack zone or behind it. Most chemical grouting within the crack zone involves placement of a low viscosity, reactive, epoxy, urethane, or

acrylic-based polymer. These reactive polymers fill the cracked section and theoretically plug the void. They bond to the crack sidewalls in various degrees depending upon crack cleanliness. These various reactive polymers exhibit different degrees of elongation. The grout selection must consider crack width, movement, orientation, age, and sequence.

The cost of injection grouting varies considerably based on mobilization and access, quantity of work, security requirements, time duration per shift, and material used. Rough cost ranges may be as follows: 1) Backside Injection (curtain grouting); variable cost range = $35.00 to $100.00 per square foot 2) Internal Injection (interception grouting); variable cost range = $75.00 to $485.00 per linear foot 3) Surface Mounted Injection; variable cost range = $20.00 to $70.00 per linear foot

Water Management and Drainage This concept can be very simple to complex.

Simple water management solutions may involve cutting a slot into a floor slab adjacent to leakage area(s) and channeling it to a nearby drain. Slot depths and widths vary based on water flow rates. Costs vary, but $25.00 per linear foot, plus mobilization, is common.

A more comprehensive solution may involve cutting out a much wider and deeper slot into or under the floor slab (may include soil removal), adjacent to leakage areas, and installing perforated drain pipe or a manufactured drainage mechanism that collects water and channels it to a sump collection area. Costs vary from $25.00 to $100.00 per linear foot, plus mobilization.

The next water management and drainage step up involves placement of a drainage media to move water from the leakage area to a collection point. Collected water is either pumped to the surface or drained. Water management materials usually consist of some type of deformed plastic sheeting attached to the wet substrate that collects, channels and deposits water to centralized locations. Concrete, masonry, or gypsum sheeting often cover these systems for aesthetics and fire protection. Costs vary from $75.00 to $400.00 per linear foot, plus mobilization.

Coatings, Sealers, Mortar Reactants This process involves placement of a bonded layer, or chemically reactive mortar agent, on the concrete interior surface experiencing water leakage (negative side treatment). All coatings and reactive agents require the substrate to be

free of permeating water prior to installation.

Thus, chemical grouting may be first performed to alleviant active water leakage prior to coating or reactive mortar agent installation.

Interior coatings generally come from the same generic family of polymers as used for pressure injection, i.e., epoxy, urethane, acrylics and/ or latex. Interior coatings must resist both the effects of negative side water and water-vapor pressure. These coatings can be “breathable” (vapor permeable) or “non-breathable” (vapor retarders). Interior coatings depend upon adhesion to the concrete substrate exceeding liquid and water vapor pressures. Further, they must be flexible to accommodate substrate movement.

Costs vary from $5.00 to $20.00 per square foot, plus mobilization.

Some coatings may be chemical reactive agents, commonly referred to as crystalline growth slurrys or mortar treatments. These are surface applied mortars with reactive chemistries to the concrete substrate, meaning that they react with cement hydration by-product(s). Calcium hydroxide is a high pH, soluble salt by-product, contained within the micro voids and pores of the concrete gel matrix.

Surface-applied reactive treatments to a damp concrete substrate can be formulated to react with un-hydrated cement, free calcium oxide and calcium hydroxide, thus creating silicate based crystal growth in pore spaces and micro voids within the concrete gel matrix.

These crystal growth by-products can plug micro voids and pores, and very fine cracks in the concrete matrix, thus creating a water resistant barrier. Costs vary from $4.00 to $12.00 per square foot, plus mobilization.

Electro-Osmotic Pulse (EOP) Technology This technology is an electrical solution for drying out concrete and is capable of protecting reinforcing steel in concrete. EOP systems fundamentally consist of a power supply and two oppositely charged electrodes. The power supply charges an anode (+) terminal at one end of a concrete element and a cathode (-) terminal at the other end. Low voltage (24 to 28 volts) output from the power supply, across the terminals, is created through the concrete element via the water containing micro-voids. Current flows from cathode to anode and electrons flow from anode to cathode. EOP installations are designed to create low intensity electric field(s) within wet concrete element(s) and adjacent soil.

Fundamentally, the design places oppositely charged electrodes on each side of a wet concrete element or area. If the concrete element and adjacent soil is conductive (wet), and the micro-voids are partially filled with water, ions can move from

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electrode terminal to electrode terminal because an electric field was created in the damp concrete between said terminals.

Over time, water moves from anode to cathode and dries the concrete out.

Wet concrete is more conductive than dry concrete, thus high internal moisture content concrete is more conductive than dry concrete.

Lower strength concrete is usually more conductive as well. The highest electrical conductivity is at water leakage locations because the concrete micro-structure is close to saturation.

EOP system design depends on many factors. Placement of anodes is either in a grid system or at wet locations where defects in the concrete element exist. Cathodes are spaced in a manner whereby the electric fields are relatively uniform across the concrete element. Because this is an electrical solution, the designer needs to ensure that outside electric field(s) will not interfere with the EOP system. The cost of EOP installations vary considerably, however a range of $400.00 to $1,200.00 per linear foot of wall length is common. Slabs may be in the range of $25.00 to $80.00 per square foot.

Conclusions Facility owners tend to approach water leakage problems in a systematic way. They tend to explore solutions on a lowest-to-most-costly basis, coupled by spot location-focused to a broad-based scope repair. Engineers and contractors, with input from a facility owner, generally will take a similar approach. Consider further that each water control approach can use a vast array of products with material properties that seem similar; however, they can have quite different results. Be mindful that the contractor’s experience may be more important than the design approach selected.

When engineers and consultants are involved with the water control process, they typically want to determine leakage root cause prior to design. A systematic engineering approach for identifying and solving moisture problems could be outlined as follows: 1) Gather history of problem, 2) Understand the design, 3) Search for the leak path, 4) Perform proper tests, 5) Discover the root cause, and 6) Determine solution approach.

After the water leakage problem root cause is determined, the engineer/consultant and/or contractor must match a cost effective solution with the budgetary criteria that provides the longest service life. This requirement involves considerable experience and knowledge about the concrete structure, materials and tradesmen capabilities.▪

SAN MARCOS HIGH SCHOOL San Marcos, California

By Hossain Ghaffari, Ph.D., P.E.

Classroom building and central quad area.

T

he $136 million 420,000-square-foot San Marcos High School opened in January 2014 in a phased reconstruction of the entire project site. This project transformed the existing 1,800 student capacity single-story complex to a 3,000 student capacity state of the art multi-story high school complex, more than doubling the size of the old school. This new facility provides equity with the other District high schools and includes College Prep and Career Technical Education spaces for the humanities, math/science, technology, performing arts, practical arts, agricultural sciences, and special education programs. The new San Marcos High School Campus features several separate structures that utilized tilt-up and cast-in-place concrete and structural steel construction, including: a 2-story Performing Art Center with a 400-seat theatre, a 2-story Athletic Center with a 3-court gym, a 3-story Academic Building, and a 1-story Academy Building. There are also additional one story structures housing the mechanical equipment, athletic fields shower and lockers and press boxes.

Concrete played an important role in the project, serving as a durable and regional material that has recycled content when teamed with rebar and fly ash. Its thermal properties allow spaces to stay cooler during the day, further reducing loads on the campus’ mechanical systems. Therefore, for the buildings where concrete façade was used, it was an easy decision to use concrete shear walls as the lateral force resisting system for the structure and tilt-up construction was preferred based on two critical concepts. It was imperative that the finish of the exposed concrete surfaces was as flawless as possible, making tilt-up

construction feasible as they are formed on one side; by using a smooth slab-on-grade casting bed, that goal was reached. The construction schedule also played an important role in the decision to utilize tiltup construction since additional time for erecting the formwork was eliminated by casting the panels flat on the ground. There were 312 panels, some of them as tall as 65 feet. The casting and lifting sequence of the panels, along with erection of the structural steel around temporary braces for the panels, was very challenging. Considering the extremely demanding construction schedule, timely delivery and assembly of the panel reinforcing and embeds and concrete pour was crucial for the on time completion of the project.

John A. Martin Associates (JAMA) designed the panels with the constraint to optimize the panels’ thickness to meet the lifting requirements, while minimizing steel congestion to avoid the risk of honeycombing during concrete placement and consolidation on the cast side of the panels. Some of the walls had large openings, making their design challenging. JAMA had to decide how to break up the panels in these walls to accommodate the openings so that the lifting of the panels and their connections together, to meet the chord and shear demand, was achievable while making sure that the location of the panel joints were architecturally acceptable. At the locations where structural steel drag members were to be connected to the shear walls and the force to be dragged into the shear wall, designing the proper embed to fit into thin tilt-up panel ends and providing the proper mechanism to complete the load path became challenging. These embeds would be inside the boundary element of

Classroom and art buildings.

Art, gymnasium and shop buildings and central quad area.

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the walls. The situation became more complex at the locations where the embed was to be used for the connection of two drag members that were perpendicular to each other, and each drag member force was to be dragged into different panels at the panel joints. Again, the issue of steel congestion for such embeds being placed into the boundary element of the shear walls had to be proactively addressed at the schematic design phase to ensure there were enough shear walls with a proper system to reduce the drag force to be accommodated in thin tilt-up panel walls.

Three Story Academic Building The Academic Building, at 250,000 square feet, is a three story structure with a cast-in-place special reinforced concrete shear wall lateral system and structural steel gravity framing constructed at grade-over-spread and wall footings. Floors consisted of composite light weight concrete over metal deck. Tilt-up panels could not be used for this building since it housed all of the classrooms. Ribbon windows were used in a curtain wall system; thus, there were not enough solid wall sections at the building exterior to be utilized as shear walls. Therefore, mostly thick cast-in-place core shear walls were used for the lateral force resisting system.

Gymnasium building.

Two Story Athletic Center Building The Athletic Center Building is a two story structure (82,000 square feet) with a precast tilt-up special reinforced concrete shear wall lateral system and structural steel gravity framing. The building is located on the sloped portion of the site. Therefore, the north portion of the building is constructed over a partial basement with cast-in-place concrete walls, while the south side of the building is constructed at grade-over-wall and spread footings. Floors consisted of composite light weight concrete-over-metal deck.

Two Story Performing Art Center Building

Erected tilt-up panels.

The Performing Art Center Building (63,000 square feet) is a two story structure with a precast tilt-up special reinforced concrete shear wall lateral system and structural steel gravity framing constructed at grade over spread and wall footings. Floors consisted of composite light weight concrete-over-metal deck.

One Story Academy Building and Support Buildings The Academy Building and other support buildings are one story structures with precast tilt-up special reinforced concrete shear wall lateral system and structural steel gravity framing constructed at grade-over-spread and wall footings.▪

Project Team

Steel framing and concrete shear walls.

Owner: San Marcos Unified School District Structural Engineer: John A. Martin & Associates Architect, Civil and Landscape: LPA, Inc., Irvine, CA General Contractor: Lusardi Construction Company, San Marcos, CA

STRUCTURE magazine

Hossain Ghaffari is a Project Manager at John A. Martin & Associates Inc. and a lecturer at California State University Northridge. He can be reached at hghaffari@johnmartin.com.

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Houston’s Hobby Airport Gets New

INTERNATIONAL UPGRADE

By David W. Hillery, P.E., Matt Henderson, P.E. and Raxit Patel, P.E. Figure 1. Structural framing at boarding pier.

H

ouston’s William P. Hobby Airport, named after the 27th Governor of Texas, was established in 1927 as a private airfield, with a main airport passenger terminal added in the 1950’s. Hobby Airport was the primary commercial airport for the city until a new Houston Intercontinental Airport opened in 1969. After that, Hobby continued as Houston’s secondary airport for domestic corporate and private airline service.

A major addition to the terminal building was done in 1999, and a new construction project in 2015 added a Federal Inspection Services (FIS) terminal for international travelers.

It was mostly Southwest Airlines that made use of Hobby Airport in modern times and now Houston is its seventh-largest-focus city, so it was Southwest that constructed the international terminal there last year. The new terminal, as part of the Houston Airport System (HAS), allows Southwest Airlines to provide service to South America, Central America and Mexico. With 280,000 square feet of new space and five new boarding gates, Hobby Airport has become substantially more than it ever was.

Along with the new boarding gates, many features were included in the project. Renovation of the existing lobby, 16,000 square feet of additional concession space, reconfiguration of existing security screening with an increase from 8 to 14 checkpoint lanes, and relocation of office spaces also were accomplished in the new design. An expansion of the Baggage Handling System (BHS) was placed in a new

tunnel, shared with other utilities connected to a new central utility plant. The project includes space to allow 800 arriving passengers to be processed through 16 passport inspection stations.

Construction costs totaled $156 million. That sum paid for such building features as terrazzo flooring, high ceilings, modern restrooms, a new moving walkway, more collaboration areas, large column-free spaces, and a very visible, tall and artistic exterior tree-like column.

The project structural design was done by Henderson + Rogers, Inc. (H+R) in Houston. They worked with the architectural firm of Corgan Associates, Inc. for Southwest Airlines and the HAS to provide the new facilities. There were a number of challenges in design and construction. While new structures were constructed and connections from the older to the newer features were being made, all airport-related traffic, concessions and other businesses had to be maintained without interruption.

Figure 2. BIM model – boarding pier.

Figure 3. BIM model – ticketing area.

STRUCTURE magazine

Structural Challenges Due to Existing Conditions One challenge came in the form of an electrical room in the existing terminal building. This room had been providing essential daily services for critical airport operations. Relocating this electrical room without interruption of airport operations would be too costly.

Therefore, the decision was made to keep the room intact rather

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than move it. The challenge was twofold. First was the possibility of undermining the room’s foundation during excavation of a nearby underground tunnel. So, a temporary soil retention system, 12 to 14 feet tall, was used (Figure 6 ). This system safely shored up the soil in the excavation, so the electrical room remained in constant use during construction.

Second, there was a need for the electrical room’s roof to act as a concourse floor for the new terminal building. The roof could not simply be removed and replaced with a stronger system, because the structure supporting the roof was insufficient to support the new floor loads. The existing single-T precast roof system of the electrical room, built in 1962, was strengthened with additional rebar and structural lightweight concrete. Steel posts were added under the roof to reduce the effective span, and this brought its load carrying capacity up to 100 psf, as required by the International Building Code. All this was done while operations inside the room continued without interruption.

The new terminal building is connected to the existing terminal at both the second floor and the roof. New frame structures were strategically placed to minimize added loading to the existing members.

Computer software, including RISA-3D, was used to model and analyze the existing building as well as the proposed structures. One result of the analysis was the decision to add new columns which pass through the existing roof down to supports on new cantilevered steel beams.

Another connection of the new to the existing structure is where framing for a new cantilevered canopy extended out from the existing 1950 structure. To achieve the desired height of the roof, existing steel columns received new extensions.

In addition to RISA-3D, other computer software used for advanced structural analysis and vigorous gravity and lateral design included ETABS and SAFE from Computers and Structures, Inc.

Selection of Structural Systems and Their Benefits The initial new building foundation was designed with straight-sided drilled piers. However, the design was modified after it was discovered that substantial money could be saved by using auger cast piles instead. Subsequent to a requested pile load test, the pile diameters were reduced from 24 to 18 inches. Incorporating changes could have affected the schedule of the project, so H+R redesigned the foundation and revised drawings in days rather than weeks for a savings in the overall cost of the foundation of approximately one million dollars.

The number of piles per column varied from one to four, and pile cap depth ranged from 36 to 42 inches. Four different pile lengths, 40, 50, 60 and 70 feet were incorporated in the design, depending on column locations and base reactions. The longer piles were needed under columns in close proximity to the tunnel and where they supported loads from large roof or floor areas.

An existing tunnel, approximately 1,000 feet long, accommodates the airport’s Baggage Handling System and other utilities. A new tunnel was designed to run from the existing tunnel to the new international services, where customs requirements are more complex than for domestic flights. The new tunnel width varies from 22 to 48 feet along its length (Figure 5).

The new tunnel’s foundation is a 12-inch thick, cast-in-place, steelreinforced concrete slab thickened to 24 inches below walls. The walls are 12 inches thick and approximately 12 feet tall. The tunnel roof design considered heavy concentrated wheel loads from baggage transfer tugs and other airport vehicles passing overhead. The tunnel roof had to meet a stringent deflection requirement and carried a STRUCTURE magazine

Figure 4. Cantilevered low roof truss supporting high roof framing.

Figure 5. New tunnel floor adjacent to existing tunnel.

Figure 6. Soil retension system at existing electrical room.

thin-set terrazzo floor finish. The cheapest and most quickly built solution used 12-inch thick hollow-core concrete planks spanning approximately 30 feet and supporting a 4-inch concrete topping slab.

At the end of the tunnel where its width was at a maximum of 48 feet, the roof was composed of a cast-in-place, pan-formed, beamand-slab system 25 inches deep.

The new terminal building is more than 1,000 feet long and was constructed in three approximately equal sections connected with two expansion joints. The structural system to resist wind loads consisted of concrete moment frames, providing lateral support at the second floor level. Concrete columns at the east end of the building in the ticketing area extend above the second floor and provide lateral support to new steel trusses that are 5 to 8 feet deep. At each continued on page 40

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April 2016

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Figure 7. Low roof truss supporting high roof – RISA 3D model.

Figure 8. Curved embed plate.

column line, there are steel columns supported by cantilevered low roof trusses. These columns extend up and connect to 5-foot-deep steel high roof trusses, and provide lateral support to the high roof framing (Figure 4, page 38).

At the west concourse, to give the boarding area a feeling of open space, several column locations were skipped, creating longer spans between columns above the second level. 66-foot-long steel trusses were designed to span this length and support the roof framing. Composite frame action between the concrete columns and the 5-foot-deep trusses provides lateral support for the roof. Curved steel embed plates with hooked deformed bars were installed in round cast-in-place concrete columns as connection points for these steel trusses (Figure 8).

A key architectural feature for the new FIS facility is a tree-shaped column supporting sloped high roof framing, located strategically

along the existing roadway near the drop-off area of the new terminal building. The tree column has a 4-foot diameter “trunk” which splits into two tapered branches. Like the trunk, each branch is 4 feet in diameter at its intersecting base, and then tapers down to 2 feet at the top. The trunk and branches were rolled and fabricated from half-inch-thick steel plates (Figure 11).

Sloped high roof framing at the ticketing area was designed using a combination of long span steel roof trusses, wide flange beams and bar joists supported by steel columns. The high roof steel columns are mounted on the cantilevered ends of the steel trusses of the lower roof. The cantilevered lengths reach up to 35 feet, giving the desired architectural open spaces and visually pleasing high roofs.

Cloud Room

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April 2016

Existing Condition One of the most magnificent areas of the new Hobby Airport houses a semicircular projection of the 1950 terminal building, known as the “Cloud Room.” The structure originally served as an office space for the airport. The entire area (Figure 10) gives the impression, by its size and with electric and natural lighting, of an almost outdoor experience. Passing by the Cloud Room on the way to a gate may make a traveler feel well prepared for flight. However, making this expansive dream come true presented engineering challenges amid the project schedule requirements.

The Cloud Room is located above the lobby of the original terminal, and the desire was to remove columns and provide more uninterrupted space in the area below. Its floor structure consists of a concrete slab on composite metal deck supported by steel floor trusses. The floor trusses were cantilevered out over steel pipe columns with ends tapered out to a mezzanine perimeter. The columns below were arranged in a colonnade pattern bearing directly on the lobby floor.

Figure 10. Cloud room – RISA 3D model.

Figure 9. Cloud room – existing condition.

The request was to eliminate these columns to allow a smoother flow of pedestrians, and to increase the beauty and atmosphere of the area.

The architect originally suggested removing the 1950 Cloud Room altogether. However, this would require relocating existing mechanical ducts, electrical, and plumbing equipment serving the main lobby, which would have required an interruption of heating and cooling for a substantial duration. This would come at a much greater cost to the owner than the actual solution which was implemented.

Structural Solution The solution was to support the Cloud Room from the roof structure and then remove the columns below. H+R designed a system of beams and steel pipe hangers in the same geometry already present in the colonnade orientation, and coordinated with the existing MEP system.

The hangers were spliced with the existing pipe columns extending up to the 1999 addition’s long span steel trusses.

To minimize the additional weight added to the high airport roof ’s steel trusses, existing miscellaneous framing at the penthouse floor and roof structure was removed, and an in-plane truss system was designed to provide the lateral stability for this hanging penthouse structure. The existing roof trusses were analyzed using 3D analysis software (RISA-3D) and some trusses had to be reinforced. Subsequent to the installation of the hanger supports, and with the new reinforcement in place, the existing columns bearing on the lobby floor were removed. The process was well-planned and sequenced to minimize impact loading. The general contractor monitored deflections of the high roof trusses during this procedure, and all measured less than ½ inch, well within the code prescribed limits. The solution prevented interruption to MEP services and proved economical as well as architecturally beneficial to the project.

Houston’s Hobby Airport Deserves Enthusiastic Celebration

Figure 11. Tree column.

In Houston’s Hobby Airport, these facilities were made possible not only by HAS and Southwest Airlines, but by architects, structural engineers and builders who met many challenges and solved them with creativity, advanced technology and hard work. When you visit Hobby Airport on your way through Houston, take a look around and consider all the elements that went together to make such an important aviation facility beautiful as well as functional.▪

If you find yourself traveling in the near future, on a domestic or international flight into or out of Houston, you will be able to enjoy with some enthusiasm and interest what might otherwise be a mundane, ordinary trip out of town. The enterprises that process passengers on their way with efficiency have made it possible for us all to travel in comfort. This is due to the cooperation and coordination of many inter-related facilities found at the airport, all housed in massive structures of concrete and steel.

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David W. Hillery, P.E., is a Senior Structural Engineer working in Construction Administration for building projects with Henderson + Rogers. He can be reached at dhillery@hendersonrogers.com.

Matt Henderson, P.E., is Principal-in-Charge at Henderson + Rogers. He can be reached at mhenderson@hendersonrogers.com.

Raxit Patel, P.E., is a Project Manager for Henderson + Rogers. He can be reached at rpatel@hendersonrogers.com.

April 2016

Building Blocks updates and information on structural materials

B

y definition, innovative means “tending to innovate or introduce something new or different”. Within the context of the International Building Code (IBC), Section 104.11 Alternative materials, design and methods of construction and equipment provides a mechanism for how building officials can approve innovative, new or alternative building materials, design and methods of construction that are not adequately addressed in the code. Alternatives to what are listed in the IBC are acceptable as long as the quality, strength, effectiveness, fire resistance, durability and safety are proven equivalent. This code provision has stood the test of time and provided a pathway to building code approval for countless new and innovative building materials through the conformity assessment process.

Conformity assessment applies across the spectrum of products and systems used in daily life including electronics, medical devices, appliances, automobiles that we drive, and even building material products used in construction of our homes and businesses.

The framework for evaluating building material products for compliance with codes and standards is ultimately regulated by the International Organization for Standardization (ISO) through the development and publication of ISO/IEC 17065. Conformity assessment is a means to protect the public and boosts consumer confidence that products have met accepted industry standards. It also helps building officials ensure life safety and environmental requirements of the code are met. For building material manufacturers, it provides a means for significant differentiation from competitors with independent proof of a better, more effective product.

Three key elements of conformity assessment include testing, certification and inspection.

Building material products are commonly tested through accredited testing laboratories, such as those accredited by the International Accreditation Service (IAS), in order to establish compliance and confirm performance characteristics as required in ASTM test standards and Acceptance Criteria. Certification is carried out by an independent party that issues a certificate stating the product meets required codes and standards. This is third party conformity assessment. Inspection involves the process of checking the product quality system periodically to ensure it continues to meet required standards. All three aspects of conformity assessment are necessary in order to ensure the safety, reliability and effectiveness of building material products used in today’s complex structures.

A Deep Dive into Conformity Assessment Evaluation of Innovative Building Products

By William Gould, P.E.

William G. Gould is VicePresident of External Relations and Client Services at ICC Evaluation Services, LLC. He can be reached at wgould@icc-es.org.

42 April 2016

ISO maintains many different standards. Three are of particular importance to construction and the building material product industry. Testing laboratories are governed by ISO 17025 General Requirements for the Competence of Testing and Calibration Laboratories. Certification bodies are governed by ISO 17065 Conformity assessment – Requirements for bodies certifying products, processes and services. Inspection is governed by ISO 17020 Conformity assessment – Requirements for the operation of various types of bodies performing inspection. These three ISO standards include separate requirements for the specific entities involved, and underpin the entire building material evaluation process.

So Why is This Important to Practicing Structural Engineers?

One of the reputable bodies for evaluating and certifying building material products, ICC Evaluation Service (ICC-ES) is a non-profit subsidiary of the International Code Council (ICC), the organization that writes the IBC, International Residential Code (IRC) and many other model codes. ICC-ES has been engaged in the process of evaluating innovative building products for compliance with the codes for decades. ICC-ES is the only conformity assessment body accredited by the American National Standards Institute (ANSI) to ISO 17065 as having the capability of conducting product evaluation to ICC-ES acceptance criteria, and fully complies with IBC Section 1703 Approvals. These provisions contain requirements for approved agencies, building material product performance, labeling and follow-up inspection services. Approval is based on information provided to the Building Official by the approved agency. The Building Official continued on page 44

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Most Widely Accepted and Trusted

What’s in an ICC-ES Evaluation Report ICC-ES Evaluation Reports from ICC Evaluation Service® are the most preferred resource used by code officials to verify that new and innovative building products comply with code requirements. The ICC-ES Evaluation Reports provide information about what code requirements or acceptance criteria were used to evaluate the product, how the product should be installed to meet the requirements, how to identify the product, and much more. ICC-ES Evaluation Reports are divided into eleven major areas.

CSI Division Number––ICC-ES Evaluation Reports, and the building

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Specifications Institute’s (CSI) Masterformat system.

2

1 products represented in them, are organized according to the Construction

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Evaluation Scope––The code(s) that were used to evaluate the product.

3 4 5

Properties Evaluated––A brief description of the properties the product was

5 evaluated against such as fire resistance and wind resistance. This section also

6

shows if the product can be used for structural purposes.

7

Uses––Identifies the scope of the ICC-ES Evaluation Report and relates the

6 product evaluated to code provisions.

Description––Provides a general description of the product and its features,

7 such as length, thickness, etc.

8

Installation––Identifies general and often specific requirements to help

8 the inspector ensure the product is installed properly according to the code

9

M

Evaluation Subject––The specific product(s) covered by the report.

SA

3

PL E

Report Holder––The name and address of the company or organization that has

2 applied for the ICC-ES Evaluation Report.

10 11

requirements or acceptance criteria.

Conditions of Use––Statement that the product, as described in the ICC-ES

9 Evaluation Report, complies with or is a suitable alternative to the requirements of the applicable code and a list of conditions under which the report is issued.

Evidence Submitted––Data (i.e. test reports, calculations, installation

10 instructions) that was used in evaluating the product.

Identification––Information that can be used to identify the product, including

11 the manufacturer’s name, product code, ICC-ES Evaluation Report number, etc.

View current ICC-ES Evaluation Reports online: www.icc-es.org/Evaluation_Reports

12-06514

must first determine if the agency meets the applicable requirements of IBC Section 1703.

ANSI accreditation is not the sole determining factor for compliance with Section 1703 however. Approved agencies must be independent, well-equipped and thoroughly staffed with experienced personnel. To be approved by a Building Official, such agencies must demonstrate their objectivity by disclosing any potential conflicts of interest. They must also have educated and trained personnel experienced in conducting and supervising product evaluations. Due to the relationship with the ICC parent organization, ICC-ES is the most well recognized and approved evaluation agency. Evaluation reports developed by ICC-ES technical staff are widely accepted and trusted technical reports across jurisdictions throughout the U.S.

How Are ICC-ES Evaluation Reports Developed?

The ICC-ES process entails development of Acceptance Criteria through a transparent process that is open to the public. Comprised of Building Officials from throughout the U.S., the ES Committee convenes three

times annually to review and approve Acceptance Criteria proposals. These can be for new Acceptance Criteria or revisions to existing Acceptance Criteria. Acceptance Criteria are internal documents intended for use solely by ICC-ES within the ICC-ES scope of accreditation. Over many years, ICC-ES has developed and currently maintains hundreds of Acceptance Criteria for innovative, alternative products and systems. A few examples of ICC-ES Acceptance Criteria for innovative products include AC13 Acceptance Criteria for Joist Hangers and Similar Devices, AC14 Acceptance Criteria for Prefabricated Wood I-Joists, AC43 Acceptance Criteria for Steel Deck Roof and Floor Systems, AC156 Acceptance Criteria for Seismic Certification by Shake-Table Testing of Nonstructural Components and AC308 Acceptance Criteria for Post-Installed Adhesive Anchors in Concrete Elements. This is just a small sample of many ICC-ES Acceptance Criteria, each representing a tremendous engineering and research effort.

In developing Acceptance Criteria, ICC-ES seeks input from interested parties including product manufacturers, researchers, standards developing organizations, structural

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engineers and other design professionals.

Various structural engineering associations have also historically been involved in the ICC-ES Acceptance Criteria development process and have volunteered their valuable time and expertise to provide technical input.

This collaboration with structural engineering associations and other subject matter experts strengthens the ICC-ES process.

Acceptance Criteria can also be vetted through an Alternative Criteria Process via website postings at www.icc-es.org for cases where the subject of the proposed criteria is nonstructural, does not involve life safety, and is addressed in nationally recognized or generally accepted industry standards. Where a new Acceptance Criteria is needed but other criteria and/or the code provide precedent for its content, or where relatively minor revisions are being proposed to an existing Acceptance Criteria, are also considerations.

The ICC-ES Alternative Criteria Process can provide a quick turn-around for approval or a springboard for review and approval at an ES Committee hearing.

Once the Acceptance Criteria has been reviewed and approved by the ES Committee, the roadmap is set for ICC-ES

use, evidence submitted and product identification (see Report).

ICC-ES ESRs are developed to ensure that materials, designs and products are tested to safeguard public safety while allowing innovation to thrive. The ESR allows the structural engineer and building official to readily approve building products rather than having to spend valuable time and resources to research whether or not the building product meets numerous code and standards requirements. Supplemental evaluations to the California Building Code (CBC) and Florida Building Code (FBC) are also possible, and may include separate seismic or high wind evaluations for these unique and demanding applications.

Independent evaluation reports are a key feature of the building product market, and structural engineers and building officials look for them. Holding a building product evaluation report streamlines the approval process, saving time and money before and during construction.

How Can I Get Involved and What’s In It For Me? First, go ahead and visit www.icc-es.org and request to be added to the ICC-ES

mailing list. This will keep you abreast of updates on ICC-ES Acceptance Criteria, new ESRs and other code related news.

As part of your due diligence, require current ICC-ES ESRs from building product manufacturers in your design practice. This establishes a basis of design and level playing field for product manufacturers requesting your approval and project specification, and will allow you to specify with confidence.

Check the ESR Evaluation Scope to make sure it references the right building code version for your design project, and the ESR Evidence Submitted to make sure it references the appropriate version of the Acceptance Criteria. This reduces potential error by improperly designing with a product that hasn’t been thoroughly evaluated to the appropriate version of the code. Verify ESR Conditions of Use for the product to understand any limitations. This avoids designing with a product that hasn’t been tested and evaluated for special conditions, such as seismic loading or fire resistance.

Finally, provide feedback to ICC-ES as part of the Acceptance Criteria process, or when questions arise regarding ESRs. Opening a dialogue with ICC-ES will get you involved in the process and let them know what’s important to you and your design practice.▪

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to issue Evaluation Service Reports (ESRs).

The ESR provides the building officials with evidence under the IBC Section 104.11.1 Research Reports requirement. Building product manufacturers submit applications with performance test data in the form of qualified test reports conforming to ICC-ES AC85 Acceptance Criteria for Test Reports.

Test reports are based on testing done by an IAS or a signatory to the Mutual Recognition Arrangement (MRA) of the International Laboratory Accreditation Cooperation (ILAC) testing laboratories. Accreditation for the specific type of testing required by the applicable test standards and Acceptance Criteria is essential. Other materials submitted by the building product manufacturer include product information, installation instructions, engineering calculations and manufacturing quality control documentation.

Separate, but parallel evaluations are done for both the technical and manufacturing quality aspects of the submittal. Once all issues are resolved on the technical and manufacturing quality reviews, an ESR is issued and published on the ICC-ES website directory. The manufacturer is then able to apply the ICC-ES mark of conformity and ESR number to the evaluated product labels as proof of conformity, and market the recognition for use under specific versions of the IBC or IRC. Periodic follow-up inspections of the manufacturing locations are then conducted by ICC-ES for the life of the ESR to ensure the evaluated building product continues to conform to the requirements of applicable protocols. This is a critical component of the evaluation process that is not seen by structural engineers and building officials, but goes on behind the scenes between ICC-ES and the report holder.

How Can This Improve the Quality of My Structural Engineering Practice?

The ICC Evaluation Service mark of conformity and ESR number on building product packaging provides confidence and peace-of-mind to structural engineers and building officials alike. The authorized ICC-ES mark shows that the building product has been subjected to a rigorous technical and manufacturing quality review. The ESR contains technical details including scope of evaluation, product use, design and installation, conditions of

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April 2016

Seattle • Tacoma • Lacey • Portland • Eugene • Sacramento • San Francisco • Los Angeles • Long Beach • Pasadena • Irvine • San Diego • Boise • Phoenix • St. Louis • Chicago • New York

Guest Column dedicated to the dissemination of information from other organizations

T

he April 2014 issue of STRUCTURE magazine featured an article in the Structural Failures column, titled Design Deficiencies in Edge Barrier Walls in Parking Structures, by Mohammad Iqbal, D.Sc., P.E., S.E., Esq. The article brought up important points related to the adequacy of upturned cast-in-place (CIP) concrete barrier walls supported on slab edges to withstand code-prescribed vehicle barrier loads in parking structures. We, members of the National Parking Association’s (NPA) Parking Consultants Council (PCC), could not agree more that all types of vehicle barriers in parking structures must be designed, constructed, and maintained to withstand the code-prescribed vehicle barrier load in an effort to protect the health, safety and welfare of the public; however, we would like to provide clarifications to the article.

The PCC’s structural committee has been actively involved in barrier wall design for decades. The PCC’s Recommended Building Code Provisions for Open Parking Structures, published in July 1980, first prescribed that a 10,000 pound ultimate load (6,000 pound service load) located 18 inches above the floor be used as the bumper load criterion, long before any of the national model building codes adopted such a criterion.

As specialists in parking structure design and restoration, PCC members are aware of about 25 accidents in parking structures in the past 10 years where vehicle barriers failed and vehicles fell off the edge as a result, causing property damage, personal injury, or death. For the purposes of this article, failure of the vehicle barrier is defined as the barrier breaking upon impact to such an extent that it was incapable of restraining the vehicle inside the parking structure at the same level as it was parked.

Concrete cracking and other barrier damage that requires repair is not considered “failure,” if the impacting vehicle is kept from going over the edge.

The 2014 article noted that many of the failures occurred for the following reasons: • The parking structure was constructed when the applicable building code did not require a perimeter vehicle barrier or prescribe the design vehicle barrier load.

• Instead of a vehicle barrier, just a wheel stop or curb and either a handrail or an architectural panel were used, which together were inadequate to withstand vehicle impact.

• Concrete Masonry Unit (CMU) walls with inadequate reinforcement were used.

• Cable rail barriers with inadequate anchoring of the cable were used.

• The vehicle hit the barrier at a high speed, resulting in an impact load well in excess of the code-prescribed load.

Design Considerations Cast-in-Place Concrete Edge Barrier Walls in Parking Structures

By Gary Cudney, P.E.

Gary Cudney is President and CEO of Carl Walker, Inc., a national parking consulting firm. He is a Past Chairman of the National Parking Association’s (NPA) Parking Consultants Council (PCC), member of the PCC structural committee, and a contributing author of the committee’s article High Bumpers Prompt Change in IBC Code in 2009.

46 April 2016

The PCC structural committee evaluated the vehicle barrier issue and realized that vehicles today have higher bumpers than vehicles in the mid-1970s when the 10,000 pound ultimate (6,000 pound service load) vehicle impact load at 18 inches above the floor was recommended for reasons explained in a published article titled High Bumpers Prompt Change in IBC Code (January/ February 2009, PARKING magazine). Based on its research of vehicle statistics, the PCC submitted a change proposal to the International Code Council (ICC) in 2008 to increase the bumper impact height. The ICC adopted a vehicle impact height of either 18 or 27 inches (whichever produces the more severe loading) in the 2009 International Building Code (IBC), as recommended by the PCC. In its 2009 article, the PCC also recommended that significant further study of the magnitude of the code-prescribed static bumper load is required to approximate what is actually a dynamic loading condition. This committee intends to develop future recommendations based on: • Vehicle weight, • Vehicle speed, • Energy absorbing mechanisms within the vehicle, • Energy absorbing mechanisms within the barrier wall, and • Statistical analysis of a “design” vehicle hitting the barrier at a “design” speed.

The PCC is currently seeking grant funding and a university research partner to further study these issues, so that an IBC change proposal can be developed and submitted to amend the magnitude of the vehicle barrier load, if it is found to be warranted.

The referenced 2014 STRUCTURE article discussed whether the cantilevered CIP concrete barrier wall on a slab edge can withstand the code-prescribed vehicle barrier load without brittle failure of the wall-slab corner joint. PCC members conferred to clarify the information provided in the article as follows.

1) The article stated, “Many failures occur in concrete structures because of inadequate detailing of reinforcement in joints and connections.

The failure of perimeter vehicular barriers in concrete parking structures offer grim examples where numerous parking patrons have died or have suffered bodily injuries as their vehicles plunged down to the street during the past several years.”

PCC members are aware of about 25 vehicle barrier failures in parking structures in the past 10 years. Based upon a review of accident records, about two thirds of these failures occurred where a CMU block wall, cable rail, or precast concrete spandrel barrier was used, and one third occurred where a CIP concrete wall was used. It is not known if these CIP concrete wall failures occurred due to inadequate detailing of reinforcement in

engineering practice to design the wall-slab joint to be ductile such that yielding of the reinforcing steel occurs prior to a sudden brittle failure of the concrete at the corner.

When using a CIP concrete barrier wall in parking structures, the following is recommended by the PCC: • Use code-prescribed vehicle barrier load and height of impact • Apply the principal goal of having a ductile connection, which can be obtained by considering the following: o Maintain a low reinforcement ratio as described in the paragraph above

o Maintain code prescribed hooked bar development lengths in both the wall reinforcing, as well as the supporting slab reinforcing.

• Provide adequate horizontal reinforcement in both the wall and the supporting structure to distribute the vehicle impact load horizontally over the section of wall/slab joint used to resist the load.

We believe that this performance criteria can be achieved using an appropriate thickness of wall with a single layer or double layer of reinforcing with 90° hooks and careful

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joints and connections or for other reasons.

This data makes it clear that all types of vehicle barrier systems must be designed, constructed, and maintained to be adequate to withstand the code-prescribed vehicle barrier load.

2) The article stated, “The test results show that concrete wall-slab barrier systems do not meet the IBC’s minimum threshold.”

It would be beneficial to view the test results that support this statement. Concrete wallslab barrier systems can be designed and constructed to meet and exceed IBC requirements, as indicated in item 4 below.

3) The article stated, “The issue is whether the barrier system was capable of resisting the code-prescribed 10,000 pound ultimate impact load. The evidence suggests that it does not have the capacity to resist the prescribed load. Rather, its capacity is about one-fourth of the prescribed load.

As such, the barrier system has a significant design deficiency.”

The capacity of the concrete wall-slab barrier system depends on many factors such as the wall thickness; slab thickness; slab perimeter wash thickness; concrete strength; and steel reinforcement amount, location (cover), and configuration. The CIP concrete wall barrier system can be designed to properly resist the code-prescribed vehicle barrier load, as indicated in item 4 below.

4) The article stated, “The assumption that the wall shear force and bending moment at the base of the wall are fully transferred to the slab through the joint region appears to have no basis.”

The wall-slab joint can be capable of transferring the shear force and bending moment resulting from the code prescribed vehicle barrier load. Standard Department of Transportation bridge railing designs use an upturned wall supported on a thin slab edge similar to what is sometimes used in parking structures.

Further, research by Ingvar H.E. Nilsson and Anders Losberg, published in the ASCE Journal of the Structural Division in June 1976, in a paper titled Reinforced Concrete Corners and Joints Subjected to Bending Moment, indicates that when a single layer of steel is used in the wall and slab with standard 90° hooks and the reinforcement ratio is less than or equal to 0.30%, the wall-slab joint is 100% efficient. However, the paper also indicates that if the reinforcement ratio exceeds 0.30%, brittle failure of the joint controls the capacity and no amount of additional reinforcing steel will help make the wallslab joint stronger. It is good structural

consideration of reinforcing steel cover requirements, supported on an appropriately designed slab edge (note the slab edge thickness can be a combination of the base slab thickness plus any thickness of a perimeter wash beneath the wall). Further, most often the wall-slab joint is at the edge of a post-tensioned (P/T) concrete slab where the P/T tendons (structural and temperature) and pair of P/T anchor back up bars provide additional reinforcement in the wall-slab joint that strengthens the corner beyond what laboratory tests might indicate.

5) The article stated, “To improve the joint efficiency, the concrete in the joint region and the members should be bound or confined with straps, hoops, and ties.”

While the use of straps, hoops, and ties will improve the joint efficiency, they are not required for the CIP concrete wall barrier system to resist the code-prescribed vehicle barrier load, as indicated in item 4 above.

6) The article stated, “To avoid any further loss of life, it is suggested that the wall-slab system should not be used in the parking structures as a vehicular barrier.”

CIP concrete wall-slab systems are a viable method of providing a safe vehicle barrier in parking structures. When properly designed, constructed, and maintained, the wall-slab system can withstand the code-prescribed vehicle barrier load without incurring the risk of catastrophic brittle failure.

7) The article stated, “Further, it is recommended that such barriers that are already in place in constructed facilities should be retrofitted.”

Many existing parking structures using CIP concrete barrier walls have no need to be retrofitted, as they may be capable of resisting the code-prescribed vehicle barrier load. The PCC agrees that existing parking structures without vehicle barriers, or those which were constructed before the code included vehicle barrier requirements, should be evaluated related to the currently applicable code(s). At present, the decision to retrofit vehicle barriers that are not in compliance with the currently applicable code is at the discretion of the building owner, as the code does not require that existing structures be brought into compliance with the current code in this regard. It is suggested that engineers who are contracted to work on parking structures without vehicle barriers, or on those which were constructed in the past before the code included vehicle barrier requirements, apprise the owner that the vehicle

barriers do not meet the current code and that this results in risks to parkers and the owner. The owner can make an informed decision about whether to have the vehicle barriers analyzed and retrofitted if needed to withstand the currently applicable codeprescribed vehicle barrier load. Of course, engineers are not qualified to provide legal advice to their clients, so they should refrain from doing so in this matter as well.

The article referred to an incident where a CIP concrete barrier wall failed and a picture of the failed wall was included.

The inference was that the failed wall was constructed in accordance with Figure 2 in the article; however, information about the details of the wall, slab, or vehicle speed was not included. The PCC’s opinion is that the length of the failed wall in the picture makes it doubtful that inadequate detailing of the wall-slab corner reinforcement was the sole reason for its failure or the cause of the failure at all. The article also included a photograph of a failed specimen tested at Banaras Hindu University in India. It would prove beneficial to know the reference and details related to the photo, including how the joint was reinforced. The article indicated that the specimen failed at 22% of the design load. In order to determine if this is correct, the following needs to be answered: “What design load is this?” and “How does it relate to the vehicle barrier design load of the IBC?” It is agreed that the wall-slab corner detailing requires attention. However, to fix a “problem”, one needs to truly understand its causes. The fact that a 6-inch wall with #4 reinforcing bars may not strictly comply with ACI 318 development length requirements and has a reinforcement ratio slightly above 0.30% does not automatically render it inadequate to resist the code-prescribed vehicle barrier load. 6-inch CIP concrete vehicle barrier walls have been constructed in many parking structures. PCC members are not aware of any failures of such walls, whose cause could be specifically attributed to the alleged inadequacy of the cited detail.

The incident presented in the article may be an exception. But then, again, the relevant details of that incident were not cited.

Prior to jumping to the conclusion that all existing 6-inch CIP concrete vehicle barrier walls in parking structures require retrofitting, we recommend further study in view of ACI 318-11 Section 1.4. This section allows approval of construction “which does not conform to or is not covered by this code.”

The 2012 IBC has a similar provision in

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Section 104.11. Although some 6-inch wall details may not strictly comply with every ACI 318 provision that does not necessarily mean that it is inadequate to resist the code-prescribed vehicle barrier load. We recommend that a research project be conducted to assess the adequacy of such walls in existing parking structures.

8) The article stated, “For example, installing a downturn beam or installing an upturned beam instead of a wall can help avoid the deficiency.”

While installing downturned or upturned beams at slab edges with CIP concrete barrier walls is a possible solution, it is believed that doing so may not be necessary. The added expense may not be warranted.

Designing and installing a wall-slab barrier that can withstand the code-prescribed vehicle barrier load without brittle failure of the corner joint is a solution that is much more cost-effective.

9) The article stated, “Further, a singlyreinforced wall is inadequate to distribute the impact load or to resist shear properly. It is suggested to use a wall that is reinforced each way, each face and to justify rationally the impact load flow from the point of application to the underlying structure.”

A properly designed CIP concrete barrier wall with reinforcing steel in a single layer can meet code requirements to transfer the shear and moment from the code required vehicle barrier load into the slab without sudden brittle failure of the concrete at the corner joint, as described in item 4 above.

Conclusion All types of vehicle barrier systems in parking structures, including CIP concrete walls, precast concrete walls, tensioned cables, steel guard rails, and CMU walls must be properly designed, constructed, and maintained to withstand the code-prescribed vehicle barrier load. As indicated above, the PCC members believe that CIP concrete walls can safely be used for the vehicle barrier.▪

Acknowledgment Gary Cudney acknowledges the valuable contributions of PCC structural committee members John Purinton, S.E., Principal of Watry Design, Inc., and Adam Cochran, P.E., Vice President of Kimley-Horn and Associates, Inc., in the preparation and editing of this article.

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Smart Structures

By Dilip Khatri, Ph.D., S.E.

Dilip Khatri is the Principal of Khatri International Inc. and Khatri Construction Company located in Pasadena, California. He has served as an expert witness for several construction-law firms and as an insurance/forensic investigator of structural failures. He serves as a member of STRUCTURE’s Editorial Board and may be reached at dkhatri@aol.com.

S

tructural Engineering is an evolving field.

Our profession continues to innovate with brilliant new technology, materials, and analysis methods, at an ever increasing pace. I can remember when I started as a junior structural engineer in 1983, the introduction of personal computers was just beginning to take place, along with the finite element method for structural analysis. This was a significant step forward from the previous generation of engineers who grew up on slide rules. After 33 years, I’m still learning.

What are Smart Structures? Think of the human body. It is by far the most advanced and technologically “Smart Structure” that exists. Let’s recap what a conventional structure is: A building is subjected to a lateral wind pressure load and reacts by transmitting these loads through its structural system (e.g., steel/concrete/masonry/ wood) to the foundation. The structural stiffness response is the same regardless of the wind pressure. Whether it’s a hurricane force wind or a mild 10 mph wind gust, the building’s stiffness, damping, and structural response are identical. Reaction forces, internal stresses, and deformations will change, but the stiffness distribution remains constant. This is a conventional structure.

A Smart Structure will adjust the stiffness, damping, and material properties to respond to the loading, and shift the internal stiffness accordingly as it pertains to the demand. Think of the human body – when you are thrown a baseball, your brain sees the ball and assesses the velocity and consequent impact force. Based on this determination, you will raise your hand and your arm will respond with the appropriate stiffness to catch the ball. If it’s a slow pitch, then you will take it easy in the catch. If it’s a

50 April 2016

fastball, then your body will react accordingly to provide a stiffer resistance to prevent missing the ball. Similarly, your legs adjust to the reaction of your body.

Over the past 20 years, the research into Smart Structure Technology has been intense, and many research papers have been published on the topic with interesting applications towards building systems. Two excellent reference papers are provided by Zhang and Lu, and Song & Sethi (full references for these texts are included in the online version of this article, www.STRUCTUREmag.org). The development of Smart Structure Technology emanates from the aerospace and mechanical engineering disciplines, and is moving to the civil and structural engineering industry. The basic tenants of a Smart Structural System are: 1) Records and reports defects and damage to the owner/engineer 2) Mitigates the impact of dangerous events such as earthquakes, explosions, hurricanes, fire, wind storms, etc.

3) Self-heals and self-repairs Going back to the human body, it’s amazing to think that our own physical structure does all of these tasks brilliantly.

Smart Materials go one step further by responding to external stimuli with an internal change in the material properties to prevent damage/collapse. There are smart materials in development: piezoelectric materials, shape memory alloys, magnetostrictive materials, magnetorheological fluids, and other “self healing” materials.

The Smart Structure System uses internal sensors (i.e., accelerometers, stress sensors, and deflection measurement) to assess the impact force/demand and then routes this information to a central processing unit (computer) which will adjust the damper/stiffness devices in the building at critical locations to respond to the force. The entire process occurs in just milliseconds, and the intent is to create a structural system that adapts to its environment. Although there are significant hurdles towards practical implementation of this technology, such as the loss of power in an event which would disable the system, the idea poses innovative advancement for the structural profession. The mechanical and aerospace engineering fields are leading the way here, and this reminds us of the 1980s when the introduction of fiber composites, personal computers, and finite element analysis were just coming into the horizon for structural engineers.▪

Basics of Piezoceramics Materials Piezoceramic material refers to the substances that have the following unique property: an electric charge produced when a piezoelectiric substance is subjected to a stress or strain (direct effect), and conversely a mechanical deformation, i.e., the stress or strain produced when an electric field is applied to a piezoelectric substance in its poled direction (converse effect). Hence, the direct piezoelectric effect is useful in sensors such as accelerometers and the converse effect is useful in actuators such as ultrasonic motors.

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code developments and announcements

Code Updates

Significant Changes between ACI 318-11 and ACI 318-14 Part 1: Organizational Changes

By S. K. Ghosh, Ph.D.

T

he American Concrete Institute (ACI) published the Building Code Requirements for Structural Concrete (ACI 318-14) and Commentary (ACI 318R-14) in the Fall of 2014. ACI 318-14 has been adopted by reference into the 2015 International Building Code (IBC). Adoption of the 2015 IBC by cities, counties, and states has been rather slow. However, major adoptions are scheduled to follow. The 2016 California Building Code (CBC), based on the 2015 IBC, will be effective in California on January 1, 2017. As of that date, ACI 318-14 will be law within the State of California.

There are very significant organizational as well as technical changes between ACI 318-11 and ACI 318-14. This is the first of a two-part article on these changes. This part is devoted to the organizational changes.

Part 2 will describe the technical changes.

Organization of ACI 318-11 As is fairly well known by now, ACI 318 has undergone a complete reorganization from its 2011 to its 2014 edition. The organization of ACI 318-11 followed the framework of ACI 318-71, which remained essentially unchanged through eight more editions dated 1977, 1983, 1989, 1995, 1999, 2002, 2005, and 2008.

ACI 318-11 started with chapters on materials and construction aspects.

Analysis and design, general considerations and strength and serviceability requirements were dealt with in two succeeding chapters. Three behavior-based chapters followed: on flexure and axial loads, shear and torsion, and development and splices of reinforcement. A switch was then made to member-based chapters: on two-way slab systems, walls, and footings. The last few chapters were on precast concrete, composite concrete flexural members, prestressed concrete, shells and folded plate members, strength evaluation of existing structures, earthquake-resistant structures, and structural plain concrete. There were also four appendices, including one on strut and tie models and one on anchoring to concrete.

Member-Based Organization for ACI 318-14 While the ACI 318 cycle that produced ACI 318-05 and -08 was still in full swing, it was decided, after long deliberation within ACI, that ACI 318 should be reorganized to be a memberbased document. External input was actively sought and considered in the course of those deliberations. The idea was that, within each chapter devoted to a particular member type such as beam or column, the user will find all the requirements necessary to design that particular member type. According to Cary Kopczynski, a member of the ACI 318 committee that produced ACI 318-14 , “This will eliminate the need to flip through several chapters to comply with all of the necessary design requirements for a particular structural member, as was necessary with the old organization format. The codes’ new design can be compared to a cookbook: all the ingredients for baking a cake such as eggs, flour, sugar, oil – along with the baking instructions – are in one chapter, instead of individual chapters on eggs, flour, and sugar.”

Toolbox Chapters One challenge in converting to a memberbased organization was where to place the design information that applies to multiple member types, such as development length requirements. To repeat essentially the same information in multiple chapters did not sound like a good idea. So the decision was made to place such information in so-called “toolbox” chapters and to reference the information from the member-based chapters.

Chapters 21 through 25 are the toolbox chapters in ACI 318-14.

Overall Changes There are some overall changes in the makeup of ACI 318-14 that should be noted.

There are two new chapters: 4, Structural System Requirements and 12, Diaphragms.

Appendix B of ACI 318-11, Alternative Provisions for Reinforced and Prestressed Concrete Flexural and Compression Members, and Appendix C, Alternative Load and Strength Reduction Factors, have been discontinued.

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Appendix A, Strut-and-Tie Models is now Chapter 23 and Appendix D, Anchoring to Concrete, is Chapter 17 in the reorganized document. No changes of any significance have been made in the provisions of these two appendices/chapters. Two additional chapters have been relocated without change of content: Chapter 20, now 27, Strength Evaluation of Existing Structures, and Chapter 22, now 14, Structural Plain Concrete.

Chapter 21, now 18, Earthquake-Resistant Structures, has been relocated with change of content; significant technical changes have been made in this chapter. The first three chapters have also remained intact, but with technical changes. These are: Chapter 1, General Requirements, now General; Chapter 2, Notation and Definitions, now Notation and Terminology; and Chapter 3, Materials, now Referenced Standards.

Chapter 16, Precast Concrete, and Chapter 18, Prestressed Concrete no longer exist as separate entities. The provisions of those chapters are now spread over several of the new chapters.

Chapter 19, Shells and Folded Plates, is no longer part of the reorganized document. ACI Committee 318, in collaboration with ACIASCE Committee 334, Concrete Shell Design and Construction, has developed ACI 318.214, the contents of which match those of ACI 318-11 Chapter 19. The reader may wonder why this document was designated ACI 318.2, rather than ACI 318.1. This is because it was initially planned that ACI 318-11 Chapter 22 on plain concrete would become a separate standard: ACI 318.1. The number was reserved for that purpose. It was later decided to place the contents of ACI 318-11 Chapter 22 in ACI 318-14 Chapter 14.

The Table shows a side-by-side comparison of the organizations of ACI 318-11 and ACI 318-14.

Construction Documents and Inspection A unique chapter that will probably require some time to get used to is Chapter 26, Construction Documents and Inspection. The chapter starts with the following: 26.1.1 This chapter addresses (a) through (c):

Reorganization of ACI 318-14.

ACI 318-11 Description of Provisions

ACI 318-14 Description of Provisions

Chapter and Title 1 – General Requirements

Introductory

Materials/ Construction

Other

Member-Based

2 – Notation and Definitions

Introductory

2 – Notation and Terminology

3 – Materials

3 – Referenced Standards

4 – Durability Requirements

4 – Structural System Requirements

5 – Concrete Quality, Mixing, and Placing

5 – Loads

6 – Formwork, Embedded Pipes, and Construction Joints

Other

New

6 – Structural Analysis

7 – Details of Reinforcement

7 – One-Way Slabs

8 – Analysis and Design – General Considerations

8 – Two-Way Slabs

9 – Strength and Serviceability Requirements

9 – Beams Member-Based

11 – Shear and Torsion

10 – Columns 11 – Walls

12 – Development and Splices Of Reinforcement

12 – Diaphragms

13 – Two-Way Slab Systems

13 – Foundations

14 – Walls

Other

New

14 – Plain Concrete

15 – Footings

Intact

15 – Beam-Column and Slab-Column Joints

16 – Precast Concrete

Connections

17 – Composite Concrete Flexural Members 18 – Prestressed Concrete

Other

19 – Shells and Folded Plate Members 20 – Strength Evaluation of Existing Structures Other

Comment

1 – General

10 – Flexure and Axial Loads Behavior-Based

Chapter and Title

16 – Connections between Members 17 – Anchoring to Concrete

Intact

18 – Earthquake-Resistant Structures

Intact

19 – Code Requirements for Thin Shells and Commentary

Materials

21 – Earthquake-Resistant Structures

21 – Strength Reduction Factors

22 – Structural Plain Concrete

22 – Sectional Strength

App. A – Strut-and-Tie Models

23 – Strut-and-Tie Models

App. B – Alternative Provisions for Reinforced and Prestressed Concrete Flexural and Compression Members (Discontinued)

Toolbox

(a) Design information that the licensed design professional shall specify in the construction documents, (b) Compliance requirements that the licensed design professional shall specify in the construction documents, (c) Inspection requirements that the licensed design professional shall specify in the construction documents, Thus, construction and inspection requirements have been consolidated and they are now related to construction documents. The construction requirements are designated either as “design information” or “compliance requirements.” These are largely existing material that has been rearranged.

The inspection requirements in Section 26.13 are largely taken from Chapter 17 of the 2015 IBC; much of it was previously not part of ACI 318.

Intact

24 – Serviceability Requirements

App. C – Alternative Load and Strength Reduction Factors (Discontinued) App. D – Anchoring to Concrete

ACI 318.2

20 – Steel Reinforcement Properties, Durability, and Embedments

25 – Reinforcement Details Construction

26 – Construction Documents and Inspection

Other

27 – Strength Evaluation of Existing Structures

Intact

Conclusions ACI 318 has undergone a complete reorganization from its 2011 to its 2014 edition; the last such complete reorganization was from the 1963 to the 1971 edition of ACI 318.

The new organization is member-based. The idea is that, within each chapter devoted to beam or column or some other member type, the user will find all the requirements necessary to design that particular member type.

Contrary to the fairly widely held perception that the reorganization is all that has happened, ACI 318-14 does contain a number of significant technical changes, which will be discussed in Part 2 of this article.▪ The online version of this article contains detailed references. Please visit www.STRUCTUREmag.org.

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S. K. Ghosh is President at S. K. Ghosh Associates Inc., Palatine, IL and Aliso Viejo, CA. He is a long-standing member of ACI Committee 318, Structural Concrete Building Code, and its Subcommittee H, Seismic Provisions. He can be reached at skghoshinc@gmail.com.

This article was originally published in the PCI Journal (March/April 2016) and this condensed version is reprinted with permission.

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Spotlight

Columbia Medical Center’s Vertical Campus

By Daniel Sesil, P.E., S.E., Matthew Melrose, P.E., Michael Hopper, P.E. and Andrew Polimeni, P.E. Leslie E. Robertson Associates was an Outstanding Award Winner for the Columbia University Medical Center Graduate Education Building project in the 2015 NCSEA Annual Excellence in Structural Engineering awards program (Category – New Buildings $30M to $100M).

T

he Columbia University Medical and Graduate Education Building (CUMGEB) is a 100,000 squarefoot, 15-story, state-of-the-art medical education facility, whose multifaceted goals include the linking of students and teachers, of interdisciplinary study and interactive learning, and of function and experience, all while providing an identity and focal point for Columbia University’s Washington Heights campus. CUMGEB aspires to be an iconic facility for the university and neighborhood, helping to attract the world’s top medical students.

The design team included Diller Scofidio + Renfro (DS+R) in collaboration with executive architect Gensler. Leslie E. Robertson Associates (LERA) provided structural engineering services. F.J. Sciame Construction is the project’s construction manager.

The project’s main feature is a southern facing “Study Cascade” that contains interconnected study and social spaces to encourage collaboration between students. The study cascade is envisioned as a vertical campus of stacked “neighborhoods”, which are two to three story, near atrium-like clusters of diversified social spaces. The southern campus-facing façade is a highly articulated all-glass system that is crucial to the building’s expression. The northern half of the building is organized for classrooms and administrative space, in addition to a midtower mechanical space to accommodate the needs of the building’s Anatomy Labs.

CUMGEB’s main structural design challenge was to find vertical load paths through the Study Cascade while respecting the varied spatial planning of the stacked neighborhoods. To minimize the structure’s impact on these spaces, the cascade floors are supported by a pair of inclined composite concrete columns that are architecturally exposed and cast with high strength (10 ksi), self-consolidating concrete. These two exposed columns slope from the foundation level up to the 8th floor in order to direct loads around a columnfree auditorium at the base of the Cascade.

The thrusts that result from the changes in direction of the sloping columns are resisted

by in-floor trusses constructed with posttensioning and high-strength rebar.

An additional structural challenge was to provide long, open floor spans with minimal structural depth that could simultaneously accommodate the tight deflection performance requirements of the all-glass façade.

The cascade structure has no perimeter columns, which results in a unique sequence of cantilevered concrete flat slabs. To meet the slab performance requirements, the cantilevered slabs are reinforced with a bonded post-tensioning system. Void formers, manufactured by Cobiax USA, are placed between bands of post-tensioning to create long-span, beam-like framing with flat formwork and to reduce the structure’s self-weight. The cantilevered slabs utilize high strength concrete (8 ksi) and taper in thicknesses from 24 inches at supports to 8 inches at the cantilever tips.

The curtain wall of the cascade is arranged in multi-story planes that do not align in plan between neighborhoods and are not parallel with the slab’s edges, creating detailing challenges for both the structure and façade.

Through a design assist phase, expected deflections from slab curvature were coordinated at each glass mullion with the curtain wall contractor, Gartner, and together the project team decided on an acceptable long-term deflection limit of 1¼ inches for cantilevers up to 26 feet. The bonded post-tensioned slabs were tuned to meet these performance requirements and were detailed to accommodate a range of façade attachment methods.

The building’s structural design achieves efficiency by embracing the building’s stacked neighborhoods. The structural system of the cascade leverages the natural interconnections that come from the unique arrangement of the program spaces of the vertical campus.

Single story walls and ramps connect and stiffen the cantilevered slabs, allowing for material savings in the slabs.

Long-term column shortening of the two Cascade columns causes amplified deflections at the tips of the cantilevers they support.

To account for this phenomenon, a staged construction analysis was performed and

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April 2016

Courtesy of Matthew Melrose/Leslie E. Robertson Associates.

summarized into a simple planar cambering schedule for the Cascade slabs. Super-elevated slab positions were determined to help assure that the slabs would be level after longterm column shortening occurs. Curtain wall installation procedures are intended to account for the slabs’ super-elevated positions.

Although the project is relatively small in area, CUMGEB is a complex building with broad aspirations. The design and construction challenges of CUMGEB are similar to those often found in much taller buildings and longerspan structures. The goals of the project were achieved through the successful use of proven construction technologies, extensive analysis and coordination, and a strong integration of architecture and structure.▪ Daniel Sesil is a Partner at LERA and is the Partner in charge of the CUMGEB project. Daniel can be reached at daniel.sesil@lera.com.

Matthew Melrose is an Associate Partner at LERA. He was the Project Director of the CUMGEB project in Construction and served as Project Manager in the design phases. Matthew can be reached at matt.melrose@lera.com.

Michael Hopper is an Associate at LERA. He performed the design of the post-tensioned slabs for CUMGEB and served as Project Manager in Construction. Michael can be reached at michael.hopper@lera.com.

Andrew Polimeni is an Associate at LERA. He performed the staged construction analysis. Andrew can be reached at andrew.polimeni@lera.com.

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NCSEA News

News form the National Council of Structural Engineers Associations

NATIONAL

Structural Licensure Committee Update The NCSEA Licensure Committee continues to actively advocate structural licensure in every U.S. jurisdiction. Progress continues to be made toward this goal. Several states have moved forward in their efforts: Alaska In Alaska, the state board proposed changes that would make the SE a post PE license. Public comments were open through February 2016. This is a regulation project that would move the SE license from just another PE license to a post PE license. It would ease comity with Washington and Oregon. The regulation also requires the use of a structural engineer on significant structures. The definition of significant structures closely parallels Washington and Oregon. With the public hearings complete, the Board may take action at their May meeting.

It is time that we as Structural Engineers become more actively engaged in the political arena and let our voices be heard through our Structural Engineers Associations.

California SEAOC has proposed language that would expand the types of structures required to be designed by Structural Engineers in California. Currently schools and hospitals are required to be designed by SEs; all other structures are required to be designed by California-licensed Civil Engineers. The proposal is that as of the date that the proposed law goes into effect, Civil Engineers licensed after that date would no longer be able to design significant structures. Civil Engineers licensed in California prior to that date would be able to continue their practice as they had previously, meaning they could design all buildings except schools and hospitals. SEAOC has had several meetings with the Civil and Structural Technical Advisory Committees of the Board for Professional Engineers, Land Surveyors and Geologists. This led to a general consensus on the definitions of these significant structures. SEAOC is still in discussions with other stakeholders (such as ACEC and PECG – Professional Engineers in California Government) but anticipates looking for a legislative sponsor in the not too distant future.

Florida The proposed changes in Florida were introduced in the house and senate with sponsors in each chamber. The licensure committee proceeded without a lobbyist, at the suggestion of their sponsor, but with the support of a number of professional organizations including FSPE, the Florida chapter of NSPE. The measure passed both chambers of the Legislature but was vetoed by the Governor. It was later learned that the “grandfathering” provisions included in the proposed legislation were not acceptable to the governor and this formed the basis of the veto.

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Georgia Georgia’s House Bill 592 (PE, SE legislation) passed the House in February and is going to the Senate in March, where it has some resistance in the Senate Regulated Industries Committee.

Hopes and efforts are at a high level.

Texas The structural engineers in Texas worked to prepare a Structural Licensure Bill to the Texas Legislature in 2015. The bill died in committee and did not make it to the floor of the Legislature.

Advocates are refocusing their efforts and using a lobbyist to help with all legislative issues relating to structural engineering, not just licensure.

Oklahoma In Oklahoma, the Structural Engineers Association (OSEA) worked with the Oklahoma Board of Professional Engineers and Land Surveyors (OKPELS) to develop mutually agreeable language for an SE Title Act. The SE Title Act was bundled with other statute updates in a bill submitted to a State Senate Committee. Ultimately, it was removed so that the rest of the bill could move forward. OSEA will try again next year.

Tennessee The SE Licensure committee of TNSEA is currently in the process of finalizing proposed draft documents for SE Licensure that will be presented to the TNSEA Board of Directors in 2016 for approval. Representatives of the SE Licensure committee have also begun discussions with representatives of the Tennessee Society of Professional Engineers and ACEC of Tennessee, in efforts to address any concerns that they may have regarding SE Licensure and to educate their membership on the reasons why the structural engineering community in Tennessee is largely in favor of such legislation.

Several other states continue to make progress toward specific licensing of Structural Engineers, either as title acts or partial practice acts. These include Connecticut and Ohio.

The road to structural licensure in all states will be a long and arduous one. In part this is because of the strong resistance from national engineering organizations such as the National Society of Professional Engineers (NSPE). This was made even more evident recently in Oklahoma, where NSPE addressed a letter to the Oklahoma State Board of Professional Engineers and Surveyors stating why the efforts for structural licensure in that state should be resisted.

But even more important is that Structural Engineers have let other organizations speak for all engineers. This has resulted in our losing our own voice. It is time that we as Structural Engineers become more actively engaged in the political arena and let our voices be heard through our Structural Engineers Associations.

Joe Luke, P.E., SECB Structural Licensure Committee Chair Tim Gilbert, P.E., S.E., SECB Structural Licensure Committee Member

April 2016

NCSEA’s library of over 150 recorded webinars is now available on demand.

Viewers can watch recorded webinars anytime of the day or night, take quizzes, and receive certificates. In addition, changes were made that allowed NCSEA to drop the $30/recorded webinar fee for subscribers.

There is no time like the present to become a subscriber. For $995, you can receive one year of live webinars (at least 20/year) and as many NCSEA online recorded webinars as you would like to view.

Above and below: Disney’s Contemporary Resort, host hotel of the 2016 NCSEA Summit.

Interested in using your engineering expertise to assist post-disaster efforts following earthquakes, tornadoes, hurricanes or other natural disasters? Obtain certification through the California Office Of Emergency Services (CalOES) Safety Assessment Program (SAP) that will be presented by NCSEA on May 5.

Licensed design professionals and certified building officials will be eligible for SAP Evaluator certification and credentials following completion of this program and submission of required documentation.

This SAP program is highly regarded as a standard throughout the country for engineer emergency responders. The training has been reviewed and approved by FEMA’s Office of Domestic Preparedness.

Based on ATC-20/45 methodologies and documentation, the SAP training course provides engineers, architects and code-enforcement professionals with the basic skills required to perform safety assessments of structures following disasters.

The class consists of three webinar segments over one day’s time and is taught

by Jim Barnes, who has worked for 20 years for the State of California’s disaster agency. He has served as the lead statewide coordinator for the Safety Assessment Program (SAP) for seven years and has given over 150 classes in the subject since 2004. He also serves as the lead for preliminary damage assessment for potential federal disasters in California.

The Course cost is $500 per connection, and a proctor is required, who may also take the course.

News from the National Council of Structural Engineers Associations

Registration for the 2016 NCSEA Structural Engineering Summit is now open online at www.ncsea.com.

The Summit will be held at Disney’s Contemporary Resort, which is just a short monorail ride, water-launch trip or walk to the Magic Kingdom Park. Hotel reservations are now open as well, accessible through a link online at NCSEA’s website.

The Summit will feature keynote speaker Kent Estes, Ph.D., S.E., of Walt Disney Imagineering. The remaining slate of educational sessions on two tracks is also available at www.ncsea.com.

The Summit draws together the best in the structural engineering field and features technical and nontechnical educational sessions, social and networking events, the NCSEA Excellence in Structural Engineering Awards, and the trade show.

Safety Assessment Program Scheduled for May 5

NCSEA News

NCSEA Recorded Webinars Now Available on Demand, Online

NCSEA Webinars

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Geoff Bomba, P.E., S.E., Senior Associate, Forell Elsesser Structural Engineers

More detailed information on the webinars and a registration link can be found at www.ncsea.com. Subscriptions are available ! 1.5 hours of continuing education. Approved for CE credit in all 50 states through the NCSEA NCSEA Diamond Review Program. www.ncsea.com.

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May 10, 2016 Introduction to Building Structural Dynamics for Seismic Design Structural Engineers

Pawan R. Gupta, Ph.D., P.E., S.E. LEEP AP, Principal & Managing Director, Diagnostics

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Brian Kukay, Ph.D., P.E., Associate Professor, Montana Tech

May 24, 2016 Designing with Post-Tensioned Concrete

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April 28, 2016 Fire Damage and Post-Fire Assessment of Structural Wood Members

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Structural Columns

The Newsletter of the Structural Engineering Institute of ASCE

Geotechnical & Structural Engineering Congress a Great Success The recent Geotechnical & Structural Engineering Congress was a resounding success. Held in Phoenix, Arizona, February 14 – 17, 2016, close to 2000 attendees participated. This was the first ASCE conference drawing on the strengths of two of the society’s technical institutes. The GeoInstitute and the Structural Engineering Institute worked closely together to offer attendees the best of both institutes’ stand-alone congresses and more.

Congratulations to the 2016 SEI Fellows

Attendees enjoyed a large selection of technical sessions covering both structural and geotechnical topics. In addition, there were joint sessions exploring subjects of interest to both. Short courses and lightning sessions were also featured in the program.

Student and Younger Members had many events focused on their needs. These included a career fair, Meet the Leaders networking event, and their own reception. Undergraduate teams of both geotechnical and structural engineering students vied in the wall, video, and prediction competitions, held in the exhibit hall.

A large and varied number of networking and social events, including a celebration of both institutes’ 20th anniversaries, rounded out the program. These included receptions in the exhibit hall with an opportunity to visit with vendors, and an off-site reception at Chase Field, home of the Arizona Diamondbacks.

Vision for the Future Event A special evening reception, hosted

by Computers & Structures, Inc., President and CEO, Ashraf Habibillah was a highlight of the congress. The event, held at the Phoenix Art Museum, was a gala to support the SEI Futures Fund and highlight the SEI Vision for the Future. Attendees were treated to great food, compelling art exhibits, live music, and the company of other structural engineers.

Errata SEI posts up-to-date errata information for our publications at www.asce.org/SEI. Click on “Publications” on our menu, and select “Errata.” If you have any errata that you would like to submit, please email it to Jon Esslinger at jesslinger@asce.org.

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SEI was proud to recognize the 2016 Class of SEI Fellows at the Closing Plenary of the Geotechnical & Structural Engineering Congress.

Abdeldjelil Belarbi, Ph.D., P.E., F.SEI, F.ASCE Dilip Choudhuri, P.E., F.SEI, M.ASCE Reginald DesRoches, Ph.D., F.SEI, F.ASCE Wassim Ghannoum, Ph.D., P.E., F.SEI, A.M.ASCE Nathan Gould, P.E., S.E., F.SEI, M.ASCE Perry Green, P.E., F.SEI, M.ASCE Emily Guglielmo, P.E., S.E., F.SEI, M.ASCE Riyadh Hindi, Ph.D., P.Eng, F.SEI, M.ASCE Robin A. Kemper, P.E., LEED AP, F.SEI, F.ASCE Mahmoud Khoncarly, Ph.D., P.E., F.SEI, M.ASCE Mustafa Mahamid, Ph.D., P.E., S.E., SECB, F.SEI, M.ASCE Jack Moehle, Ph.D., P.E., F.SEI, M.ASCE Cristopher Moen, Ph.D., P.E., F.SEI, M.ASCE Michael Mota, Ph.D., P.E., SECB, F.SEI, F.ASCE James Ray, P.E., F.SEI, M.ASCE David Sanders, Ph.D., F.SEI, F.ASCE Lip Teh, CP.Eng, F.SEI, A.M.ASCE Marlon Vogt, P.E., F.SEI, M.ASCE Andrew Whittaker, Ph.D., P.E., S.E., F.SEI, M.ASCE SEI Members that wish to advance to the SEI Fellow grade are invited to submit their completed application packages by December 1 at www.asce.org/structural-engineering/sei-fellows.

International Workshop on Disaster Resilience The SEI Disaster Resilience of Structures, Infrastructures, and Communities Committee is participating in organizing the 1st International Workshop on Disaster Resilience, September 20 – 22, 2016 in Torino, Italy. The program includes two days of sessions at the magnificent Hall of Honor in 16th century Valentino’s Castle. An additional day of sessions and visits will be held at the Joint Research Centre in Ispra, which includes the Elsa Lab and Crisis Management Center. Learn more on the workshop website at www.workshop-torino2016.resiltronics.org.

April 2016

ASCE’s new Guided Online Courses are highly interactive, instructor-led programs in which you will move through a 12-week learning experience with a cohort of peers. A rich variety of content, including video lectures, interactive exercises and case studies, and weekly discussion board topics help you master the course material. Complete weekly modules at the time and pace that is most convenient for you, from any device.

Earthquake Engineering for Structures – New Course Starts April 4 Earthquake Engineering for Structures introduces the fundamental concepts of earthquake engineering, and provides

Report From Chile Earthquake Assessment Team Now Available

CALL FOR PROPOSALS NOW OPEN 2017 Structures Congress April 6 – 8, 2017, Denver, Colorado Now accepting individual paper and complete session proposals for consideration.

Structures Congress 2017 is a forum to advance the art, science, and practice of structural engineering. The SEI National Technical Program Committee (NTPC) is seeking proposals for complete sessions and abstracts for individual papers to be presented at Structures Congress 2017.

SEI encourages submissions from practitioners, educators, researchers, structural engineers, bridge and building designers, firm owners, codes and standards developers, and others.

The due date for abstract and session proposals is June 2, 2016. Visit the congress website, www.structurescongress.org, to submit your proposals. The conference website will have detailed information and step by step power points to assist you. Questions?

Contact Debbie Smith at dsmith@asce.org or 703-295-6095.

Two SEI Members Elected to National Academy of Engineering ASCE is proud to congratulate two SEI members who have been elected to the National Academy of Engineering.

Gary J. Klein, P.E., M.ASCE Mr. Kline is an executive vice president and senior principal at Wiss, Janney, Elstner Associates Inc., Northbrook, Ill. He is being honored by the academy for investigations of national and international infrastructure, and conveying knowledge from these investigations to the profession.

Jon D. Magnusson, P.E., S.E., F. SEI, Dist.M.ASCE Mr. Magnusson is a senior principal at Magnusson Klemencic Associates, Seattle. He is being honored by the academy for building designs that enable high-rise buildings in seismic STRUCTURE magazine

sensitive regions and for innovations in modern structural engineering practice worldwide.

Election to the National Academy of Engineering is among the highest professional distinctions accorded to an engineer.

Academy membership honors those who have made outstanding contributions to “engineering research, practice, or education, including, where appropriate, significant contributions to the engineering literature” and to “the pioneering of new and developing fields of technology, making major advancements in traditional fields of engineering, or developing/implementing innovative approaches to engineering education.” The new members will be formally inducted at the NAE’s Annual Meeting in Washington, D.C. on October 9, 2016. See the NAE website at www.nae.edu for more information.

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April 2016

The Newsletter of the Structural Engineering Institute of ASCE

After the February 2010 earthquake in Chile, SEI/ASCE sent a team to assess structures in the affected zone focusing on identifying strengths and weaknesses, in order to gather information that would be useful in developing future U.S. code.

The new report, Chile Earthquake of 2010: Assessment of Industrial Facilities around Concepción, looks at the performance of heavy industrial structures in this large seismic event. The earthquake in 2010 was the largest in 50 years to strike off the coast of Chile. During that preceding half century, Chile enacted codes, similar to U.S. code, to improve the seismic resilience of structures. For structural engineers, this report provides critical information for the development and implementation of seismic codes and standards, as well as for focusing retrofit efforts in heavy industrial facilities. Purchase your copy today at www.asce.org/publications.

the foundation for understanding the analysis and design requirements in ASCE 7. Covered in the course are seismic hazard analysis, structural dynamics, development of response spectra, inelastic behavior of structures, seismic resistant structural systems, and seismic load analysis. This course is one of ASCE’s new Guided Online Courses that are highly interactive, instructor-led programs in which you will move through a 12-week learning experience with your peers. The content includes video lectures, interactive exercises, case studies, and weekly discussion board topics to help master the course material. To learn more and to register, visit the ASCE Continuing Education website at http://mylearning.asce.org/ diweb/catalog/item/id/820283/q/c=79&t=5621

Structural Columns

ASCE Announces New State-of-the-Art Guided Online Course on Earthquake Engineering

CASE in Point

The Newsletter of the Council of American Structural Engineers

CASE Winter Planning Meeting Update On February 11 – 12, the CASE Winter Planning Meeting took place in Phoenix, AZ. CASE does two planning meetings a year to allow their committees to meet face to face and interact across all CASE activities. Over 30 CASE committee members and guests were in attendance, making this another well attended and productive meeting. During the meeting, break-out sessions were held by the CASE Contracts, Guidelines, Membership, Toolkit, and Programs & Communications Committees.

Current initiatives include: I. Contracts Committee Ed Schweiter (ews@ssastructural.com) • Will be creating a “How to” sheet educating people on using the CASE Contract Documents • Working on developing a “pro-bono” sample contract for small projects II. Guidelines Committee John Dal Pino (jdalpino@degenkolb.com) • Revising the following current Practice Guideline Documents: CASE 962B – National Practice Guidelines for Specialty Structural Engineers CASE 962-E – Self-Study Guide for the Performance of Site Visits During Construction CASE 962-F – A Guideline Addressing the Bidding and Construction Administration Phases for the Structural Engineer • Working on the following new documents: Commentary on ASCE-7 Wind Design Provisions Commentary on ASCE-7 Seismic Design Provisions Began preliminary discussion on a potential Geotech guideline document/white paper

III. Membership Committee Stacy Bartoletti (sbartoletti@degenkolb.com) • Recruitment campaign netted 25 new members for CASE during 2015; working on engaging with new members for them to understand what CASE has to offer • Revising polling question survey for members IV. Programs and Communications Committee Nils Ericson (nericson@m2structural.com) • Working on market information for new risk management seminar August 4-5, 2016.

• Creating track of risk management sessions for 2017 ASCE/SEI Structures Congress • Creating track of risk management / business practice sessions for 2016 ACEC Fall Conference • Putting together the 2015/2016 editorial calendar for articles to Structure Magazine from CASE V. Toolkit Committee Brent White (brentw@arwengineers.com) • Updating the following current Tools: Tool 10-1: Site Visit Cards • Working on the following new tools: Tool 8-3: Contract Clause Commentary Tool 9-3: Deferred Submittals The CASE Summer Planning Meeting is scheduled for August 3 – 4 in Chicago. New this year will be a day-long education seminar focused solely on risk management/contracting issues for Structural Engineers. Speakers will include experts in the insurance, legal, business world. More information will be announced, including schedule, in the May edition.

If you are interested in attending the meeting or have any suggested topics for the committees to pursue, please contact CASE Executive Director Heather Talbert at htalbert@acec.org.

ACEC Business Insights

Donate to the CASE Scholarship Fund!

Applying Expertise as an Engineering Expert Witness – SAVE the DATE! The CASE scholarship, administered by the ACEC College of Fellows, is awarded every year to a deserving student seeking a May 19 – 20, 2016; Chicago, IL Bachelor’s degree, at minimum, in an ABET-accredited engineering program. Since 2009, the CASE Scholarship program has given over $18,000 to engineering students to help pave their way to a bright future in structural engineering.

We encourage our fellow structural engineering colleagues to support this popular and successful program. Your contribution today will help CASE and ACEC increase scholarship funds to promising students who need this assistance the most. This is an exceptional opportunity to encourage growth in the structural engineering profession and ensure that the highest caliber of students become the future of our industry.

Your monetary support is vital in helping CASE and ACEC increase scholarships to those students who are the future of our industry. All donations toward the program may be eligible for tax deduction and you don’t have to be an ACEC member to donate! Contact Heather Talbert at htalbert@acec.org to donate.

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Engineers are often asked to serve as expert witnesses in legal proceedings – but only the prepared and prudent engineer should take on these potentially lucrative assignments. If asked, would you be ready to say yes? Developed exclusively for engineers, architects, and surveyors, this unique course will show you how to prepare for and successfully provide expert testimony for discovery, depositions, the witness stand, and related legal proceedings.

Applying Expertise as an Engineering Expert Witness is a focused and engaging 1½ day course that will run you through each step of the qualifications, ramifications, and expectations of serving as an expert witness.

For more information about the course and/or to register, www.acec.org/calendar/calendar-seminar/applyingexpertise-as-an-engineering-expert-witness-chicago-il.

April 2016

Engineers to Lead, Direct, and Get Involved with CASE Committees!

If you’re looking for ways to expand and strengthen your business skillset, look no further than serving on one (or more!)

CASE Committees. Join us to sharpen your leadership skills – promote your talent and expertise – to help guide CASE programs, services, and publications.

Please submit the following information to htalbert@acec.org • Letter of interest • Brief bio (no more than 2 paragraphs)

Follow ACEC Coalitions on Twitter – @ACECCoalitions.

Expectations and Requirements To apply, your firm should: • be a current member of the Council of American Structural Engineers (CASE) • be able to attend the groups’ two face-to-face meetings per year: August, February (hotel, travel partially reimbursable) • be available to engage with the working group via email and conference call • have some specific experience and/or expertise to contribute to the group Thank you for your interest in contributing to your professional association!

Foundation 4 Communication – Communicate to Match Expectations with Perceptions Tool 4-1 Status Template Report This tool provides an organized plan for keeping your clients informed and happy. This project status report is intended to be sent to your Client, the Owner and any other stakeholder whom you would like to keep informed about the project status.

Tool 4-2 Project Kick-Off Meeting Agenda Effective communication is one of the keys to successful risk management. Often times we place a significant amount of effort and care into communication with our clients, owners and external stakeholders. With all that effort, it’s easy to take for granted communication with our internal stakeholders – the structural design team. If a project is not started correctly, there is a good chance that the project will not be executed correctly either. Tool 4-2 is designed to help the Structural Engineer communicate the information that is vital to the success of the structural design team and start the project off correctly.

Tool 4-3 Sample Correspondence Guidelines (Updated in 2015!)

The intent of CASE Tool 4-3, Sample Correspondence Guidelines, is to make it faster and easier to access correspondence with STRUCTURE magazine

appropriate verbiage addressing some commonly encountered situations that can increase your risk. The sample correspondence contained within this tool is intended to be sent to the Client, Owner, Sub-consultant, Building Official, Employee, etc., in order to keep them informed about a certain facet of a project or their employment.

Tool 4-4 Phone Conversation Log Poor communication is frequently listed among the top reasons for lawsuits and claims. It is the intent of this tool to make it faster and easier to record and document phone conversations.

Tool 4-5 Project Communication Matrix This tool is to provide an easy to use and efficient way to (1) establish and maintain project-specific communication standards and (2) document key project-specific deadlines and program/ coordination decisions that can be communicated to a client or team member for verification.

You can purchase these and the other Risk Management Tools at www.acec.org/bookstore.

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April 2016

CASE is a part of the American Council of Engineering Companies

CASE Risk Management Tools Available

CASE in Point

WANTED

Structural Forum

opinions on topics of current importance to structural engineers

Who Hijacked My Building Code?

By David Pierson, S.E., SECB

I

believe that the majority of Americans understand the need for some kind of building code to regulate construction.

Millennia ago, Hammurabi gave us the “eye-for-an-eye” version of the building code.

Since the Chicago fire of 1871 and the San Francisco earthquake of 1906, there have been building codes in America.

The original purpose of our building codes was to protect the occupants of a building from disasters such as fires and earthquakes.

Other natural events, such as high winds or snow, are also considered. Provisions are directed at various elements of a building that affect life safety for the public; most prevalent are the fire safety and structural systems.

Other life safety issues concern indoor plumbing, electricity, and mechanical systems.

I know of no rational argument against governmentally imposed regulations for items that significantly affect life safety. However, there are obviously some inherent risk factors that must be considered in light of the overall cost to society and the benefits to the building owners/users. Some good ideas might save lives, but at what cost? Risks need to be evaluated, and costs must be measured.

As a society, we don’t have enough resources to completely eliminate risk from life. If the building code mandated that every home be built adequately to survive after a bomb is dropped on it, few people would have a home to live in.

Thus, the term “life safety” must be used in context of reasonable risk vs. cost to society.

Obviously, everyone wants the lives of firemen and rescue workers to be protected.

But we also innately realize that those professions carry some risk. So, how much cost should be borne by society (because every dollar spent by an “owner” is, in reality, spent by “society”) in order to reduce the risks further? At what point are the risks adequately low?

Structural engineers, by our very nature, perceive the consequences of building failures as being very high. However, in our training, there is very little focus on understanding risks from a societal perspective.

Hence, we may view the risks we deal with as being the most important risks for society to address. Without a mechanism to weigh the costs, anything that reduces risk can be added to the building code and justified by the suggestion that it might save lives. For instance, the 1997 UBC was, in my opinion, a code that adequately protected lives.

So, why has the building code changed, six times, since 1997?

I understand that we are continually learning and, with our advances in knowledge and technology, there will inevitably be new ideas and new ways of looking at design.

But, are they really better? Who gets to decide if they are better, and what criteria do they use?

For instance, who decided that we should map wind speeds at a strength level rather than at service level? Since the 1994 UBC, I have learned four new ways to find the design wind pressures on buildings. Yet, recently, while researching the construction drawings of a building built in Florida in 1962, I found this note: “Wind Design Pressure = 20 psf ”.

I have to believe that this building has been exposed to very high winds in its 50 year life, and yet there it stands, occupied and undamaged, and nobody is calling it a dangerous building.

Revisions to building codes should be made slowly, except in dramatic discoveries such as the Northridge steel moment frame issue. As an example of having moved too quickly, consider the maps of seismic coefficients found in ASCE 7 and the IBC. I call these the “yo-yo” maps of the building code. In some places, the design seismic ground motions have gone up and down by 20% or more through the last several editions of the code. Buildings built in 1998 may have been okay per the 1997 UBC, then significantly under-designed per the 2006 IBC, then again just fine under the 2012 IBC. Let’s be honest and admit that we really don’t know seismic demands well enough to justify changes in the capacity

equations when the capacities change by only 5% or 10%.

Beyond the provisions concerning lifesafety, other things are creeping into the building code that go well beyond the purpose of a building code. Consider the energy code. This is simply an exercise in social engineering and has no place in a building code. Those defending the energy code claim that it will save the owners money. However, that is not the purpose of a building code. That is what a freemarket economy is for. If the laws of supply and demand are allowed to freely operate, energy will be conserved, and people who so desire will save money and use less energy, without taking more freedom of choice from American citizens.

Many other provisions, both structural and non-structural, have found their way into the building code, and have nothing to do with life safety. Consider Section 1204.1 of the IBC: “Interior spaces intended for human occupancy shall be provided with active or passive space-heating systems capable of maintaining a minimum indoor temperature of 68°F at a point 3 feet above the floor on a design heating day”.

What a great thing! I would love my home to have that – and the free market society I live in allows me to choose to have that.

But this should not to be in the building code. Instead, it should be in a book called “Great Ideas for Architects, Engineers, and Builders to Offer to Clients Who Want Nice Comfortable Buildings.” And that is just one example of many things in the current IBC that should be similarly considered.

Our building code has been hijacked. Is anyone willing to offer a ransom?▪ David Pierson (davep@arwengineers.com) is a Vice President at ARW Engineers in Ogden, Utah. He currently serves as vicechairman of TMS 402/602, and is past chairman of the Utah Uniform Building Codes Commission.

Structural Forum is intended to stimulate thoughtful dialogue and debate among structural engineers and other participants in the design and construction process. Any opinions expressed in Structural Forum are those of the author(s) and do not necessarily reflect the views of NCSEA, CASE, SEI, C 3 Ink, or the STRUCTURE® magazine Editorial Board.

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April 2016