STRUCTURE magazine - July 2018

A Joint Publication of NCSEA | CASE | SEI

STRUCTURE

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July 2018 Wind/Seismic Inside: 432 Park Ave., New York City

Build to Last Seismic and lateral forces may be unavoidable, but ACI provides you with on-demand courses and publications so you can stay informed and plan ahead.

Standard Requirements for Seismic Evaluation and RetroďŹ t of Existing Concrete Buildings (369.1) and Commentary Guide for Seismic Rehabilitation of Existing Concrete Frame Buildings and Commentary

SpeciďŹ cation for High-Strength Concrete in Moderate to High Seismic Applications

Guide to Nonlinear Modeling Parameters for Earthquake-Resistant Structures

www.concrete.org

LeMessurier Calls on Tekla Structural Designer for Complex Projects Interoperability and Time Saving Tools

Tekla Structural Designer was developed specifically to maximize collaboration with other project parties, including technicians, fabricators and architects. Its unique functionality enables engineers to integrate the physical design model seamlessly with Tekla Structures or Autodesk Revit, and to round-trip without compromising vital design data.

“We’re able to import geometry from Revit, design in Tekla Structural Designer and export that information for import back into Revit. If an architect makes geometry updates or changes a slab edge, we’ll send those changes back into Tekla Structural Designer, rerun the analysis and design, and push updated design information back into Revit.”

Tekla Structural Design at Work: The Hub on Causeway

For over 55 years, LeMessurier has provided structural engineering services to architects, owners, contractors, developers and artists. Led by the example of legendary structural engineer and founder William LeMessurier, LeMessurier provides the expertise for some of the world’s most elegant and sophisticated designs while remaining true to the enduring laws of science and engineering.

Known for pushing the envelope of the latest technologies and even inventing new ones, LeMessurier engineers solutions responsive to their clients’ visions and reflective of their experience.

An early adopter of technology to improve their designs and workflow, LeMessurier put its own talent to work in the eighties to develop a software solution that did not exist commercially at the time. Their early application adopted the concept of Building Information Modeling (BIM) long before it emerged decades later.

While LeMessurier’s proprietary tool had evolved over three decades into a powerhouse of capability, the decision to evaluate commercial structural design tools was predicated on the looming effort required to modernize its software to leverage emerging platforms, support normalized data structure integration and keep up with code changes.

After a lengthy and thorough comparison of commercial tools that would “fill the shoes” and stack up to the company’s proprietary tool, LeMessurier chose Tekla Structural Designer for its rich capabilities that addressed all of their workflow needs. According to Derek Barnes, Associate at LeMessurier, ” Tekla Structural Designer offered the most features and the best integration of all the products we tested. They also offered us the ability to work closely with their development group to ensure we were getting the most out of the software.”

One Model for Structural Analysis & Design

From Schematic Design through Construction Documents, Tekla Structural Designer allows LeMessurier engineers to work from one single model for structural analysis and design, improving efficiency, workflow, and ultimately saving time. “Our engineers are working more efficiently because they don’t need to switch between multiple software packages for concrete and steel design. Tekla Structural Designer offers better integration of multiple materials than we have seen in any other product,” said Barnes.

LeMessurier engineers use Tekla Structural Designer to create physical, information-rich models that contain the intelligence they need to automate the design of significant portions of their structures and efficiently manage project changes.

TRANSFORMING THE WAY THE WORLD WORKS

“Tekla Structural Designer has streamlined our design process,” said Craig Blanchet, P.E., Vice President of LeMessurier. “Because some of our engineers are no longer doubling as software developers, it allows us to focus their talents on leveraging the features of the software to our advantage. Had we not chosen to adopt Tekla Structural Designer, we would have needed to bring on new staff to update and maintain our in-house software. So Tekla Structural Designer is not just saving us time on projects, it is also saving us overhead.

Efficient, Accurate Loading and Analysis

Tekla Structural Designer automatically generates an underlying and highly sophisticated analytical model from the physical model, allowing LeMessurier engineers to focus more on design than on analytical model management. Regardless of a model’s size or complexity, Tekla Structural Designer’s analytical engine accurately computes forces and displacements for use in design and the assessment of building performance.

“Tekla Structural Designer offers better integration of multiple materials than we have seen in any other product.”

Positioning a large scale mixed-use development next to an active arena, a below grade parking garage, and an interstate highway, and bridging it over two active subway tunnels makes planning, phasing and engineering paramount. Currently under construction, The Hub on Causeway Project will be the final piece in the puzzle that is the site of the original Boston Garden.

Despite being new to the software, LeMessurier decided to use Tekla Structural Designer for significant portions of the project. “Relying on a new program for such a big project was obviously a risk for us, but with the potential for time savings and other efficiencies, we jumped right in with Tekla Structural Designer. It forced us to get familiar the software very quickly.”

“Tekla Structural Designer allowed us to design the bulk of Phase 1 in a single model,” said Barnes. The project incorporates both concrete flat slabs and composite concrete and steel floor framing. “Tekla Structural Designer has the ability to calculate effective widths based on the physical model which is a big time saver,” said Barnes. “On this project, the integration with Revit, along with the composite steel design features enabled us to work more efficiently. Adding the ability to do concrete design in the same model was a bonus because we had both construction types in the same building.”

“Tekla Structural Designer helped this project run more efficiently, and in the end it was a positive experience,” said Blanchet.

“Tekla Structural Designer gives us multiple analysis sets to pull from, which gives us lots of control. Most programs don’t have the capability to do FE and grillage chase-down. For the design of beam supported concrete slabs, Tekla Structural Designer allows us to separate the slab stiffness from the beam stiffness, so if we choose to we can design the beams without considering the influence of the slab. In the same model we can use a separate analysis set to review the floor system with the beams and slab engaged,” said Barnes.

Barnes also shared similar benefits with concrete column design. “Tekla Structural Designer does grillage take-downs floor-by-floor, finds the reactions and applies them to the next floor. This allows us to view column results both for the 3-dimensional effects of the structure as a whole and from the more traditional floor-by-floor load take-down point of view.

Doing both has always required significant manual intervention, but Tekla Structural Designer puts it all in one place.” “We reduce the possibility for human error because with Tekla Structural Designer less user input is required,” said Barnes. “Tekla Structural Designer automatically computes many of the design parameters, such as column unbraced lengths. The assumptions made by the software are typically correct, but we can easily review and override them when necessary.”

“Tekla Structural Designer provided the best fit for our workflow compared to other commercially available software.”

Want to Evaluate Tekla Structural Designer? tekla.com/TryTekla

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July 2018

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STRUCTURE® magazine (ISSN 1536 4283) is published monthly by The National Council of Structural Engineers Associations (a nonprofit Association), 645 N. Michigan Ave, Suite 540, Chicago, IL 60611 312.649.4600. Application to Mail at Periodicals Postage Prices is Pending at Chicago, IL and additional mailing offices. STRUCTURE magazine, Volume 25, Number 7, C 2018 by The National Council of Structural Engineers Associations, all rights reserved. Subscription services, back issues and subscription information tel: 312-649-4600, or write to STRUCTURE magazine Circulation, 645 N. Michigan Avenue, Suite 540, Chicago, IL 60611. The publication is distributed to members of The National Council of Structural Engineers Associations through a resolution to its bylaws, and to members of CASE and SEI paid by each organization as nominal price subscription for its members as a benefit of their membership. Yearly Subscription in USA $75; $40 For Students; Canada $90; $60 for Canadian Students; Foreign $135, $90 for foreign students. Editorial Office: Send editorial mail to: STRUCTURE magazine, Attn: Editorial, 645 N. Michigan Avenue, Suite 540, Chicago, IL 60611. POSTMASTER: Send Address changes to STRUCTURE magazine, 645 N. Michigan Avenue, Suite 540, Chicago, IL 60611.

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CONTENTS

32 C over Feature

432 PARK

By Silvian Marcus, P.E., Hezi Mena, P.E., Fatih Yalniz, P.E., and Chris Shirley, P.E.

Feature

The tallest residential tower in the western hemisphere, this super-slender structure used more than 70,000 cubic yards of concrete. Challenges were abundant, including wind/seismic issues and strength requirements. High-performance concrete materials were integral to many of the solutions.

26 REBUILDING YEARS

By Benjamin Pavlich, S.E., Elaine Shapiro, S.E., Abhiram Tammana, P.E., and William D. Bast, P.E., S.E., SECB Renovations at the iconic Wrigley Field required innovative solutions to strengthen foundations and reinforce the stadium. Raker encasements, composed of CIP concrete, were an integral part of solving issues with the existing lateral system and its ability to withstand code-prescribed wind loads.

Columns and Departments

ENGINEER’S NOTEBOOK

STRUCTURAL DESIGN

22 Special Moment Frames in Reinforced Concrete

By David A. Fanella, Ph.D., S.E., P.E.,

EDITORIAL

48 Increased Seismic Design Forces

By Philip Line, P.E., Michelle Kam-Biron, P.E., S.E., S.E.C.B., and Michael Cochran, P.E., S.E.

and Michael Mota, Ph.D., P.E., SECB

7 Why Did They Leave?

BUSINESS PRACTICES

By Corey M. Matsuoka, P.E.

PROFESSIONAL ISSUES

34 2016 – NCSEA Practitioner Survey STRUCTURAL FAILURES

By Paul Hopkins Ph.D., P.E., S.E.,

8 Revisiting the Galloping Gertie

53 You Hired a New Graduate, Now What?

By Jennifer Anderson

and Kevin Dong, P.E., S.E.

By Sumanth Cheruku, E.I.T.

SPOTLIGHT

55 Creative Rigor: Retrofit of the Desmond, Los Angeles

HISTORIC STRUCTURES

38 Hell Gate Bridge

CODES AND STANDARDS

12 ASCE 7-16 Wind Load Provisions

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

By Donald R. Scott, P.E., S.E. INSIGHTS

45 Marketing Services in an Amazon World

CODE UPDATES

16 Technical Aspects of ASCE 7-16

By William L. Coulbourne, P.E.,

By Michael Bernard, AIA

and Philip Line, P.E. EDUCATION ISSUES

18 Wood Bowstring Trusses – Part 2

47 Reimagined Structural Design in Capstone Classes

By Filippo Masetti, P.E., Gloriana Arrieta

By Deb O’Bannon, Ph.D., P.E.,

Martinez, Ph.D., and Milan Vatovec, Ph.D., P.E.

and Jim Palmer, P.E.

STRUCTURAL REHABILITATION

By Mark Sarkisian, P.E., S.E., Neville Mathias, P.E., S.E., and Rupa Garai, P.E., S.E. STRUCTURAL FORUM

62 Eureka! Road to Progress

By James Lefter, P.E.

IN EVERY ISSUE 4 Advertiser Index 50 Resource Guide – Concrete Products 56 NCSEA News 58 SEI Structural Columns 60 CASE in Point

Publication of any article, image, or advertisement in STRUCTURE® magazine does not constitute endorsement by NCSEA, CASE, SEI, the Publisher, or the Editorial Board. Authors, contributors, and advertisers retain sole responsibility for the content of their submissions.

STRUCTURE magazine

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July 2018

Editorial Why Did They Leave?

By Corey M. Matsuoka, P.E., Chair CASE Executive Committee

E

mployees leave bosses, not companies. If you have worked long enough, it is a statement you have probably heard sometime during your career. The reason? It is true. According to a Gallup study, approximately 50% of employees that leave their company exit to get away from their boss. To make it even worse, recent Department of Labor statistics indicate that the average tenure of an employee in the U.S. is now only 1.5 years. That number is likely higher for engineering companies, but it is still an indicator of where we could be headed.

Recently, one of our better employees submitted their resignation letter and the theory of employees leaving their boss really hit home. He was not leaving for more money or a promotion; he just was not happy. In the staff of 40 that I manage, this is the first voluntary resignation I have experienced in three and a half years.

In today’s economy, where jobs are plentiful, that is a pretty good record. Retention has not historically been a challenge for us, so this came as a surprise. Naturally, I began asking myself - was it something that I did or did not do that caused him to leave? What should I be doing differently to make my staff want to stay?

After some soul searching and restless nights, here are the five areas I decided were critical to employee retention…

1) Promote a culture where communication is a two-way street.

As managers, we need to listen as well as direct. When we direct, we need to provide clear instructions and expectations.

When we listen, we need to treat our employee’s concerns as our own; they should leave the conversation believing that we will take whatever action we can. If nothing can be done, we should provide a logical explanation why. The bottom line is, our employees need to feel comfortable enough to approach us when things are not going well and then have faith that we will attempt to make it better for them. If we can achieve this one goal, we will know long before we get the resignation letter that something is wrong.

2) To facilitate two-way conversations, we need to check-in regularly with our staff. We need to give them the opportunity to discuss their strengths, what is going on in their personal lives, and items they are struggling with. Glenn Furuya, the founder of Leadership Works, LLC, recommends LBWA (Lead by Walking Around ), stating that real leaders operate at the grass-roots level, maintaining high visibility and accessibility. Walking around and holding regular check-ins will allow for a better perspective of what is happening, see things first hand, and assess the wellbeing of the staff. Leaders who “LBWA” have team members who view them as humble, concerned, and connected.

STRUCTURE magazine

3) Show appreciation for the work our staff does. According to Maslow’s Hierarchy of Needs, Esteem is one of our most basic needs.

Esteem can be built in a number of ways, from simply voicing our appreciation to formal recognition programs. One great way to show our appreciation is to provide opportunities for high performing staff to travel and attend educational sessions. I definitely plan to use these opportunities as rewards and to show staff how much we appreciate their work and commitment to the firm.

4) Put Employees, not Clients first. While that may seem counterintuitive, Richard Branson, Chairman of Virgin Galactic puts it best, “Take care of your employees, and they will take care of your business. It’s as simple as that!” When employees are put first, they feel a sense of ownership and take the initiative to solve problems and look out for the best interest of the company. On the other hand, when employees are overlooked and become disengaged, they cost companies vast sums of money in lost productivity and inattention to detail. Gallop found that actively disengaged employees cost the U.S. $450 to $550 billion per year. When you consider the expense associated with employee turnover, you can expect it to cost 30-50 percent of annual salary to replace an entry level employee and upwards of 150 percent of annual salary to replace a mid-level employee.

5) Tied in with putting employees first is providing them with an acceptable work/life balance. Employees and managers need to be on the same page when it comes to expectations of work commitments. If not, life for one or both will be miserable. The good news is that we do not have to measure this by hours in the office. In a results-oriented work environment, it does not matter where or when you work, if you get the job done. Laptops, smartphones, hot spots, flexible work hours, work from home, and the ability to bring children to work all help in the effort.

Before he left, I did sit down with this employee to thank him for his dedicated service to the company, express my sorrow that he was leaving, and offer my apology to him for not being there when he needed me. At the end of the lunch, he asked for feedback on his performance. I told him that he was a model employee, hardworking, eager to learn, and a team player. I told him the only thing I wished he did differently was to talk to me when things got tough for him. This is a conversation that I should have had with him six months ago.▪ Corey M. Matsuoka is the Executive Vice-President of SSFM International, Inc. in Honolulu, Hawaii. He is the chair of the CASE Executive Committee. (cmatsuoka@ssfm.com)

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July 2018

structural

FAILURES

T

his article reviews the failure mechanisms of the Tacoma Narrows Bridge (TNB) on November 7, 1940, and the characteristics of the original bridge that facilitated the resultant theories on its failure. The design of the bridge pushed the boundaries of knowledge at the time, unfortunately with undesired consequences. The failure resulted in a re-evaluation of the design practice. The objective of this article is to illustrate the concept of aeroelasticity and its consequences on structural behavior through this historic failure and to evaluate its applicability to some unsuspecting structures.

Bridge Design The Tacoma Narrows Bridge is located in the Tacoma Narrows of Puget Sound, Pierce County, Washington. Clark Eldridge’s original $11 million design ($192 million: 2017) of the bridge was modified for a more economical $6.4 million design by Leon Moissieff. Eldridge’s original design consisted of 25-foot-deep trusses that would have stiffened the deck. Experts believe the bridge might have survived the winds on November 7, had those trusses been installed (WSDOT, 2005). The original bridge was designed for 120 mph winds.

Moissieff designed a two-lane bridge with two 1100-foot side spans and a 2800-foot main span.

Within these constraints, Moissieff used deflection theory, which depends on the stiffness due to the dead load of the structure to resist the deflections due to the live load. This led to the consideration that the stiffness of the proposed trusses did not contribute considerably to the stiffness of the suspended deck and led to the design of the stiffening girders for resisting lateral wind forces. Deflection theory was common

Revisiting the Galloping Gertie

By Sumanth Cheruku, E.I.T.

Sumanth Cheruku is an Engineer with Pivot Engineers in Austin, TX. He is a member of ACI committees 348, 377, 423, Forensic and Wind Engineering Divisions of the ASCE and serves as the Secretary of Chapter 29 task sub-committee of ASCE 7 for 2022 code cycle.

Golden Gate

for suspension bridge designs of the time. For example, bridges like the Manhattan Bridge and the Bronx-Whitestone Bridge were designed using deflection theory. The TNB design pushed the boundaries of this design philosophy as evidenced by some characteristic features (Figure 1). The width of the bridge and depth of the girders were smaller, leading to large slenderness ratios. The span/width ratio (75:1) of the TNB was 1.5x and the span/depth ratio (375:1) was more than two times that of the Golden Gate Bridge. The lighter steel resulted in a center span that is around 3.5x lighter than the Golden Gate Bridge.

The final superstructure consisted of built up stiffening girders spaced 39 feet on-center, 52-inch-deep plate girders as transverse floor beams at 25 feet, supporting (5) 21-inch rolled beams as longitudinal stringers at 5 feet-9 inches, which in turn supported the 5¼-inch concrete roadway. The stiffening girders were built up with a 96-inch x ½-inch web, (4) 8- x 6- x ½-inch angles and (2) 20- x ½-inch cover plates. The web was stiffened longitudinally with “zees” on one side and transversely with vertical channels on the other. Each of the 17⅛-inch diameter cables consisted of 19 strands of 332x No. 6 cold drawn galvanized wires, constructed at a sag ratio of 1/12 with (4) 1¼-inch diameter suspenders at 50 feet along each cable.

Bridge Behavior and Collapse During construction, which commenced in November 1938, workers experienced significant vertical vibration of the deck consequently attributing to the title, “Galloping Gertie.” Professor Burt Farquharson at the University of Washington was tasked with monitoring these vibrations and studying retrofit measures. An observation of vibrations (Ammann, 1941), documented after opening the bridge to the public, reported that

Torsional flexibility

Bronx - Whitstone Tacoma Narrows

Deflection of center span due to center spanLL(in)

Center span/ width (47:1)

Center span/ girder depth (168:1)

1/ Weight of center span per linear foot

Figure 1. Characteristics of Tacoma Narrows normalized to the Golden Gate bridge, data from (Ammann, 1941).

STRUCTURE magazine

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July 2018

Type 10Six Nodes 27.0 Cycles per Min. Type 11Seven Nodes 34.0 Cycles per Min.

Type 12Eight Nodes 38.0 Cycles per Min.

Figure 2. Observed vertical (plunge) oscillations on the Tacoma Narrows Bridge (Ammann, 1941).

oscillations with amplitudes of 48 inches were observed at 16 cycles/minute at wind speeds of 3 to 4 mph. However, monitoring also revealed certain characteristics like oscillations having no effect due to wind turbulence or traffic loading. It was also reported that the bridge remained motionless on occasions in winds varying from 0 to 35 mph. Initial retrofits to reduce the vibrations included plate girders being tied down, adding 1½-inchdiameter inclined stays from cables to midspan of the stiffening girders, and the addition of hydraulic dampers. The dampers were not as effective in comparison to similar installations on other bridges, and the stay ropes slipped and were ineffective. Professor Farquharson’s recommendation of adding semicircular deflector shields to streamline the girders, based on wind tunnel model studies, was approved early November 1940 by the Washington Toll Bridge Authority.

Videographic documentation of the failure is available (https://bit.ly/2xw174p) for posterity to observe, investigate, and recreate the failure for those interested in understanding the failure mechanism. It should be noted that some inconsistencies in recording (16 fps (frames per second)) and documentation (24 fps) led to inadvertently speeding up the video, which might be inaccurate for reconstruction. The morning, on the day of failure, saw the center span oscillating with 8 to 9 nodes at frequencies of 36 to 38 cycles/min (Figure 2) while wind speeds in the range of 42 mph were recorded. At around 10 AM, the frequency changed from 37 to 14 cycles/ min with torsional movement observed about a node at mid-span. This change in motion resulted in oscillations with cable amplitudes of approximately 28 feet, causing an angular twist of the superstructure of about 45 degrees at quarter points. At 11 AM, the 600-foot suspended superstructure dropped, culminating

in the collapse of the remaining central span superstructure at 11:10 AM.

Resonance and Vortex Lock-in

the Strouhal constant. The calculated vortex shedding frequency for the bridge superstructure with 8-foot-deep girders, 42 mph wind, and a Strouhal constant of 0.11 would equate to 1Hz, while documented oscillations on the day varied from 0.6Hz (37 cycles/min before 10 AM) to 0.2Hz at failure (14 cycles/min).

This acted as sufficient evidence to refute the theory of resonance due to synchronization with wind and Karman vortices.

This calculation also disproved the hypothesized vortex lock-in effects as being a cause of failure. Vortex lock-in may be characterized as mechanical excitation in the presence of vortices at the frequency of the structure.

Lock-in vibrations are believed to be the cause of in-service vibrations observed by the bridge, but not a cause of failure (Billah, 1991). Lock-in effects typically excite the structure at its resonant frequencies; however, as the amplitude of vibrations increase, changes in boundary conditions introduce self-limiting forces resulting in Van-der-Pol type limiting oscillations. In the case of the TNB, the observed vortices are concluded to be a consequence of oscillations but not a primary cause for its failure.

Early thoughts on the failure mechanism were directed towards resonance from external wind loading (NYT, 1940). Historical failures of the Broughton suspension bridge in 1831 and Angers suspension bridge in 1850 due to marching troops may have contributed to this Modern Consensus line of thought. Federal Works Agency (FWA) report’s statement, “Its [Tacoma Narrow’s] The FWA report concluded: “The vertical failure resulted from excessive oscillations oscillations of the Tacoma Narrows Bridge caused by wind action,” was not very clear were probably induced by the turbulent charand inadvertently corroborated the theory. acter of wind action. Their amplitudes may While some attribute the periodicity required have been influenced by the aerodynamic for resonance to turbulence in wind (Miller, characteristics of the suspended structure.

1977, McCormick, 1969), others attributed There is, however, no convincing evidence it to the shed Karman vortices. However, the that the vertical oscillations were caused by sovariation in the characteristics of wind loading called aerodynamic instability. At the higher at the site could not account for the required wind velocities, torsional oscillations, when periodicity for the resonance of the bridge. once induced, had the tendency to increase Interaction of fluids with static, bluff (not streamlined) bodies results in the formation and shedding of vortices in the wake, referred to as “Karman vortex street.” Figure 3 shows the formation of the Karman street in atmospheric cloud movement due to Guadalupe Island, as seen from a weather satellite. The frequency of vortex shedding will depend on the cross-flow dimension (diameter of the island), Figure 3. Karman vortex street on GOES-9 satellite observed due to free stream velocity, and Guadalupe Island (CIMSS, 2001).

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July 2018

Figure 4. CFD simulation of H-section deck in increasing fluid flow – created from (Wei, 2011).

their amplitudes.” The body of knowledge on aeroelastic phenomenon was limited to Theodorsen’s paper on aerodynamic instability and flutter of airfoil published in 1934, but limited extension to bridges until Scanlan (Scanlan, 1971). Under limited evidence for observation of these phenomenon, the statement in the FWA report about the failure of the bridge seems justified.

The last line of the statement refers to an instability in the torsional mode of oscillation. This instability, dependent upon the aerodynamic characteristics of the bridge, is believed to be a consequence of aeroelastic phenomenon referred to as torsional galloping or stall flutter (stall not due to viscous effects).

Aeroelastic phenomena occur in the domain of the intersection of aerodynamic, elastic, and inertial forces. The lack of inertial forces results in a static phenomenon like divergence, while the inclusion of inertial components results in dynamic phenomenon like flutter. Scanlan demonstrated that the failure mode was “SDOF torsional flutter” of a bluff body. Subsequent publications supported this mechanism. A non-catastrophic 1D flutter in plunge motion translated into a large amplitude 1D torsional flutter observed at the instance of collapse (Blevins, 1977; ASCE, 1987). The reason for the change in the mode of vibration from plunge to torsional is not well understood, with explanations ranging from slip-of-cable-mount during the plunge phase (Ammann, 1941; Malik, 2013) to a theoretically based energy threshold approach (Arioli, 2013; Arioli, 2015).

Aeroelastic Flutter Flutter may be conceptualized as a self-exciting, aerodynamic phenomenon wherein a condition of positive feedback is established on the structure’s vibration by the

Figure 5. CFD simulation illustrating the torsional instability of single-axis solar trackers (Rohr, 2015).

aerodynamic forces. Note that this simplification is nuanced, and readers are advised to follow up with literature for a more accurate understanding of the phenomena. From the perspective of an oscillator, flutter may be conceptualized as an instability arising due to a negative net damping as a consequence of aerodynamic damping exceeding the inherent damping of the structure. An example of the oscillations considering a quasi-steady model (for illustration only, recent calculations utilize flutter derivatives for characterizing fluid force) is presented below (Blevins, 1977) to illustrate the onset of torsional galloping.

Jθθ¨ + 2Jθ ζ θ ω θθ. + kθ θ = FFluid = 1 ρU 2D 2 C + ∂CM |αα=0 + . . .

M | α=0 ∂α 2

(

)

(

)

Jθθ¨ + 2Jθ ζ θ ω θ + 1 ρURD2 ∂CM θ. + 2 ∂α kθθ - 1 ρU 2D2 ∂CM θ = 0 2 ∂α

(

)

where Jθ is the polar moment of inertia, ζθ is the torsional damping, ωθ is the torsional frequency mode, kθ is torsional stiffness, ρ is the density of fluid, U is the fluid velocity, D is the cross-flow dimension, R is the Reynolds number, θ is the angular rotation, α is the angle of attack, and CM is the moment coefficient.

Upon examination of the damping term, the positive feedback (negative net damping) can occur under two conditions, 1) R ∂C∂αM is negative (or can become negative due to motion), (Den Hartog Criterion) and 2) U exceeds a certain magnitude. The first condition, variation of lift coefficient (moment coefficient) with the angle of attack, is characteristic of the shape of the body.

Circular sections are mostly insensitive to angle of attack (inclined cable stays in rain are excluded). The torsional oscillator equation shows that as the normalized wind speed for bluff body increases, the aerodynamic

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damping changes sign and, beyond a certain wind speed (critical velocity), results in a net negative damping introducing instability in structural vibration.

Mechanistically, this behavior may be visualized as aerodynamic forces deforming the structure while the elastic forces are restoring beyond the original undeformed state, providing positive feedback to the aerodynamic force. A visual illustration of the behavior can be viewed online (youtu.be/YzvFxF5LrRA).

Figure 4 shows the CFD simulation of the deck section in increasing fluid flow. At low speeds, the flow is relatively consistent with the entire deck acting as a solid body. As speed increases, vortices form and oscillation occur at these speeds, if the frequency of shed vortices match the natural frequency of the deck.

Further increases in wind speed will result in motion-induced forces due to vortices formed in the immediate vicinity, leading to large torsional moments and rotations.

Other Structures The intricate nature of aeroelasticity is challenging to capture in the provisions of the design code. However, this behavior is expected in common structures like tall buildings and bridges, and some unsuspecting structures like single-axis solar trackers (Rohr, 2015). Figure 5 presents CFD simulation of single-axis solar trackers stowed near-flat, illustrating behavior similar to the bridge deck.

A review of the failure of TNB is provided to illustrate the role of aeroelasticity on structural behavior. The objective is to encourage designers to contemplate possible aeroelastic effects of the designed structure due to wind.▪ The online version of this article contains references. Please visit www.STRUCTUREmag.org.

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CODES AND T standards

he new ASCE 7-16 Minimum Design Loads and Associated Criteria for Buildings and Other Structures (Standard) is adopted into the 2018 International Building Code (IBC) and is now hitting your desks. The 2018 IBC and the referenced Standard are being adopted by a few jurisdictions and will become more widely used in 2019. Thus starts the time when practicing engineers learn the new provisions of the Standard and how they apply to their practices. To help in this process, changes to the wind load provisions of ASCE 7-16 that will affect much of the profession focusing on building design are highlighted.

Basic Wind Speed Maps An updated study of the wind data from over 1,000 weather recording stations across the country was completed during this last cycle. This study focused on the nonhurricane areas of the country and used a new procedure that separated the available data by windstorm type and accounted for changes in the site exposure characteristics at the recording anemometers. This separation was between thunderstorm and non-thunderstorm events.

Also, a small revision was made to the hurricane wind speeds in the Northeast region of the country based upon updated hurricane models.

Consequently, wind speeds generally decrease across the country, except along the hurricane coastline from Texas to North Carolina. The wind speeds in the northern Great Plains region remain approximately the same as in ASCE 7-10. The most significant reduction in wind speeds occurs in the Western states, which

ASCE 7-16 Wind Load Provisions How They Affect the Practicing Engineer

By Donald R. Scott, P.E., S.E., F.SEI, F.ASCE Donald R. Scott is a Senior Principal at PCS Structural Solutions, Tacoma, WA. He is also Chair of ASCE 7 Wind Load Subcommittee and Chair of NCSEA Wind Engineering Committee. (dscott@pcs-structural.com)

Table 26.9-1 – ASCE 7-16 ground elevation factor.

Ground elevation above sea level

Ground elevation adjustment factor

ft

(m)

Ke

0

(0)

1.00

1000

(305)

0.96

2000

(610)

0.93

3000

(914)

0.90

4000

(1219)

0.86

5000

(1524)

0.83

6000

(1829)

0.80

decreased approximately 15% from ASCE 7-10 (Figures 1 and 2). To meet the requirements of Chapter 1 of the Standard, a new map is added for Risk Category IV buildings and other structures (Figure 3). These new maps better represent the regional variations in the extreme wind climate across the United States.

Additionally, “effective” wind speed maps are provided for the State of Hawaii. These maps differ from the other maps because the wind speed contours include the topographic effects of the varying terrain features (Figure 4). Thus, a Topographic Factor value, Kzt equal to 1.0 is to be used.

Not many users of the Standard utilize the Serviceability Wind Speed Maps contained in the Commentary of Appendix C, but these four maps (10, 25, 50 & 100-year MRI) are updated to be consistent with the new wind speed maps in the body of the Standard.

Ground Elevation Factor, Ke The new Ke factor adjusts the velocity pressure to account for the reduced mass density of air as height above sea level increases (see Table). This reduction was provided in the Commentary of previous editions of the Standard; however, it is being brought into the body of the Standard to facilitate its use. This factor provides a simple and convenient way to adjust the velocity pressure in the wind pressure calculations for the reduced mass density of air at the building site.

The adjustment can be substantial for locations that are located at higher elevations. For example, in Denver, CO, the “Mile High City,” the ground elevation factor, Ke, is 0.82 which translates to an 18% reduction in design wind pressures.

Rooftop Equipment Figure 1. Example of ASCE 7-10 Risk Category II Basic Wind Speed Map. Printed with permission from ASCE. See ACSE 7-10 for important details not included here.

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The provisions contained within ASCE 7-10 for determining the wind loads on rooftop equipment on buildings is limited to buildings with a mean roof height h ≤ 60 feet. This limitation

Figure 2. Example of ASCE 7-16 Risk Category II Basic Wind Speed Map. Printed with permission from ASCE. See ASCE 7-16 for important details not included here.

Figure 3. Example of ASCE 7-16 Risk Category IV Basic Wind Speed Map. Printed with permission from ASCE. See ASCE 7-16 for important details not included here.

was removed in ASCE 7-16, and thus the provisions apply to rooftop equipment on buildings of all heights. One new clarification is that the basic design wind speed for the determination of the wind loads on this equipment needs to correspond to the Risk Category of the building or facility to which the equipment provides a necessary service. This means that if a cooling tower is located on an administration building (Risk Category II) of a hospital but serves the surgery building (Risk Category IV) of the hospital, the wind loads determined for the cooling tower would be based on the Risk Category IV wind speed map.

Wind Loads on Rooftop Solar Panels New additions to the Standard are provisions for determining wind loads on solar panels on buildings. These provisions give guidance to the users of ASCE 7 that has been missing in the past. Previously, designers commonly attempted to use a combination of the component and cladding provisions and other provisions in the Standard to determine these loads, often resulting in unconservative designs.

There are two methods provided in the new Standard. One method applies specifically to

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Figure 4. Example of ASCE 7-16 Risk Category II Hawaii effective wind speed map. Printed with permission from ASCE. See ASCE 7-16 for important details not included here.

a low-sloped roof (less than 7 degrees) (Figure 5, page 14 ) and the second method applies to any roof slope where solar panels are installed parallel to the roof. Each of these provisions was developed from wind tunnel testing for enclosed structures. Thus, these provisions are not applicable to open structures because the flow of the wind over the roof of enclosed structures and open structures varies significantly. Further testing is currently underway for open structures, and these results will hopefully be included in future editions of the Standard.

The wind loads for solar panels do not have to be applied simultaneously with the component and cladding wind loads for the roof.

However, the roof still needs to be designed appropriately assuming the solar panels are removed or not present.

Roof Pressure Coefficients (h < 60 feet) The component and cladding pressure coefficients, (GCp), for roofs on buildings with an h < 60 feet, have been revised significantly in ASCE 7-16. The new roof pressure coefficients are based on data from recent wind tunnel tests and then correlated with the results from full-scale tests performed at Texas Tech University. The full-scale tests indicated that the turbulence observed in the wind tunnel studies from the 1970s, that many of the current roof pressure coefficients were based on, was too low.

Also, the technology available to measure the results of these wind tunnel tests has advanced significantly since the 1970s.

Therefore, the new wind tunnel studies used flow simulations that better matched

those found in the full-scale tests along with improved data collection devices; these tests yielded increased roof pressures occurring on the roofs. Thus, the roof pressure coefficients have been modified to more accurately depict roof wind pressures.

In conjunction with the new roof pressure coefficients, it was determined that the existing roof zoning used in ASCE 7-10 and previous editions of the Standard did not fit well with the roof pressure distributions that were found during these new tests for low-slope (≤ 7 degrees) roof structures. These tests established that the zoning for the roof on these low-slope roof structures was heavily dependent on the building height, h, and much less dependent on the plan dimensions of the building. The tests showed that the “corner zones” were too small for the high roof pressures that were being measured at these locations on the building. Considering all of these effects, a new zoning procedure for low-sloped roofs for buildings with h ≤ 60 feet was developed. The zones are shown best in the Commentary Figure C30-1 as shown in Figure 6.

The roof zoning for sloped roofs kept the same configurations as in previous editions of the Standard; however, many of the zone designations have been revised (Figure 7 ). This revision in zone designations was required because the values in zones around the roof in previous editions of the Standard were shown as having the same pressure coefficient, i.e., corners at the eave versus corners at the ridge have been found to have varying pressures.

Figure 5. Example of ASCE 7-16 Figure 29.4-7 Excerpt for rooftop solar panel design wind loads.

Printed with permission from ASCE. See ASCE 7-16 for important details not included here.

Bleast > 2.4h

2.4 > Bleast > 1.2h

Bleast < 1.2h and Blargest > 1.2h

Blargest < 1.2h

Bleast – least horizontal building dimension Blargest – largest horizontal building dimension h – mean roof height

Figure 6. Example of ASCE 7-16 low slope roof component and cladding zoning.

Attached Canopies on Buildings New provisions have been added to determine the wind pressures on canopies attached to the sides of buildings. This is the first edition of the Standard that has contained such provisions.

Previously, designers were required to use various provisions of overhangs, free roof structures, and more to determine the wind loads on canopies. Research became available for the wind pressures on low-slope canopies during this last code cycle of the Standard.

This research was limited to low-slope canopies and only for those attached to buildings with a mean roof height of h < 60 feet. Research is continuing on sloped canopies, and the Committee hopes to be able to include that research in the next edition of the Standard.

Figure 7. Example of ASCE 7-16 Sloped Roof Component & Cladding Zoning for 7 to 20 degree roof slopes. Printed with permission from ASCE. See ASCE 7-16 for important details not included here.

Summary Major revisions to ASCE 7-16 that affect the wind design of buildings have been highlighted. There are also many minor revisions contained within the new provisions. Each of these revisions is intended

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to improve the safety and reliability of structures while attempting to reduce conservatism as much as possible. It is necessary to look at the impact of the provisions as a whole, instead of individually, to understand how design procedures are affected.▪

CODE

updates

C

omponent and cladding (C&C) roof pressures changed significantly in ASCE 7-16, Minimum Design Loads and Associated Criteria for Buildings and Other Structures. For flat roofs, the corner zones changed to an ‘L’ shape with zone widths based on the mean roof height and an additional edge zone was added. Additional edge zones have also been added for gable and hip roofs. These changes are illustrated in Figure 1. For gable and hip roofs, in addition to the changes in the number of the roof wind pressure zones, the smallest and largest effective wind areas (EWA) have changed.

And, the largest negative external pressure coefficients have increased on most roof zones. Hip roofs have several additional configurations that were not available in previous editions of ASCE 7. The coefficients for hip roofs are based on the h/B ratio (mean roof height to the building width ratio) and, for roofs with slopes from 27° to 45°, the coefficients are a function of the slope.

The significance of these changes is the increase in pressures that must be resisted by roof construction elements subject to component and cladding wind loads including but not limited to roof framing and connections, sheathing, and attachment of sheathing to framing. To resist these increased pressures, it is expected that roof designs will incorporate changes such as more fasteners, larger fasteners, closer spacing of fasteners, thicker sheathing, increased framing member size, more closely spaced roof framing, or a change in attachment method (e.g., change smooth shank nails to ring shank nails or screws). An example of these wind pressure increases created by the increase in roof pressure coefficients is illustrated in Table 1. This Table compares results between ASCE 7-10 and ASCE 7-16 based on 140 mph wind speeds in Exposure C using the smallest EWA at 15-foot mean roof height in Zone 2.

Pressure increases vary by zone and roof slope.

In some cases not shown in Table 1, such as

for Zone 1, the revised coefficients produce an approximate doubling of roof pressures.

C&C Wind Pressure Comparisons

There are several compensating changes in other wind design parameters that reduce these design pressures in many parts of the country. These changes are: 1) Wind speed maps west of the hurricane-prone region have changed across the country. Wind speeds in the Midwest and west coast are 5-15 mph lower in ASCE 7-16 than in ASCE 7-10.

2) The elevation/exposure coefficient, Kz, has been reduced for C&C pressures for Exposure B buildings up to a height of 30 feet. Since most buildings are in Exposure B, this reduction in Kz will affect many structures. Table 26.10-1 in ASCE 7-16 provides the Kz coefficients. The Kz coefficient used in ASCE 7-10 for C&C was listed in Chapter 30 for use with C&C design. Now that the Kz coefficient is the same for both the Main Wind-Force Resisting System (MWFRS) and C&C, that table has Determining Components been moved to Chapter 26. and Cladding Roof 3) There is an elevation factor, Ke, that reduces the velocity pressure q for a site elevation above Design Pressures 1000 feet. This reduced pressure considers the lower air density at higher elevations; thus this factor modifies the 0.00256 multiplier used

By William L. Coulbourne, P.E., in the velocity pressure equation. Over 20 and Philip Line, P.E. states have a mean elevation over 1000 feet, so a significant part of the country could take William L. Coulbourne is a Structural advantage of the reduced velocity pressure creConsulting Engineer at Coulbourne ated by the new Ke factor. This factor is listed Consulting, Rehoboth Beach, DE. in Table 26.9-1 in ASCE 7-16. (bill@coulbourneconsulting.com) Table 2 illustrates the Zone 2 (20- to 27-degree slope) C&C pressures for ASCE 7-10 compared to the pressures developed in accordance with Philip Line is Director of Structural ASCE 7-16. The comparison is for 10 different Engineering at American Wood cities in the US with the modifiers for Exposure Council, Leesburg, VA. (pline@awc.org) B taken at 15 feet above grade, location elevation factor, smallest applicable EWA, and reduced wind speeds from new maps applied from ASCE 7-16 as appropriate.

As illustrated in Table 2, the design wind pressures can be reduced depending on location elevation, wind speed at the site location, exposure and height above grade, and roof shape. Wind pressures have increased in the hurricaneprone regions where Exposure C is prevalent and wind speeds are greater. The added pressure zones and EWA changes have complicated the application of these changes for the user.

Figures 2 and 3 illustrate the Figure 1. Examples of ASCE 7-16 roof wind pressure zones for flat, gable, and hip roofs. Printed with permission from ASCE. changes in the number of zones

Technical Aspects of ASCE 7-16

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Table 1. Comparative C&C negative pressures, 140 mph, 15-foot mean roof height, Exposure C. Roof Shape

Slope

ASCE 7-10 Coefficient (Roof Zone)

ASCE 7-16 Coefficient (Roof Zone)

ASCE 7-10 Pressure (psf)

ASCE 7-16 Pressure (psf)

Flat

0 degrees

-1.8 (2)

-2.3 (2)

-71.8

-89.9

Gable

7 – 20 degrees

-1.7 (2)

-3 (2n, 2r)

-68.2

-115.3

Gable

20 – 27 degrees

-1.7 (2)

-2.5 (2n, 2r)

-68.2

-97.2

Gable

27 – 45 degrees

-1.2 (2)

-2 (2n)

-50.0

-79.0

Hip

7 – 20 degrees

-1.7 (2)

-2.4 (2r)

-68.2

-93.5

Hip

20 – 27 degrees

-1.7 (2)

-2 (2e, 2r)

-68.2

-79.0

NA

-104.4

Hip 27 – 45 degrees NA -2.7 (2r) NA: Hip roofs with this slope were not covered explicitly in ASCE 7-10.

Table 2. Comparative C&C negative pressures for select locations, 15-foot mean roof height, Exposure B, Zone 2 or 2r (20- to 27-degree slope).

Figure 2. ASCE 7-10 Gable Roof Coefficients 20- to 27-degree slope. Printed with permission from ASCE.

Location

ASCE 7-10 Design Wind Speed (mph)1

ASCE 7-16 Design Wind Speed (mph)2

Elevation (feet above sea level)3

Boston, MA

129

120

23

Miami, FL Houston, TX

Figure 3. ASCE 7-16 Gable Roof Coefficients 20- to 27-degree slope. Printed with permission from ASCE.

171 138

169 136

7 47

Pittsburgh, PA

115

110

765

Denver, CO

1154

107

5232

Oklahoma City, OK

115

109

1200

Spokane, WA

110

102

1909

San Francisco, CA

110

92

53

Des Moines, IA

115

110

800

Salt Lake City, UT

115

103

4261

Roof Shape (Gable/Hip)

ASCE 7-10 pressures (psf)

ASCE 7-16 pressures (psf)

Gable

-47.7

-47.8

Hip

-47.7

-38.9

Gable

-83.7

-94.9

Hip

-83.7

-77.2

Gable

-54.5

-61.4

Hip

-54.5

-49.9

Gable

-37.9

-39.1

Hip

-37.9

-31.8

Gable

-37.9

-31.5

Hip

-37.9

-25.6

Gable

-37.9

-37.8

Hip

-37.9

-30.8

Gable

-34.6

-32.3

Hip

-34.6

-26.3

Gable

-34.6

-28.1

Hip

-34.6

-22.8

Gable

-37.9

-39.1

Hip

-37.9

-31.8

Gable

-37.9

-30.2

Hip

-37.9

-24.6

Wind speeds developed using www.atcouncil.org/windspeed.

Wind speeds developed using ASCE online hazard tool.

3 Elevation obtained from ASCE online hazard tool for selected locations.

4 Wind speed given in www.atcouncil.org/windspeed is Special Wind Region, yet ASCE tool calls out 107 mph.

Assumed location is basically in the 115 mph area on the ASCE 7-10 maps.

1 2

as well as the increases in the roof zone coefficients from ASCE 7-10 to 7-16 for gable roofs. Designers are encouraged to carefully study the impacts these changes have on their own designs or in their standard design practices. The reduced pressures for hip roofs in ASCE 7-16 are finally able to be demonstrated in Table 2; the design premise for hip roofs has always suggested this roof shape has lower wind pressures, but the C&C tables used for design did not support that premise until this new ASCE 7-16 edition.

There is interest at the ASCE 7 Wind Load Task Committee in studying ways to make these changes simpler and reduce possible confusion in the application of C&C provisions for the ASCE 7-22 cycle.

ASCE 7-16 Wind Loads and the Model Codes ASCE 7-16 is referenced in the 2018 International Building Code (IBC) for wind loads. In the 2018 International Residential Code (IRC), ASCE 7-16 is referenced as one of several options where wind design is required in accordance with IRC. Other permitted options based on ASCE 7-16 include the 2018 IBC and the 2018 Wood Frame Construction Manual (WFCM).

Other permissible wind design options which do not reflect updated wind loads

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in accordance with ASCE 7-16 include ICC-600 and AISI S230.

For more information on the significance of ASCE 7-16 wind load provisions on wind design for wood construction, see Changes to the 2018 Wood Frame Construction Manual (Codes and Standards, STRUCTURE, June 2018).

As described above, revised roof construction details to accommodate increased roof wind pressures include revised fastener schedules for roof sheathing attachment, revised sheathing thickness requirements, and framing and connection details for overhangs at roof edge zones.▪

structural

REHABILITATION

Wood Bowstring Trusses Part 2: Investigation, Repair, and Rehabilitation

By Filippo Masetti, P.E., Gloriana Arrieta Martinez, Ph.D., and Milan Vatovec, Ph.D., P.E.

Filippo Masetti is a Senior Project Manager at Simpson Gumpertz & Heger, Inc. (fmasetti@sgh.com) Gloriana Arrieta Martinez is a Junior Structural Engineer at Simpson Gumpertz & Heger, Inc. (gamartinez@sgh.com) Milan Vatovec is Consulting Principal at Simpson, Gumpertz & Heger, Inc. (mvatovec@sgh.com)

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

P

art 1 of this 2-part series (STRUCTURE, June 2018) addressed structural behavior and assessment methods. Part 2 focuses on analysis and repair options.

Bowstring trusses were a popular solution for structurally supporting roofs from the 1900s through the 1950s, especially in buildings where large, open spans were desired (manufacturing facilities, garages, warehouses, among others). Many buildings with this type of roof support are still in service today; given their age and inherent vulnerability (e.g., to environmental, load, and other factors), their adequacy and reliability have become a common reason for concern. This article focuses on potential retrofit options for bowstring trusses that have been identified, through structural assessment (see Part 1 of this series), to be in need of repair.

Analysis After information on existing conditions has been collected in the field, structural analysis is performed to evaluate the behavior and determine the structural adequacy of the trusses.

The member service load demands, determined through structural analysis or modeling (based on the current or planned use and codes), are compared to the allowable service level capacities for each member and connection in the truss. The calculated structural demandto-capacity ratios for each truss component then allows the engineers to assess the adequacy of the truss to withstand the requisite building-code-prescribed loads. Recurring typical considerations associated with the analysis and design-check processes are discussed below.

Changes in Design Snow Loads Until approximately the 1970s, building codes did not include consideration of drifting or unbalanced snow loads. Nevertheless, significant additional loads can result from the accumulation of snow against parapet walls, adjacent buildings, added mechanical equipment, and modifications to the roof layout (e.g., the formation of valleys). These conditions result in member forces that are different from those considered in the original design.

Specifically, an increase in bending moments and/or axial forces in localized areas of both top and bottom chords, as well as an increase in axial loads in the web members, can be expected.

Changes in Design Dead and Live Load Buildings may undergo several renovations or other modifications throughout their life-span.

Often, changes such as reroofing, the addition of mechanical equipment (over the roof or hung from the trusses), or addition of ceiling finishes STRUCTURE magazine

18 July 2018

Figure 1. Through-bolt inserted through the depth of the top chord of a bowstring truss

happen without the supervision of a registered professional engineer. These changes can result in increased uniformly-distributed loads and/ or in new load-patterned conditions that were not considered in the original design.

Boundary Conditions The accuracy of results in structural analyses depends, among other things, on proper assumptions and interpretation of the boundary conditions. The calculated tensile force in the bottom chord of the truss is particularly sensitive to these assumptions. For example, a pin-roller truss model (horizontal movement is restrained at one end only) would generally yield the highest tensile force in the bottom chord, whereas a pin-pin truss model (horizontal movement restrained at both ends) would yield the lowest tensile force in the bottom chord. The authors have found that actual field conditions typically do not warrant selection of a pin-pin model. If necessary, the design tensile force in the bottom chord can be limited by considering the actual lateral stiffness of truss support elements (e.g., columns and kickers, masonry piers, walls, etc.) in the analysis. If such consideration is made, the adequacy of the support elements to withstand the lateral loads imposed by the truss should be verified.

Top Chord Composite Action The top chord is a truss member typically subjected to compressive and bending stresses. As such, the ability of the laminations, if present, to behave compositely (act as one section) may substantially affect the overall truss capacity. If composite action cannot be developed, the ability of the top chord to withstand the design loads may be compromised. This behavior should be investigated when determining the allowable capacity of the top chord. Any analysis that relies on partial or full composite action of the top chord laminations requires an evaluation of the adequacy of the connection between laminations to transfer the horizontal shear flow. Different methods to connect the

top chord laminations exist in practice. In a lattice truss, all laminations are typically nailed to each of the closely-spaced web members. Trusses with discrete web members rely on bolts through the depth of the top chord (through bolts) to transfer the forces; one through bolt is typically found at each side of the panel points (Figure 1). Finally, the laminations may be glued together (glue-laminated construction); however, glue-laminated construction was not standardized nor was it used in the production of bowstring trusses prior to the 1930s.

Allowable Wood Design Values There are two methods for selecting allowable wood design values: 1) stress grading rules in combination with reference design values published by the National Design SpecificationÂŽ for Wood Construction (NDSÂŽ) or other local ordinances, or 2) by applying the visual stress grading method, in accordance with ASTM D245, Standard Practice for Establishing Structural Grades and Related Allowable Properties for Visually Graded Lumber, in conjunction with published clear wood strength values. Typically, the first method provides more conservative values than the second one. When applying the first method, it is important to recognize which

Figure 2. Bottom chord of bowstring truss retrofitted by installing steel tension rods along the span of the truss (left). The steel bracket at the end of the truss (right) transfers the force from the top chord to the new steel rods.

edition of the NDS standard includes reference design values that are most applicable to the investigation at hand. For example, prior to the 1960s, the allowable tensile stress parallel to grain was determined from bending tests on small, clear wood samples. In the 1960s, tensile tests on full-size lumber pieces (with natural imperfections) revealed that the allowable tensile stress was significantly lower than that determined from bending tests. Currently, reference design values for tension parallel to grain are approximately at 60% of the reference values for bending. Care ADVERTISEMENTâ&#x20AC;&#x201C;For Advertiser Information, visit www.STRUCTUREmag.org

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July 2018

should be taken to avoid using reference wood design values determined based on obsolete knowledge. Care should also be exercised to avoid the use of reference design values that are not representative of wood produced at the time the trusses in question were constructed. When using the visual stress grading methodology, careful consideration should be given to the method used to calculate the allowable design values, and to accurately assess the representativeness of the limited size of members sampled (e.g., 95% probability of exceedance method). continued on next page

Typical Repair Options When structural analysis reveals that some components of the truss are inadequate to withstand the building-code-prescribed loads, repair/strengthening is warranted. Repair strategies can vary depending on the level of overstress, cost, access, level of current load on the trusses, etc. Different repair/strengthening details that the authors have considered in their past projects with bowstring trusses are listed below.

Design Loads – When drift is the controlling condition in the calculation of design snow loads, installation of sacrificial roof framing over the existing roof may be used to preclude formation of a snow drift. This adds dead load to the trusses, but it may still result in lower overall design loads.

Top Chord – Partial or full composite action among the laminations can be achieved through installation of (additional) lag screws (or proprietary screws) at sufficient spacing and edge distances, which would enhance the shear flow through the section depth.

Careful considerations should be made with respect to access, the location of splices of single laminations, ease of drilling through all laminations, and overall ease of installation.

Web Members – Overstressed or distressed diagonal members can be repaired by installing new “sister” members bolted (or nailed) to the existing members. In some instances, replacement of web members is warranted or easier.

Bottom Chord – The bottom chord can be retrofitted by installing steel tension rods along the span of the truss. This can be accompanied by steel brackets at the ends of the truss, designed to transfer the force from the top chord to the new steel rods (Figure 2, page 19).

Alternatively, installation of new “sister” members bolted (or nailed) to the existing members may be considered.

Bolted Connections – Inadequate bolted connections can be reinforced by installing supplemental steel plates with proper consideration of boundary conditions (e.g., spacing, end, and edge distances of bolts) and compatibility (differential hygrometric behavior between steel and wood).

Bearing Ends – When decay associated with moisture intrusion is found at the ends of the trusses and the remaining, sound bearing areas are inadequate to transfer loads, repair may include installation of supplemental (e.g., steel) framing support tight to the underside of the bottom chord. This can be a seat connected to the existing column, pier, or wall. If

the decay is driven by excessive moisture, the U-shaped steel straps at the ends of the truss may also be severely corroded. Depending on the degree of corrosion and decay, reinforcement of the steel strap may also be required through installation of additional steel plates and bolts.

Conclusions To achieve long-lasting performance, to increase the expected service life, and to avoid chronic, recurring structural problems, the repair strategy for bowstring trusses, as for any other structure, must focus on, consider, and eliminate the underlying sources of identified issues or problems. For example, rather than just strengthening the decayed or corroded elements, the source of moisture should also be eliminated (through repairing leaks, installing waterproofing and flashing details at masonry piers, etc.). Typical repair approaches and methodologies include installation of sacrificial framing to preclude formation of a snow drift, establishing full composite action of the top chord, sistering members, installing steel tension rods in the bottom chord, and installation of seats and additional steel plates at the bearing ends.▪

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DESIGN

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he overall integrity and performance of a special moment frame, which is required in buildings assigned to Seismic Design Category (SDC) D, E, and F, is dependent on the behavior of the beam-column joints in the frames. The inelastic rotations at the faces of the joints produce strains in the beam longitudinal reinforcement well in excess of the strain corresponding to the yield strength of the reinforcement. As such, joint shear forces are calculated using a stress equal to 1.25fy in the beam longitudinal reinforcement that passes through the joint. Determining the adequacy of the joints in a special moment frame should occur early in the design phase because column sizes, beam sizes, concrete strength, or a combination thereof may need to be adjusted to satisfy joint shear strength requirements. A modification in member size generally requires reanalysis of the structure.

Special Moment Frames in Reinforced Concrete Determining Preliminary Joint Sizes

General Design Procedures

Typically, member sizes in a special moment frame are initially estimated based on experience or

By David A. Fanella, Ph.D., S.E., P.E., F.ACI, on serviceability requirements. It is common to F.ASCE, F.SEI, and Michael Mota, Ph.D., go through many iterations before reasonable P.E., SECB, F.ACI, F.ASCE, F.SEI member sizes are established. General guidelines David A. Fanella is Senior Director for overall economy should also be used in deterof Engineering at the Concrete mining initial member sizes; for example, the Reinforcing Steel Institute and can be maximum longitudinal reinforcement ratios in reached at dfanella@crsi.org. the columns and beams should be no more than about 2% and 1%, respectively. Architectural Michael Mota is Vice President limitations may also have an impact on crossof Engineering at the Concrete sectional dimensions of these members.

Reinforcing Steel Institute and can be Once preliminary member sizes are obtained, reached at mmota@crsi.org. seismic forces are determined and a lateral analysis of the building is performed. Drift requirements are checked and member sizes are adjusted accordingly. Beam design proceeds in accordance with the American Concrete Institute’s ACI 31814, Building Code Requirements for Structural Concrete and Commentary, Section 18.6, and the required amounts of negative and positive longitudinal reinforcement are determined at the critical sections of Figure 1. Free-body diagram of an interior column in a special moment frame. the beams.

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22 July 2018

After all of this, the shear strengths of the joints are checked. Often, the shear requirements are not satisfied, and the design process outlined above must be performed again using revised member sizes or revised areas of longitudinal reinforcement, or both. To help expedite the overall process, a relationship between the required joint area and the area of the beams framing into the joint can be established based on joint shear strength requirements. Preliminary member sizes can be obtained using the following procedure.

Based on those sizes, interstory drift requirements can then be checked, and member sizes can be adjusted accordingly prior to final design and detailing if required.

Approximate Method Consider the free-body diagram of a typical interior joint in a special moment frame where beams frame into opposite faces of the joint in the direction of analysis (Figure 1). The required joint shear force, Vj, is determined from equilibrium assuming flexural yielding occurs at the ends of the beam that frame into the joint (that is, the probable flexural strengths Mpr = As(1.25f y) (d-a ⁄ 2) of the beams are developed at the faces of the column).

For columns above the first story, it is reasonable to assume that points of inflection occur at the midheight of the column, as indicated in Figure 1. Thus, the length, lc, is equal to the depth of the beams plus one-half the clear story height above and below the joint. The shear force in the column, Vcol, can be obtained by summing moments about the center of the joint: Vcol =

Mpr+ + Mpr- (Vu,1 + Vu,2) × (c1 ⁄ 2) + lc lc

In this equation, Mpr+ and Mpr- are the positive and negative probable flexural strengths, respectively, of the beams framing into the joint and Vu,1 and Vu,2 are the corresponding design shear forces due to the factored gravity loads and the probable flexural strengths.

Joint Shear The joint shear, Vj , is obtained from equilibrium of horizontal forces on the joint. A free-body diagram of the joint in Figure 1 is depicted in Figure 2, where it is assumed that any axial forces on the beams are negligible. To satisfy equilibrium, the flexural compressive force in the beam on one side of the joint must be equal to the flexural tension force on the same side of the joint.

When calculating the force in the beam longitudinal reinforcement, the stress must be set equal to 1.25fy in accordance with ACI 18.8.2.1; this multiplier considers the likelihood that, due to strain hardening and actual yield strengths greater

Figure 2. Shear force in an interior joint of a special moment frame.

than the specified value, larger tensile forces can develop in the bars which would result in larger shear forces in the joint.

The following expression for Vj is obtained by summing forces in the horizontal direction: Vj = 1.25As- fy + 1.25As+ fy -Vcol A similar set of equations can be derived for sidesway in the opposite direction.

Where the same top reinforcement and the same bottom reinforcement are used in the beams on both sides of the joint, the above derivation is also valid for sidesway in the opposite direction.

For columns in the first story of a moment frame or for moment frames where the above assumption regarding the location of the inflection point is not valid, similar ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org

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July 2018

analyses can be performed to determine Vj using appropriate assumptions for the case at hand. Overall analysis of the moment frame can be used as a guide to locate points of inflection in the columns.

Shear strength requirements for joints in special moment frames are given in ACI 18.8.4. In general, the shear strength of a joint is a function of the concrete strength and the cross-sectional area of the joint only.

Tests have shown that joint shear strength is not altered significantly with changes in the amount of transverse reinforcement, provided a minimum amount of such reinforcement is present in the joint.

The required shear force, Vj, must be less than or equal to the design shear strength, φVn, where φ = 0.85 in accordance with ACI 21.2.4.3 and Vn is determined using the requirements in ACI 18.8.4.1: φVn = φfv λ√fć Aj In this equation, fv is a strength coefficient that is defined in ACI Table 18.8.4.1 based on the joint configuration: fv =

{

20 for joints confined by beams on all four faces 15 for joints confined by beams on three faces or two opposite faces 12 for all other cases

continued on next page

A joint face is considered to be confined by a beam if the beam width is at least three-quarters of the effective joint width (ACI 18.8.4.2).

The effective joint area, Aj, is defined in ACI 18.8.4.3 and is equal to the area of the column where beams are as wide as or wider than the column in the direction of analysis. Wider beams typically result in overall economy and help reduce congestion.

When checking shear strength requirements, it is conservative to assume that the shear force, Vcol, is equal to zero (Figure 2).

Therefore, Vj can be determined from the following equation where ρ- = As-/bw d and ρ+ = As+/bw d are the longitudinal negative and positive reinforcement ratios in the beam, respectively: Vj = 1.25As- fy +1.25A+s fy = 1.25f y bw d(ρ- + ρ+) Assuming d ≅ 0.9h and Grade 60 reinforcement, the above equation for Vj reduces to the following: Vj = 67.5Ab ρj where Vj has the units of kips. In this equation, Ab = bw h is the area of the beams framing into the joint (it is assumed that the beam size is the same on both sides of the joint) and ρj = ρ- + ρ+ is the sum of the negative and positive longitudinal reinforcement ratios for the reinforcement that passes through the joint.

Assuming the effective area of the joint, Aj, is equal to the area of the column, Ac = c1 × c2, the following equation must be satisfied for joint shear strength, assuming normal weight concrete: Ac 79,400ρj ≥ Ab fv√ f´c

Reinforcement Ratios It is evident that the ratio discussed above is a function of the total amount of beam longitudinal reinforcement that passes through the joint. Minimum reinforcement in accordance with ACI 9.6.1.2 must be provided at both the top and bottom of the beams. Also, for overall economy, it is advantageous to design beams such that all sections are tension-controlled. Therefore, the maximum reinforcement ratio should be taken as the tension-controlled reinforcement ratio ρt = 0.319β1 f´c ⁄ fy instead of 0.025 given in ACI 18.6.3.1 where β1 is defined in ACI 22.2.2.4.3. Thus, a range for both ρ- and ρ+ is established. Also, ACI 18.6.3.2 requires that the positive nominal flexural strength, Mn+, at the face of a joint be greater than or equal to one-half of the negative flexural strength, Mn-, at that joint.

This roughly translates to ρ+ ≥ ρ-/2. Finally, it

Figure 3. Preliminary joint size in a special moment frame.

is good practice to use a longitudinal reinforcement ratio of no more than about 1% for the negative flexural reinforcement in a beam in a special moment frame; among other things, limiting the amount of flexural reinforcement helps alleviate congestion at the joints. The above reinforcement range, the requirement in ACI 18.6.3.2, and the guideline regarding a reinforcement ratio of 1% can all be used in establishing an appropriate value of ρj, which is needed to determine Ac /Ab. Depicted in Figure 3 is the ratio Ac /Ab as a function of the reinforcement ratio, ρj, for each of the three strength coefficients, fv, assuming the following: • Normalweight concrete with f´c = 4,000 psi • Grade 60 reinforcement • Beam width, bw ≥ Column width, c2 The vertical dashed lines in Figure 3 correspond to the minimum and assumed maximum reinforcement ratios ρj,min(%) = 0.33 + 0.33 = 0.66% and ρj,min(%) = 1.81 + 1.81=3.62%, respectively. Given a beam size that has been established based on strength and serviceability requirements and a reinforcement ratio, ρj, determined using the guidelines above, a conservative estimate of the required column area that satisfies joint shear strength requirements can be obtained from Figure 3. Alternatively, in cases where the column size is fixed for architectural or other reasons, an appropriate beam area can be determined. Finally, if both column and beam sizes are given, the required longitudinal reinforcement, ρj, can be obtained.

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Figure 3 can also be used in cases where only one beam frames into the joint in the direction of analysis. The reinforcement ratio, ρj, in such cases is the larger of ρ- and ρ+. Typically, ρ- ≥ ρ+, so ρj = ρ- should be used in the figure.

Conclusion The beam and column sizes at all locations within the special moment frame that are determined by this approximate method can be used in a model of the building.

Based on these member sizes, drift requirements can then be checked. Based on those results, the sizes can be adjusted accordingly, if required. After drift requirements are satisfied, the longitudinal reinforcement in the columns needs to be determined.

Finally, the minimum flexural strength requirements of ACI 18.7.3 need to be satisfied at all the joints in the special moment frame in both directions.

Additional information and numerous workedout examples on the design and detailing of special moment frames of reinforced concrete, including ones that illustrate how to implement this approximate method for joints, can be found in the Concrete Reinforcing Steel Institute’s (CRSI) publication, Design and Detailing of Low-Rise Reinforced Concrete Buildings.▪ The online version of this article contains references. Please visit www.STRUCTUREmag.org.

Rebuilding YearS Renovations b Wrigley Field

I

By Benjamin Pavlich, S.E., Elaine Shapiro, S.E., Abhiram Tammana, P.E., and William D. Bast, P.E., S.E., SECB

n 2014, Wrigley Field turned 100 years old. In 2016, the Chicago Cubs played their 100th year at the ballpark and won the World Series for the first time since 1908. The Ricketts family has been pursuing an extensive renovation of Wrigley Field, including the stadium and surrounding area, since purchasing the Chicago Cubs baseball team and Wrigley Field in 2009. Following months of negotiations between the team, Alderman Tom Tunney, and Chicago Mayor Rahm Emanuel, the project received endorsements from the Commission on Chicago Landmarks, the Chicago Plan Commission, and final approval by the Chicago City Council in July 2013.

The lineup of renovations called for a $575 million, privately funded rehabilitation of the stadium to be completed over the course of five years. The proposal included improvements to the stadium’s façade, infrastructure, restrooms, concourses, suites, press box, bullpens, and clubhouses, as well as the addition of restaurants, a patio area, batting tunnels, a 5,700-square-foot video board, and an adjacent hotel, plaza, and office-retail complex. The renovations are now expected to be completed in six phases during consecutive off-seasons, shortened by the end-of-season playoffs.

Thornton Tomasetti (TT) was recruited as the structural engineer of record for the ballpark renovations, plaza, and an office-retail complex. This article focuses on some of the structural and geotechnical challenges associated with evaluating the design and condition of the 100-year-old stadium and the structural engineering behind the improvements mentioned above.

To evaluate the site soil conditions, TT called to the pen for GEI Consultants, Inc. Their findings identified a high water table and sandy to clayey soil below the ground surface. Based on a combination of these findings, additional and higher loads in the new design, and the need to prevent undermining of existing shallow footings due to the adjacent excavations, it was determined that converting the shallow footings on the A-line and F-line to deep foundations using micro-piles was the most efficient way to strengthen them in lieu of enlarging or replacing them. The A-line footings adjacent to the plaza/office building excavation were tied together with a grade beam supported on micro-piles. The columns along A-line were connected with plates that were embedded inside the concrete curb on top of the grade beam. The remaining A-line footings, not adjacent to an excavated area, were enlarged based on the load carrying capacity required of them by the new program.

Significant corrosion found at the base of the F-line columns required a different approach to strengthen the existing footings. To address the issue of corrosion and to strengthen the existing unreinforced F-line column footings at the same time, a reaction frame and a shoring frame assembly were used to temporarily support each column and transfer the load down to new micro-piles. Initially, the existing footings were selectively drilled to allow for the installation of the micro-piles that

Strengthening Foundations The proposed improvements to the stadium required the transfer of additional loads through the columns to the foundations. Right off the bat, TT determined that the structural capacity of the existing typical “wedding cake”-style footings was not sufficient to support the new program and required strengthening. In addition to the higher loads, the new program also involved construction of a basement below the ground level on the field side of column line F and the plaza/office building on the street side of column line A (Figure 1).

The load above the terrace level, including the roof, upper deck, suites, and ramps, is carried only by the A-line and F-line columns, while a series of intermediate columns carry the load at the mezzanine and terrace levels. Most of the column footings not located on the A-line and F-line had to be enlarged to carry the additional vertical loads.

Also, additional combined footings were required at new braced frame locations to complete the lateral load resisting system in the stadium. Figure 1. Typical cross-section of steel stadium structure.

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July 2018

The existing truss members were welded to the gusset plates so that shoring would not be required to lead off the node reinforcement process. These temporary connections were analyzed for the loads expected during the construction season when the stadium would remain unoccupied, but could potentially carry snow loads. Next, the rivets were removed through a process honed by the ironworkers, contractor, and design team to be time efficient and to maintain as much original base material as possible (Figure 3). Each rivet head was cut off; the shaft was then heated with a torch; and finally, the remaining rivet material was hammered out. Once the rivets were removed, any damage from the torching process was repaired and new “finger” gusset plates, shaped to align with the geometry of the truss members, were installed on each side of the assembly and fastened with high strength bolts. These plates were thicker than a typical gusset plate located at the center of the double angle members but had a lower visual impact on the overall appearance of the trusses.

Creating a Diaphragm

Figure 2. F-Line underpinning process.

provide support to the reaction and shoring frame assemblies. After the column was temporarily supported by the frames, the top of the existing footing was demolished to allow for repair of the corroded base of the column, and a new seat within the reaction frame was installed on which the column would bear. After the column was completely supported on the reaction frame, the shoring frame was removed and subsequently used at other F-line columns. The reaction frame assembly supporting the column was ultimately protected by embedding it in reinforced concrete. The different stages involved in the underpinning of the existing F-line footings are shown in Figure 2.

Reinforcing Existing Trusses

TT’s review and analysis of the Wrigley Field structure indicated that the existing lateral system was ill-defined and unable to demonstrably withstand code-prescribed wind loads. To create a reliable lateral system, TT developed a scheme that would utilize the concrete deck of the lower seating bowl as a diaphragm.

The lower seating bowl construction is a patchwork of both cast-inplace (CIP) and precast concrete of varying ages. TT determined that these concrete sections were adequate to serve as a diaphragm, and independent testing concluded that the concrete had 40 to 50 years of service life remaining. However, the connection details at the end of the precast planks were unable to transmit the calculated diaphragm forces. Therefore, using the lower seating bowl as a diaphragm required a solution to create continuity between the CIP and precast concrete elements. Providing expansion joints would have been structurally difficult and architecturally undesirable, so a design was developed that could function without them.

The chosen solution was to create a concrete encasement around the steel raker beams supporting the CIP and precast concrete spans (Figure 4 , page 28). In coordination with Chicago Landmarks Commission, the raker encasements were designed to be approximately 1 foot 6 inches deep by 3 feet wide utilizing CIP concrete. In addition to creating the diaphragm, the raker encasements allowed the design team to execute a triple play by addressing two other lingering design issues. First, due to increased loads imposed by other modifications to the stadium, the rakers themselves required strengthening. The raker encasements were designed to carry the full raker beam load, making the existing steel rakers redundant. Second, many of the precast planks had severe damage at their support points and required repairs. The raker encasements provided new end support for the precast planks by encapsulating the plank ends within the raker encasements.

The main trusses of the stadium span approximately 65 feet between the A-line column at the perimeter of the stadium and the F-line column adjacent to the concourse (Figure 1). A 30-foot cantilever projects past the F-line column towards the field. In the existing continued on next page design, the trusses support the upper seating deck and roof above and the suites below. The renovation project includes expanding the suites and adding a roof deck open to fans during events.

The original trusses consist of relatively light double- and single-angle members ranging from 2½ to 6 inches deep connected by rivets at gusset plates. Reinforcement was required for both the individual members and the nodal connections to support the larger suites and new roof deck. Member capacity was increased through various combinations of faceplates welded to the angle webs or existing flanges and Figure 3. Truss node with truss members welded to gusset plate and rivets removed (left) flange plates added to create I-sections. and reinforced with new finger gusset plates and high strength bolts (right).

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July 2018

Conclusions The desired upgrades to Wrigley Field required innovative structural engineering solutions to economically and expediently strengthen the foundations and reinforce the superstructure of the iconic stadium.

Despite being thrown a few curveballs, the repairs developed by the project team allowed Wrigley Field to maintain its iconic and historic character, with a structure to withstand the next 100 years of use.▪ A similar article was initially published online in ASCE’s Civil Engineer Magazine. The author has expanded on the topic and provided detailed information on the structural engineering involved in the project.

Portions are reprinted with permission.

Figure 4. Schematic raker encasement detail.

Carbon fiber reinforcement was applied to the top side of the raker encasements to provide a complete load path to transmit diaphragm forces in tension. Compression forces were transmitted through nonshrink grout which was packed in the joints between precast planks.

Lastly, the effects of volume change in the new continuous diaphragm needed to be analyzed. Shrinkage was no longer a consideration because of the age of the precast. However, by locking all the concrete sections of the lower bowl together, thermal stresses became much larger than they were before implementing the repair.

In fact, the thermal stresses controlled the design. Due to the shape of the stadium, thermal forces cause the diaphragm to try to open and close like a clamshell. The highest thermal forces in the diaphragm occur at the apex of this movement, behind home plate.

Drag struts and related detailing were provided in these areas to carry the diaphragm chord forces.

Benjamin Pavlich, S.E., is an Associate. (bpavlich@thorntontomasetti.com) Elaine Shapiro, S.E., is a Project Engineer (eshapiro@thorntontomasetti.com) Abhiram Tammana, P.E., is a Senior Engineer. (atammana@thorntontomasetti.com) William D. Bast, P.E., S.E., SECB, is a Principal. (wbast@thorntontomasetti.com) All authors work in the Chicago office of Thornton Tomasetti, Inc.

Project Team Owner – Chicago Cubs Owner’s Representative – CAA ICON EOR – Thornton Tomasetti, Inc. Architects – Populous; Stantec (formerly VOA Associates Inc.) Contractor – Pepper Construction Group

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432

and simplicity of the architectural intent coexist in juxtaposition of a complex structural solution involving a series of two-story open mechanical floors, outriggers, core shear walls, and tuned mass dampers.

Park

Structural Solution

By Silvian Marcus, P.E., Hezi Mena, P.E., Fatih Yalniz, P.E., and Chris Shirley, P.E.

Courtesy of DBOX for Macklowe Properties & CIM Group.

T

he tallest residential tower in the western hemisphere and the third tallest building in the United States is now located at 432 Park Avenue in Midtown, Manhattan. The super-slender structure has 86 residential floors comprising 104 condominium apartments, and stands at 1,396 feet high. The total construction cost was estimated at $1.25 billion.

A Super-Slender High-Rise The design architect behind 432 Park Avenue is Rafael ViĂąoly, who envisioned the building on the basis of the square, a purist geometric form. With identical width and length of 93.5 feet and a total height of 1,396 feet, the slenderness ratio of the building is 1:15. The architectural concept, the aspect ratio of the building, and its specified structural performance resulted in interesting challenges which required the pioneering of several structural engineering solutions.

The design incorporates energy efficiency and renewable technology approaches which have made the building LEED certified.

The main architectural attributes of 432 Park Avenue are symmetry and simplicity. The regular 15.5-foot by 15.5-foot grid defined by exposed structural members is perfectly matched by large squared glass windows, which allow for amazing views of Manhattan. The orthogonality of structural members further conveys a sense of strength and stability to a slender structure. The compact footprint of the project, in combination with its extraordinary height, has permanently changed the paradigm of economical design of high-rise buildings.

The aesthetics of the project rely on clean lines and regularity as opposed to the frills found in modern structures. It was only natural for the building to be capped by a flat roof. Nonetheless, the regularity STRUCTURE magazine

The structural concept consisted of a dual tube-intube system formed by an exoskeleton of perimeter moment frames integrated by spandrel beams and columns, which were interconnected to the interior shear wall core by outriggers placed at key elevations.

This configuration allowed for unobstructed open spaces at practically every floor (Figure 1).

The building is a reinforced, cast-in-place concrete construction which is supported on architecturally exposed white concrete columns around its perimeter and a central shear wall core around the elevator shafts and staircases serving as the spine of the building. The residential floors are reinforced concrete two-way flat plates, ten inches thick, supported by the exterior columns and the central core. The construction sequence had the central core cast three stories ahead of the perimeter moment frame. Figure 2 shows an overview of the building after completion of construction.

In order to provide adequate strength and lateral stiffness to the building, five outriggers, each spanning over two stories, were devised throughout the height of the tower to serve as positive linkages between the interior core and the perimeter framing, which enhanced the overall performance of the structure. The location of the outriggers, identified by red rectangles in Figure 3, roughly corresponds to the location of the open floors.

In consideration of the slenderness and height of the building, which is more than twice the height of neighboring buildings with increased exposure to high winds, it was necessary to pay special attention to the control of wind-induced dynamic motion. Also, other wind-related effects like lateral accelerations, vibrations, and the perception of movement by the occupants had to be addressed.

The goal for minimal displacement, accelerations, and vibrations to meet the most stringent standards was achieved through a combination of innovative engineering implementations. For instance, increasing the slab thickness to eighteen inches on the upper stories of the building added the required mass-to-limit displacements.

Figure 1. Detail of the open floor layout during construction.

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July 2018

Furthermore, introducing five two-story open floors along the height of the building contributed to significant reductions of wind demands and their effect on the structure, in particular by reducing the vortex shedding phenomenon. Finally, the installation of two 660-ton opposed pendulum tuned mass dampers in the top portion of the building was deemed the best engineering solution to maintain lateral accelerations within the acceptable limits adopted as industry standard (Figure 4).

Arriving at these structural solutions required careful review of the wind tunnel testing and repeated interaction with RWDI, the firm in charge of the testing.

For additional information on the challenges associated with slender high-rise buildings subjected to wind demands, see the Feeling at Home in the Clouds article in the December 2017 issue of STRUCTURE.

two-hour workability periods, and access to newly cast horizontal surfaces within five hours of placement of fresh concrete.

In order to achieve the required material performance and appearance, white Portland cement was used in the exposed structural elements and sustainable mixtures replacing up to 70% of regular Portland cement with pozzolanic materials were employed for the interior shear wall core. The successful production of high-strength, pumpable, white concrete was, undoubtedly, one of the most demanding construction challenges of the project.

Conclusion

The main structural engineering challenges of 432 Park were not only triggered by the aesthetics of Rafael Viñoly’s vision but also by the financial considerations of such a unique and ambitious project. Nevertheless, the structural High-Performance Materials approach developed for the project was able More than 70,000 cubic yards of concrete and to address the requirements of the client while approximately 12,500 tons of reinforcing bars providing the most cost-effective solution and were used for the construction of the super- Figure 2. Overview of 432 Park Avenue after maintaining a balance between aesthetics and structure. The specified concrete compressive completion of construction. functionality. The collaborative relationship strength of the structural elements varies from among the design and construction 14,000 psi at the lower 38 stories to 10,000 psi at the upper levels. team members was instrumental in addressing the project The increase in compressive strength of concrete had a two-fold challenges and successful completion of the project.▪ objective. First, the reduction of the footprint and overall size of structural elements and, second, an increase in stiffness. Furthermore, Silvian Marcus is Director of Building Structures at WSP, Principal high-strength reinforcing steel, spliced by means of mechanical conin Charge of the project. nectors, was required in the columns and shear walls of the lower Hezi Mena is Senior Vice President of Building Structures at WSP, Project Director. portion of the building.

All concrete cast in the 432 Park Avenue project was designed for Fatih Yalniz is Structural Analysis Manager and Vice President of Building Structures at WSP. enhanced durability by minimizing the ratio of water to cementiChris Shirley is Associate of Building Structures at WSP, Project Manager. tious materials to as low as 0.25. Moreover, to allow for the proper placement of concrete to each casting location and to improve the Additional Credits finish of the exposed structural elements, the concrete was required Ahmad Rahimian, Ph.D., P.E, S.E, F.ASCE, is Director of Building to be pumpable, self-consolidating, and with a low heat of hydration.

Structures at WSP. These material and mechanical properties resulted in shorter casting Gerardo Aguilar, Ph.D., is Technical Manager of Building Structures at WSP. procedures, low internal temperatures leading to minimal shrinkage,

Figure 3. General depiction, structural detail and location of outriggers.

STRUCTURE magazine

Figure 4. Location of open drums and tuned mass dampers.

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July 2018

professional T

ISSUES

he Basic Education Committee (BEC) launched two surveys in 2016 related to the National Council of Structural Engineers Associations (NCSEA) recommended curriculum: • the Curriculum Survey, which canvassed colleges and universities to gauge course offerings (STRUCTURE, September 2016), and • the Practitioner Survey, which targeted design professionals to better understand the skills necessary to enter the structural engineering profession.

The Practitioner Survey was administered via email and web links published in STRUCTURE and is summarized in this article.

Structural engineering firms have a vested interest in selecting new employees that possess the skills to be successful and that have an education that prepares them to solve technical issues. As a resource for structural engineering firms to better understand the education provided by universities, the Curriculum Survey was developed. This provided the “supply side” of the equation but lacked the “demand side.” What type of education do structural engineering firms desire and require of their new employees? The Practitioner Survey provided a resource to describe the skills and the educational requirements that structural engineering firms would like new employees to possess.

The Curriculum Survey focused on the 12 recommended core structural engineering courses offered at accredited engineering and engineering technology institutions. The current NCSEA BEC recommended structural engineering curriculum is as follows:

2016 NCSEA Practitioner Survey

By Paul Hopkins Ph.D., P.E., S.E., and Kevin Dong, P.E., S.E.

Paul Hopkins is a Principal Engineer with TD&H Engineering. He has been an adjunct professor at the University of Idaho and Widener University since 2008. He presently co-chairs the NCSEA Basic Education Committee. (paul.hopkins@tdhengineering.com)

• Structural Analysis I • Structural Analysis II • Steel Design I • Steel Design II • Concrete Design I • Concrete Design II • Technical Writing • Timber Design • Masonry Design • Matrix Methods • Dynamic Behavior (including seismic) • Foundation Design/Soil Mechanics The Curriculum Survey showed that a few of the recommended courses were not readily offered, such as timber and masonry design.

As a follow-up to the Curriculum Survey, the Practitioner Survey was open to design professionals from September 2016 to December 2016 in the form of a web-based survey. Over 400 practitioners responded to the survey. These professionals ranged in experience from new graduates to seasoned engineers, as can be seen in Figure 1.

The geographic distribution of survey respondents was balanced between the Northeastern, Southeastern, Southwestern, Midwestern, and Western United States (Figure 2). Some respondents indicated their firm has multiple locations or their work is in multiple regions, and this was considered when evaluating the data. The committee presents this data to demonstrate that the results of the survey reflect opinions from across the country and that regional differences were not significant.

In the Practitioner Survey, the focus was on the education of the structural engineering student and how it relates to real-world applications, industry demand, and technical preparedness. In addition to addressing the

Kevin Dong is a Professor in the Architectural Engineering Department at California Polytechnic State University and a member of the NCSEA Basic Education Committee. (kdong@calpoly.edu)

Figure 1. Respondent professional experience distribution.

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34 July 2018

core classes, the BEC sought feedback on technical and communication skills embedded in traditional coursework to gauge its importance and necessity in the workplace.

Examples of evaluated skills are determining load paths, evaluating structural stability, and writing technical communications.

Figure 3, page 36 shows the extent of the coursework and skills surveyed.

With the exception of matrix-methods coursework (at 85%), all core classes were viewed as a necessary component of a structural engineering student’s education. More than 90% of the practitioners responding indicated that the recommended curriculum topics should be included in, or are very important to, structural education.

The highest-ranked, non-core class or technical skill was loading and load paths.

Technical skills are generally integrated into a group of design courses. A few institutions have courses dedicated to loading, load paths for members/elements, building systems, and connection details. The importance of this topic and how the BEC will address this in the recommended course curriculum is noted in the following.

Figure 2. Respondent geographic location.

The survey attempted to attract a distribution of respondents from across the structural engineering profession by practice work type, firm size, geographical region, and years of experience. The goal was to identify if these variables played a role in ranking the importance of topics for an education in structures. The results showed

that these variables were not a differentiator for “most important topics” such as structural analysis, steel design, and concrete design, nor for lower ranked topics such as timber design and masonry design (Figure 4 , page 36 ). Additionally, the survey was successful in attracting a diverse sample of respondents. As expected, most

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respondents primarily work on buildings, which is consistent with the NCSEA membership.

The Practitioner Survey provided insight through survey responses and from personal comments provided by the practitioners. In general, comments focused on how practitioners value the education of structural engineering students and what they view as important to sustaining their profession and business. Technical communications and writing skills were both strongly acknowledged in the survey responses, as well as the personal comments portion of the survey.

“Above all else, the structural engineering curricula should first address technical writing Figure 3. Practitioner response on the importance of subjects offered at colleges/universities.

Figure 4. Practitioner response on the importance of subjects offered at colleges/universities by Region.

Figure 5. Survey personal responses.

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and communication skills” – practitioner The chart shown in Figure 5 shows a distribution of personal responses that were categorized based on the context of the message. Most of the responses had strong views and opinions regarding the need for classical structural analysis methods, along with the use of computer modeling and interpreting results. Many practitioners also expressed the need for students to be involved with real-world applications, design projects, and introduction to full building design and load path analysis.

Detailing, construction techniques, and understanding load paths were a common critique mentioned by respondents.

Likewise, many respondents (~43%) feel that basic knowledge and hand calculation methods are required; however, computer programming, modeling, and software is needed at the university level to complement students’ education (~57%).

Figure 6 shows the actual response distribution from Question 6 on the survey.

From the responses, it can be derived that structural analysis and classical methods should not leave the curriculum. However, from both Question 6 and the personal responses, understanding structural behavior and interpreting computer analysis results are also important.

The Practitioner Survey has highlighted, in our opinion, the need for students to bridge the gap between using computer models and successfully understanding and checking results. Furthermore, education of the structural engineering student is essential to the sustainability and

safeguarding of the profession. Without proper training and knowledge, billable time is potentially affected along with concerns for public safety.

The BEC is currently working on a new Curriculum Survey with outcome-based questions that incorporate information gathered from prior curriculum surveys and the Practitioner Survey. It will be released in 2019 with the intent that trends can be identified. The Curriculum Survey will also attempt to address questions and responses from the 2016 questionnaires, such as the importance of wood, masonry, light gauge metal design, and structural behavior. These surveys aim to influence the education of structural engineering students, promote continuing education of the design professional, and identify the qualifications of entry-level engineers who will be the future leaders in the profession.

Figure 6. Question 6 – classical methods and computer modeling.

“Existing curricula is extremely deficient in the fields of engineered wood structures, CMU design, and cold-formed metal framing” – practitioner

STRUCTURE magazine

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Using the results from the Curriculum Survey and the Practitioner Survey, changes to the recommended curriculum may be forthcoming. It is the goal of the BEC to assess the results from the two surveys, administer a future student survey, then measure the effectiveness and adequacy of preparing structural engineers as technical leaders. A possible response is changing the recommended core curriculum. However, a curriculum change alone will not satisfy nor meet all needs of the profession, nor address the evolving nature of structural engineering.

These courses are only one piece of the preparation, training, and skill requirements sought in graduating students by structural engineering firms. The survey responses help to define where additional training is sought and demanded by the structural engineering community.

Ultimately, the BEC would like the results of these surveys to be utilized by students, universities, and the structural engineering community. The surveys provide an avenue to better understanding educational requirements, raising awareness of the obstacles in providing the recommended curriculum, and, hopefully, inspiring the industry to support and augment student education.▪P

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historic

STRUCTURES

Hell Gate Bridge

By Frank Griggs, Jr., Dist. M.ASCE, D.Eng., P.E., P.L.S. Dr. Frank Griggs, Jr. 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. (fgriggsjr@twc.com)

G

ustav Lindenthal was chief engineer of the New York Connecting Railroad for many years. The length of his section was 3.38 miles long and extended from a point in the Bronx at the intersection with the New Haven Railroad to Stemler Street in Long Island City. The line from north to south crossed the Bronx Kill, ran over Randall’s Island, across the Little Hell Hell Gate Bridge from a postcard with less ornate tower treatment.

Gate, across Wards Island and over the East River at Hell Gate, and then by and architectural treatment of the main piers at a long viaduct to the southerly-most point of the same time. He was then planning to use steel his Division. The largest of the three bridges on towers and girders for his approach viaduct. the line was the Hell Gate.

As was common with Lindenthal’s unique designs, Lindenthal looked into several designs before he considered the erection procedure in detail, as the arriving at the style of bridge he considered most highest loads in the members frequently occurred economical for the site. He considered a stiffened during erection. He adopted a cantilever technique suspension bridge with eyebar chains as he had similar to that of James Eads on the St. Louis Bridge earlier proposed for his North River, Quebec, (STRUCTURE, December 2017). His method tied and Manhattan Bridges; a three-span continuous his cables/chains back to a deadman that was braced truss bridge, like he built in Pittsburgh and had off four lines of stringers placed between the deadman once considered for his North River Bridge; and and the bridge piers. a three-span cantilever bridge. Due to the heavy The Engineering Record wrote, “Besides planloading and sharp curves approaching and leav- ning a bridge of ample strength, the company ing the bridge, Lindenthal chose the arch design. has endeavored to make it a thing of beauty. Mr. He actually considered two competing steel arch Gustav Lindenthal designed the structure and designs. The first design was similar to Gustav associated with him was Mr. Henry Hornbostel, Eiffel’s Garabit Viaduct in France. The second consulting architect. Mr. Lindenthal’s conception design, a flatter “spandrel arch,” had the lower is that of an imposing portal, or gateway, from the chord begin at the bottom of the abutment while Sound into the East River, just as the Brooklyn the upper chord began at the top. The latter design Bridge forms a gateway from the harbor.” was inspired by similarly designed bridges over the Between 1907 and the start of construction in Rhine River in Germany.

1912, Lindenthal made many changes in the He prepared his preliminary designs from 1904 design. He significantly modified his portal with to 1905. In June 1907, Scientific American was an archway rather than towers on each side of running articles on the bridge with the head- the tracks. The change in the tower was the result line, “The Largest Arch Bridge in the World.” The of the Municipal Art Commission’s rejection of Engineering Record published a profile of the bridge the plans. The New York Times reported, “Hell

Alternative designs of Hell Gate Bridge (Ammann 1918).

STRUCTURE magazine

Arch designs, with steel viaducts (Ammann 1918).

38 July 2018

Profile of Hell Gate (Engineering Record) with original steel approach towers and spans.

Proposed erection procedure (Scientific American 1907).

Gate Bridge Plans. Engineers Will Try Again to Please Municipal Art Commission…The original plans for the structure were rejected by the Municipal Art Commission on the single ground that the structural designs were not up to the aesthetic standard now required by the city.” O. H. Ammann, his assistant, wrote of the tower, “The commission, although not objecting to the design

as a whole, disapproved of the decorative features of the towers and their bases.” The revised plans were not submitted to the Art Commission until May 29, 1911, and were finally approved on June 13, 1911. The original 1907 plan as noted called for steel girders and steel piers to be used on the viaducts, but Lindenthal changed to concrete piers as the prison authorities on Ward’s and Randall’s

Islands “feared that inmates of the municipal institutions on those islands would climb them and make their escape. It was insisted that the design adopted should prevent this.”

His final design, completed with the help of David B. Steinman and Othmar H. Ammann, was for a 1,017-foot span bridge, 977 feet 6 inches center-of-skewback to center-ofskewback, between Astoria in the borough of Queens and Wards Island. At the time, this made it the longest and most heavily loaded railroad bridge with four (4) tracks in the world.

The project, along with more than 17,000 feet of approach spans and viaducts, also included an inverted bowstring truss bridge with four 296-foot 6-inch spans crossing the Little Hell Gate and a bridge of two 175-foot fixed trusses with abutting masonry arches across the Bronx Kill.

Lindenthal’s assistant, O. H. Ammann, wrote a lengthy 152-page paper on the project in the Transactions of the ASCE in 1918. The article had a 132-page discussion in which many leading engineers of the time, including Lindenthal, contributed. Most of them were very complimentary of Lindenthal and his design. One of the most significant

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STRUCTURE magazine

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July 2018

things Lindenthal included was a program to measure stresses in his arch during construction under the guidance of D. B. Steinman.

Steinman wrote a companion paper to Ammann’s entitled Stress Measurements on the Hell Gate Bridge in which he described measurements made on the structure to determine the accuracy of the computations. Steinman indicated that Lindenthal “certainly deserves all possible credit for his initiation of a public service in personally defraying the expenses of this investigation as a contribution to engineering science.”

The bridge opened in 1917. It continues to carry railroad traffic on one of the most heavily traveled rail lines in the country. Leon Moisseiff, in his discussion of Ammann’s paper, wrote, “The Hell Gate Bridge is an excellent example of what engineering genius can accomplish if the project is entrusted to one mind to plan and direct, unhampered by red tape and lay commissioners. The bridge reflects credit on the Engineering Profession, and much praise is due to Mr. Lindenthal and his able associates…” The bridge remained the longest arch bridge in the world until 1931 when Ammann opened his Bayonne Bridge with a span of 1,675 feet.

Ammann summarized the project as follows:

Hell Gate Bridge, Viaduct, Little Hell Gate Bridge (inverted bowstrings) foreground. Courtesy of HAER.

A great engineering work cannot be spontaneously created in its final, perfect form, but has to grow and develop gradually, in its entirety as well as in its constituent parts. Although the layman can only judge such a work in the light of an accomplished fact, the engineer must ever be conscious that it is only through extensive and laborious preliminary studies, and untiring efforts to improve, that he can hope to achieve a perfect work.

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INNOVATION IN ARCHITECTURE

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In the execution of a great and complex engineering or scientific undertaking, collaboration of experts in various fields is essential, but a great structure of monumental character must be the product of an individual creative and directive mind.

A great structure cannot be the result of a set of rules and specifications, nor of elaborate, mathematical computations. Such a work requires wide experience and sound judgment, and therefore, should be entrusted only to engineers of high professional attainments and reputation.

Throughout this paper, the importance of rigidity in bridge construction has been pointed out. Rigidity ensures greater durability and safety. There are remarkable examples of structures which have stood up under excessive strains under which they would have failed had it not been for the rigidity of their members or connections. Large bridges must be built for generations to come. Engineers to-day [sic] cannot afford to build important structures cheaply, to serve their purpose for the time being, and incur the risk of having to replace them after a short period of usefulness.

Emphasis has been laid on the appearance of the structures described.

Engineering structures are still regarded by many engineers as mere works of utility, which deserve no consideration in architectural or artistic treatment.

So long as this opinion prevails, the Engineering Profession will not lift itself to a higher plane, and it is even running the risk of being relegated to second place – or after the architect – in the creation of such monumental structures as properly belong in its domain.▪

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2018 NCSEA STRUCTURAL ENGINEERING SUMMIT October 24–27, 2018 · Sheraton Grand Chicago Can’t Miss Events Wednesday, October 24

Atlas Tube Plant Tour Take part in a tour of the Atlas Tube manufacturing mill to see how Hollow Structural Sections are made. Atlas Tube, a division of Zekelman Industries, manufactures a wide range of steel tubular products and is the leading provider of hollow structural sections (HSS) in North America. This tour has been NCSEA Diamond Review-approved for 1 continuing education hour.

Wednesday, October 24

Structural Engineering Cruise on the Chicago River This one-of-a-kind event, sponsored by Atlas Tube and brought to you by NCSEA and SEAOI, will offer a river’s-eye view of the structural engineering and architectural marvels along the Chicago River. The cruise will feature special presentations about the architecture surrounding the river delivered by Chicago Engineers & SEAOI Members, our personal docents of the evening. Food and cocktails will also be available on the fully enclosed, climate-controlled boat.

Thursday, October 25

A Celebration of Structural Engineering at Navy Pier Hosted by Computers & Structures, Inc., and held at one of Chicago’s top attractions, Navy Pier. This extravagant event includes dinner, champagne, and live music that will be enjoyed with extraordinary views of the lake and Chicago’s magnificent skyline. Come celebrate the immeasurable contributions of the structural engineering profession and the ways in which structural engineers are essential to the progress of society while experiencing the architecturally stunning environment that showcases the vitality of Chicago.

Friday, October 26

NCSEA Awards Banquet & Reception This banquet features the presentation of the NCSEA Excellence in Structural Engineering Awards, honoring the best examples of structural engineering ingenuity throughout the world, and the NCSEA Special Awards, given to NCSEA members who have provided outstanding service and commitment to the association and to the structural engineering field.

Rates increase on September 7th, register today to save! Visit www.ncsea.com/register

Don’t miss this year’s Structural Engineering Summit – NCSEA’s 2018 event is the best & biggest it has ever been!

EDUCATIONAL OFFERINGS HAVE BEEN INCREASED FOR MORE CHOICES Over 25 presentations led by SE & business experts; 5 education tracks on Thursday, 4 on Friday, an Opening Keynote, a Leadership Plenary, and a Luncheon Plenary!

Opening Keynote

Always Striving For Better with Ron Klemencic, P.E., S.E., Hon. AIA Engineering is an ever-evolving discipline. Advances in material science, construction methods, analytical tools, and design methodologies continue to provide opportunities for improving on what has been accomplished in the past.

In his presentation, Ron Klemencic will review how some of the most impactful innovations in recent years were developed, and he will speculate as to what areas are ripe for the next wave of advancements.

Leadership Plenary

Influence Redefined…Be the Leader You Were Meant to Be, Monday to Monday® with Stacy Hanke See yourself as others see you. Are you as good – or bad – as you think you are when you communicate with influence?

This presentation will help you persuade, sell, influence, and communicate face-to-face with a clear message.

Luncheon Plenary

Empowering The Next Generation of Structural Engineers...to lead, influence, and inspire a changing world! with Ashraf Habibullah, S.E. The presentation will discuss how the structural engineer’s education and role must change if our profession is to triumph and flourish in these rapidly-changing times, and why engineering students need to be exposed to much more than just our technology if they are to fully leverage the limitless potential of the profession.

THE TRADE SHOW HAS EXPANDED BY MORE THAN 30% This year’s Trade Show will be the largest in NCSEA history!

The Trade Show opens on Wednesday night for the Welcome Reception. This is your first chance to meet with fellow attendees and to connect with the companies that provide the software, materials, and tools for structural engineers. Thursday’s breakfast and lunch, along with Friday’s breakfast, will be held for additional time to connect with exhibitors.

ATTENDANCE HAS INCREASED BY MORE THAN 100% IN THE LAST 3 YEARS The Summit provides many great opportunities for networking. With increased attendance, you have a better chance of making the important connections you need within the profession!

Designed by structural engineers for practicing structural engineers, this event was developed to advance the industry.

View the complete schedule on www.ncsea.com

InSIghtS Marketing Services in an Amazon World

By Michael Bernard, AIA

W

hen a nationally-known organic food market arrived in my neighborhood, I was very excited. The store radiated an idiosyncratic “crunchy granola” vibe. Fresh flowers, a coffee bar, and a shoeshine station situated at the store entrance communicated the message that this market would be unlike any other. The youthful, hip staff seemed enthusiastic about their work, making eye contact and small talk at the register. I felt cool and trendy buying organic and largely local products. I was only too happy to stop shopping at the generic local branch of a major national supermarket chain just across the street.

Over time, though, the vibe of the new market began to diminish and so did its allure. The shoeshine bench disappeared, as did the fresh flower stand. The aisles and entrances were soon jammed with online order employees, who were oblivious to the walk-in clientele. Gradually, the store shed its cool ethos. The company had strategically changed its business model, and the store became more of a food warehouse, promoting convenience and lower cost. The customer experience that initially drew me in, driven more by community than low cost, now existed only as a memory.

Many of the products I sought were available, but the shopping experience had changed.

So I walked back across the street to the major chain supermarket. What did I find?

The management had seized the opportunity to compete and began stocking many of the same products as the new store. There is more, though; I had known the staff at the supermarket for over 25 years – often by name. When the organic food market moved in, the lure of novelty distracted me from the familiarity and reliability of the ordinary supermarket. I reconnected with the community I had left behind.

The business model for each company had gradually changed, revealing different goals and intentions. For some customers, the convenience of low-cost, online grocery shopping is of paramount importance; no human contact, just make sure apples and milk are in my food locker by 5 PM. However, my preferences for connection and relationship were more important than lowest possible cost and convenience. Recognition and prioritization of these fundamental values brought me back to my familiar supermarket.

Both stores have business models that respond to customer trends and values. My experience

of evolving customer needs in the grocery store stimulated my thinking about how to strategically market consulting services in an age where convenient, impersonal transactions are on the rise. A friend calls this “The Amazon World.”

When we circumvent the need for relationships, do we also lose a sense of the importance of value? How do we market when we think we are to compete on price alone?

Maintaining awareness of the value of your service offerings and how they meet evolving customer needs is essential. It is very easy to get caught up in the competition to win on price alone, offering more service for less fee and fighting to the bottom. The best way of staying on top of this dynamic challenge is to establish and strengthen personal relationships.

In the context of ANY challenge (technology, delivery method, price, etc.), it is the only way

What are the key things to do to make your relationships “sticky”? If your repeat clients love working with you, trust and rely on you, they will be far less likely to look for random options acquired online to meet their needs.

Create a case study for each of your repeat clients. In each instance, identify the catalyst that transformed a transaction into a durable professional relationship.

Make a habit of integrating up-to-date postcompletion feedback into your evolving pitch to prospective clients. Internalize what others tell you that makes your professional relationship valuable. Share that information internally with your entire team, from top to bottom; you never know which of your employees will find themselves in a situation where they can nurture a potential client relationship.

It is really a question of how you provide service in a manner that distinguishes you and your firm such that people do not want to work with anyone else. How do you communicate it?

Finally, all of this points to a longer conversation about identifying and communicating the value you deliver. Start with the intention of making contact. Learn what prospective clients want. Try to avoid an early impulse to merely make a sale. First, focus on building relationships that eventually lead to sales – and to repeat clients.

In the tale of two grocery stores, one company places a higher value on convenience and made significant changes affecting customers without communicating that message to the clientele. The actual customer experience, driven now by online sales and lack of personal connection, is inconsistent with the original mission of the company – and sales are down. The other company looked inward, made adaptability part of its mission, and communicated that change clearly, both internally and externally. In fact, they never really deviated from the initial message of community and value – they are again drawing crowds.

Which would you rather be?▪

How do we market when we think we are to compete on price alone? to reliably ensure your client base is more likely to be aware of what you offer and why this is important to them – and to stick around.

Creating awareness of the content and value of what we sell, not just its cost, can and should be seen as the means to get people to pick up the phone. This creates the pretext for conversation, where the real relationship-based sales process can begin. Create the context that gives a prospective client enough motivation and curiosity to call to ask you more about what you do. Once you connect with them, WOW them with personto-person interaction. Do not rely on email alone to communicate; pick up the phone.

Make a personal connection.

Of course, the question then becomes: what do you put out there as the lure to get them to make the call? What, outside of cost, makes your offering unique and worth the pursuit?

Before contacting a prospect, develop a clear outline and understanding of your process.

Avoid jargon. Be authentic. Avoid reliance on canned phrases. Listen to your prospect and understand their needs. Hold off jumping in immediately with solutions. Start this outreach with the people that you find are easiest with whom to communicate. Hone your pitch as you increase the challenge of your outreach.

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July 2018

Michael Bernard is the Founder and Principal at Virtual Practice, a consultancy firm based in San Francisco that focuses on management mentoring, firm organization, staff development, and sales/marketing techniques, specifically tailored to the small design practice. (mbernard@v-practiceconsulting.com)

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Education issuEs Reimagined Structural Design in Capstone Classes

By Deb O’Bannon, Ph.D., P.E., F.ASCE, and Jim Palmer, P.E.

W

hat if students in capstone design classes completed structural designs for real sites, interacted with a real client, and added value for future construction?

In undergraduate education, structural capstone designs are usually retrospective or invented, even when planned for a real site. Universities create competitive design climates, even incorporating virtual reality into capstone design courses. Some universities invite practitioners to judge the students’ design presentations. However, the projects are not constructed. The students know that the project will never be constructed: it is just about learning and, ultimately, a grade.

An alternative is illustrated by the civil engineering capstone design class at the University of Missouri-Kansas City (UMKC), which has incorporated real general civil engineering projects into capstone classes since 2003 and real structural engineering projects since 2016. The classes frequently and spontaneously engage in discussions and analysis of registration and ethics. The practitioners and faculty are quite transparent about their opinions, experience, and limitations. Ashraf Habibullah’s dream for the future of structural engineers is shared with the design teams.

The capstone students at UMKC have the professional satisfaction of knowing that their project is of real value to the client.

The capstone design class is a two-semester studio class where students work in teams of 6-8 with a practitioner (P.E.) on small projects for area municipalities and other clients. In the fall semester, the students define their project scope and present their design options and budget at the client’s site (city hall, corporate headquarters, etc.) as both a presentation and a design report. Over the winter break, the client decides which design options they want to be developed; in the spring semester, the students develop 30% construction drawings. Typical general civil projects have included intersection improvements, urban stormwater improvements, and rural box culvert replacements. All students attend an engineering public meeting and learn about easements, rights-of-way, utility conflicts, and interactions with the public. There are very few traditional classroom events as part of the course – it is almost entirely a studio class.

A recent alumnus, working in a structural design firm, was asked for his advice on project components for a structural engineering

capstone. His suggestions have been incorporated into the structural projects: 1) Determine the loading in the structure (ASCE 7, IBC) 2) Include references to codes in the client’s report 3) Include design process justification in the report 4) Use a commercial structural analysis program 2017-18 structural engineering student design 5) Provide load calculations in the recommendation for boiler enclosure at KCP&L location. report to the client 6) Include structural connections in the designed by the students) by in-house condrawing set struction staff at the municipalities, or redrawn A right-sized structural design project was and stamped at the DOT. For KCP&L, the volunteered by Kansas City Power & Light structural project group creates a technical (KCP&L), a power generating and distribu- concept study for the company’s budgeting and tion company in western Missouri and eastern long-range planning, which will help the comKansas. Jim Palmer, P.E., is the program pany create bid documents for construction. manager of the KCP&L central engineering The role of the practitioner within the classprogram and the practitioner for the struc- room is central to the success of the course. tural capstone group. The “Redcone Project” Ultimately, these practitioners are responsible for reinforces personal, professional responsibility keeping the students within scope, maintaining and the consequences of engineering actions focus, ensuring quality, and providing profesbecause it is a real project for an actual client. sional mentorship. The practitioners ensure The 2016-2017 project was a 45- x 45-foot student ownership of the project by using their enclosure for fly ash loading under an existing expertise to provide guidance, not direction, to fly ash silo. The project also included iden- the university, students, client, and the worktifying a dust control system and designing force. The practitioners in the UMKC capstone the deck on which the equipment would sit class meet weekly with their design group, so above the trucks. The students had to con- full support from their employers is essential. sider the truck driver’s safety and create an The structural capstone design project enclosure that would be robust enough to applies to universities that a) have a relationuse a skid steer to remove accumulated fly ship with a client who needs small, structural ash inside the enclosure while choosing an improvements to their property, such as a easily maintainable external material. The power company; and b) have a structural engigroup also recommended rubber overhead neer who can mentor the students through the doors that would re-seat themselves if hit design. The authors encourage fellow civil and by a truck and a dust suppression system for structural engineering design departments the enclosure. Their design calculations cited to consider including a real project-based the AISC Steel Construction Manual, IBC, structural capstone design option that will ASCE 7, and LFRD Load Combinations. satisfy the students and better prepare them The 2017-2018 project is a design for the for professional practice.▪ demolition and relocation of existing components of a boiler building, and a 31- x 55-foot Deb O’Bannon is a Professor of Civil enclosure that would house new auxiliary boilEngineering at the University of Missouri-Kansas ers. The project team created designs utilizing City. She redesigned the civil engineering a variety of materials including concrete, steel, capstone class to incorporate real projects and masonry, and precast/prefabricated options. real clients in 2003. (obannond@umkc.edu) The design incorporated building codes for Jim Palmer is a Consulting Engineer with personnel egress with fire protection, includKansas City Power & Light and is the ing a firewall. practitioner for the structural capstone design The structural design project completed by group at the University of Missouri-Kansas City. the UMKC students is of real value to KCP&L. (jim.palmer@kcpl.com) General civil projects are usually built (as

STRUCTURE magazine

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July 2018

EnginEEr’s notEbook

Seismic Design Forces

1.60

ASCE 7-16 Revised Capping Provision for Short Period Regular Structures

SDS (site coefficient =1.0)

D

ASCE 7-10

1.40

By Philip Line, P.E., Michelle Kam-Biron, P.E., S.E., SECB, and Michael Cochran, P.E., S.E. esign forces for short period, regular structures, five stories and less in height, in high seismic hazard areas, are permitted to be designed for less seismic force than would otherwise be required by use of the mapped ground motion parameters. The reduced force levels are permitted under ASCE 7 Minimum Design Loads and Associated Criteria for Buildings and Other Structures, Section 12.8.1.3, which caps the level of design force for such structures based on engineering judgment formed by observations of good seismic performance in prior California earthquakes.

The concept of the cap first appeared in the 1997 Uniform Building Code (UBC) with permissible use of a reduced nearsource factor under certain conditions. An alternative form of the cap appeared in the 2000 NEHRP Recommended Provisions for Seismic Regulations for New Buildings and Other Structures. This is the basis of language capping maximum values of the calculated seismic response coefficient, Cs, for short period, regular structures five stories and less in height in ASCE 7-02 through ASCE 7-10.

For reference, ASCE 7-10 provisions follow: 12.8.1.3 Maximum S S Value in Determination of Cs. For regular structures five stories or less above the base as defined in Section 11.2 and with a period, T, of 0.5 s or less, Cs is permitted to be calculated using a value of 1.5 for SS. In development of ASCE 7-16, which is referenced in the 2018 International Building Code (IBC), the cap language was judged to be overly broad when considering original intent based on observations of good seismic performance of certain regular buildings.

The revised capping provision of ASCE 7-16 more narrowly scopes applicability.

For example, use of the capping provision is not allowed for Risk Category III and IV structures and on sites classified as E or F. The force reduction is also limited to 30%, which is more in line with the maximum level of force reduction permissible under the 1997 UBC. Additionally, the applicability of the cap based on number of stories is revised to count each mezzanine level as a story and by counting the number of stories relative to the grade plane. The phrase “above the base” for counting number of stories in ASCE 7-10 allowed for interpretation that

ASCE 7-16

1.20 1.00

the story limit applied to the 0.80 number of stories above the top 0.60 of a rigid podium. For ease of reference, provisions appearing 0.40 in ASCE 7-16 follow: 0.20 12.8.1.3 Maximum SDS Value in Determination of Cs and 0.00 Ev. The value of Cs and Ev are 1.5 1.75 2 2.25 2.5 2.75 3 permitted to be calculated using a SS, Mapped MCER, 5% damped, spectral response accelera on parameter at short periods value of SDS equal to 1.0, but not less than 70% of SDS as defined in Comparison of SDS in accordance with capping provisions of Section 11.4.5, provided that all ASCE 7-16 and ASCE 7-10 Section 12.8.1.3. (Fa = 1.0). of the following criteria are met: 1) The structure does not have irregularities, structure with two levels of mezzanines is as defined in Section 12.3.2; considered a structure with seven stories for 2) The structure does not exceed five stories the purpose of this cap and would exceed the above the lower of the base or grade plane five-story limit for applicability of reduced as defined in Section 11.2. Where present, seismic design forces. Similarly, a five-story each mezzanine level shall be considered a structure over a two-story rigid podium, in story for the purposes of this limit; accordance with the two-stage analysis pro3) The structure has a fundamental period, T, cedure, is considered a structure with seven that does not exceed 0.5 s, as determined using stories for the cap and would also exceed the Section 12.8.2; five-story limit for applicability of reduced 4) The structure meets the requirements nec- seismic design forces. Additional informaessary for the redundancy factor, ρ, to be tion on ASCE 7-16 Section 12.8.1.3 can be permitted to be taken as 1.0, in accor- found in ASCE 7-16 Commentary. dance with Section 12.3.4.2; Designers of residential multi-story light5) The site soil properties are not classified framed over-podium structures should check as Site Class E or F, as defined in Section with the local jurisdiction to see if they have 11.4.3; and adopted any of the ASCE 7-16 Section 6) The structure is classified as Risk Category I 12.8.1.3 requirements early. Some jurisdicor II, as defined in Section 1.5.1. tions are considering adopting ASCE 7-16 The design 5% damped spectral response Section 12.8.1.3 requirements now rather than acceleration parameter at short periods, SDS, in waiting until the local adoption of the 2018 accordance with capping provisions of ASCE IBC, which adopts the ASCE 7-16 design 7-16 and ASCE 7-10 used to calculate seismic requirements by reference. For example, the base shear, is shown in the Figure.

City of Los Angeles has already adopted the Under the revised capping provisions of ASCE 7-16 Section 12.8.1.3 changes as part ASCE 7-16 Section 12.8.1.3, design seismic of their 2017 Los Angeles City Building Code forces for short period, regular structures, instead of waiting for their next building code five stories and less in height are increased adoption cycle in 2020, knowing of the signifiin areas of high seismic hazard when com- cant changes forthcoming with ASCE 7-16.▪ pared to ASCE 7-10. The increase in forces is largest for areas of greatest seismic hazard.

Philip Line is a Senior Director of Structural The revision does not affect design seismic Engineering at the American Wood Council. forces in low seismic hazard areas. While (pline@awc.org) seismic design forces are higher for these Michelle Kam-Biron is a Senior Director of structures in high seismic areas, the changes Education at the American Wood Council. in the applicability of the provisions based (mkambiron@awc.org) on clarifications to agree with original intent are likely the most significant. For example, Michael Cochran is Vice President at Thornton under the revised capping provisions of Tomasetti. (mcochran@ThorntonTomasetti.com) ASCE 7-16 Section 12.8.1.3, a five-story

STRUCTURE magazine

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July 2018

ConCrete ProduCts Guide ADAPT Corporation

Cortec Corporation

Euclid Chemical Co.

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American Concrete Institute Phone: 248-848-3700 Email: ACICustomerService@concrete.org Web: www.concrete.org Product: ACI Collection of Concrete Codes, Specifications, and Practices Description: Over 300 of the most used codes, specifications, and practices on concrete technology.

Documents constantly updated to provide the most current and frequently demanded information. Contains all ACI codes, specifications, and practices to answer questions about code requirements, specifications, tolerances, concrete proportions, construction methods, evaluation of test results, and more.

BASF Corporation Phone: 800-526-1072 Email: christopher.perego@basf.com Web: www.master-builders-solutions.basf.us Product: MasterProtect® C350 Description: Part of BASF’s Master Builders Solutions product family, MasterProtect C350 is a hydrophobic coating that is expertly engineered by BASF chemists to enhance and protect your building’s appearance, performance, and structural integrity.

Concrete Masonry Association of California and Nevada

Phone: 937-866-0711 Email: pamelafurneaux@daytonsuperior.com Web: www.daytonsuperior.com Product: Bar Lock® Couplers Description: Provides a simple, quick, cost effective method for splicing smooth or deformed rebar in high strength tension, compression, and seismic applications. Versatile, the Bar Lock Coupler System is an ideal choice for new construction as well as repair and rehab projects.

Dlubal Software, Inc. Phone: 267-702-2815 Email: info-us@dlubal.com Web: www.dlubal.com Product: RFEM Description: Strength and serviceability limit state designs of reinforced beams, columns, slabs, and walls according to ACI 318, CSA A23.3, and other international standards. Capabilities include non-linear analysis of reinforced concrete elements in the cracked state for a realistic view of deformations, stresses, and crack widths for the serviceability limit state.

ENERCALC, Inc.

Phone: 916-722-1700 Email: info@cmacn.org Web: cmacn.org Product: 2015 Design of Reinforced Masonry Structures Description: Based on the 2013 edition of TMS 402/602-13 developed by MSJC and the 2015 IBC. Calculations for design loads referenced to ASCE 7-10. In addition to several practical design examples and aids, the new edition includes complete design of the major concrete masonry elements of three typical masonry buildings.

Phone: 800-424-2252 Email: info@enercalc.com Web: http://enercalc.com Product: Structural Engineering Library/Retain Pro/ ENERCALC SE Cloud Description: SEL quickly completes calculations for the design of footings, columns, beams, pedestals, shear walls, and other concrete structures. New 3D sketches let you avoid expensive, complicated software. RetainPro provides detailed concrete earth retention design/calculation tools. Clear, concise reports are ideal for client/agency reviews.

Fibercon International Inc Phone: 724-538-5006 Email: Keith@Fiberconfiber.com Web: www.fiberconfiber.com Product: Steel Reinforcing fibers Description: Fibercon steel fibers have extended slab joints out to 100 feet plus. Fewer joints means less maintenance issues in the future It is all about fiber count, therefore, we can drastically reduce microcracking before it becomes a major crack in composite steel decks, tunneling and precast segments, and warehouse flooring.

Headed Reinforcement Corporation (HRC) Phone: 714-852-1333 Email: Jeremy@hrc-usa.com Web: www.hrc-usa.com Product: HRC 670 HeadLock Description: Field installed anchorage when standard hooks or heads cannot be prefabricated. Great for correcting elevations on rebar. Full capacity developed by pushing the HeadLock onto the end of the bar.

The Torque bolt ensures that the bar is fully gripped and wedged for a tight, ultimate connection.

Hohmann & Barnard, Inc. Phone: 800-645-0616 Email: weanchor@h-b.com Web: www.h-b.com Product: TBS - Thermal Brick Support Description: A fully adjustable bracket system that moves the shelf angle away from the wall. This allows for more continuous insulation while reducing thermal transfer through the cavity for a more efficient masonry building.

A MiTek - BERKSHIRE HATHAWAY COMPANY

IES, Inc.

Not listed?

All 2018 Resource Guide forms, including the 2018 Trade Show in PrinT, are now available on our website. www.STRUCTUREmag.org STRUCTURE magazine

50

July 2018

Phone: 800-707-0816 Email: info@iesweb.com Web: www.iesweb.com Product: VisualFoundation Description: The easy software solution for mat foundations, combined footings, and pile caps. Model complex geometry with grade beams, wall, and tank loads, quickly. Checks stability, punching shear, and helps you design the reinforced concrete slab. Get a free trial and pricing at our website.

ConCrete ProduCts Guide RISA

S-FRAME Software

Simpson Strong-Tie®

Phone: 949-951-5815 Email: info@risa.com Web: risa.com Product: RISAFloor ES Description: RISA offers everything you need for concrete design. For concrete floors, including beams and two way slabs, nothing beats RISAFloor ES for ease of use and versatility. The design of columns and shear walls with RISA-3D offers total flexibility.

Integration between RISA-3D and RISAFloor ES provides a complete building design.

Phone: 604-273-7737 Email: info@s-frame.com Web: s-frame.com Product: S-CONCRETE Description: The most efficient concrete design and detailing solution available for columns, beams, and walls with ACI 318-14 code support. Easily modify design parameters to quickly generate the optimum design. Optimize a single section or simultaneously evaluate thousands of concrete section designs.

Automatically generate comprehensive and transparent engineering design reports.

Phone: 800-925-5099 Email: web@strongtie.com Web: www.strongtie.com Product: Stainless-Steel Titen HD® Heavy-Duty Screw Anchor Description: Now available in Type 304 and Type 316 stainless steel, with serrated carbon-steel threads at the tip. Type 316 is optimal for corrosive environments, and Type 304 is a cost-effective solution for less extreme applications where the environment may be wet or damp.

SDS/2

Strongwell

Phone: 402-441-4000 Email: david@sds2.com Web: www.sds2.com Product: SDS/2 Concrete Description: Provides the necessary tools to automate detailing and fabricating rebar for concrete footings, walls, columns, and beams. Rebar detailers can automatically generate detailed bending and placing schedules, as well as placement drawings, from 3D model information, saving time over traditional 2D workflows.

Phone: 276-645-8000 Email: bmyers@strongwell.com Web: www.strongwell.com Product: GRIDFORM™ Stay-in-Place FRP Concrete Form Description: A prefabricated fiber reinforced polymer (FRP) double-layer grating, concrete-reinforcing system with integral stay-in-place (SIP) form generally used for vehicular bridge decks. Eliminate costly and timeconsuming efforts with rebar and provide a superior end product that will outlast traditionally reinforced concrete.

Listings are provided as a courtesy. STRUCTURE® magazine is not responsible for errors.

Product: Fabric-Reinforced Cementitious Matrix (FRCM) Description: FRCM combines a high-performance sprayable mortar with a carbon-fiber grid to create a thin structural layer that doesn’t add significant weight or volume to an existing structure. FRCM can be used to repair and strengthen concrete and masonry structures for seismic retrofit or load upgrades.

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STRUCTURE magazine

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July 2018

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This suite is dedicated for design of columns, walls, beams, slabs, mat foundations, slabs-ongrade, and circular and rectangular tanks.

The Masonry Society Phone: 303-939-9700 Email: info@masonrysociety.org Web: www.masonrysociety.org Product: Masonry Codes and Standards and Publications Description: A non-profit, professional organization of volunteer Members, dedicated to the advancement of masonry knowledge.

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STRUCTURE magazine

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2/19/18 July 2018

8:44 AM

Business Practices You Hired a New Graduate, Now What?

By Jennifer Anderson

Y

ou recently hired a new college graduate to join your team – congratulations!

Adding someone new to the team feels great and has the potential to be very rewarding for you, the existing team members, and the new hire. In this article, four key points about assimilating your new graduate into your company will help you and the new hire have more success.

Onboard

3-Month Mark The first 3 months will be a time of transition and growth; a new college graduate probably has not had a “real job” previously. Many

companies have a 90-day probationary evalu- to get to know a variety of people in the ation, but the same goes for the new hire. The company so that they are learning about new hire is evaluating you to make sure that your firm from different points of view, they still want to stay with the company. If any not just their peers. of the promises that you made in the interview process are not coming to fruition, the new Mentor hire is going to be more and more frustrated until those promises are met. It is vital that An effective way to make sure that the new you ensure that the new hire’s experience will college graduate feels like they are a part align with what was communicated to them of the team is by facilitating a mentoring during the interview process. If their expecta- program in your company. In a previous tions are not met, then you will experience STRUCTURE article about mentoring rapid turnover in new recruits.

(Mentoring in the Workplace, April 2018), New employees flock together and talk. you will find advice and techniques on They will compare notes on how work is how to effectively implement a mentoring going, what the managers are like, how program at your company. Mentoring, speto navigate the new job, etc. So, if one of cifically for new college graduates, is critically them is not happy, it is likely their bad important because they are coming from opinion will spread to other new recruits; a lifetime of always having a mentor – be likewise, if they are happy and enthusiastic to Demos at www.struware.com be at your firm, they will encourWind, Seismic, Snow, etc. Struware’s Code Search program calculates these and age each other other loadings for all codes based on the IBC or ASCE7 in just minutes (see online to stay and work video). Also calculates wind loads on rooftop equipment, signs, walls, chimneys, trussed towers, tanks and more. ($250.00). hard. While it is great to hang out CMU or Tilt-up Concrete Walls Analyze solid walls for out of plane loading and panel legs next to or between openings by automatically calculating loads to the wall with “like-minded leg from vertical and horizontal loads at the opening. ($75.00 ea) people,” especially Floor Vibration Program to analyze floors with steel beams and/or steel joist. during the first 3 Compare up to 4 systems side by side ($75.00). months, encourConcrete beam/slab Program to provide bending, shear and/or torsional reinforcing. age and support Quick and easy to use ($45.00). new employees

STRUCTURE magazine

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July 2018

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The onboarding process is as important, if not more important than the recruiting and interview process. Over the years, the author has heard from countless new employees who have expressed frustration with the onboarding process at their new employer. It is ironic that companies go to great lengths to improve their recruiting and interview process and, when they finally bring on the new hire, it is as if they have forgotten that the new hire is still evaluating their decision to join the company.

If you have hired anyone in the last 3 to 6 months, ask them about their onboarding experience. Look for gaps in their expectations. Clean up any discrepancies in what new hires were told during the recruiting and interview phases in comparison to their actual onboarding experience. A fruitful source to recruit new employees is from the contacts of your new hires, so take their feedback seriously. It does not mean that their perspective is accurate, but it is their reality which means it is true to them.

Ultimately, you want to have an onboarding process that is simple to navigate for the new hire, the manager, and HR. Cut out anything that is not helpful and aim to make their first day – and week – as comfortable as possible. You are concerned that you have hired a good person; likewise, they are concerned that they have joined the right firm. Building your employer brand during the onboarding process will make a big difference in ongoing recruiting efforts.

it a college professor, University advisor, teacher’s assistant, friends, parents, or family members – who have guided them through major decisions and turning points in their life. Now that they are working at your company, they will still appreciate and seek career guidance and counsel from a mentor. If they are going to seek guidance, you want them to get advice from someone who is committed and experienced in your firm.

When connecting them to a mentor in the company, look for opportunities to pair

them with someone who is only a few years older. Mentoring from someone who is close in age, but has at least 5 years of working experience, will help the new graduate feel like they are getting relevant career guidance. After they have been with the company for at least a year, they can look for another mentor from the senior team and get additional career development assistance. In the first year, they need help with basic things that may be in the too distant past for senior team members.

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The height of structural protection.

Literally.

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If you feel your company is doing a good job with onboarding and communicating with and mentoring the new hires, you may want to survey them to confirm that they feel just as good about being there as you think they are. A short anonymous online survey with a few questions is ideal so that you can get feedback on your specific new hire processes. Always include a way for the survey respondents to comment in general and encourage suggestions. If you have fewer than 10 new hires in the last 6 months, it may be better to talk to each of them individually and get direct feedback. Ten people is a reasonable number for sending out a new hire survey without them feeling like it is not really an anonymous survey.

Keep in mind that new graduates are sensitive to doing a good job; they might not be accustomed to giving honest feedback. Encourage honesty and candor as much as possible. Once you receive the feedback, compile and review for trends and tangents.

Review the results with the management team and develop a plan for how to assimilate new hire feedback and suggestions. You probably will not be able to do everything they have suggested but start with at least one thing.

Tell the new hires – and the rest of the company, for that matter – that you heard their suggestions and what you are doing about them. If you listen to and move forward with their idea(s), they will be more invested with their time at your firm and will honestly respond to future surveys.

With new hire onboarding, attention to the first 3 months, short and long-term mentoring, and surveying, you will connect with your college new-hires in helpful and satisfying ways. Ultimately, when hiring a recent college graduate, you will find that they want to succeed and have a great career. Make the most of their time with your company and odds are they will stay and help grow your firm while they are growing their successful careers.▪ Born into a family of engineers but focusing on the people side of engineering, Jennifer Anderson has over 20 years helping companies hire and retain the right talent. (www.CareerCoachJen.com)

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STRUCTURE magazine

Survey

54

July 2018

Spotlight Creative Rigor: Retrofit of the Desmond

By Mark Sarkisian, P.E., S.E., LEED, M.ASCE, Neville Mathias, P.E., S.E., LEED, M.ASCE, and Rupa Garai, P.E., S.E., LEED, M.ASCE

Skidmore, Owings & Merrill LLP was an Outstanding Award winner for The Desmond Building project in the 2017 Annual Excellence in Structural Engineering Awards Program in the Category – Forensic/Renovation/Retrofit/Rehabilitation Structures under $20M.

L

ocated in downtown Los Angeles’ rising South Park commercial district, The Desmond Building has recently been infused with new life through a full renovation, expansion, and seismic retrofit. Before the renovation and seismic retrofit, independent research had identified the Desmond as one of Los Angeles’ many existing seismically vulnerable, non-ductile concrete buildings at risk of being significantly damaged in the next major earthquake. Mayor Eric Garcetti of Los Angeles, in December 2014, issued his Resilience by Design initiative – introducing guidelines that require all vulnerable nonductile concrete buildings in LA to undergo a seismic retrofit. The Desmond exemplifies how similar historic properties can be innovatively renovated to include additions without exceeding code retrofit triggers.

Designed in 1916, the building was initially a Willys-Overland car dealership and assembly plant, which later became a Desmond’s department store warehouse. The building stood mainly empty for many years before finally being purchased by a prominent development company in 2013 to renovate for high-end creative office use.

The existing five-story-tall concrete structure, approximately 100 x 157 feet, consisted of columns framed by shallow girders and two-way flat slabs. The columns and beams constituted non-ductile moment frames in two directions.

Existing condition surveys classified the structure as in very good condition. Fortuitously, good quality original drawings were also made available to the design team.

Because of the low original design material strengths, and the proposal to add a story

Courtesy of David Lena

to the building, stringent criteria were established through in-depth discussions with the Los Angeles Department of Building and Safety (LADBS).

To meet these criteria, the project team devised a solution in which the sixth-floor addition was made as light as possible, coupled with resourcefully reducing seismic weight throughout the building. Multiple Courtesy of Robert Meyers Studio two-way steel special moment frames were provided for the addition, with columns cen- and anchored to the new pier and link beam tered on columns below to uniformly distribute framing structure, maintaining the exterior and balance the seismic loading effects. A light- appearance. Unobstructed multi-lite steel weight roof system and exterior cladding were windows were refurbished. used. Mechanical system equipment was disAlong the solid north wall, two single bay tributed over the height of the building rather long shear wall piers were provided and linked than concentrated on the roof (as is typical). to the diaphragms using steel collector beams.

New lightweight architectural finishes were At the base of all the new piers on the other used throughout the building. As a result of three sides of the building, an interconnected controlling weight, the need for a seismic retrofit foundation system of grade beams and new was not triggered per code. A complete seismic footings was provided. Lastly, composite fiber retrofit was nevertheless provided. wrap confinement was provided at the ends of The internal structure supporting gravity all internal gravity columns to meet deformaloads – floor framing, columns, and founda- tion compatibility requirements. tions – was originally designed to support a The rigorous, code-prescriptive retrofit solulive load of 100 psf on all floors including the tion enabled the addition of income-generating roof. Changing to office usage with a live load space while preserving the historic character of 50 psf (reducible) allowed the addition of the of the century-old building. This resulted in new floor without triggering the need for ret- the project developers finding a tenant for the rofit of the gravity load supporting members. entire building, well before construction was Additional measures were taken to minimize complete, who ended up buying the building the loading on individual members. Existing upon its completion. This renovation and retrostair and elevator openings were re-used, and fit project successfully improved the street appeal cast-in-place concrete stairs were replaced with of the building and increased The Desmond’s lighter steel stairs. New openings for MEP total square footage from 75,000 square feet to systems were minimal and unnecessary exist- 82,000 square feet. The Desmond’s structural ing weight was removed. Controlling weight solution exemplifies how many other nonto avoid triggering a retrofit was so fine-tuned ductile historic properties in Los Angeles can that an inch of architectural concrete topping be safely and sustainably renovated for creative was removed at two floor levels. office use – to preserve each neighborhood’s culEven though the loads were controlled so ture and history while still adding more “Class that a retrofit was shown not to be required A” spaces with appropriate structural resiliency.▪ by code, the owner desired to assure tenants Mark Sarkisian is a Partner in the San Francisco that the structure was safe and designed to office of Skidmore, Owings & Merrill LLP resist the same seismic forces as a new building (mark.sarkisian@som.com) under current codes. An internal perimeter retrofit was developed to mimic the original Neville Mathias is the Associate Director at Skidmore, Owings & Merrill LLP in San Francisco, CA. industrial look in a non-intrusive manner, using new concrete wall piers and upturned Rupa Garai is an Associate Director at Skidmore, link beams to envelop the perimeter on three Owings & Merrill LLP in San Francisco, CA. sides. Exterior brick façades were restored

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July 2018

News form the National Council of Structural Engineers Associations

This year’s Structural Engineering Summit in Chicago, IL is set to be the best and the biggest event in NCSEA history. There are more sessions, more opportunities to network, and more exhibitors than ever! This is a can’t-miss event!

Each year, the Summit draws the best of the structural engineering field together for excellent practical education opportunities designed for them by practicing structural engineers. The Summit also honors the best of structural engineering with the Excellence in Structural Engineering Awards recognizing ingenuity throughout the world, and the NCSEA Special Awards highlighting members who have provided outstanding service and commitment to the organization. This event has been built to advance the industry.

The Summit is designed with you in mind. Will you attend? Registration is open now, but fees are set to increase on September 7th. Registration rates for 2018 are available in two main categories: Full Conference Plus and Basic Conference Registration. Both categories offer full conference options for First Time Attendees, Young Engineers, and Spouse/Guests.

Full Conference Plus Registration Includes: • All Educational Sessions & Resources • Over 25 presentations led by SE & Business Experts • SE River Cruise • A Celebration of Structural Engineering hosted by CSi • Morning & Afternoon Meals • Multiple Networking Opportunities • Refreshment breaks • Trade show access • NCSEA Awards Reception & Banquet • Tour of the Atlas Tube manufacturing mill Basic Full Conference Registration includes all of the above except for the SE River Cruise.

Rates increase on September 7th. Register now to save! Visit www.ncsea.com for more information about this year’s Summit, including registration information, this year’s host hotel, exhibitors, and the current schedule.

Can This NCSEA Benefit Jumpstart Your Next Project?

NCSEA News

NCSEA Grant Program Applications due August 1st

The NCSEA Grant Program began in 2015 to award SEAs funding for projects that grow and promote their SEA and the structural engineering field in accordance with the NCSEA Mission Statement: NCSEA advances the practice of structural engineering by representing and strengthening its Member Organizations. One of the highlights of the NCSEA Structural Engineering Summit is the announcement of the Grant Award recipients and the projects they will undertake to advance the profession.

The Grant Program is open to all NCSEA Member Organizations.

Requests can be submitted for any program or endeavor that is consistent with, and supportive of, NCSEA’s Mission Statement. All applications must be approved by the appropriate Member Organization.

Want to learn more about the Grant Program directly from your peers?

NCSEA held a webinar focused on the program in June with past winners; the webinar covers the history and process of the Grant Program as well as testimonials from past recipients. Learn about how this benefit could jump start your next project and about how SEAOI and SEAONY used their grants to fund events! Visit www.ncsea.com to view this webinar and to apply for the 2018 Grant Program.

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July 2018

2017 Grant Recipients: Structural Engineers Association of Georgia to promote visibility for the profession.

Structural Engineers Association of Hawaii for a shake table.

Structural Engineers Association of Illinois to host a Young Engineers Symposium.

Structural Engineers Association of Massachusetts to host an ACE Mentor Program.

Structural Engineers Association of New York for a diversity launch party with the SE3 committee and to host networking skills events.

Structural Engineers Association of Ohio to enhance their existing student mentoring program.

Submissions for the 2018 Excellence in Structural Engineering Awards are due. This program annually highlights some of the best examples of structural engineering ingenuity throughout the world. Structural engineers and structural engineering firms are encouraged to enter the awards program. Projects are judged on innovative design, engineering achievement, and creativity.

Projects can be entered in one of seven categories: • New Buildings Under $20 Million • New Buildings $20 Million to $100 Million • New Buildings over $100 Million • New Bridges/Transportation Structures • Forensic/Renovation/Retrofit/Rehabilitation Structures up to $20 Million • Forensic/Renovation/Retrofit/Rehabilitation Structures over $20 Million • Other Structures

Start studying for the fall NCEES SE Exam now! The NCSEA SE Refresher & Exam Review Course offers a thorough review of a majority of the topics that will be covered on the SE Exam. The course offers 30 hours of On-Demand Instruction, taught by experts in each field. The course will give you exam preparation tips and problem-solving skills to pass the exam. All lectures are up-to-date on the most current codes and include handouts and quizzes.

Registrants will receive instant, unlimited access to the course! Sign up now and start studying within minutes!

Continued access is also included, so if you don’t pass the exam this Fall you can start preparing for the next exam. PLUS, registrants are added to the Virtual Classroom, which provides an online chat room for course discussion with instructors and other attendees.

At $495 for members and $695 for nonmembers, this on-demand course is the most economical SE Exam Prep Course available. Group pricing is also available!

Visit www.ncsea.com for the complete course listing and to register now!

NCSEA Webinar Bundle:

Introduction to Seismic Design with Thomas F. Heausler, P.E., S.E. July 19, 2018 Introduction to Seismic Design - Low Seismic A simple one-story building, located in a region of low seismic risk, will be presented with the procedures for defining seismic loads and associated criteria for the structure using ASCE 7 Seismic provisions. Formulas will be presented and their underlying theory will be explained.

The resulting calculations will be formatted so that they may be utilized as a flowchart and checklist for future use when designing actual buildings.

July 26, 2018 Introduction to Seismic Design - High Seismic A simple multi-story building, located in a region of high seismic risk, will be presented with the procedures for defining seismic loads and associated criteria for the structure using ASCE 7 Seismic provisions. An introduction to the material standards, such as AISC 341 Seismic and ACI 318 Chapter 18 Seismic, will be presented. The nonstructural components equations will be described and implemented. The resulting calculations will be formatted so that they may be utilized as a flowchart and checklist for future use when designing actual buildings.

Register at www.ncsea.com. The bundle includes both Introduction to Seismic Design courses. $350 for Members, $400 SECB/SEI/CASE Members, $450 for Nonmembers.

Courses award 3 hours of continuing education after the completion of a quiz following each webinar.

NCSEA Webinars August 2, 2018 Dealing with Floor Vibration in a Modern Structural Consulting Firm Lessons from the Field James Lamb, Ph.D. August 16, 2018 Ground Improvement for Structural Engineers: Benefits, Limitations, and Considerations Alex Potter-Weight, P.E. Register at www.ncsea.com. Courses award 1.5 hours of continuing education after the completion of a quiz.

Diamond Review approved in all 50 states.

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July 2018

News from the National Council of Structural Engineers Associations

Entries are due by 11:59 p.m. on Tuesday, July 17, 2018.

The process is now entirely online and can be completed by visiting the Awards section of www.ncsea.com.

The Best Instructors. The Best Material.

Available to you immediately when you register.

NCSEA News

NCSEA Excellence in SE Awards NCSEA SE Exam Review Course

SEI Online

New SEI Online Voting

Structural Columns

The Newsletter of the Structural Engineering Institute of ASCE

Vote in SEI Online Election for SEI Board Members by July 31 The SEI Board of Governors is comprised of two representatives from each of the five SEI Divisions (Business & Professional, Codes & Standards, Global, Local, and Technical Activities), one appointee from ASCE, the SEI President, SEI Past President, and the SEI Director as a nonvoting member. The Division representatives each serve a four-year term. In accordance with the SEI Bylaws, this year SEI is conducting an election for one Business & Professional and one Codes & Standards representative to the Board of Governors, terms effective October 1. The respective Division Executive Committees have nominated the following: For SEI Business & Professional Activities Division (BPAD) Representative to the SEI Board: Randall P. Bernhardt, P.E., S.E., F.SEI, F.ASCE

For SEI Codes & Standards Activities Division (CSAD) Representative to the SEI Board: Donald R. Scott, P.E., S.E., F.SEI, F.ASCE

Current SEI members above the grade of Student will receive an email July 1 from Association Voting on how to verify and submit your secure ballot online. Ballots are due online no later than July 31.

Other news at www.asce.org/SEI: • Embracing Structural Fire Protection • New Thinking for Power Line Structures • SEI Visit and Seminars in Israel • SEI Student and Young Professional Experiences and Connections at Structures Congress

Kevin LaMalva, P.E., M.ASCE

Michael Miller, P.E., M.ASCE

Mustafa Mahamid, Ph.D., P.E., S.E., F.SEI, F.ASCE

Jayne Marks, EIT, A.M.ASCE

ASCE 7 Online

Visit www.asce.org/SEIStandards to: • View ASCE 7-22 Committee Meeting schedule and archive • Submit proposals to revise ASCE 7

Skylar Calhoun, EIT, S.M.ASCE

Luis Duque, EIT, A.M.ASCE

Follow SEI on Twitter @ASCE_SEI

Students and Young Professionals

ASCE Younger Member Leadership Symposium August 10 – 12 at ASCE

Open to ASCE Younger Members, age 35 and under. Provides early-career professional skills development to succeed and lead in the workplace. Space is limited and fills up quickly. Registration deadline July 19. www.asce.org/event/2018/younger-member-leadership-symposium

Advancing the Profession

Call for Nominations for ASCE Distinguished Membership ASCE Members and Fellows who demonstrate eminence in civil engineering or its related arts and sciences are eligible.

Consideration is through a confidential nomination process due October 1.

Learn more at www.asce.org/distinguished_members or contact awards@asce.org.

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July 2018

SEI Local Leaders Conference

Local SEI Chapter Chairs: Save the date for the SEI Local Leaders Conference October 5-6 at ASCE for best practices and leadership training. If you are a local SEI Chapter Chair and are not on the local SEI leaders email list, contact Suzanne Fisher sfisher@asce.org. Connect with your local SEI professional or Grad Student Chapter at www.asce.org/SEILocal.

Save the date for a career-invigorating event of inspiring speakers, dynamic learning, networking, collaboration with partners, and fun social events. #Structures19 www.structurescongress.org Learn about scholarship opportunities for young professionals at www.asce.org/SEIYoungProfessionals.

Share What Inspires You in Structural Engineering Do your summer travel plans include visiting some great examples of structural engineering – buildings, bridges, towers, etc.? Share your experiences and what inspires you in structural engineering by tweeting @ASCE_SEI or email a brief message and photo to Brittany Boyce at bboyce@asce.org.

Your Blueprint for the Future

Begin Your Career Search with Career Connections.

• Job listing database w/600+ jobs • Searchable by title, geography, salary and more • Interviewing & resume tips

Careers.asce.org @ASCEJobs

NEW SEI/ASCE Live Webinars – Learn from the Experts July 16  10-Step Design of Post-Tensioned Floors July 20  Non-Linear Time History Analysis August 3  Significant Changes to Tensile Membrane Structures, ASCE 55-16 Register at Mylearning.asce.org for these and much more.

Prepare for Fall Exams ASCE P.E./S.E. Live Exam Review Courses

Interactive, expert-led classes begin August 1. Group rates are available for two or more engineers at the same location.

Sign up at www.asce.org/live_exam_reviews.

Errata

SEI Standards Supplements and Errata including ASCE 7. See www.asce.org/SEI-Errata.

If you would like to submit errata, contact Jon Esslinger at jesslinger@asce.org.

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July 2018

The Newsletter of the Structural Engineering Institute of ASCE

The must-attend conference on transmission line and substation structures and foundation construction issues.

Unparalleled learning and networking for utilities, suppliers, contractors, consultants, and more.

Learn more and register at www.etsconference.org #ETSC18

Structural Columns

Learning / Networking

CASE in Point

The Newsletter of the Council of American Structural Engineers

CASE Risk Management Tools Available Foundation 3: Planning – Plan to be Claims Free • Must have a plan for the firm in order to be claims free.

• Train staff to plan, then implement the plan.

• The plan needs to be simple, understandable, and inclusive to be effective.

• Have Policies and Procedures that are workable and followed.

• Communicate and repetitively reinforce the plan.

• The plan may need to adjust as conditions change.

Tool 3-1: A Risk Management Program Planning Structure This tool is designed to help a Firm Principal design a Risk Management Program for his or her firm. The tool consists of a grid template that will help focus thoughts on where risk may arise in various aspects of their engineering practice and how to mitigate those risks. Once the risk factor is identified, a policy and procedure for how to respond to that risk are developed.

This tool contains 10 sample risk factors with accompanying policies and procedures to illustrate how one might get started.

The tool is designed to insert custom risks and policies to tailor the product to individual firms.

Tool 3-2: Staffing and Revenue Projection Firms are provided a simple-to-use and easy-to-manipulate spreadsheet-based tool for predicting the staff that will be necessary to complete both “booked” and “potential” projects. The spreadsheet can be further utilized to track historical staffing demand to assist with future staffing and revenue projections.

Tool 3-3: Website Resource Tool (Updated May 2018) This tool lists website links that contain information that could be useful for a Structural Engineer. A brief description of the website is also included. For example, there is information about doing business across state lines, information regarding the responsibility of the Engineer of Record for each state, links to each State’s Licensing Board, etc.

Tool 3-4: Project Work Plan Templates Preparing and maintaining a proper Project Work Plan is a fundamental responsibility of a project manager. Work Plans document project delivery strategies and communicate them to the team members. Project Managers will use this template to create a project Work Plan that will be stored with the project documents.

Foundation 4: Communication – Communicate to Match Expectations with Perceptions • A high percentage of claims occur because of poor communication.

• Be proactive in communications. Not reactive.

• Create an atmosphere for good and open communication.

• If in doubt, communicate early and often.

• Select the best method of communication (email may not always be the best approach).

• Communicate effectively.

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. We often place a significant amount of effort and care into communication with our clients, owners, and external stakeholders. With all that effort, it is 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. 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 The intent of CASE Tool 4-3, Sample Correspondence Guidelines, is to make it faster and easier to access correspondence with appropriate verbiage addressing some commonly encountered situations that can increase risk. The sample correspondence contained within this tool is intended to be sent to the Client, Owner, Subconsultant, Building Official, Employee, etc., to keep them informed about a particular 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 provides 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.

Follow ACEC Coalitions on Twitter – @ACECCoalitions.

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July 2018

When you’re packing for summer travel – think light for business insights!

Pathways to Executive Leadership Class Three Registration Open Soon!

A practical, focused program for new leaders facing the challenges of a continuously evolving business environment.

To be successful at taking on higher levels of leadership responsibility and prepare for the demands of being owners, new practice builders need specific and relevant training in the intricacies of leading an A/E firm in ever-changing, always uncertain economic times.

Pathways to Executive Leadership is an intensive leadership program for early-career elites and promising mid-career professionals with 8-12 years of experience who are just beginning to lead and think strategically about their practices and careers. The reality-based curriculum focuses on the core skills necessary to think strategically in their markets, build effective teams, and deliver great service for their most valued clients.

Target Audience: Pathways to Executive Leadership fills a vital gap and creates a strong connection between ACEC’s Business of Design Consulting curriculum and the Senior Executive’s Institute capstone program. It targets those who are making the transition between managing one team (e.g., project managers) to those managing managers and multiple teams. This program is designed to establish habits for long-term high-performance and to create a trusted, national network of colleagues with which to make the journey.

STRUCTURE magazine

Flow of Learning: Budding practice builders face numerous challenges; new skills are required to manage people and the uncertainty of a continuously evolving business environment.

Pathways to Executive Leadership will lead participants through a practical curriculum focused on becoming more balanced in their personal and professional life, more influential in team development, coaching, and client relationships, and more strategic in their business relationships to build a strong client portfolio.

For more information, contact Katie Goodman, 202-6824332, or kgoodman@acec.org.

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July 2018

CASE is a part of the American Council of Engineering Companies

With a range of topics from proposal writing to project delivery, these digital resources are a perfect addition to your business library – instantly available in PDF, MOBI, or E-PUB – at a great price. Download one or all!

• Can I Borrow Your Watch? A Beginner’s Guide to Succeeding in a Professional Consulting Organization • 33 Proven Secrets to Writing Successful Client-Centered Proposals • Construction Management at Risk, Second Edition • Project Delivery Systems Owner’s Manual, Second Edition • Winning Strategies for A/E/C Firms: An Executive’s Guide to Maximizing Growth and Profitability, Third Edition • Win More Work: How to Write Winning A/E/C Proposals To purchase these and other resources, go to https://programs.acec.org/digitalsummer.

CASE in Point

Catch Up on Your Summer Reading!

Structural Forum Eureka! Road to Progress

By James Lefter, P.E.

E

ureka is the moment when someone (an Innovator) suddenly realizes that information organized into a new pattern solves a problem or gives new insight. Eureka moments have occurred frequently in engineering, science, medicine, law, economics, and all other areas of study. Many engineers mention Eureka moments experienced when facing an apparently insoluble design, construction, or failure problem.

This article draws inferences from “Eureka moments” examples about the characteristics of the Innovators and the Eureka moment.

It also lists a few of the barriers to a Eureka insight and its acceptance.

Eureka (I found it!) was supposedly shouted

by Archimedes (mathematician, engineer, inventor) who had been charged to determine if the king’s gold crown contained base metal.

While he was bathing, Archimedes observed that a body immersed in water sinks until the volume of water displaced is equal to the volume of the immersed body. This insight, coupled with density calculations, allowed Archimedes to prove that the crown included base metals.

Archimedes’ Principle is used in fluid mechanics.

Isaac Newton, at age 25, was considered a poor to average student. His laws of statics and dynamics are the foundation for structural engineering. Along the way, he also invented calculus and tracked the movements of the solar system. Then he saw an apple fall from a tree and, in that Eureka moment, was inspired to develop the theory of gravity.

Albert Einstein was an examiner in the Bern patent office. He had not yet earned his doctoral degree. In 1905, age 26, Einstein wrote five papers that revolutionized science: molecular dimensions (dissertation), Brownian Motion, his special theory of relativity, light and quantum mechanics (Nobel Prize 1921), and the equivalence of mass and energy. A few years later, he saw a worker on the roof of a nearby building and suddenly realized that the worker, if falling off the roof, would not feel his own weight until he hit the ground. That Eureka insight later inspired him to extend his special theory of relativity to his general theory of relativity by redefining gravity.

In areas prone to earthquakes, engineers design structures to resist the lateral ground

motion induced by the sudden release of energy during an earthquake. The design forces were set by building codes, generally in proportion to the level of ground motion predicted. Professor Mete A. Sozen, then at the University of Illinois, and his students, noted that a trivial increase in the design forces as set by the codes led to as much as a fourfold increase in the lateral displacement of the structure (called “drift”). After further testing, in a Eureka moment, he realized that drift was the critical criterion for seismic-resistant design of structures.

Modern building codes reflect his insight.

This insight was introduced in the 1972 edition of the Veterans Administration’s building code and promulgated by the National Science Foundation.

William LeMessurier was a prominent structural engineer and a part-time teacher.

On behalf of his students, he contracted, through an MIT team, to develop a new design approach to high-rise steel-framed residential structures. He was having a restless night when his Eureka moment struck, envisioning the “Staggered Truss Framing System” that offered many advantages over other widely used structural systems.

Characteristics From these examples, what may be assumed as the characteristics of the innovators?

Immanuel Kant wrote about the need for knowledge about the heavens and the moral

law within humans. Knowledge about the heavens is understanding the known laws of nature and science. They are the grist for that work. Louis Pasteur wrote that chance most favors the prepared mind. On those terms, the Innovators were well prepared. They all had intensely studied and thought about the laws of science. These can be taught.

But human responses to stimuli cannot be taught. It was chance that the Innovators saw an apple fall, a man on a roof, seismic drift, but it took years of preparation and study in the field coupled with human imagination to turn the chance observations into Eureka moments.

The passion, the search for new knowledge, the heat and intensity, the independence, the creativity all drive the Innovator.

Coincidentally, the Innovators were taking a break (taking a bath, watching a man on a roof, pacing on a restless night). The Innovator’s conscious mind focused on other matters at that instant, while the subconscious mind was still working on the problem.

The personal characteristics of Innovators include a commitment to problem-solving, concentration, determination, background knowledge, tenacity, creativity, independence, and an interest in exploring solutions.

The tools and locales preferred by the Innovators vary widely. Thomas Edison worked in his laboratory. Einstein seldom went to the laboratory; he worked at his desk with a ruler, compass, and pencil.

Interestingly, most of these Eureka moments occurred to the young (20-30 somethings).

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, the Publisher, or the STRUCTURE® magazine Editorial Board.

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July 2018

Roadblocks

Summary

Once the Innovator has a Eureka moment, the first hurdle is to determine whether the new concept has merit. The most common error is assuming a correlation that indicates causation.

Some Eureka moments are never recognized as such or are not pursued to their full potential. Some rely too heavily on experience and simply do not recognize the value of the Moment. Sometimes insights may be rejected because there is insufficient evidence (statistical, mathematical, or practical) to support them. Jealously, the bias of peer reviewers, lack of support from colleagues and others within the community, employment restrictions, and even intellectual property theft can put a halt to the fruition of Eureka Moments.

Edison, a dedicated experimenter, developed direct current. Nikola Tesla, a trained engineer and former Edison employee, developed alternating current, an innovation that Edison entirely rejected. Their “battle of the currents” continued for years, costing millions of dollars and delaying electrification progress.

Finally, current trends toward Artificial Intelligence (AI), with its emphasis on replacing engineers, may have a long-run damping effect on Eureka insights.

Although this article was written to encourage Eureka Moments, one cannot go looking for them. They will just happen. The key to being an Innovator is to recognize those Moments and be willing to pursue them. Pasteur’s “chance most favors the prepared mind” is a guide. Those with prepared minds have the background to understand the nuances of the problem and explore solutions.

However, there is no way to teach the inner fire and determination needed. And, awareness of potential roadblocks may be a measure towards overcoming them.

In conclusion, the road to progress, Eureka, follows a zig-zag path – one that needs to be traveled.▪ James Lefter (retired) was Visiting Professor and Lecturer at the University of Illinois and at Virginia Tech. He held Senior Executive Service positions in the Office of Facilities, Veterans Administration.

He served on the American Concrete Institute Committee for Building Code Requirements for Structural Concrete (ACI 318), and as Director of the Learning From Earthquakes Program of the Earthquake Engineering Research Institute.

Further Reading Blastland, M. and Dilnot, A., The Tiger That Isn’t, Profile Books LTD, Great Britain, 2008 Hossli, R. and Flucker, R., William LeMessurier, STRUCTURE magazine, June 2013 Ioannidis, JPA, Why most published research findings are false, PLOS Medicine, August 30, 2005 Kounios, J., and Beeman, M., The Eureka Factor, Random House, NY, 2015 Livio, M., Brilliant Blinders, Simon and Shuster Paperbacks, NY, 2013 Sozen, M.A., A thread through time, School of Civil Engineering, Purdue University, West Lafayette, IN, 2015 Weighman, G., EUREKA How Invention Happens, Yale University Press, New Haven, 2015

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