August 2025

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STRUCTURE AUGUST 2025

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Contents

AU G US T 2 0 25

THE STRUCTURAL GENOME OF SPHERE

26

By Cawsie Jijina, PE, Steve Reichwein, PE, SE, and Sindi Krasta

An exploration of the structural systems of the new Las Vegas icon.

F E A T U R E S ELEVATING THE CONNECTION BETWEEN PEOPLE, ANIMALS, AND THE NATURAL WORLD

36

By Thomas Root, PE, Craig Huhtala, PE, and Will McDevitt, SE, PE

A focus on adaptive reuse transforms a decommissioned monorail structure into the longest elevated pedestrian loop in the world, the Treetop Trail at the Minnesota Zoo.

TIGHT SITE, BRIGHT FUTURE: UPMC’S PRESBYTERIAN EXPANSION

By Ben Shock, PE , and Jeffrey Millmann, PE

42

The hospital project integrated a street-level loading dock within the building's footprint and implemented a cantilever over the courtyard.

SKYLINE COLLEGE BUILDING 2: MEANS AND METHODS COLUMN SHORING

46

By James Enright and John Dal Pino

The project team for a college located near the San Andreas fault faced many column shoring challenges while implementing a complicated seismic retrofit.

AU G U ST 2 025

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C O L U M N S a n d D E PA RT M E N TS

9 Editorial

Engineering Gameday: A New Tradition That’s Just Getting Started

52

Transforming Structural Engineering: Embracing the AI Revolution

By Kristopher Dane, D.Eng., CPEM, and M. Z. Naser, Ph.D, PE

By Chris Bridges

10 Structural Design

inSights

Saving Time, Costs, and Materials with EngineeringBased Structural Fire Protection

64

Structural Forum

Getting Ahead by Thinking Ahead: Cultivating Mental Load

By Angelina V. Stasulis, PE, SE

By Bob Glendenning and Nestor Iwankiw, Ph.D, PE

16 Structural Design

In Every Issue

Indeterminate Beam Solutions by Finite Difference Methods

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AU G U ST 2 025

7

EDITORIAL Engineering Gameday: A New Tradition That’s Just Getting Started

By Chris Bridges

T

hree years ago, the ACEC Arizona board sat around a table grappling with a challenge that resonates across the country: too few students entering engineering programs, and too many graduates arriving in the workforce without the skills they need to succeed. At the time, they didn’t yet have a formal workforce development committee, but they knew they couldn’t stand by while the pipeline of future talent continued to shrink.

It was during the ACEC-Arizona annual Roads and Streets Conference that they asked a question that would change everything: How do we inspire students before they tune out math and science? Again and again, they heard the same insight: by ninth grade, it’s often too late to change a student’s path.

If they wanted to make an impact, they had to reach students in middle school—while curiosity was still alive and possibilities felt limitless.

That was when we began to dream a little bigger. What if we could introduce students to engineering somewhere unforgettable—not in a classroom, but in a stadium? The idea sounded ambitious, maybe even unrealistic. But the then-Chairman, Greg Haggerty, had a vision that resonated with everyone: “You can’t have a Gameday without engineers.”

In the spring of 2023, under Greg’s leadership and with the dedication of countless volunteers, ACEC Arizona hosted the first STEM Gameday at Arizona State University’s Sun Devil Stadium. One hundred and twenty middle schoolers stepped onto the field and discovered that behind every scoreboard, bridge, and concrete beam are engineers who make it all possible. Many of those students left seeing engineering not as an abstract concept, but as a career they could picture themselves pursuing.

We didn’t stop there. In 2024, the newly formed Workforce Development and Education Outreach Committee, chaired

by Nicolai Oliden, took the lead in scaling the event across all three of Arizona’s major universities. More than 1,500 students

STRUCTURE magazine

attended, and the energy was undeniable. In Nicolai’s words, “We’re building momentum here in Arizona. It’s not just about the kids—it’s about creating a community of professionals, students, and volunteers who are proud to shape the future.”

This year, the team refined the model to create an even more impactful experience, capping attendance to about 600 students per campus and mobilizing 200 volunteers statewide. None of this would have been possible without the extraordinary partner-

These peer-to-peer connections are a reminder that building the workforce of tomorrow is a shared responsibility.

ships among member firms, public agencies like ADOT and MCDOT, university staff, and stadium managers who opened their doors to a new kind of learning.

One of the most powerful moments of every Gameday is watching a middle schooler connect with a college student volunteer—someone only a few years ahead of them—and then see that same college student network with a practicing professional. These peer-to-peer connections are a reminder that building the workforce of tomorrow is a shared responsibility.

STEM Gameday is more than an event. It’s

a new tradition— one that reflects a commitment to giving back and investing in the next generation.

And in Arizona, We’re just getting started. For years, ACEC Arizona has operated the Leadership in Engineering Administration Program (LEAP), which equips professionals with the tools to lead, mentor, and grow. Today, LEAP graduates and participants are stepping up to help expand STEM Gameday, ensuring that they are not only inspiring students but also cultivating the leaders who will guide them.

For any organization or chapter wondering whether you can do something similar, the advice is simple: just try it. Start with one school, one stadium, one day. You’ll be amazed at how quickly momentum builds— and you won’t be alone. Volunteers and organizers in Arizona are ready to share what they’ve learned every step of the way and are currently in the process of establishing pilot programs with other ACEC MOs utilizing a newly completed STEM Gameday Playbook. The goal is to refine the Playbook with experiences from other States and refine it so anyone in the future could use this document to plan their events.

As engineers, we don’t just design roads and buildings. We design opportunities.

And sometimes, those opportunities begin in a stadium where a young student learns, maybe for the first time, that the future they dream about is within reach. ■ Chris Bridges is Executive Director of ACEC Arizona.

With more than two decades of experience in transportation planning and infrastructure development, he advocates for workforce initiatives that advance the structural engineering profession.

This editorial is published in collaboration with the CASE Coalition. (chris.bridges@acecaz.org)

AUGUST 2025

9

structural DESIGN Saving Time, Costs, and Materials with Engineering-Based Structural Fire Protection Accounting for steel’s reserve strength enables optimized building designs.

By Bob Glendenning and Nestor Iwankiw, Ph.D, PE

T

he effort to optimize building construction costs is a slippery slope—one that requires balancing the vision of the structure’s design against the realities of its budget. Securing sound footing requires the consideration of numerous variables, including the building’s design elements, the weight of its steel and, perhaps surprisingly, the type and amount of fire resistive materials (FRMs) used on the building’s structural steel to protect it from collapse during a fire.

Finding the optimal combination of variables was once a major chore for building owners, architects and engineers, as any adjustment to the weight or size of steel profiles means a potential adjustment to the applied thickness of FRMs—not to mention the entire building’s cost structure. Today’s advanced software programs simplify and streamline that process by showing the real-time cost increases or savings associated with any design adjustment. However, truly optimizing the entire process requires thinking outside the traditional box of “prescriptive” fire-based design.

The traditional, prescriptive building method assumes full structural loading conditions and follows a worst-case fire scenario, thereby erring on the side of applying thicker FRM coats than may actually be necessary. Those FRM thicknesses can be reduced when using a calculated approach to structural fire engineering design (SFED) that considers the building’s actual structural design loading conditions.

Yet, engineers can do even better by combining the principles of the two approaches. This combined method assumes the structure has 20% reserve strength availability, meaning the thickness of FRMs applied to individual steel members can be further reduced while achieving the same level of fire protection.

Adopting the more realistic combined method for building designs often leads to the unexpected result that a building using heavier (and, sometimes, more costly) steel can be less expensive overall because it requires a lesser amount of FRMs to be applied to steel to maintain the intended fire rating. That’s because the additional material and labor costs associated with applying the coatings thicker on lighter steel profiles may otherwise exceed the material savings realized by using that lighter steel.

This article will review how combining the prescriptive and calculated SFED approaches can lead to optimized building designs that save owners time, costs and materials.

Assumptions Drive the Prescriptive Approach The traditional prescriptive approach to engineering buildings and their required fire protection uses numerous assumed and 10 STRUCTURE magazine

Fig. 1. The “Standard Fire Curve” established in 1917 for cellulosic fires helped to define the prescriptive method of fire engineering and enabled standardized testing of FRM performance.

worst-case conditions, many of which do not realistically occur in an actual fire event. Therefore, many of these assumptions can be reconsidered when using today’s more advanced fire protection design methods.

Devised based on the development of the “Standard Fire Curve” (Fig. 1), which was established in the 1917 version of ASTM E119, the prescriptive method of fire engineering became a helpful basis for creating a perceived safe and generally conservative (i.e., deemed-tosatisfy) building fire protection solution. It offers a reproducible and comparable basis for testing FRMs, so manufacturers can compare product performance against the same test criteria and conditions.

This standardized curve and another version developed in the 1980s for hydrocarbon fuel sources (Fig. 2, as published in ASTM E1529 and UL1709) represent what are referenced in code as nominal fires, for use in prescriptive or standard fire-resistance design (SFRD), as referenced in ASCE's Manuals and Reports on Engineering Practice No. 138 (ASCE MOP 138).

Both curves show the typical temperature rise when materials burn, with a continued temperature increase over time in the case of cellulosic fires or a plateau at around 2,000F (1,100C) for hydrocarbon fires. However, no standard fire continues to burn indefinitely, nor at a consistently elevated temperature, meaning the two curves do not represent real fires. As a result, FRM thickness calculations

thicknesses being required, as a member that is not using all its strength to resist the structural demand has reserve resistance to fire. Therefore, if the resulting critical temperature value would exceed tabulated limits cited in a prescriptive design approach, the thickness of applied FRMs could be reduced when using the SFED approach. Of course, the opposite may be true, with select members requiring a greater FRM thickness. The goal is to optimize that thickness for the actual thermal load conditions for each steel member to ensure safety.

Reserve Strength Drives the Combined Approach Fig. 2. Established in the 1980s for hydrocarbon fuel sources such as gasoline and oil, this standardized fire curve shows a much faster rate of initial temperature development compared to cellulosic fires.

based solely on using these curves as part of the prescriptive building design method favor using more fireproofing material than may be needed.

Actual Data Drives the SFED Approach In North America, the advanced fire safety engineering design approach is referenced in the 2021 International Building Code (IBC) Section 703.2.3 , ANSI/AISC 360-22 (Appendix 4) as well as ASCE/SEI 7-22 (Appendix E). However, confusion often arises with the term “Performance-Based Structural Fire Design” (PBSFD), which encompasses all relevant advanced techniques, including those beyond structural steel protection. These processes include the use of design fires (also known as real fires), which are different than the nominal fire curves discussed earlier to test FRMs. In the context of a full holistic building review, the “Cardington Fire Tests” performed between 1994 and 1997 in the United Kingdom provided a greater understanding of how fire behaves in structures featuring composite steel beams with reinforced concrete floor slabs.

The tests helped fire engineers recognize they could reduce or even eliminate the application of FRMs on some steel members for economy without compromising safety. Instead, they can include FRMs on only the essential positions required to ensure structural stability for the building’s designated fire condition.

Further development of fire protection design standards has led to a calculated approach to SFED, as referenced in ASCE MOP 138.

In this context, individual structural steel members are evaluated in the standard fire condition, considering the actual structural design loading conditions defined by the structural engineer, not assumed loading conditions as in the prescriptive design method. This SFED approach more accurately reflects the structural behavior of the supporting steel members (for demand and capacity).

In this SFED-based approach, the goal is not to eliminate FRMs but rather tailor the exact level of FRM thickness to be applied to each steel member. The engineer of record (EoR) can calculate an individual member’s “critical temperature” at which it will begin to lose its ability to carry the actual applied structural design loading.

Of note, higher critical temperature values result in lower FRM

True fire protection cost balance optimization is possible when combining the prescriptive and SFED approaches to building design.

Calculations have shown that this optimization usually comes from having thicker steel members with thinner applied FRM thicknesses (Fig. 3). Following the SFED approach, specifiers would look to published data for steel member sizes to determine the appropriate FRM thicknesses and follow those guidelines. However, the combined approach to fire protection design would recognize there is additional “reserve strength” (assumed at about 20% reserve strength) baked into the thicker steel and therefore allow for further reductions of FRM thicknesses on individual steel members—while achieving the same intended level of fire protection. Of course, other considerations, such as the potentially larger size of the building's foundation to accommodate the heavier steel, will be part of the cost balance optimization and should also be calculated.

Combining the reserve strength revelation with structural fire engineering principles, which allow for the actual applied loading conditions, can help building owners and designers optimize designs for cost, efficiency, and sustainability or a combination of all three. It is recommended for building designers to work with FRM suppliers and engineers to finetune these details. The earliest collaboration possible during the building design process is always the preferred option and may be initiated from multiple directions.

Connecting the FRM suppliers with the main contractor, designer,

Fig. 3. The optimization of fire protection costs and benefits usually results from using thicker and heavier steel members with thinner applied FRM thicknesses.

AUGUST 2025

11

Table 1. Comparison of Overall Savings Realized When Switching From a Four-sided Exposed Column W10x22 (22lb/ft) to a W10x26 (26lb/ft) One When Using Different Fire Protection Approaches Variables

Baseline

Option 1: Prescriptive (Standard) Approach

Option 2: SFED Approach (assuming 0% reserve strength availability)

Option 3: Combined Approach (assuming 20% reserve strength availability)

Steel Member

W10x22 (22lb/ft)

W10x26 (26lb/ft)

W10x26 (26lb/ft)

W10x26 (26lb/ft)

Raw Steel Weight

–

+18%

+18%

+18%

No. of FRM Coats

3

3

2

2

Applied FRM Thickness

–

-13%

-17%

-22%

Overall Costs

–

-22%

-27%

-30%

fire engineer, and other key parties during that early window—and before specifications are finalized—will allow for greater optimization benefits.

The following simple examples demonstrate the benefits of the combined fire protection design approach: First, a W10x22 (22 pounds/foot) four-sided exposed column is the baseline, and it is compared to the prescriptive (standard) design method for 2-hour fire resistance when using a FIRETEX epoxy FRM from Sherwin-Williams. Table 1 compares this size column to a slightly heavier W10x26 (26 pounds/foot) four-sided exposed column. Each example assumes using the typical supply cost of material, application waste and

labor rates, and the market rate for bare steel.

This example demonstrates the drop in cost that’s enabled by the combined “help” from the thick steel’s inherent reserve strength. This leads to a reduced coating thickness and lower applied costs since fewer coatings and less labor are required.

The next example in Table 2 looks at tubular steel. Tubular FRM is notoriously costly, particularly when using epoxy FRMs. The table compares a common 8x8-inch square tube, again with a 2-hour epoxy FRM, when using various tube wall thicknesses of ¼-, 5/16-, 3/8- and ½-inch.

The examples again assume using the typical coating and steel material costs, as well as application waste and labor rates.

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Why to Avoid Extrapolation Optimizing FRM thicknesses should be done carefully based on published data, as testing to specific standards for specific steel member sizes and load conditions is required to define the proper applied thickness. It may be tempting for building designers to extrapolate data between two published data points when determining the appropriate FRM thickness for a steel member size that is not listed in a recognized fire test standard such as UL263

Table A. Multi-Temperature Assessment of Acceptable Steel Column Sizes for 1.5-Hour Fire Protection Prescriptive Critical Temperature Hp/A

W/D

240

0.56

270

0.50

300

0.45

330

0.41

350

0.38

370

0.36

390

0.35

400

0.34

410

0.33

900F

1,000F

W8x10

SFED Critical Temperature 1,100F

1,200F

W8x10

or ASTM E119. However, they should not calculate an FRM thickness value that falls between a slightly larger and slightly smaller listed steel member.

Extending this data set beyond what is listed—and has been proven via actual fire testing—can be dangerous, as the design then moves into unproven territory.

Example: To enable an advanced building design process, FRM manufacturers must independently perform a “multi-temperature assessment” (MTA) of coated steel members in a fire test using different FRM thicknesses and then publish that data.

In Table A, the gray shading indicates which steel member sizes the manufacturer has MTA data for—and therefore what FRM thickness values are permitted for different steel member sizes. It includes values for both a prescriptive critical temperature limit of 1,000F and an SFED limit of 1,200F for 1.5-hour fire protection.

For the extremely lightweight and slender profile shown—a W8x10 member, which in turn has a very low W/D ratio (0.33)—data does not exist for the FRM product at the assumed prescriptive critical temperature. Therefore, the designer should not extrapolate an increased value for the applied FRM thickness and use that size member. Without test data to consult, one cannot assume the extrapolated thickness would deliver the intended fire protection.

However, should the EoR be able to justify, due to the actual load demand of the steel member based on SFED principles, that a critical temperature of 1,200F is acceptable, data does exist at this higher temperature, so the W8x10 member can be used.

This example therefore shows a great benefit to using the SFED approach to tailor the level of fire protection individually, based on the member’s structural design requirements. It can also be used to legitimately extend the availability of smaller, more lightweight steel profiles. By tailoring the level of protection, the EoR may therefore be able to significantly lower the project cost—especially when considering the potential reduced FRM product and labor costs realized by using less material and applying fewer coats to reach the required thickness.

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Table 2. Comparison of Overall Savings Realized When Switching the Thickness of an 8x8-inch Square Tube From ¼-inch to 5/16-inch to 3/8-inch to ½-inch When Using Different Fire Protection Approaches Steel Member

¼-inch

5/16-inch

3/8-inch

½-inch

Variables

Baseline

Option 1: Prescriptive (Standard) Approach

Raw Steel Weight

–

+23%

+47%

+93%

No. of FRM Coats

3

3

3

2

Applied FRM Thickness (mils)

382*

349 (-9%)

324 (-15%)

275 (-28%)

Overall Costs

–

-21%

-34%

-53%

Variables

Baseline

Option 2: SFED Approach (assuming 0% reserve strength availability)

Raw Steel Weight

–

+23%

+47%

+93%

No. of FRM Coats

3

3

3

2

Applied FRM Thickness (mils)

372 (-3%)

338 (-12%)

312 (-18%)

252 (-34%)

Overall Costs

–

-23%

-36%

-55%

Variables

Baseline

Option 3: Combined Approach (assuming 25% reserve strength availability)

Raw Steel Weight

–

+23%

+47%

+93%

No. of FRM Coats

3

2

2

2

Applied FRM Thickness (mils)

331 (-13%)

298 (-22%)

266 (-30%)

215 (-44%)

Overall Costs

–

-38%

-44%

-59%

* All Applied FRM Thickness value and percentage reductions are based on the ¼-inch Baseline value for Option 1.

Crunching the Numbers As demonstrated, designers focused on reducing building costs will often arrive at the surprising conclusion that thicker steel can lead to a less expensive build. The counterintuitive result—based on using a combination of the prescriptive and calculated SFED building design approaches—stems from the material and labor costs associated with applying FRMs to protect the building’s structural integrity during a fire event. Fewer FRMs and labor are required with thicker steel, thereby reducing costs. Of course, a balance exists where it may become more costly or simply unfeasible to use thicker steel, in which case the building design can be optimized below that level of steel thickness.

To create a building design that optimizes time, costs and materials, software tools that can adjust costs on the fly based on different designs and different FRM thicknesses are necessary. Designers should work with coatings providers using software featuring integrated BIM and 3D electronic transfer technology to refine their designs, so the team can seamlessly synchronize a steel 3D model with the software and calculate coating thickness values and volumes along the way toward optimization. ■

14 STRUCTURE magazine

Full references are included in the online version of the article at STRUCTUREmag.org.

Bob Glendenning is a structural engineer and the retired Global Fire Engineering Manager for the Fire Engineering and Estimation Team at Sherwin-Williams Protective & Marine, which supports the specification of engineered fire-protection solutions based on simple and complex calculations, as well as inputs from Building Information Modeling (BIM) software. (bob.glendenning@sherwin.com) Nestor Iwankiw, Ph.D, PE, is a consultant for Jensen Hughes with extensive experience in various aspects of structural and fire protection engineering. He uses both analytical and experimental methods to develop practical solutions for unique issues in performance-based design, forensic investigations, new and existing construction problems, onsite inspections, engineering peer reviews and judgments, research development, and product acceptance for fire resistance. (niwankiw@jensenhughes.com)

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structural DESIGN

Indeterminate Beam Solutions by Finite Difference Methods

When applicable, finite difference methods are highly efficient and readily programmable, and they can be easily deployed in the field.

By Douglas La Prairie

I

n carrying out structural analysis, the engineer is engaged in solving the governing differential equations of structural members, directly or indirectly. The tools of daily practice, such as the black box of prepackaged software and closed-form solutions of beam tables, hide the calculus at the heart of structural calculations. Following graduation, many engineers are happy to relegate differential equations to the past, but neglecting the underpinning mathematics is at the peril of misunderstanding the fundamental behavior of the structures we analyze.

Most structural engineers are generally familiar with finite element methods, whereas finite difference methods are typically associated with problems in fluid and thermal mechanics. Basically, both are numerical methods that solve differential equations by discretizing the equations, dividing the problem domain into small segments to be solved piecewise. By these means a complicated continuous system is converted into numerous small, simpler systems. It transforms the governing differential equation into a series of algebraic equations for which we can use the techniques of linear and matrix algebra.

Finite difference and finite element differ in how they discretize a differential equation across a physical body. The finite difference method solves the differential equation as it applies to the actual continuous structure and so this method can only be used on bodies describable by a regular grid, such as plates or beams. The finite element method, on the other hand, is applicable to arbitrary shapes.

Using finite difference methods, the numerical solution is found by directly solving the differential equation, whereas finite element methods are iterative, solving for continuity and equilibrium at each element, indirectly solving differential equations. Largely owing to the physical limitation of finite difference methods, they have not gained wide acceptance for solving structural problems. However, where the physical structure allows the use of either finite difference or element methods, finite difference uses about a half to a third of the number of equations of finite element methods. Finite difference methods are also considerably simpler and readily programmed compared to finite element methods.

Beams and related members described as beams, such as strip footings and one-way slabs, are staples of the structural engineer’s practice.

Physically definable along a 1-D grid, beams are well suited to analysis by finite difference methods. The essence of finite difference formulas is the numerical approximation of derivatives, or in its most basic form in the context of beams, the slope. Consider the curve depicted in Figure 1.

To find the approximate slope at xi an obvious choice is to use socalled one-sided formulas:

dy yi + 1 - yi dx , m 16 STRUCTURE magazine

(1a)

Fig. 1. Numerical first derivative, or slope, approximations

and

dy yi - yi - 1 dx , m

(1b)

where λ is the spacing along the x-axis between adjacent y locations.

These are known as forward- and backward-difference formulas and have errors on the proportional to λ. Clearly a more accurate slope approximation is found by interpolating between xi+ λ and xi-λ, or averaging the one-sided approximations to get:

dy yi + 1 - yi - 1 dx , 2m

(2)

This is known as a central-difference formula and the error is proportional to λ2, which for small λ is much smaller than for the one-sided formulas. Similarly, we calculate the second derivative as:

d2 y y x - m - 2y x + y x + m 2 , dx m2

(3)

succinctly expressed in matrix form as:

d2 y 1 , 2 " y ,6C2@ dx2 m

(4)

where {y} = {yi-1 | yi | yi+1} and [C2] = [1 -2 1] is a matrix of differential coefficients related to the second derivative in Eq. (3). One can derive the coefficients for the central difference third and fourth derivatives as [0 -1 3 -3 1] and [1 -4 6 -4 1] corresponding to {y} = {yi-2 | yi-1 | yi | yi+1| yi+2}. Conveniently for those interested in applying finite difference methods without the task of derivation, tables of forward-, backward- and central-difference coefficients are readily available.

In addition to being relatively easy to program, finite difference methods applied to beam analysis are amenable to statically indeterminate and beam on elastic foundation problems. For practitioners the method lends itself to the development of generic solutions in spreadsheets

and

!V + = ! M +6C1@ (9b)

Fig. 2. Show is an example beam with a 19.7 inches ( 500mm) x7.9 inches ( 200mm) cross section and Young’s modulus of E = 11 GPa (1595 ksi), corresponding to oak.

or symbolic math packages, such as Excel or Mathcad, which can be deployed on-site, with no requirement for internet connection or specialized structural software. And the method is intelligible, so the user understands what is being done and why. Although the moment distribution (i.e., Hardy Cross) method offers similar benefits, an advantage of the finite difference method is that a suitably detailed generic model works for virtually any beam support condition without modification. Moreover, the finite difference solution returns not only the moments and reactions, as does moment distribution, but also the deflection, moment and shear diagrams.

Consider a simply supported beam with distributed load for which the bending moment M and load q are related by the differential equation:

d2 M = - q (5) dx2 In vector, or finite difference, form we can rearrange and express the moments along the beam:

! M + = m2 " q ,6C2@-1 (6)

Dividing the beam into, say, five segments, the coefficient matrix for the interior nodes is:

JK- 2 1 0 0 NO KK O KK 1 - 2 1 0 OOO (7) C2 = K KK 0 1 - 2 1 OOO KK O 0 0 1 - 2O L P with the bending moment at the first and last nodes equal to zero.

Thus, we have a simple solution to the bending moment distribution for the discretized beam. Using, for example, the Excel functions for matrix multiplication and inverse mmult() and minverse(), respectively, we quickly obtain bending moment values for the discretized points along the beam.

With the bending moments in hand approximate solutions for deflections and shears described by the differential equations:

EI

d2 y = - M (8a) dx2

and

dM V = dx (8b) are expressed in finite difference form as:

EI " y ,6C @ 2 = - ! M + (9a) m2

This illustrates the fundaments of the finite difference method in application to beams. The statics of statically determinate beams are unique, so knowing the bending moments at the supports give sufficient information to find the moments at internal points. For statically indeterminate, or hyperstatic, beams the statics are not unique. The recourse is to first find deflections using the known proportionality between the elastic curvature and bending.

The differential equation relating slope and thus deflection to loading is:

d4 y d2 M =- EI 4 =- q (10) dx dx2 which is expressed numerically in matrix form as:

EI

" y ,6C4@ q (11) m4

Where [C] is a diagonal matrix of finite difference fourth derivative coefficients. Rearranging to solve for y we get:

" y , = m " q ,6C4@-1 (12) EI 4

Using the relationship between deflection and moment from Eq. 11 we calculate the bending moment in vector form as:

!M + =

EI " y ,6C2@ (13) m2

where [C2] is the matrix of second derivative coefficients. Shear, from the relationship Eq. 9b is written in vector form as:

!V + =

EI ! M +6C1@ (14) m

Where [C1] is the matrix of central difference first derivative coefficients, [-1/2 0 1/2].

Ascribing a moment of inertia to each discretized beam segment allows one to account for the effects of varying cross section along the length of the beam and elastic foundations. This is achieved by defining the coefficient matrix as:

5C*? = ! I +5C? (15)

or, for the fourth derivative of Eq. 11, in long form as: kim 4 C 4*i = Ii - 1 ; - 2 ] Ii - 1 + Iig ; Ii - 1 + 4Ii + Ii + 1 + E ; - 2 ] Ii + Ii + 1g ; Ii + 1 (16)

Where ki is the modulus of subgrade reaction at the ith node in units of lbf/in3 or kN/m3, for example. From this point, finding bending and shear stresses are a simple matter of applying stress formulas familiar to structural engineers:

My v = I (17a) and

VQ x = It (17b) To satisfy boundary conditions at beam ends we modify the differential coefficients at the end and adjacent nodes from those of the AUGUST 2025

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interior nodes. Determination of coefficients for boundary conditions are well described elsewhere, so, the details are not belabored here. It is found that constraining deflection to zero is efficiently done by ascribing an arbitrarily high spring constant at support nodes, in variance from that proposed by Ghali and others (see references in the online article at www.structuremag.org).

While the differential equations and matrix operations of the foregoing might be dissuasive of the method, in practice it is straightforward.

Using symbolic math software such as Mathcad or a spreadsheet, the matrix operations are written exactly as stated previously.

To demonstrate the finite difference method, Figure 2 shows a beam 10 m (32.8 feet) long with a fixed end, pin supports and cantilever end with distributed and point loads.

In the model, the beam was divided into 100 segments, corresponding to 101 nodes spaced

at 0.1 m (4 inches). Using 100 segments allows load and support locations to be simply defined in terms of absolute distance or integer percentage along the beam length and produces results within 1% of exact values. The added overhead involved in creating a model with 100 divisions versus 10 is marginal; using symbolic math software there is no difference, using a spreadsheet there are simply more cells to drag and copy. As for execution time, the difference in overhead is measured in milliseconds, so there is virtually no efficiency gained in being parsimonious with the number of calculations.

For the beam of Figure 2 the plots of Figure 3 show numerical results with exact results superimposed.

Why create our own calculation routines rather than use off-the-shelf software? First, as an intellectual exercise we gain insight into the problem, the physical structure to be analyzed, in a way that plugging numbers into prepackaged

software does not allow. Understanding a problem better mitigates potential errors and produces more reliable results and interpretations of those results. Second, programmed in a spreadsheet, for example, the finite difference method, like moment distribution, can be used in the field or anywhere where a laptop or tablet computer with a spreadsheet is available.

Third, with ease we can augment our model for physical conditions that are not easily handled in pre-packaged software. Having included a term for subgrade modulus, as in Eq. 16, we obtain results for the beam on an elastic foundation, as might be done for a grade beam. Figure 4 shows the deflection results for the beam but now resting on soil with vertical stiffness of 5500 kN/m3, or about 20 lbf/in3.

Incomplete information and crude models compel structural designers to conservatism. Over-design with attendant extra costs is the normal Fig. 4. For the beam in Figure 2, deflection results are shown for an input soil spring of outcome. A familiar problem, especially in dealing with existing build5500 kN/m3 (20 lbf/in3) acting along the length. ings, is the retrofit of columns landing on slabs on grade. In the absence of ready models to quantify the behaviour of the slab-subgrade interaction the alternative is frequently excessive design and intervention that might have been obviated by more robust analytical tools. Good models are good economics.

The finite difference method can also account for change in section along beam length. For old wood framed buildings, loss of section because of rot and ill-placed plumbing lines is common. In the author’s practice for which old buildings are central, the finite difference beam model brings welcome convenience, speed and versatility. Further, the finite difference Save time and money with the world-leading method can be extended to add axial loads for structural design software. use in the analysis of beam-columns.

The above solution applies a method conventionally used in fluid and heat flow problems to Connection design at its best structural ones. Besides being practical and useful, the finite difference method illustrates yet another Steel anchorage workflow connection between engineering disciplines.

Supplement your strut and tie analysis Analogies between structures and hydrologiAny geometry, any loading, in minutes cal circuits, for instance, are long recognized.

Consider Daniel Bernoulli (1700-1782) who Intergates with your software conceived the eponymous ‘Bernoulli Equation’ fundamental to problems in fluid mechanics.

He is also credited with finding that an elastic beam bends so as to minimize strain energy and with developing the differential equations relating elastic bending to the deflection of a beam.

While we might not be Bernoullis, we can take inspiration from his example. Curiosity and a cross-disciplinary approach may reveal new solutions to well known problems. After all, we have the essential tool to translate from one field to another. Mathematics, the universal language of engineering and science, is a language in which we are all versed. ■

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Full references are included in the online version of the article at STRUCTUREmag.org.

Douglas La Prairie, ing., P. Eng., is Principal at Strake Engineering Ltd in St John’s, Newfoundland and also licensed in Quebec and British Columbia.

He specializes in timber, steel and masonry design.

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structural INTEGRITY

How Reliable Are Solar Piles?

Though targets for structural reliability have not yet been rigorously explored, reliability can be qualitatively examined in terms of four categories: safety, authority, ownership, and engineering.

By Kory Rankin, PE

I

n 2023, an estimated 15 million steel piles were installed for largescale solar fields in the U.S. Although the rapid installation and expansion of solar fields throughout the country may come as no surprise, this quantity of piles equates to roughly 1% of annual steel consumption in the U.S. with projected expansion for years to come.

Of further and increasing interest to the industry is the topic of structural reliability (i.e., safety or risk) for large-scale solar fields. It is easy to assume that traditional design methods imply acceptable reliability targets for these piles, but more accurate and useful reliability predictions may require much more scrutiny than commonly applied in practice to aid owners, engineers, AHJs, and others with rational, informed decisions.

Structural reliability is a building block of standard and code development in the U.S. Work here began in earnest in the 1970s and included large amounts of research, surveys, and models to develop a more rational method to address a problem facing structural engineers and owners: buildings built with different materials, structure types, and

controlled by different loads could have drastically different reliabilities when designed using the same code. Experts carefully, though often approximately, calibrated this new method within reason to existing design practices, which recognized the importance of human judgement in design. The method was formally proposed to the industry in 1980, which looked and felt very similar to what practitioners were used to, likely contributing to its acceptance. Findings and recommendations of the method were implemented in ANSI A58.1-82, followed by ASCE 7-88, and ASCE 7-02 presented the first published reliability targets that we commonly refer to as the basis LRFD. One of the key differentiators between LRFD and its ASD predecessor involves a consistent and interchangeable statistical framework for modeling, i.e., predicting, load and resistance probabilities. In simpler terms, carefully sorted data from weather events and calibrated load test results can be combined using statistics and engineering to predict the probability of virtually any type of applied load or member capacity. No method can exactly quantify or predict the uncertainty of all AUGUST 2025

21

Safety

Fig. 1. Life-safety targets according to ASCE 7 risk category.

design variables such as wind speed, yield strength, rebar diameter, or snow density, but the underlying approach of LRFD allows a direct comparison of results in terms of probability. For example, the failure probability of a compact steel beam subject to dead and live load can be computed by following the simple procedures listed in the ASCE 7 commentary or via some other method like a Monte Carlo Simulation (MCS) as used for the example in Figure 1. Setting both dead and live load factors to 1.0, a live-to-dead load ratio to 2.0, and an influence area to 1,800 ft2, either method shows that increasing the factor of safety (FS) from 2.5 to 3.0 improves the 50-year failure probability from about 0.04% to about 0.001%, respectively. This 40-fold reliability increase may or may not be worth the cost of increasing the FS by 20%, but at least such risk-based decisions can be considered when applying the building blocks of LRFD. The term structural reliability best describes the tools that underpin many if not most modern-day ASD and LRFD load combinations, although it is often lumped into the more generic term called Performance-Based Design or PBD. Regardless of design methods, all should aim to draw upon everimproving understanding of loads and resistances and importantly rely on rational, consensus-based assumptions. However, in the case of new materials or structure types, there is potential for widespread disagreement or misapplication of the basic principles of reliability analysis despite modern standards and codes providing guidance to avoid such situations. Steel piles used for solar fields are an interesting example of a new structure type, in terms of reliability, even though at first glance they look and feel no different than typical beam-columns or piles used in building applications worldwide. Though many similarities do exist between solar piles and structural building or bridge elements, closer examination reveals a very useful question: how reliable are solar piles?

At least in the U.S., no published, widely accepted reliability targets have been developed for solar field applications. ASCE 7 Tables 1.3-1 and 1.3-3 provide values used as the default for most practitioners, and IBC 2024 recently prescribed reliability targets for large-scale solar fields that reduce lifetime failure probability by around 5 times than historically used. These sources are an excellent starting point for stakeholders, but published targets are ideally prescribed based on research, surveys, and models, which to date are in very short supply for solar piles. Interest in solar pile design has grown significantly in the past decade as evidenced by the recent ASCE subcommittee on solar reliability, but solar piles likely have significant fluctuations in reliability using traditional design methods. Furthermore, optimal reliability targets for solar piles may vary from what U.S. engineers commonly use. Stakeholders may find the topic of reliability more useful if subdivided into safety, authority, ownership, and engineering.

22 STRUCTURE magazine

Safety is likely the easiest aspect of structural reliability to envision but possibly the most difficult to accurately define. A recent article highlights longstanding work reproduced in Melchers (1987) showcasing that typical structures can range from hundreds to thousands of times safer than many common activities like swimming, smoking, driving, etc. Madsen, Krenk, and Lind (2006) compare risk of death from a structure failing to “death from lightning [or] snake bite.” ASCE 7 section C1.5-1 provides guidance on how Risk Category typically relates to life safety. These examples portray life safety in terms of orders of magnitude that represents the large amount of uncertainty inherent in accurately predicting injury or death as the result of structural or non-structural damage. The beam example in Figure 1 confirms this wide range of uncertainty and reliability implied by prescriptive approaches. This effect is by design since a small but manageable number of load combinations and factors can only achieve reliability and thus safety targets in a broad or averaged fashion.

This topic is critically important for selecting reliability targets for solar piles that have historically been treated in the U.S. as Risk Category 1 structures based on their apparent similarities (in terms of life safety) to “agricultural facilities” (IBC Table 1604.5) and “other structures that represent low risk to human life” (ASCE 7 Table 1.5-1). Skourup, 2023, provides a detailed examination of solar structure reliability targets and highlights the potential impacts to industry including increased costs and slower transition to solar if suboptimal targets are selected. Safety and by extension reliability targets in ASCE 7 were developed via the rigorous, rational, and collective works of experts. It seems reasonable then that stakeholders may wish to explore and even predict solar asset reliability to validate or improve upon targets implied by current practice. Those interested in such improvements will eventually notice how gravity loads are largely independent of the Risk Category selected for a given project, though this impact is often minor given the large wind-to-dead load ratios that can dominate piles. Additionally, ASCE 7 targets are explicitly not calibrated for structural deterioration (corrosion) that further complicates structural reliability predictions. A generally conservative treatment for corrosion in design involves applying a uniform section loss, i.e., strength and stiffness reduction, as if some of the steel cross-section was never there in the first place. Using reliability or performance-based approaches, such as a time-varying MCS as hinted at within the ASCE 7 commentary, reliability can be predicted consistently and accurately for any year of service, including the decade or so that zinc-coated piles may undergo no corrosion at all. Extra rigor can be a worthy expense when specifying a single pile type 50,000 or more times across a large solar field. Curious individuals may review Melchers and Beck, 2018 (3rd edition) or Straub et al., 2019 for more details on reliability of deteriorating structures.

Authority Authorities having jurisdiction (AHJ) for building structures are well established in the form of officials with requisite knowledge and experience with engineering as well as local knowledge and needs of the communities they serve. AHJs have highly variable involvement in solar field projects across the country, in large part due to the apparent (and very real) differences between solar piles and typical building designs and materials. The IBC defines a building official as the “officer or other designated authority charged with administration and enforcement of this code,” but very few provisions administer or enforce specific to solar field structures. It wasn’t until around 2010 that the U.S. had installed 1GW of solar fields, which increased to over 200GW as of 2022. This expansion is extremely rapid, especially since many states lag one or two code cycles behind the IBC.

As of January 2024, about 25% of states had not yet updated from IBC 2015, putting them nearly a decade behind the latest edition. AHJs might appreciate more detailed solar-specific provisions to enforce and interpret for their communities, especially as PBD and other riskbased methods gain popularity. Ideally such provisions would be developed using the same reliability-based and consensus-driven framework from which LRFD is derived, especially considering the rise in solar construction has amounted to approximately 1,000,000 tons of solar piles installed in 2023 alone.

engineers for solar piles are in a unique position. Their roles might include helping craft proposal or bid language to align with owner intent and expectations or providing partial or preliminary designs or reviews. Banks and insurers often hire engineers to assess both risk and project asset value over time. It comes as no surprise that insurance-based engineering decisions must consider the likelihood and impacts of damaging events like floods, hurricanes, and earthquakes; however, the solar industry likely and often overestimates and underestimates unique solar risks given that few engineers have direct experience with structural reliability

methods and lack widely available datasets of solar-specific test or design data. Large initial imperfections (install tolerances), time-varying corrosion rates, and dynamic response sensitivity are a few unique variables that come to mind, many of which are proprietary. To illustrate, design equations for building columns generally account for a vertical tolerance around L/500 while beam equations account for about 1 degree of twist per AISC 360 commentary. Flexural buckling and lateral-torsional buckling capacities are influenced by these variables, but the assumptions used in building design can vary significantly from solar piles, which often have

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Solar field owners and operators have numerous short and long-term stakeholders to consider, including their customers (private or public), shareholders, developers, government agencies, and various partners throughout the plant service life. They often must weigh competing interests of these parties against their own risk appetite, their design and brand philosophy, and financial projections that are tied to, among other things, an increasingly complex national electrical grid. The lack of rigorous and rational industry guidance on reliability targets for solar fields is a difficult challenge for owners to consider let alone manage when faced with so many other pressing considerations. Owners very commonly rely on AHJs, designated engineering firms, and third party reviews to manage the technical aspects of solar pile design, which in practice can have variable impacts to reliability based on the lack of industry-wide investigation. Contracts are often signed with little to no specific provisions for structural reliability beyond a selected Risk Category per ASCE or IBC. Also, owners generally specify a 25- to 35-year service life, much less than the 50-year reference period used for ASCE and IBC reliability target calibration. These factors and more can introduce significant variability in the specified (implied) and expected (desired) reliability owners may truly desire to align with the various needs of themselves and their stakeholders.

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Engineering In many cases, engineers appear to be both the first and the last lines of defense for solar pile design in terms of reliability. Since AHJs have very few code provisions to administer and enforce, and since owners often rely on designated or third-party engineers to achieve an approximate and implied reliability from documents calibrated for building structures,

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vertical tolerances around L/30 for a pile with 5 feet of reveal and initial twist tolerances around 2 or 3 degrees (or more).

Engineers can influence the planning and design phases of a project, and in many cases a project’s construction and projected life cycle. Generally, engineers make decisions and recommendations based on codes, standards, design guides, etc. that are based on peer-reviewed data, analysis, and expert consensus, which is mostly the case for building structures but is generally not the case for solar fields. Additionally, engineers are expected to exercise professional judgement, which is a wonderfully creative responsibility, but one that can come with a significant degree of uncertainty Fig. 2. Solar pile nomenclature for initial imperfections. and variability when it is a very large portion of the design as can be the case for solar piles.

Solar pile reliability should be explored in more detail as evidenced by the ASCE subcommittee for solar reliability as well as practitioners outside the Full references are included in the online version of the article U.S. The key points here are meant to provide stakeholders with general at STRUCTUREmag.org. but useful topics to consider when planning, designing, maintaining, and ultimately upgrading or replacing solar piles. For now, it seems unlikely that optimal decisions are within the industry’s current reach regarding annual and lifetime risk, maintenance, and repair costs without a deeper dive into Kory Rankin is a structural engineer with Kiewit. He has worked as both a client solar reliability. Structural practitioners have attempted to calibrate and and consultant for a wide range of power delivery and power generation collaborate as best they can over the decades as stakeholder needs change structures across the country with growing interest in performance-based design and as industries grow, change, or form anew. Many references and adjacent and structural reliability. (kory.rankin@kiewit.com) industries have information to draw upon to help guide the solar industry in terms of reliability and risk assessment, which over time seem likely to lead to more optimal and consistent solutions for all. ■ ADVERTISEMENT–For Advertiser Information, visit STRUCTUREmag.org

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Your vision. Our purpose.

The Structural Genome of Sphere An exploration of the structural systems of the new Las Vegas icon.

By Cawsie Jijina, PE, Steve Reichwein, PE, SE, and Sindi Krasta

26 STRUCTURE magazine

L

as Vegas’s Sphere, the next-generation entertainment venue located just east of the Strip, officially opened at the end of September 2023. A 516-foot-diameter semi-spherical building rising 366 feet above ground, Sphere encloses a bowl-shaped theater for approximately 18,000 guests, seated beneath a domed roof and suspended media plane. It is currently the largest spherical structure in the world (Fig. 1).

Overview of the Structural Systems The overall structure of the venue has five distinct parts: 1. A foundation system composed of drilled shaft piles socketed into cast-in-place concrete caps interconnected by a grid of grade/tie beams (where necessary); the piles were designed as fixed-head for lateral resistance.

2. The stadia bowl and main venue superstructure stabilized by four cast-in-place concrete shear wall cores and a proscenium shear wall.

3. The dome roof arch system (which hangs the immersive LED display plane).

4. A hung grillage system (supported off the dome roof steel frame and used to support the media plane, catwalk system, and A/V equipment).

5. The exterior Geosphere.

Although labeled as distinct systems, these structural systems act together to form a cohesive, balanced, elegant, and efficient superstructure, which significantly benefits the overall design and performance of the venue.

Fig. 1. The various structural components of Sphere are identified.

AUGUST 2025

27

Fig. 2. A pile-supported mat foundation is constructed at a shear wall core.

Foundations Sphere’s foundation is comprised of 24-inch diameter auger cast-in-place (ACIP) piles supporting cast-in-place concrete pile caps and tie beams. These piles extend up to 100 feet down into the bearing stratum (generally comprised of dense sand) to provide the necessary support for the massive structure, ensuring stability and load distribution throughout with minimal potential for differential settlement. The piles and foundation elements are arranged in two closely spaced rings at the perimeter; the outer ring supports both the outer venue columns and the Geosphere base, while the inner ring supports the inner column of the venue’s ring of paired columns. An array of individual pile caps supports the seating bowl and concourses.

Pile supported concrete mats support the shear wall cores, providing additional stability and resistance for overturning moments and shears induced by lateral loads; the mats are generally 4-feet deep (Fig. 2).

The Venue Sphere’s interior is designed to offer an immersive theater experience for up to approximately 18,000 guests. The venue features a horseshoe-shaped seating bowl beneath the dome roof and suspended media plane. From the ground to the fifth level, the building is framed with concrete slabs, beams, and columns, providing a robust and durable base. Above the fifth level, structural steel is used to frame the building, allowing for greater construction speed and flexibility.

The seating is supported by raker beams carrying precast concrete stadia, ensuring that the audience has a stable and secure viewing 28 STRUCTURE magazine

Fig. 3. Shown is an analytical structural model of the lateral force resisting system of the venue.

Fig. 4. Shown is an analytical model of the dome roof.

experience. Two 18-foot-deep composite concrete and steel transfer girders, similar to “Speed Core” (shear wall system comprised of concrete-filled composite steel plates) but horizontal, span the proscenium over the stage to create a column-free opening for versatility, while also minimizing differential settlement for the six-dome roof columns which transfer at this elevation.

Four concrete shear wall cores are coupled by diaphragm rings at each level to provide uniform lateral support for the entire venue (Fig. 3). The concourses, which encircle the seating to provide access, collect lateral loads and deliver them to the diaphragm rings which then deliver all the loading into the cores and stage walls. This integrated approach to structural design ensures that the venue can handle the stresses associated with large crowds and dynamic performances.

Dome Roof Sphere’s dome roof is a 440-ft. diameter steelframed structure designed for efficiency and function (Fig. 4). It provides excellent load-carrying capacity and adequate stiffness, enabling the precise placement of the media plane's LED tiles (for discussion, see further on in article).

The dome roof 's design optimizes its depth and the number of circumferential rings, ensuring that it can support the significant weight of the roof and media plane.

Pairs of adjacent half-arches, intermediate framing, and temporary tie rods were prefabricated into units and lifted into place between the perimeter columns and a temporary center shoring tower (Fig. 5). This modular approach allowed for efficient construction and ensured that each component was accurately positioned, using only one shoring tower. A 10-inch-thick

Fig. 5. This model shows the various components of half arches used for the modular construction of Sphere’s dome roof.

(approximately 330 total) were used during erection to adjust elevations of each hanger and reduce as-built out-of-plane-tolerances; the hangers connected to these jacks supports the primary structural frame of the media plane.

Although locked off, the jacks were permanently left in place to make future adjustments, if necessary. Secondary framing with attachment clips allowed for precise positioning of the LED tiles, achieving a spherical surface within an eighth inch of theoretical. This meticulous approach to construction ensured that the media plane's high-resolution display would be perfectly aligned, providing an unparalleled visual experience for guests. The combination of precise shape and 16K resolution results in visual presentations that cannot be discerned from reality, immersing visitors in a truly unique and captivating environment.

Geosphere

Fig. 6. Isometric cut of the various layers of the media plane support.

concrete slab on metal deck, placed by shotcreting where steeply sloped, offers permanent stability and acoustic damping. The flat roof at the base of the dome roof acts as a tension ring to resist the dome’s thrust; only vertical forces are delivered to the supporting columns under gravity load. The connections to the columns allow the dome roof to move radially without restraint, while circumferential restraint is locked in order to deliver lateral loads, mainly seismic loads, to the venue diaphragm ring and eventually into the concrete cores and walls.

All field connections of the dome were bolted —not field welded. Fabrication and erection tolerances were expected to be on the order of only three inches over the 400-foot long span of the dome roof (1/800); however, the steel contractor was able to deliver the dome to within about one inch of ideal geometry.

Nonetheless, the 160,000 square-foot media plane—whose high-resolution LED display is key to the immersive experience—required even smaller tolerances. By layering in a hanging grillage structure, and several media plane structural layers, the tolerance of the media plane LED tiles (fractions of an inch) was able to be achieved.

Grillage and Media Plane The media plane is a key feature of Sphere, consisting of a high-resolution LED display that creates an immersive visual experience. The grillage system, hanging solely from the dome, supports rigging and catwalks and provides a transition from the dome roof to the media plane configuration (Fig. 6). Hydraulic jacks

The Geosphere is the venue's outer latticed grid shell composed of steel pipe sections and cast steel connecting nodes. It is covered with 580,000 sq. ft. of programmable LED lighting, presenting stunning visual displays. The Geosphere features a hybrid solution of 14 horizontal continuous ring members and 32 pairs of crisscrossing diagonal geodesic elements, continuous between the base and a ring near the crown (Fig. 7). The oculus (or apex ring), framed radially at the topmost part, adds to the structural stability and visual lightness of the design.

Starting from a traditional geodesic arrangement (icosahedron based spherical model), structural engineers employed parametric design and optimization to determine the lightest tessellation possible with pieces that could be easily shipped and erected. The design team, working in collaboration with the steel contractor, studied several alternate configurations that would facilitate fabrication and erection and finally arrived at the hybrid solution that was eventually built (Fig. 8). Extensive analyses revealed that fabricated nodes presented daunting constructability issues, mainly due to large, multi-pass welds and the potential for heat distortion.

Cast steel nodes, on the other hand, offered significant advantages starting with material optimization (Fig. 9). Without the need for stiffener plates and other appurtenances, the cast nodes resulted in a 40 percent reduction in weight compared to built-up nodes.

Furthermore, the cast nodes have only a quarter of the surface area, which afforded significant savings in the Geosphere’s three-part, highperformance weatherproof coating. All the AUGUST 2025

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castings are essentially identical, eliminating concerns about fabrication tolerances. Grid shell structures are sensitive to angular variations at the nodes and length variations of the members.

The geometry of the cast nodes, with computer numerical control (CNC) machining of the flanges, was very precise—with an order of magnitude smaller than for fabricated nodes.

Bolted end-plate connections allowed the use of shims to accommodate variations in the length of the members, which were fabricated slightly short by design. The system provided greater control of the overall geometry during erection, which reduced construction risk by simplifying erection and minimizing the potential for outof-tolerance errors, resulting in further cost and schedule savings.

Fig. 7. The Geosphere features a hybrid solution of 14 horizontal continuous ring members and 32 pairs of crisscrossing diagonal geodesic elements.

Parametric Design and Structural Optimization Parametric analysis played a crucial role in the structural design and engineering of Sphere. It helped address complex geometric challenges, ensuring structural integrity, optimizing aesthetics, and improving efficiency.

Parametric analysis involves running simulations using structural and architectural design parameters and systematically changing these parameters to evaluate their impact on the structure. This approach empowers structural engineers to tackle uncertainties and challenges involved in engineering complex designs.

Using computational algorithms, engineers optimized various sphere sizes concerning tessellations of the icosahedron. Conversations regarding fabrication and erection led to a more constructable spherical geometry, the Geosphere, which balanced costs, economies of scale, constructability, and tolerances.

The process involved several steps: • Defining Parameters: Identifying key parameters like radius, base, gravitational and environmental loads, number of rings, and number of diagonals.

• Creating a Model: Developing a digital model incorporating various parameters using specialized software like Rhino with Grasshopper, Autodesk Revit, and other parametric design tools.

• Running Simulations: Performing structural simulations to see how changing each parameter affected the design.

30 STRUCTURE magazine

Fig. 8. Parametric Comparison of Spherical Models

•

•

Analyzing Results: Evaluating simulation results to determine the best values for aesthetics, structural integrity, costs, and other criteria.

Iterating: Refining the design by iterating through different combinations of parameters and continually improving the model based on analysis results.

Engineering and Selection of Structural Steel Castings The engineering and selection of structural steel castings for Sphere were driven by the need to address complex geometry, tight tolerances,

and load demands. The design process began with parametric modeling followed by more advanced 3D finite element analyses (FEA) of the superstructure but was intertwined with hand sketching to determine optimal shapes for the nodes. Early collaboration between design and fabrication teams ensured the feasibility of castings versus fabricated nodes.

Key challenges for fabrication and erection of the nodes included: • Complex Geometry and Extremely Tight Tolerances: Accurate and precise connections between elements, with tolerances in fractions of an inch.

• Structural Load Demand and Distribution: Exceptional load-carrying

Fig. 9. Comparison of cast nodes versus fabricated nodes. (Graphic courtesy of W&W and CastConnex.)

Construction Challenges and Solutions

Fig.10. The stability provided by the partially completed ring meant construction did not require shoring and needed minimal temporary support.

capacity, especially given that six or more members often met at one three-dimensional node.

• Durability: Components needed to withstand environmental forces and heavy operational loads over the structure’s lifespan.

The team chose high-performance steel alloys capable of meeting strength and durability criteria while allowing for precision casting. This kept the structural weight of the casting to a minimum and matched the main member thickness.

Before full-scale production, prototypes were created and subjected to rigorous testing, including stress analysis and fatigue tests.

This iterative process ensured the castings met design specifications, structural requirements, safety standards, and strict tolerances. Testing included simulating the environmental conditions and operational loads to ensure the castings' durability and performance.

Installing castings required precise alignment and coordination between fabricators, contractors, and the design team. Digital modeling tools, such as Building Information Modeling (BIM) software like Revit and Tekla, played a vital role in streamlining this process. The integration of castings into the construction process ensured that the structural components aligned with both architectural and structural goals.

Erection planning and construction of the Sphere faced several challenges that were addressed through innovative design, early and thorough collaborations, and engineering solutions. The Geosphere's geometry included a full horizontal ring of steel at each latitude, providing temporary stability without the need for shoring and minimizing temporary support during construction (Fig. 10).

A staged construction analysis ensured minimal temporary shoring needed for geometry control. The Geosphere’s goal was to be within 2 inches of target geometry and out-of-tolerance between any two adjacent nodes to be less than 1/500. Only a handful of conditions exceeded these tolerances and were carefully reviewed for structural concerns. The staged construction analysis informed the erection sequence for the completely self-supporting Geosphere. The first ring cantilevered from the foundation, and once fully bolted, it and each succeeding ring was able to support the framing of the next, up to the oculus (apex), which was erected in a single unit (Fig. 11).

With essentially no need for shoring, the overall cost was significantly reduced. The Geosphere is completely self-supporting and isolated from the rest of the building; it rests on its own ring of pile caps and grade beams.

Diurnal temperature ranges are as high as 100 degrees in the summer and vary from one side AUGUST 2025

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of the structure to the other. Isolation allows the Geosphere to expand and contract—up to 2 inches in or out—without restraint from the venue within, which is insulated and less thermally variable.

The Geosphere base was anchored to the pile cap with anchor bolts and a shear key, supporting diagonal pipes for the subsequent latitudinal rings. The compression oculus was installed as one single piece, marking the topping-out milestone for the primary structure.

The final step was erecting the steel supporting the LED light bars, transforming the structure into a spherical screen. The trellis had a panelized design and was erected quickly to meet the schedule; this was accomplished by collecting up-to-the-minute survey data and using the data to pre-deform the panels prior to craning and setting (Fig. 12).

Collaborative Efforts Early collaboration among stakeholders was instrumental in guaranteeing success.

Integrating casting expertise into the design process from the start ensured that components aligned with architectural, structural, and construction goals. Collaboration among the design-construct team, Severud Associates, Populous (the Architect), W&W | AFCO Steel (steel fabricator and erector), CastConnex (casting designer and supplier), SDL (erection engineer), and MJ Dean (GC/CIP Concrete Contractor) allowed for precise integration of structural components and optimized the structural design.

Advanced modeling and analysis tools were essential for designing and testing castings, especially for complex geometries. Leveraging technology enabled precise integration of structural components and optimization of design and performance.

Balancing performance and cost were crucial in ensuring the project's success while meeting budget constraints. Sphere’s success underscores the growing role of castings in structural steel design, highlighting the importance of collaboration and innovation in achieving complex geometries with extremely tight tolerances.

During construction, Severud Associates had a full-time onsite presence to assist with immediate action to any construction issues as they arose. This involved working closely with various contractors to solve issues as quickly as possible, ensuring the project continued to move along smoothly. This hands-on approach allowed for rapid problem-solving and maintained the project's momentum, adhering to the planned schedule and quality standards.

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Fig. 11. The first pieces of the Geosphere—the cantilevered base—are set.

Fig. 12. Trellis panels were pre-deformed with racking frames prior to erection.

Summary and Conclusion The structural engineering of Sphere in Las Vegas demonstrates the power of computational design and parametric analysis in tackling complex designs. By leveraging software tools like Grasshopper and Dynamo, engineers were able to optimize design alternatives, enhance quality control processes and ensure accurate data management throughout the design and construction of the project. The lessons learned from Sphere’s structural design may inform future endeavors and drive innovation in structural engineering.

The use of structural steel castings addressed key challenges of complex geometry, tight tolerances, and load demands, ensuring durability and performance. Rigorous testing and precise alignment during installation ensured

the castings met design specifications and structural requirements.

The successful collaboration between the design team, owner, and construction team highlights the importance of integrating everyone’s experience and expertise into the design process from the start. Leveraging advanced modeling and analysis tools enabled precise integration of structural components and optimized Sphere’s structural integrity. ■ Cawsie Jijina, PE is a principal at Severud Associates and served as the principal in charge of the structural design for Sphere.

Steve Reichwien, PE, SE is a principal at Severud Associates and served as the director of structural design for Sphere.

Sindi Krasta is an engineer at Severud Associates.

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Elevating the Connection Between People, Animals, and the Natural World

A focus on adaptive reuse transforms a decommissioned monorail structure into the longest elevated pedestrian loop in the world, the Treetop Trail at the Minnesota Zoo.

By Thomas Root, PE, Craig Huhtala, PE, and Will McDevitt, SE, PE

N

ature encapsulates the 485-acre Minnesota Zoo, the fifth largest in the U.S. Opened to the public in 1979, the Minnesota Zoo’s original monorail traversed a 1.25-mile loop through the landscape, within forest, above lakes and wetlands, and amongst zoo guests, expansive animal exhibits, and natural wildlife. The original structure for the monorail track was constructed of weathering steel consisting of a built-up box member spanning between wide flange columns that are embedded in concrete drilled pier foundations. This steel track weaved its way throughout the Minnesota Zoo, providing views to zoo exhibits and accessing undeveloped, forested parts of the campus that make up over half the property.

The zoo stopped monorail operations due to reduced demand, obsolescent components, and ultimately unsustainable operating costs. After decades of natural encroachment, nearby new development, and use as a support for modern data utilities, disassembling the enormous structure merely to eliminate an unsightly relic was unfavorable. The Minnesota Zoo’s mission to connect people, animals, and the natural world to save wildlife helped inspire the concept to reuse the existing structure as a platform for a walkway through the zoo and the natural

36 STRUCTURE magazine

world; the vision of the Treetop Trail was born.

The Minnesota Zoo recognized that reuse of the existing structure would guide decision making. A creative team was employed including structural design engineer Buro Happold, engineer of record Meyer, Borgman, and Johnson, and the Minnesota Zoo’s Director of Planning & Construction who is also an experienced structural engineer. The dynamic team, well versed in the intricacies of structure, was pivotal to the success of the Treetop Trail.

Access to the 1.25-miles of project site is complex.

Spread between sensitive natural settings, local endangered wildlife, and dense campus development, the trail was only feasible as a reuse project where the site below could be minimally disturbed. Exhibits were required to remain occupied, all public areas were to remain open, and seasonal campus events had to be accommodated without disruption. The execution had to be respectful of the zoological animals’ home. Noise, dust, and vibrations affect feeding, stress, and natural breeding cycles in different ways for each species, so it was necessary to sequence construction to minimize impact.

Early in design, the project team recognized the need to limit disruptive and costly foundation interventions and minimize structural strengthening. To do this, the

Steps lead to an entrance of the Treetop Trail. (Photo by Gaffer Photography) AUGUST 2025

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structural team identified five variables of the typical trail section that were tuned to produce the efficient final scheme: • Self-weight of the trail system.

• Trail width.

• Required design live load.

• Guard rail height.

• Guard rail porosity.

Multiple structural systems were considered for the trail. A cast-in-place concrete option was ruled out due to complexities with placing concrete along the length of the trail. A precast concrete option was studied. The selfweight of this system resulted in significant strengthening of the existing structure and foundations, so it was eliminated. A fiberreinforced plastic system was considered due to its high-strength, lightweight, and corrosion resistant characteristics. This system was eliminated due to the limited number of suppliers, challenges with future component repairs and replacement, and the high embodied carbon footprint of the product.

Ultimately a weathering grade structural steel system with a secondary decking was selected. This approach was lightweight, low in embodied carbon, and resulted in decreased maintenance and life cycle costs for the Minnesota Zoo. The Treetop Trail is not defined in either the International Building Code (IBC) or the American Association of State Highway and Transportation Officials Bridge Design Specifications (AASHTO). The structural team, in agreement with the local building code official, determined that the structure would be designed in accordance with the IBC and the American Society of Civil Engineers (ASCE) 7 Minimum Design Loads and Associated Criteria for Buildings or Other Structures (ASCE 7). AASHTO was referenced throughout the design for comparative purposes only.

The main walkway areas of the trail were designed as “walkways and elevated platforms” with a live load of 60 pounds per square foot, and assembly and exit ramp areas were designed with a live load of 100 pounds per square foot per ASCE 7. With the structural system and live loading requirements determined, the structural team tuned the walkway width and guardrail system with the design team, settling on a typical trail width of 8 feet. At specific locations along the trail, 12-foot-wide “bump outs” were included to create special moments in the architectural design.

Despite limited existing drawings, a schedule of as-built foundation depths and typical rail cross sections were critical in evaluating the existing trail structure. Extensive field surveys were conducted to verify bearing conditions, identifying several unique and undocumented details. In 38 STRUCTURE magazine

addition to the field survey, a full condition assessment of the existing steel and welds was conducted, including visual and non-destructive testing. Welds were repaired where necessary prior to construction of the trail structure.

Structural analysis of the monorail structure was completed in SAP2000. To accurately approximate behavior, foundation boundary conditions were modeled as lateral translation and rotational springs based on a pier analysis done collaboratively with the project geotechnical engineers. Slide bearing conditions at the rail to column connections were modeled as link elements with non-linear springs to reflect a 0.10 friction coefficient prior to engaging the full column stiffnesses.

Although the structure was consistently designed with IBC as the governing code for load determination, the continuity and curving nature of the track required consideration of both longitudinal and transverse wind loads occurring simultaneously at different points along the trail. AASHTO wind skew coefficients were used as a basis for determining these components in conjunction with ASCE 7 wind pressures. The trail structure was designed as a Solid Freestanding Sign, and the railing was designed as an Open Sign. This approach was compared with AASHTO loading and determined to be a similar and reasonable solution.

The increased wind load of the reinforced structure and railing required additional lateral capacity. Initial designs focusing on strengthening the original lateral system required a significant number of columns and foundations to be reinforced. To avoid expensive and disruptive foundation retrofits, the design team explored and selected an approach utilizing eight new braced frames and selective column reinforcement. The braced frames were intentionally located to minimize additional thermal restraint in the system.

The existing structure was constructed as a continuous beam with no expansion joints, resulting in the potential for significant thermal movement. Expansion and contraction of the existing monorail beam was anticipated in analysis and observed as the structure was exposed to the harsh extremes of Minnesota’s frigid winters and hot summers. During the design phase, project team members monitored the existing monorail beam on the hottest and coldest days of the year, observing over 7 inches of movement of the monorail beam relative to bearing conditions, closely reflecting displacements predicted from the analytical model. Analysis of the structure focused on understanding existing thermal movements and minimizing additional restraint from reinforcement schemes. Worn existing bearing pads at slip connections were replaced with

A modular walkway section is placed on the existing monorail beam for transport to its final location.

(Photo by PCL Construction)

View from the Treetop Trail. (Photo by Gaffer Photography)

Aerial image showcasing the trail winding through the natural forest setting. (Photo by Gaffer Photography)

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A 12-foot-wide "bump out" at the Reflection Overlook. (Photo by Gaffer Photography)

new material to refresh the original movement joints. This approach avoided more costly interventions, such as foundation reinforcements and new expansion joints.

In addition to extensive live load patterning and eight wind load directions, positive and negative temperature loads were considered, resulting in over 600 load combinations.

The limited self-weight and continuity of the structure highlighted vibration as a primary consideration in the early design phase. With limited opportunity for adding damping given the existing foundation constraints, the design team focused on understanding the behavior and working with the Minnesota Zoo to set expectations. While the trail may not be able to host 5k Fun Runs, acceleration due to walking excitations falls within the 5.0%g limit recommended by the American Institute of Steel Construction (AISC) Design Guide 11 for outdoor pedestrian bridges.

The design team collaborated early with the project general contractor, PCL Construction (PCL), to develop a modular construction approach for the typical trail sections. Approximately 420, 20-foot-long modules consisting of reinforcement, cantilevered walkway sections, and deck support angles were shop fabricated and shipped to the site.

Even with the modular approach, active animal habitats and natural landscapes limited erection access to the trail. PCL developed a unique mobile erection platform to safely construct the trail using an existing monorail maintenance vehicle and a new trail vehicle specially made for construction. Construction was completed in two full passes along the trail loop. The first pass inspected and repaired existing welds, added reinforcement, and relocated utilities. The second pass pushed modular trail sections out from discrete access points along the trail.

The steel sections were welded to the existing built-up box beam, and 40 STRUCTURE magazine

the composite decking made of recycled milk cartons was installed to complete the trail.

The structural design of the Treetop Trail required a deep understanding of the conditions and performance of the existing monorail track system, and creative intervention strategies to reinforce the structure while maintaining much of the original structural behavior. Intense collaboration with the full project team was required to meet the needs of the program, Snow Kreilich Architects’ design requirements, and the construction of the trail. The true success of the Treetop Trail, however, lies in its support of the Minnesota Zoo’s mission: “To connect people, animals, and the natural world to save wildlife.” This success extends beyond the technical accomplishments of the project, to the creation of a revitalized way to experience the Minnesota Zoo. ■

Thomas Root, PE (MN) is the Director of Planning & Construction at the Minnesota Zoo. Root directs and supports the activities of planning, construction, audio/visual systems, and exhibits throughout the Zoo with the goal of maintaining and improving the facility’s infrastructure, sustainability, functionality, and appearance.

Craig Huhtala, PE (MN), is a structural engineer at Meyer Borgman Johnson in Minneapolis, MN, who has worked extensively on existing building analysis and adaptive reuse projects, in addition to leading projects in the public, technology, and aviation sectors.

Will McDevitt, SE, PE, is an Associate structural engineer at Buro Happold in Chicago, IL. He is responsible for leading projects throughout the US and internationally and has worked on numerous new construction and adaptive reuse projects.

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Fig. 1. The expansion to the University of Pittsburgh Medical Center Presbyterian will create the city’s largest hospital when complete.

Tight Site, Bright Future: UPMC’s Presbyterian Expansion The hospital project integrated a street-level loading dock within the building's footprint and implemented a cantilever over the courtyard.

A

By Ben Shock, PE and Jeffrey Millmann, PE

striking new presence has risen at the intersection of Fifth Avenue and De Soto Street in Pittsburgh, Pennsylvania’s Oakland neighborhood: its dramatic cantilevers and stylish glass facade a testament to innovative design. The addition to the University of Pittsburgh Medical Center (UPMC) Presbyterian is the largest healthcare project in the state and when complete, will create the city’s largest hospital, offering 1.2 million square feet and 636 private patient rooms. The structural design strategically incorporates a 22-story steel-framed bed tower, a 450-car post-tensioned concrete parking garage featuring a rooftop terrace, all necessary mechanical and hospital support areas, and an inviting public space dubbed the “Lifestyle Village.” The congested, steeply sloping urban site presented numerous engineering challenges, most notably the

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seamless integration of a street-level loading dock within the building's footprint and the implementation of a dramatic cantilever above the sidewalk-level urban courtyard.

Divergent Grids Site constraints mandated an internal loading dock with sufficient column-free space for semi-trucks to maneuver before exiting. Access to the loading dock from the narrow and steeply sloping De Soto Street made reversing either into or out of the loading dock infeasible. The structural layout was further complicated by the central placement of the parking garage directly beneath the bed tower addition (Fig. 4).

Fig. 2. The hospital project incorporates a 22-story steel-framed tower in Pittsburgh’s Oakland neighborhood.

Each of these three distinct uses—the bed tower (configured for two patient rooms per bay), the parking garage (designed for three stalls per bay), and the loading dock (requiring a largely column-free area)—had its own optimal grid and column arrangement. The parking garage features a regular rectangular grid, while the reniform, or kidney-shaped, layouts of the bed tower and loading dock incorporate irregular, nonorthogonal grids. Consequently, it became apparent that a unified grid system accommodating all three uses was impractical.

The structural solution involved the extensive use of transfer girders, coupled with a strategic full-height column removal and a sloped frame column. The transfer members redirected upper-level columns to compatible positions within the loading dock and parking garage below.

HGA examined options for an orderly layout of the transfers but was hindered by the irregular and non-uniform upper and lower grid layouts.

The resulting system is a complex layout with seven primary transfer girders occurring at multiple levels incorporating wide-flange sections as heavy as W36x723 (rolled with high-strength ASTM A913 - 65 KSI steel) alongside substantial 72-inch-deep plate girders featuring 4-inch thick by 18-inch-wide flanges. Numerous secondary transfer girders were also utilized throughout the building. The column removal eliminated one difficult conflict creating a double-span bay that continued to the penthouse. Sloping a W14x500 frame column 12-feet over two stories allowed the column to be positioned optimally in both the bed tower and the loading dock.

Fig. 3. UPMC Presbyterian expansion is tightly packed into the urban site with De Soto Street on the right. The addition will eventually interconnect with the existing hospital to the north.

Fig. 4. The convergence of parking garage, loading dock, kidney-shaped bed tower, and lateral frames are shown.

Image created in Revit software.

Lateral Transfer The contrasting upper and lower grid systems also significantly complicated the layout of lateral braces. The reniform bed tower relies on a combination of single and multi-level X and chevron braced bays, with three transverse frames at each end and three additional longitudinal frames. On upper floors, the transverse frames needed to be situated within the central core to prevent interference with patient rooms; however, this alignment often conflicted with the spatial requirements of the levels below. The design team addressed this issue by strategically shifting brace locations to adjacent bays on lower floors (Figs. 4-5).

Frame shears as high as 1,700 kips were transferred to the adjacent bay using directly welded connections.

Two levels below the bay transfers, structural analysis revealed that a significant portion of the lateral forces were being distributed out of the steel frames and redirected to concrete walls that were present at the lower floors. Accepting this inevitability, the design team provided a viable load path that would facilitate these diaphragm transfers through

Project Team Owner: UPMC Structural Engineer of Record: HGA Architect of Record: HGA General Contractor: Joint venture between Whiting-Turner and PJ Dick Steel Fabricator: Sippel Steel Fab AUGUST 2025

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the slab-on-metal-deck. The movement of horizontal forces out of the steel frame into the diaphragm was achieved using collector beams designed for the large axial forces and shear studs. Diaphragm strength for the typical 6 1/2-inch composite slabs was exceeded for all critical loading conditions and would be supplemented using thicker, high-strength, reinforced slabs. At areas of highest diaphragm demand, the slab was increased to 9-inches of 5,000 PSI concrete and reinforced with #5 rebar at 6-inch centers in each direction.

Design wind loading for both strength and serviceability was based on wind tunnel testing, with a 3,000-year return period for strength and a 50-year return period for serviceability. The decision to pursue wind tunnel testing yielded a 20% reduction in wind forces as compared to ASCE 7 requirements. With a Seismic Design Category of A, wind would govern the design of the lateral system, with drift transverse to the slender kidney-shaped floors being the controlling factor. To limit the excessive movement that was noted in early studies, HGA interconnected the three columns that form each double bay frame within the mechanical penthouse. This hat truss concept utilized the third column as an outrigger to increase the overall frame length. With this system, frame column sizes ranged from W14x500 to W14x730, and the overall drift was reduced to around H/385.

Fig. 5. A transverse brace, including the sloping frame column, helped prevent interference with patient rooms.

44 STRUCTURE magazine

Pushing Out To maximize patient room layouts on the upper floors, HGA extended the reniform floorplates as far south as permitted by property lines. The design team concluded that extending the lower floors the same distance would create an unwelcoming street presence. Recognizing UPMC's commitment to community engagement, the design allocated 30,000 square feet at the building’s southern end for a community-focused Lifestyle Village featuring wellness rooms, convenient food options, and outdoor urban spaces. The concept of cantilevering the upper floors above this space emerged as a key design strategy to maximize the function of both areas and would ultimately become part of the project’s identity.

HGA initially explored supporting the cantilever solely at the base using story-depth trusses, but this approach was not pursued as it sacrificed space that was allocated for a dramatic public dining area. Another option considered was locating the trusses in the penthouse at the top of the building, effectively suspending the cantilevered floors. While these trusses could easily be concealed within the two-story mechanical penthouse, this solution was also deemed infeasible due to the irregular grid layout at that end of the building and conflicts with the four large cooling towers.

After much consideration, HGA selected a system with independent cantilevers at each floor. Critical serviceability constraints that were considered included curtain wall deflection tolerances and susceptibility to vibration, resulting in heavier-than-average structural members to frame the 30-foot cantilever. As can be seen in Fig. 6, prominent cantilevered framing members as large as W40x503 were utilized. Although HGA designed most steel connections for the project, the larger, complex moment connections that frame through columns and girders were delegated to the steel fabricator, Sippel Steel Fab. This decision was made collaboratively with the input of Sippel, who was brought on board early, for both design efficiency and constructability. The steel fabricator was in a better position to optimize these connections based on their knowledge of material availability and their individual shop preferences. Allowing the steel fabricator to determine the type of connection also gave them more control over the tightly choreographed erection schedule of which the large cantilevers were a key component.

For the W40x503 beam-through-column moment connection mentioned, Sippel Steel Fab opted for bolted flange plate connections utilizing a total of (144)- 1 1/8-inch diameter A490 bolts. Bolts on the backspan side of the connection were designed as bearing bolts while those on the cantilever side were designed as slip-critical to eliminate bolt slop as a component of the overall cantilever deflection. HGA anticipated that post-erection slump of the larger cantilevers related to their substantial self-weight may still cause issues with deck installation and proactively addressed this potential by noting upward preset for larger girders on the construction documents. Rather than aiming for perfectly flat cantilevered beams, just enough preset was specified so the displaced shape of larger cantilevers was compatible with adjacent, smaller members. For the W40x503 example, the upward preset specified was 1/2-inch. HGA’s method was reviewed by the steel fabricator’s engineer and has proven effective in the field.

Cutting Through The increased beam depths at UPMC's Presbyterian Tower resulted in an explosion in the number of MEP beam penetrations being requested.

It is common to coordinate a few holes through the web of a beam so that pipes or small ducts can pass through, alleviating conflicts in a

few tight areas, but the number of requests at UPMC reached more than 1,000. A particularly challenging area above the loading dock, which was constrained by ceiling height, increased framing depth, and the above food service facility, required over 250 penetrations alone (Fig. 7). Recognizing the potential for issues with coordination, HGA helped to create an efficient and collaborative process which would bring together the design team, the Construction Manager's Virtual Design Coordination (VDC) experts, and the design-assist contractors from each discipline.

The process began with the MEP trade partners accurately modeling their components and working out as many conflicts as possible before submitting a list of requested penetrations to the VDC team, which were then compiled and forwarded to the design team for review. HGA required that requests be extremely specific, including the size of each opening, location along the beam, and location within the height of the beam, and provided rules of thumb to lessen the quantity of requests that would immediately be rejected. HGA's team then carefully analyzed each request and coordinated with the VDC team using direct communication and weekly coordination meetings. Often, slight adjustments were required in the depth or location of an opening, or sometimes multiple penetrations were grouped for simplicity. Once solutions were found for all penetrations, they were documented, and in some cases required separate framing plan sheets due to the sheer quantity.

This cycle of coordination repeated itself for each floor, a dynamic process occurring in parallel with the ongoing steel fabrication for lower levels and the shop drawing reviews for those to come. HGA leaned heavily on Sippel Steel Fab to identify the last responsible moment that revised Construction Documents were needed in order to be incorporated into the next scheduled shop drawing submittal. The process was tedious at times, requiring extreme perseverance from those directly involved, but was successful at preventing the need for last-minute coordination during the shop drawing review period.

Fig. 6. Cantilevered framing allowed for additional patient rooms on upper floors.

Bright Future A testament to ingenuity and collaboration, the UPMC Presbyterian Tower reached a significant milestone with its steel topping out on October 1, 2024. Pushing through the project’s inherent complexities and unique design challenges, this achievement underscores the efficiency and success born from creative problem-solving, persistent dedication, and effective collaboration among the project team. Set to become a prominent landmark upon its completion in Fall 2026, the bed tower addition will empower UPMC to further its mission of providing outstanding patient care and driving the future of healthcare through innovation, research, and education. ■

Ben Shock (bshock@hga.com)and Jeffrey Millmann (jmillmann@hga.com) are both Structural Engineers with HGA in Milwaukee, Wisconsin.

Fig. 7. Multiple beam penetrations were required above the loading dock, which was constrained by ceiling height.

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Extensive modifications to the building’s foundations required an innovative and extensive column shoring solution.

Skyline College Building 2: Means and Methods Column Shoring The construction team for a college located near the San Andreas fault faced many column shoring challenges while implementing a complicated seismic retrofit.

By James Enright and John Dal Pino

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kyline College is located 1 mile west of the San Andreas fault on a 111-acre site west of Skyline Boulevard and south of Sharp Park Road in San Bruno, California. The community college opened in 1969, and the buildings on campus are low-rise structures, mostly constructed of reinforced concrete in a common “brutalist” architectural style of that era. The original designers of the building were Isadore Thompson, Structural Engineers, and John Carl Warnecke, Architects and Planning Consultants.

Building 2 is a three-story, 53,000-square-foot concrete structure set into a hillside on the west, creating a partial basement. The floor plates are heavy and consist of a combination of flat slabs, waffle slabs, and one-way joists mostly on a conventional 18-foot grid. The roof has a pop-up central clerestory with long-span concrete girders that create space for theater-style seating in a large lecture hall. Column dead loads range from 75 to 300 kips where each column is supported on a single concrete caisson. The loads applied to the columns supporting the pop-up roof have much greater gravity loads than other columns. The caissons are interconnected with small, lightly reinforced concrete grade beams, with some on diagonal lines between columns to distribute the earth pressure from the hillside basement walls throughout the foundation.

This Tier 3 methodology involves a detailed systematic evaluation of a building’s seismic performance using both linear and nonlinear analysis procedure.

Given the proximity to the San Andreas Fault and the heavy seismic mass of the existing concrete structure, the retrofit design involved the addition of concrete shotcrete overlay walls on the existing perimeter precast walls as well as interior concrete infill walls to eliminate vertical discontinuities in the existing lateral system. The existing caisson foundations were adequate for the much higher seismic demands required, so long as the lateral load could be distributed in a way that allowed all the caissons to work together. The original grade beam system was too small and did not provide a continuous load path to all of the existing caissons, so a

The Project A seismic retrofit was necessary to address numerous seismic deficiencies including non-ductile exterior precast concrete shear wall panels and discontinuous interior shear walls. As a community college in California, the project was under the jurisdiction of the Division of the State Architect, and a comprehensive seismic retrofit necessitated compliance with two performance levels based on the Tier 3 methodology described in ASCE 41-17 for a Risk Category III building.

The full phasing plan of the project is shown above. The area highlighted in green is shown in greater detail at right.

The concrete pad footings are shown dashed. The needle beams solid and the posts as solid dots.

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new concrete grade beam system was required to vertically support the new concrete shear walls while simultaneously acting as a truss to uniformly distribute horizontal loads to all of the existing caissons. In order to directly connect the existing caissons with the new grade beams, the top six feet of the caissons would be removed while maintaining the existing reinforcement. This approach was necessary to avoid supplementing the existing foundations with additional deep foundation elements that were limited by site and building access constraints.

The project was a traditional “hard bid” public works project, so it was paramount that the contractor develop a safe, but economical, shoring solution. The column shoring scheme also needed to allow for the work occurring simultaneously throughout the building.

Evaluating Alternatives A common approach to shoring of columns involves point-loaded needle beams that are essentially two closely spaced steel beams attached to the sides of the column, with the beams simple spanning between two temporary supports. When columns are steel, it is easy to weld short transverse beams to the columns that then distribute the load to the steel needle beams. After the construction team calculated the approximate column gravity dead loads (including small construction live load allowances), it became apparent that attachment of steel lugs or bolts into the concrete columns would not work due to the high loads. The college also wanted to be able to expose the columns in the future, so a patched, Swiss cheese look was not something they would agree with.

The next thought was to use conventional post shoring at each column location over the three levels of the building. Due to the mix Column grippers, consisting of two sets of W14 wide flange beams with eight high-strength bolts per set bearing on the of gravity load systems within a story and spreader beams which span to the needle beams. (Side elevation shown here.) vertically between stories, it became apparent quickly that a system of stacked spreader beams and four posts at too costly to design and build. Another approach was required. each column was going to be difficult to design and time consumThe design team reached out to colleagues who design construcing to construct. One experienced engineer took over four hours to tion means and methods for contractors and asked if they had ever design a system for just one column. The building has 70 columns/ been faced with similar challenges. One colleague provided informawall locations supported on caissons, and most are unique in terms tion about a project in which the means and methods engineer had of the configuration of the gravity systems they support. clamped the concrete column tightly with two short wide-flange steel Complicating the post shoring approach was the width and layout beams stressed with large, high strength bolts that spanned to needle of the new grade beams. It was not possible to post down through beams. The surface of the steel that would contact the concrete was the grade beams (too much reinforcing steel), so it was necessary “roughened” with parallel beads of weld, to create what might be to find open spots away from the columns. Unfortunately, putting called shear keys—basically a load transfer mechanism akin to shear posts farther away from the columns put them at or near the quarter friction in ACI 318. span locations in the slabs where there is typically little negative steel.

This sounded a bit crazy at first, but after some thought it made If the spreader beams were located there, the floors might be damaged more sense technically and showed great engineering instincts and or collapse. Stacked spreader beams were considered, with one set near innovative thinking. Certainly nothing like this could be found in the columns spanning to another set farther away. But doing this at the building code or other design guidelines. The colleague was able three levels at each column just did not seem like the right approach: to provide a drawing for the project which showed the column load 48 STRUCTURE magazine

Typical column shoring consisting of the grippers, spreader beams and needle beams spanning to the posts and pad footings.

and the clamping force, and from that it could be determined what the friction per square inch must have been. The project had been successful which provided one data point, but with an unknown coefficient of friction, mu, strength reduction factor, phi, and factor of safety. Anyway, it was a start.

The post approach was abandoned and back came the needle beams.

The needle beams needed to span to “something” and this “something” is often drilled micro-piles, installed using low-overhead equipment in a basement. The general contractor client knew this was going to be expensive and asked the team to develop a scheme that was simpler and something they could self-perform. The first thought was timber mats at the existing slab level that would support the ends of the needle beams. The problem with this approach was that the contractor still needed to excavate six feet down to the bottom of the new grade beam. To avoid a slope failure, the needle beams needed to be long. This idea was discarded. It was decided to instead excavate and place the temporary foundations at the lower level. Timber mats (12x12 timbers bolted together) were an obvious solution but some of the mats would need to pass under the new grade beams. Timber was not permitted to be left in place, so this idea was also abandoned.

As a result, cast-in-place concrete pads were used.

The Solution?

At this point the team thought they had a solid approach. The columns would be clamped with roughened wide flange beams, with the clamping beams (eventually called “grippers”) bearing on spreader beams spanning to needle beams. The needle beams needed to be placed above the new grade beams, so the needle beams were supported on steel posts bearing on the concrete pads. Although the building is supported on concrete caissons, the soil was found

to be reasonably good for bearing based on recommendations from the project geotechnical engineer. Each building column had two pads (mostly 5 feet by 10 feet in plan by 1.5 feet thick), with each pad supporting one or two posts. Given the column loads and what was known about the skin friction that could be developed, it was concluded that two sets of grippers would be required at each building column so that all four column surfaces could be engaged.

To address the economics issue, it was determined that two wideflange beam sizes, W24x117 and W18x76, would address the range of column loads and needle beam spans. The same grippers, fabricated from W14x159 sections, would be used at each column location regardless of load. Although posts could be re-used, the concrete pads would be left in place.

Where concrete bearing walls existed rather than columns (at stair and elevator cores, the building perimeter and certain interior shear walls), it was possible to punch holes in the walls and support the walls directly on the needle beams through bearing.

Testing the Approach With only one data point and no solid available data for steel to concrete friction, the design needed to be tested. The general contractor client was reluctant at first but eventually came to understand what was known and what was not with respect to project risks (quite high) relative to the cost of the tests (quite modest).

The test set-up consisted of a concrete pad footing with a concrete column extending upward 8 feet. The column dimensions matched those in the building, and the columns were reinforced so that the column tension strength was twice that of the highest column gravity load that needed to be lifted. The two sets of grippers could theoretically provide more capacity than needed.

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The general contractor had by then decided to hire a specialty subcontractor to install the shoring, do the actual column jacking, and assist with the monitoring. The subcontractor also assisted with the testing and developed the procedure for tightening the bolts to create a reliable normal force, akin to tightening the lug nuts on an automobile wheel. Hydraulic jacks were placed between the top of the footing and the grippers, and then the jacks were extended to load the column, while monitoring for clamp slippage. Slippage was a major concern since no alternative support system for the column could be quickly installed. The sub-contractor also recommended placing a thin, ¼-inch thick piece of plywood between the steel grippers and the contact surface on the concrete column. The benefit of the plywood was not apparent other than perhaps creating a more uniform bearing surface; the plywood might actually reduce the clamping friction.

The first test was a success since the column failed in tension, demonstrating that the grippers were able to transfer the required force. Shorter-span column shoring supports.

However, this test provided only one more data point, so another test set-up was constructed, this one including the fault. The west basement wall needed new waterproofing, so rather plywood. The second test was successful too. than excavate the west side soil in phases coinciding with the shorAfter the fact, it was learned that the sub-contractor had utilized this ing phases, all of the soil was excavated at once to eliminate the soil column clamping approach before and was very comfortable with the pressure issue entirely. As the work progressed, the soil was replaced proposed design. If only this had been known at the outset! As the when adequate lateral load capacity had been restored. project progressed, it was observed that the weld beads had pressed through the plywood and embedded themselves in the surfaces of the Detailed Shop Drawings and Design Review columns, thereby contributing greatly to the working of the grippers.

The specialty shoring sub-contractor developed shop drawings for review by the designers. They frequently made recommendations for Developing the Construction Documents small changes that improved the basic design or allowed for the re-use of materials. In the end, the collaboration between the contractor, Shoring up the entire building, or even a large part of the building, sub-contractor and designers was excellent and played a major factor at one time would be too risky. Counter-balancing considerations in the project’s success. were: 1) it would be prohibitively expensive to have enough steel to The possibility of clamp slippage or the loss of grip was a constant do major portions at the same time; 2) there concern. At the beginning, the general contracwas not enough space to store the excavated tor hired a surveyor to monitor the column soil; 3) moving materials around the work area elevations each day. This was expensive and it would be difficult; and 4) not enough workers became apparent this could not be done for the were available. life of the project. But any slippage could not After considering various solutions with input go unnoticed. After some research, the general from their structural engineers regarding the contractor purchased and installed an electronic design criteria in ASCE-37 Design Loads on survey system linked to their computers that Buildings During Construction (wind and provided a continuous record of the column seismic loads for temporary construction) and elevations. After working out the kinks and the earth pressure load from the hillside, the going through a few panicked and false alarms, general contractor decided on an eight-phase the system worked well. approach that worked around the perimeter and from north to south, ending with the eighth phase in the main access point on the The Hiccups east side of the building. This permitted enough of the building caissons to be engaged No project is perfect, but only two hiccups to resist the wind and seismic loads at all times. occurred.

The temporary wind loads surprisingly conThe first was breaking of the clamping bolts. trolled the lateral force design even though the Special ASTM A193 Grade B7 bolts were building is only a mile from the San Andreas Evidence of increased grip provided by weld beads. required to develop enough clamping force. In 50 STRUCTURE magazine

one instance, the wrong (lesser grade) bolts were inadvertently transported to the site and installed. Fortunately, the bolts failed during the tensioning process rather than when the building was supported.

The second was gripper slippage during the final phase, just when everyone thought the end of the tunnel could be seen. There had been plaster on the column which had been left in place, so that was removed. Slippage occurred again, so the column faces were bush hammered. This proved to be the solution. The clamping load and vertical jacking load were applied and left in place over a weekend just to be sure, before the demolition of the columns could commence.

Final Success The planning, design, and testing began in June 2023. Construction of the first phase started in December 2023, with the work completed on March 10, 2025, with the last concrete pour. As with all construction means and methods projects, this was the time to finally relax! ■ James Enright, SE, is an Associate Principal with Element Structural Engineers, Newark and Oakland, California.

John Dal Pino, SE, is a Principal with Claremont Engineers Inc., Oakland, California and the Chair of the STRUCTURE Editorial Board.

Above: The project team included the structural engineers (center), the contractor Wickman Development and Construction staff (right), and specialty subcontractor Sheedy Drayage Company staff (left). Below: Simultaneous column shoring at multiple columns. Note size of grade beams

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in SIGHTS Transforming Structural Engineering: Embracing the AI Revolution

AI tools, such as those that analyze complex documents or use visual data to assess infrastructure, are being developed to make engineering tasks more efficient and reliable.

By Kristopher Dane, D.Eng., CPEM and M. Z. Naser, Ph.D, PE This article is Part 3 of a three-part series on AI for structural engineering presented by the Coalition of American Structural Engineers (CASE), the National Council of Structural Engineers Associations (NCSEA), and the Structural Engineering Institute of the American Society of Civil Engineers. The corresponding webinar, put on by SEI, will be held on August 26.

Visit program.acec.org/2025-joint-summer-series-artificial-intelligence to register for this summer AI webinar series.

A

rtificial Intelligence (AI) has swiftly transitioned from a distant futuristic concept into an integral component of engineering practice. In civil engineering—and particularly structural engineering—AI now offers significant opportunities to improve efficiency, accuracy, and reliability in both routine operations and complex analytical tasks. This article discusses current AI structural engineering applications, future possibilities, and critical considerations for the profession.

Current Applications Infrastructure Inspections and Predictive Maintenance AI technologies such as computer vision (which enables computers to interpret visual data), natural language processing (NLP, which allows machines to understand and generate human language), and machine learning (ML, which uses data to improve performance without explicit programming) are increasingly integrated into structural engineering workflows. These technologies enable automation and improved precision across several critical tasks, from infrastructure inspections and code interpretation to quality assurance and control.

One notable area where AI is currently demonstrating practical value is inspections. Traditional inspections, reliant on manual visual checks and tedious documentation, are labor-intensive and prone to human error.

AI-powered computer vision now facilitates rapid, automated analysis of visual data from drone imagery, satellite photos, or stationary cameras.

For instance, when trained within specific domains, AI can swiftly detect structural anomalies, including cracks, corrosion, and deflections, and classify damage severity. These capabilities help engineers prioritize maintenance activities, drastically reducing time and cost. Similarly, AI-powered 52 STRUCTURE magazine

predictive models now help structural engineers forecast potential failures and schedule preventive maintenance. This approach relies on analyzing historical data, structural characteristics, environmental conditions, and real-time data from embedded sensors to predict and avert structural issues before they become critical, thereby significantly prolonging the lifespan of infrastructure. For instance, an AI model can continuously process vibration and strain data from sensors on a highway bridge to learn its normal structural behavior. Once this behavior is understood, the model can detect subtle changes in dynamic response patterns to predict when metal fatigue might surpass safety limits. This allows engineers to plan necessary retrofitting, such as replacing FRP or steel plates, or imposing load restrictions, long before cracks appear.

Structural Design Optimization AI-driven structural design optimization is another critical area of interest as structural engineers frequently encounter complex, multi-objective design scenarios that need to balance safety, economy, sustainability, and performance. AI algorithms, such as genetic algorithms and neural networks, can quickly generate and assess thousands of potential design configurations, identifying optimal or near-optimal solutions that human engineers might overlook due to complexity or time constraints. While these tools are currently limited to use in early design phases and are available to only a few firms, the skills and capabilities are spreading.

Real-Time Structural Health Monitoring AI-enhanced structural health monitoring (SHM) offers continuous monitoring of structures using distributed sensor networks—collecting data on strain, vibration, temperature, and other variables. Traditional SHM methods rely on periodic checks and offline data processing. In contrast, AI systems detect real-time deviations and pattern changes that may indicate structural damage. These systems are being built and trained as both engineer-in-the-loop systems reduce the time to notify the asset owner of issues but could be used as a direct notification tool, massively reducing the level of staff effort from the status quo.

Such systems are especially valuable in seismic or high-wind regions.

In California and Japan, AI-powered SHM platforms have been used to assess buildings immediately after earthquakes, supporting faster decision-making and emergency response. As these systems evolve, they are transitioning from passive reporting tools to active decision-support platforms capable of triaging risk and dynamically adjusting maintenance plans. This represents a fundamental shift from passive to active monitoring, empowering engineers and infrastructure managers with unprecedented insight into real-time structural behavior.

Future Opportunities Code Interpretation and Compliance Support While inspections are an immediate benefit, developing, interpreting, and applying building codes and standards is another area ripe for AI-driven transformation. Engineers often navigate lengthy, intricate regulatory texts, a process vulnerable to misinterpretation or oversight.

AI—particularly NLP—offers opportunities to assist engineers by parsing complex regulatory language and offering targeted answers. Tools based on GPT-like language models could eventually allow engineers to ask, “What is the live load requirement for a storage mezzanine?” and receive precise, context-specific responses.

While today’s models still struggle with ambiguous or context-sensitive language, improvements are coming to the baseline model’s ability to parse more complicated formatting such as the code-ubiquitous table.

That is, they are learning how to hold more fingers in the code book!

However, beyond waiting for the models to improve their ability to read our existing code books, embedding AI friendly formatting and logic directly into standards, developing flexible licensing models, and offering user-customizable tools may also represent new opportunities for standards organizations and their industry partners. NCSEA has released a tool called SE GPT based on a database of content in NCSEA webinars and STRUCTURE magazine content. While preparing this article, the authors have had a sneak peek of a similar ASCE initiative to provide a custom GPT interface for some of its content. This is just the beginning of tapping into the industry-wide corpus of knowledge.

Automated QAQC

analyze outputs from BIM and structural analysis models). Each solution will require a significant degree of firm-specificity that will not be addressed by vendors; thus, efforts within firms will be required to solve issues specific to their own workflows/risk patterns.

Driving Sustainability Beyond enhancing safety and reliability, AI also presents immense opportunities to address sustainability challenges within structural engineering.

As global awareness about environmental impact grows, engineers are increasingly tasked with creating structures that meet stringent performance criteria and minimize ecological footprints. AI algorithms are particularly effective at optimizing material use and reducing waste, directly contributing to sustainability goals.

Material Optimization Here, material optimization using AI involves sophisticated techniques such as topology optimization and generative design, where algorithms iteratively explore countless configurations to find the most efficient structural forms.

Unlike conventional design methods, AI-driven generative design rapidly evaluates and compares materials, shapes, and structural layouts, automatically considering environmental impact metrics such as embodied carbon, energy consumption, and material recyclability. For example, AI tools have been developed that connect key design criteria such as geometry, loading, materiality, vibration, and embodied carbon takeoff into a single live interactive interface. This directly translates into lower greenhouse gas emissions, reduced material extraction, and cost savings.

Lifecycle Analysis

The potential of AI to streamline Quality Assurance and Quality Control (QA/QC) processes is enormous. Engineering projects involve vast Additionally, AI can assist engineers in assessing the lifecycle impacts amounts of documentation, calculations, and data, all of which must be of structural materials more comprehensively. By combining historical verified meticulously to maintain compliance and structural integrity. data with predictive models, AI-powered assessments provide accurate AI algorithms can automatically analyze large datasets to identify dis- forecasts of maintenance needs, durability, and environmental impacts crepancies, errors, or deviations from established standards, significantly over the entire lifecycle of structures, promoting truly sustainable and enhancing reliability and consistency while reducing the manual effort resilient engineering practices. For example, one of Thornton Tomasetti’s required from engineers. The AI tools on the market today already allow AI-powered structural design tools, Asterisk, allows for rapid design an engineer to upload a reinforcement schedule and shop drawing set and iteration by incorporating geometry, wind and seismic loading criteria, ask AI to do a first pass cross-check review including an instance count vibration criteria, and material customization; it then allows the engineer and summary table. While this is nowhere near a complete review task, it takes a few seconds, helps the engineer assess how long the complete review may take, and draws attention to areas of concern.

This type of task can be done without customization, without training, or without prompt engineering. Using AI as a preliminary “reviewbefore-the-review” can help a senior engineer preparing for a QA/QC of a project or a junior engineer preparing to complete a review of external partner’s work. Such capabilities could allow structural engineers to reallocate their attention from routine checks to more critical design and decision-making activities, optimizing overall project efficiency and closing information gaps by cross checking basis of design, drawings, specifications, and calculation packages.

Achieving this type of QA/QC requires connecting several different AI technologies in the piecewise approach (large language models may parse specifications and emails, computer vision may be required to review drawings, and Asterisk is an AI-powered structural design platform. (Image courtesy Thornton Tomasetti) machine learning solutions would be used to AUGUST 2025

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to immediately capture outputs such as member sizes, structural quantity, and embodied carbon takeoffs.

Limitations and the Need for Standards Governance and Ethical Frameworks Despite these advancements, the widespread and effective integration of AI into structural engineering practices demands that several key challenges be addressed. First is the need for clearly defined guidelines and ethical frameworks for AI usage. Organizations such as ASCE, SEI, and NCSEA are instrumental in developing these essential standards. For instance, SEI might consider creating new standards specifically designed to govern AI-driven designs, akin to performance-based design standards and model validation frameworks already established in sectors such as marine safety and fire engineering. Such frameworks would set a clear minimum standard of care, ensuring that AI-enhanced designs achieve the necessary levels of safety, accuracy, and reliability.

While these frameworks are developed, we can lean on item 1.h of the ASCE Code of Ethics that contains a clear reminder to all of us as we seek to incorporate these new tools into our work: “consider the capabilities, limitations, and implications of current and emerging technologies…” this is a reminder that in all of the examples here, the AI tools are proposed as partners, not replacements for the engineer.

The time saved through efficiencies gained should be spent focusing on design fundamentals, deeper QA/QA, and ensuring that we are best solving our client’s and society’s needs.

AI in Standards Development Additionally, the procedures by which standards themselves are developed and disseminated could be significantly enhanced by AI technologies. Standard development typically involves extensive stakeholder collaboration, detailed record-keeping, and administrative processes, all of which consume considerable time and resources. AI can dramatically reduce the time required to synthesize stakeholder feedback, summarize comments, and manage administrative tasks such as generating meeting minutes. Moreover, AI-enabled tools could readily detect and highlight changes between code versions, simplifying engineers' ability to stay updated. By proactively developing customized AI interfaces—such as ASCE/SEI-specific chatbots—engineers could interact directly with standards via intuitive queries, significantly improving accessibility and comprehension.

Training and Workforce Development Shifting the Professional Education Model Embracing AI also demands an educational and professional paradigm shift. Structural engineers' training—both academically and professionally—needs rapid adaptation to equip engineers effectively.

Some academic institutions are already integrating "micro" educational programs designed to help students quickly adapt to emerging technological trends. Firms and professional licensing bodies must similarly respond by incorporating AI competencies into certification and training frameworks, recognizing that while it is impossible to master all AI technologies, engineers must become proficient in the tools most relevant to their specific roles.

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AI-powered asset inspection can help perform predictive maintenance, among other things. (Image courtesy of Thornton Tomasetti)

Bridging Generational Gaps Furthermore, bridging generational divides within structural engineering organizations is paramount to effectively adopting AI. Younger engineers entering the profession generally possess greater familiarity with digital technologies and AI applications, while senior engineers bring essential depth in practical experience and engineering judgment. Encouraging cross-generational collaboration ensures that organizations use both innovative technological solutions and time-tested engineering ability, fostering a robust integration of AI into practice.

Immediate Steps for Practitioners Immediate actions structural engineers should take today include actively engaging with accessible AI tools, such as ChatGPT, to gain familiarity with basic AI capabilities and to develop a sense of what AI can do and what it can’t. Although such tools represent only a fraction of AI's broader potential, routine use can foster increased comfort, creativity, and productivity in daily tasks. Engineers should also prioritize learning and adopting AI-driven technologies directly relevant to their practice, staying current with offerings from organizations like NCSEA and ASCE.

Conclusion The structural engineering profession stands at a pivotal moment in the integration of AI. While the potential for enhanced efficiency, insight, and innovation is substantial, realizing these benefits requires deliberate, ethical, and collaborative implementation. We must keep our ethical responsibility central in our mind and consistently have an engineer-in-the loop as the new systems are developed. Engineers must work alongside governing bodies and educators to shape standards, define accountability, and cultivate the skills necessary for this new era.

With thoughtful leadership and strategic investment, AI will not replace the engineering profession, it will amplify its impact. Structural engineers who engage early, skill up, and lead responsibly will be at the forefront of building a safer, smarter, and more sustainable future. ■

Kristopher Dane, D.Eng., CPEM, is Associate Principal at Thornton Tomasetti.

M. Z. Naser, Ph.D, PE, is Assistant Professor, at Clemson University and AI Research Institute for Science and Engineering.

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SE NEWS Alpha Framing Wins ISS 2025 Best in Business Award for Most Innovative Product E

levate Structures, a Central States company, announced its Alpha Framing System has been named the winner of the Inside Self-Storage (ISS) 2025 Best in Business Award for Most Innovative Product.

Elevate Structures and the Alpha Framing System were also named winners of this award in 2020.

The recognition underscores Alpha Framing’s impact on the self-storage construction industry. Engineered for speed,

precision, and scalability, Alpha Framing has delivered results across more than 450 projects nationwide.

“Alpha Framing was designed by builders to solve the real-world challenges of self-storage construction,” said Richard Allen, President at Elevate Structures. “This award validates the hard work of our employee-owners and the trust our partners place in us to deliver a system that performs in diverse climates, spaces and market conditions.”

With the ability for a single six- to eightperson crew to install up to 15,000 square feet per week, Alpha Framing accelerates timelines, reduces labor costs, and enables quicker revenue generation.

While originally developed for self-storage, Alpha Framing has been adopted in multifamily housing, hospitality developments, student housing, and educational facilities proving its value across a wide range of construction sectors. ■

Simpson Strong-Tie Awards Scholarships to 120 College Students S

impson Strong-Tie announced the winners of its 2025–2026 Student Scholarship program, a part of the company’s Strong-Tie Undergraduate Fellowship. The company awarded $3,000 scholarships to 120 college juniors and seniors studying architecture, structural and civil engineering, or construction management.

The annual scholarship encourages the design and building of safer structures in our communities by supporting education for US students

in engineering, design and construction majors.

Scholarship recipients also become part of the Strong-Tie Undergraduate Fellowship, which provides access to industry contacts, training, job leads, peer-to-peer connection and community to help build their knowledge and networks as they prepare for their careers.

The full list of scholarship recipients and their respective schools can be viewed at www.strongtie.com/about/company/ scholarships-recipients.

The Simpson Strong-Tie Student Scholarship program began in 1999. Since then, the company has awarded more than $2.1 million to more than 1,200 students across the country.

The Simpson Strong-Tie Student Scholarship is administered by Scholarship America, the nation’s largest designer and manager of scholarship and tuition reimbursement programs for corporations, foundations, associations and individuals.

Learn more at strongtie.com/scholarships. ■

ACI publishes print version of ACI CODE-31825: Building Code for Structural Concrete A

merican Concrete Institute’s ACI CODE-318-25: Building Code Requirements for Structural Concrete and Commentary is now available. ACI CODE318 is the document that presents the requirements for the design and construction of structural concrete that are necessary to ensure public safety. It is addressed to the engineer responsible for the contract documents and the building official.

As ACI’s flagship standard, ACI CODE318-25 sets the foundation for structural 56 STRUCTURE magazine

concrete design and construction in buildings and nonbuilding structures. Developed through an extensive consensus process, the document addresses all major structural systems, including cast-in-place, precast, shotcrete, plain, nonprestressed, prestressed, and composite construction.

This latest edition introduces significant updates, including a new sustainability appendix that reflects modern construction practices, revised requirements for postinstalled reinforcing bars, and enhanced

provisions for shear friction. Additional updates include improvements to deep foundation requirements across all seismic design categories and clarified guidelines for cantilever and basement wall shear design.

The 2025 edition is already accessible through the ACI 318 PLUS platform and is now available for purchase through the ACI Store. A PDF edition is also available.

To learn more about ACI CODE-318 and ACI 318 PLUS, visit concrete.org/ACI318. ■

IN BRIEF Forté Structural Engineering Adds Wesley Huseman, PE, to Leadership Team Founder Ryan Huseman’s vision to build Forté Structural Engineering into the premier independent structural engineering practice in West Texas took another step forward with the addition of Wesley Huseman, PE. Huseman brings over a decade of deep technical expertise and client trust as one of the region’s rising structural engineering leaders.

Huseman earned his Bachelor of Science in Civil Engineering and Master of Engineering in Structural Engineering from Lehigh University’s P.C. Rossin College of Engineering. He began his career at Pharis Structural Engineers in Amarillo, where he led and contributed to diverse projects ranging from retail and medical facilities to educational buildings and commercial spaces. His recent work includes convenience store locations in Amarillo and Lubbock, as well as a number of healthcare facility projects.

COWI appoints Andy Sloan as Executive VP International engineering consultancy COWI has appointed Andy Sloan as Executive Vice President of its newly formed UK and international division. The move is part of COWI’s global growth strategy as it reorganizes its international operations to form the new division. Sloan currently serves as Managing Director of COWI in the UK and Ireland. As Executive Vice President he will join the company’s Executive Leadership Team and oversee delivery and development across multiple regions with a focus on infrastructure and the green energy transition.

CHA Acquires California-based FALCON Engineering Services, Inc. CHA has acquired FALCON Engineering Services, Inc. (FALCON), Temecula, CA. FALCON brings a team of over 60 professionals with deep expertise in project management, construction management, and construction inspection.

& Engineering, Roberts Stadium, Racquet and Recreation Fieldhouse, and Cynthia Paul Field in the Meadows Neighborhood.

• Swarthmore College, Field House, Tarble Pavilion Renovation, and Cunningham Fields Facilities.

Walter P Moore Expands U.S. Presence With Seattle Office Walter P Moore, announced the establishment of its presence in Seattle, Washington. This expansion reflects the firm’s commitment to serving the Pacific Northwest’s growing and vibrant building and infrastructure markets.

The Seattle office will be led by Vlad Ivanov, Managing Director of Diagnostics, who brings extensive expertise in condition appraisals, facade evaluations, forensic investigations, and the assessment of corrosion-related deterioration. Additionally, the Structures Group has team members Pete Range and Scott Kinney in the region, supporting the firm’s future growth plans for structural engineering services in Seattle.

Walter P Moore specializes in structural engineering, diagnostics, enclosure engineering, construction engineering, civil engineering, water resources, and traffic engineering.

Frangopol honored with IASSAR’s inaugural Distinguished Service Award Dan M. Frangopol, Professor of Civil and Environmental Engineering, Emeritus, and Inaugural Fazlur R. Khan Endowed Chair of Structural Engineering and Architecture, Emeritus, at Lehigh University is the inaugural recipient of the Distinguished Service Award presented by the International Association of Structural Safety and Reliability (IASSAR).

FALCON will rebrand as FALCON, A CHA Company, effective immediately. The acquisition brings CHA’s total staff to over 2,000 professionals across more than 45 offices from Canada to Florida and now into the western U.S.

Over his decades of involvement with IASSAR, the leading professional organization in the field of structural safety and reliability of engineering systems, Frangopol has served a number of leadership roles, including Vice-President (2013-17); Executive Board Chair (2006-13); Awards Committee Chair (2017); Vice-Chair of Technical Committee 3 on System Reliability and Optimization (2001-10); and Founding Chair of Technical Committee 4 on LifeCycle Performance, Cost and Optimization (2012).

LeMessurier Expands to Philadelphia, Opening Office in Historic Old City

The Institution of Structural Engineers announces its 2025 Gold Medallist

LeMessurier, a structural engineering and enclosure consulting firm, annouinced opening of its newest office in Philadelphia.

Located in the heart of Old City, this strategic expansion positions the firm to better serve clients throughout the Mid-Atlantic region.

LeMessurier is actively hiring senior-level staff to anchor the new office and strengthen its local partnerships. Recent and ongoing projects in the area include: •

Children’s Hospital of Philadelphia, a longstanding collaboration since the early 1990s.

• Princeton University, Quantum Institute for Quantum Science

Glenn Bell CEng FIStructE was acknowledged for his exceptional expertise on building safety and forensic investigations of catastrophic failures. IStructE’s Gold Medal is awarded annually for outstanding contributions to the advancement of structural engineering. It is renowned around the world as a sign of unique accomplishments in the profession.

IStructE’s citation for the 2025 award states: “The Institution of Structural Engineers 2025 Gold Medal will be presented to Glenn Bell for his significant contributions to structural engineering, particularly in the areas of building safety, standards development, and forensic investigations of catastrophic failures.” ■

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CASE in Point

Monitoring the White House’s Impact on Engineering

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CEC is actively tracking how the Trump White House is influencing the engineering industry. You can access this page via ACEC’s homepage or by scanning the QR code below.

We are closely monitoring several important developments, including White House communications that signal shifts in policy relevant to engineering. ACEC also reviews executive orders to interpret new federal initiatives and

their effect on engineering work. Additionally, we’re observing executive actions related to the suspension of federal funding to help our members manage potential disruptions.

Agency memoranda and official guidance are also reviewed to ensure our members stay compliant and well-informed in a changing regulatory landscape.

ACEC will host a free online webinar on April 23 offering a look at Trump’s first 100

days in office. Our advocacy experts will assess key developments so far, outline what’s likely ahead, and explain what these changes could mean for engineering professionals. To register, simply scan the QR code here.

Last Chance to Register for the CASE Summer Meeting in Philadelphia August 14 to August 15!

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oin us in Philadelphia for two days of insight, collaboration, and innovation.

The Coalition of American Structural Engineers (CASE) invites you to our summer meetings in Philadelphia. This multi-day event offers valuable opportunities for education, networking, and shaping the future of our profession.

Whether you’re a CASE member or simply interested in learning more about what we do, you’re welcome to join us!

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News of the Coalition of American Structural Engineers Explore CASE’s Best-Selling Publications

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xplore CASE’s top publications that inspire and inform professionals like you. From cutting-edge research to actionable insights, this year’s bestsellers are not to be missed. Plus, if you’re not a CASE member, don’t forget to use your discount code NCSEASEI2022 at checkout for exclusive savings.

CASE 962-D: A Guideline Addressing Coordination and Completeness of Structural Construction Documents Since the mid-1990s, owners, contractors, and design professionals have expressed concern about the level of quality of structural construction documents. They have observed that the quality of these documents has deteriorated, resulting, at times, in poorly coordinated and incomplete design drawings. Inadequate and/or incomplete design drawings often result in inaccurate competitive bids; delays in schedule; a multiplicity of requests for information (RFIs), change orders and revision costs; increased project costs; and a general dissatisfaction with the project.

In an effort to address these concerns, the Council of American Structural Engineers (CASE) has prepared this Guideline. This book discusses the purpose of this guideline, the background behind the issue, the important aspects of design relationships, communication, coordination and

completeness, guidance for dimensioning of structural drawings, effects of various project delivery systems, document revisions, and closes with recommendations for development and application of quality management procedures. A Drawing Review Checklist is attached.

A companion document is also available: CASE Tool 9-1: A Guideline Addressing Coordination and Completeness of Structural Construction Documents

CASE Tool 9-1: A Guideline Addressing Coordination and Completeness of Structural Construction Inadequate and/or incomplete design drawings often result in inaccurate competitive bids; delays in schedule; a multiplicity of requests for information (RFIs), change orders and revision costs; increased project costs; and a general dissatisfaction with the project. The guidelines presented in this document will assist not only the structural engineer of record (SER) but also everyone involved with building design and construction in improving the process by which the owner is provided with a successfully completed project.

There are two PDF files included with the Tool: one with Tool 9-1 and the other with the CASE Drawing Review Checklist.

Please see companion document, CASE 962-D—Practice Guidelines Addressing

Coordination and Completeness of Structural Construction Documents

CASE 962-G: Guidelines for Performing Project Specific Peer Reviews on Structural Projects Increasing complexity of structural design and code requirements, compressed schedules and financial pressures are among many factors that have prompted the greater frequency of peer review of structural engineering projects. The peer review of a project by a qualified third party is intended to result in an improved project with less risk to all parties involved, including the engineer, owner, and contractor.

Many aspects of the peer review process are important to establish prior to the start of the review in order to ensure that the desired outcome is achieved. These items include the specific goals, scope and effort, the required documentation, the qualifications and independence of the peer reviewer, the process for the resolution of differences, the schedule and the fee. The intention of these guidelines is to increase awareness of such issues, assist in establishing a framework for the review and improve the process for all interested parties.

A companion document is available: CASE Contract #5—An Agreement for Structural Peer Reviews

Session Held on What Engineers Need to Know About Standard of Care in a Changing Climate

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CEC’s Coalitions Team held an education session on “The Standard of Care in a Changing Climate: What Engineers Need to Know.”

This initiative united professionals from the mechanical, electrical, and plumbing (MEP) fields to drive collaboration and promote sound policy, all while supporting the future of the engineering profession.

One of the key objectives was to provide timely education that empowers firms to stay ahead of emerging challenges. As climate impacts become more frequent and severe, engineers are facing rising expectations and risks, from legal responsibilities to evolving client demands. To support engineers in navigating this complex landscape, ACEC released new guidance on applying the Standard

of Care in this changing environment.

During the session, Yvonne Castillo, Director at Victor Risk Advisory, grounded attendees in the climate science driving these changes, highlighting the importance of considering future conditions in engineering decisions. Andrew Ratzkin, General Counsel at POWER Engineers and a member of WSP, provided a legal perspective, discussing how liability and duty of care are evolving in response to these new challenges. Joe Barbagallo, PE, President of Consulting at Woodard & Curran, shared practical insights on navigating these risks, emphasizing the need for informed consent and documentation when advising clients on climate impacts.

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SEI Update Carol Ellinger Haddock Elected ASCE President-Elect; Member Grade Reform Approved

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SCE members have elected Carol Ellinger Haddock, PE, MPA, F.ASCE, as the Society’s next president-elect.

A seasoned public works leader and current senior advisor at Black & Veatch, Haddock brings decades of experience in civil service and infrastructure to the role.

In a decisive vote, members also approved a constitutional amendment to simplify membership grades. The change merges affiliate, associate, and member into a single “member” category, streamlining ASCE’s structure to four designations: student, member, fellow, and distinguished member.

SEI-NIST Workshop on Forward Looking Codes and Standards for Future Hazards

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he Structural Engineering Institute (SEI) of ASCE and the National Institute of Standards and Technology (NIST) conducted a workshop on Forward Looking Codes and Standards for Future Hazards on June 4-5, 2025. This workshop included climate scientists, structural engineers, and natural hazard experts to address an urgent need to advance design practices to incorporate future hazard projections into codes and standards of building and infrastructure.

The workshop identified a broad range of research and development activities to advance forward looking codes and standards for future hazards with the goal of reducing the impacts of future hazard events.

A report is being prepared that will include recommendations on the following topics: 1. Current and ongoing synergistic work leveraging complementary efforts at the university, private, public, and government level.

2. Practice perspectives for future hazard characterization.

3. State-of-the-art and ideal state of climate science and engineering standards/practice.

4. Project data needs for hazards (such as but not limited to, level of detail [spatial, temporal], time frame/horizon, etc.).

5. Science/analysis capabilities needed to address gaps in hazard data by phase.

6. Identification and prioritization of research needs to address the gaps in hazard data by phaseFaith Shipapa, S.M.ASCE, West Virginia University.

SEI-NIST Workshop in-person attendees

SEI-NIST Workshop virtual attendees

SEI Forms New Committee to Develop Loading Guide for Zoos and Aquariums

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EI has approved the formation of a new technical committee: Structural Design for Animal Facilities. Chaired by Leif Erickson, this committee’s purpose is to develop a comprehensive guide for structural loading requirements and design considerations for animal care facilities, including zoos, aquariums, and wildlife sanctuaries. The guide will aim to establish best practices for structural engineers working in environments with diverse species, supporting improved safety, performance, and consistency across projects. To apply to join this committee or another SEI committee, visit go.asce.org/joinstandardscommittee.

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News of the Structural Engineering Institute of ASCE ASCE/SEI 24 Flood Resistant Design and Construction Standards Committee Seeking New Members

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SCE/SEI is seeking practicing engineers, researchers, building officials, contractors, and construction product representatives to join the ASCE/SEI 24 Committee chaired by Jessica Mandrick. This committee will work to align the next edition of this standard with the flood provisions of the next edition of ASCE/SEI 7, update coating requirements for materials, clarify AO zones with relationship to the building footprint, clarify requirements for healthcare facilities, and incorporate current datasets. If interested, apply online before August 15th: go.asce.org/joinstandardscommittee ASCE and/or SEI membership is not required to participate on ASCE standards committees.

Tours Announced for ETS and ASCE 2025 Convention

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EI’s Electrical Transmission & Substation Structures Conference (ETS) and the ASCE 2025 Convention both offer tours in addition to traditional conference programming. ETS tours will take place Thursday, September 18th in Dallas, Texas. Tour options include the MICA Steelworks Plant, Sabre Industries Alvarado Facility, Incab America Plant Tour, and Structural & Steel Products/Race Rock Plant Tour. More information is available at https://www.etsconference. org/program/tours The ASCE 2025 Convention in Seattle October 8-11 offers technical tours of Climate Pledge Arena, Colman Dock, and the Boeing Everette Factory as well as opportunities to explore Seattle through the Capitol Hill Food Tour and Seattle Coffee Experience Walking Tour. Visit https://convention.asce.org/program/tours-outings for complete tour information.

Towards Zero Carbon 2025: Summit & Symposium

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he University of Colorado Boulder and SEI cohosted the Towards Zero Carbon 2025: Summit & Symposium June 26th-27th in Boulder, Colorado. This program combined CU’s Embodied Carbon Bootcamp with the inaugural SE 2050 Signatory Summit, a Firm Leader Round Table, and a Symposium attended by 175 structural engineers, building officials, firm leaders, and embodied carbon champions from across the country.

ASCE publications now available Design Snow Loads for Ground Mounted Solar Panels

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his practical guide offers snow load recommendations tailored to ground-mounted solar panels (GMSP), especially in snow-heavy regions. Aligned with ASCE Standard 7-22, it addresses key factors like exposure, thermal conditions, slope, service life, and the effects of snow sliding. With clear explanations and example problems, it’s a valuable tool for engineers, architects, and solar professionals designing safe, code-compliant systems in cold climates.

Climate Pledge Arena

Upcoming ASCE Continuing Education Webinars Learn more and register at mylearning.asce.org/.

Wednesday, August 6, 2025 Managing the Design Process - Project Scoping and Developing a Project Management Plan. 2.0 PDHs. Wednesday, August 13, 2025 Managing the Design Process - Project Scoping and Developing a Project Management Plan - Part 2. 2.0 PDHS Wednesday, August 20, 2025 Digital Twin, AI, and Robotics in Construction and O&M: Transforming the Future of the Built Environment. 1.5 PDHs. Wednesday, August 20, 2025 Introduction to Tunnel Design and Construction. 24.0 PDHs.

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NCSEA News Keynotes Announced for 2025 NCSEA Structural Engineering Summit

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he 2025 NCSEA Structural Engineering Summit, taking place October 14–17 at the New York Hilton Midtown, will feature three keynote presentations that explore the evolving intersections of structural engineering, architecture, personal development, and technology.

On Wednesday, October 15, architect James von Klemperer, FAIA RIBA, will open the Summit with a keynote titled “One Vanderbilt Structure: The Interplay Between Engineering and Architecture in Midtown’s Tallest Office Building.” As president of Kohn Pedersen Fox, von Klemperer will offer a behind-the-scenes look at the technical and creative innovations James von Klemperer behind the 77-story tower. His talk will examine how engineering and architectural vision worked together to shape One Vanderbilt, highlighting elements such as computational pedestrian modeling, cantilevered design, and New York’s largest continuous concrete pour—all constructed during the COVID-19 pandemic.

On Thursday, October 16, meditation teacher and keynote speaker Kevin Hekmat will pres- Kevin Hekmat ent “Mastering the Moment,” a session focused on the role of discomfort, courage, and selfawareness in professional risk-taking. Drawing from psychology, mindfulness, and communication strategies, Hekmat will help

attendees identify the internal blockers that keep people from speaking up, taking initiative, or embracing change—and offer tools to build those muscles deliberately through strategic microstressors.

The closing keynote on Friday, October 17, titled “Small Teams with Big Impacts: Taking the Next Steps with AI Adoption,” will be presented by members of the NCSEA Foundation’s AI Grant Team: Jesse Light, S.E., P.E. (Starling Madison Lofquist), Ayush Singhania, P.E. (HOK), and Sheng Zheng, P.E. (Martin/Martin). This session will showcase how small and mid-sized structural engineering teams are using artificial intelligence to streamline workflows, improve decision-making, and build custom tools—even without large budgets or in-house tech departments. A followup discussion will offer deeper conversation and peer-to-peer exchange for firms exploring their own next steps.

Each keynote adds a distinct perspective to the Summit’s broader focus on collaboration, innovation, and the future of the profession. More than 1,000 structural engineers are expected to attend this year’s event. For information or to register, visit www.ncseasummit.com. ■

SEAoK Brings Engineers Together in Bourbon Country

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tructural Engineers Association of Kentucky (SEAoK) teamed up with The Dwyer Company and GRL Engineers, Inc. for a cross-disciplinary continuing education and social event at Whiskey Thief Distillery in June. The twohour program — which drew attendees from across the state, including geotechnical engineers and special inspectors — covered pile foundation systems, ASTM load verification methods, and best practices for their use.

After the technical session, the group enjoyed bourbon samples straight from the barrel, food from the Whiskey Thief Food Truck, and live music. Attendees left with new insights, new connections, and a pint of bourbon to remember it by. ■ 62 STRUCTURE magazine

Jesse Light

Ayush Singhania

Sheng Zheng

News from the National Council of Structural Engineers Associations SE Summit to Launch with AI Workshop Offering Two Hands-On Tracks

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CSEA will open the 2025 Structural Engineering Summit with a preconference workshop dedicated to artificial intelligence—offering attendees the opportunity to explore AI through two hands-on tracks tailored to different experience levels.

AI Applications for Structural Engineers: A Hands-On Workshop will take place Tuesday, October 14, from 1:00 p.m. to 5:00 p.m. in New York City, ahead of the full Summit program. For the first time, participants can select from two distinct tracks: one for those exploring AI tools, and one for those ready to dive into development.

The Consumer Track is designed for structural engineers who are curious about AI but not necessarily looking to write code.

This session will focus on evaluating existing tools, applying them to real-world workflows, and drafting AI-related policies

for firms of all sizes.

The Developer Track is aimed at engineers and technical professionals interested in working directly with data and models.

This session will offer opportunities to experiment with language models, integrate tools like Grasshopper and Python, and begin building custom solutions for engineering practice.

The cost to attend the workshop is $299 for NCSEA members and $499 for nonmembers. Attendees will earn 3.75 Professional Development Hours (PDHs). Registration is open to all, whether attending the full Summit or just the preconference workshop. All registration is handled through the Summit registration portal.

The 2025 NCSEA Structural Engineering Summit will be held October 14–17 at the New York Hilton Midtown. For information or to register, visit www.ncseasummit.com.

Young Members Host Annual Trivia Night

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he NCSEA Young Member Support Committee hosted its much-anticipated Annual Trivia Night on June 25, bringing together young structural engineers from across the country for an evening of laughs, learning, and lively competition.

Held virtually, the event featured teams from YMG chapters nationwide in two separate sessions—one for western states and one for eastern. Groups hosted local watch parties to add a social twist and, for some organizations, pizza! The trivia covered everything from engineering facts to pop culture, giving everyone a chance to contribute and connect.

Beyond the fun, the night served as a reminder of the strength of the YMG network. It was a chance to build community, celebrate our shared profession, and enjoy a little friendly rivalry.

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structural FORUM Getting Ahead by Thinking Ahead: Cultivating Mental Load In structural engineering, identifying priorities, understanding task interdependencies, and ensuring key assignments are followed through are key skills that create more effective teams.

By Angelina V. Stasulis, PE, SE

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n structural engineering, success is often measured by visible outputs: precise calculations, comprehensive drawing sets, on-time delivery, and profitability. These deliverables are critical—but they don’t tell the full story. Behind every successful project lies an invisible, often unacknowledged layer of effort: the mental load. This encompasses the constant coordination, anticipation, and cognitive juggling required to keep a project running smoothly. While project management provides formal structures and processes, mental load represents the fluid, moment-tomoment awareness and foresight engineers carry to bridge gaps, adapt to change, and ensure seamless progress. Far from a burdensome extra, mental load is a vital leadership skill that sustains project momentum and team cohesion. Despite its foundational role, mental load remains largely unrecognized in engineering—absent from performance metrics, training, and formal conversations about effectiveness. It’s time to name this work, understand its impact, and cultivate it intentionally as a core professional competency. Recognizing mental load as essential, learnable, and worthy of acknowledgment will help build not only better projects but stronger, more sustainable teams.

What Mental Load Is, and Isn’t Mental load is the cognitive effort required to keep the bigger picture in focus while managing the details that drive progress. In structural engineering, this means identifying priorities, understanding task interdependencies, and ensuring key assignments are followed through—often by coordinating others rather than doing the work oneself. Unlike visible task execution, mental load operates behind the scenes: anticipating deadlines at risk, spotting coordination gaps, and supporting team members before issues arise. This quiet, continuous oversight enables engineers to anticipate challenges rather than react, leading to smoother workflows, fewer surprises, and better project outcomes.

While mental load overlaps with project management, the two differ significantly. Project management involves formal roles, defined processes, and structured tools for scheduling, budgeting, and resource allocation.

Mental load, by contrast, is a more informal, continuous awareness that keeps work flowing within and across these systems. Project managers oversee the system, but engineers carrying mental load work within it—bridging coordination gaps, catching potential issues, and adapting in real time without formal authority. This gray area between organizational charts and daily execution makes mental load hard to see and easy 64 STRUCTURE magazine

to undervalue, despite its critical role in project success.

By reframing mental load as strategic oversight rather than “extra effort,” we see it as the scaffolding supporting the entire project flow. It’s a form of leadership rooted in awareness, foresight, and the ability to guide teams through complexity without controlling every task. Effective project managers exemplify this balance—carrying mental load skillfully alongside managing formal processes to keep projects on track and teams aligned.

Misidentification and Undervaluation of Mental Load Despite its importance, mental load is often misunderstood or overlooked in professional settings. Those who carry this cognitive burden effectively are praised with labels like “naturally organized,” “helpful,” or “on-top-ofit.” While well-meaning, these compliments mistake mental load mastery for innate personality traits rather than deliberate, skill-based work. This misconception obscures the effort involved and makes the competency seem out of reach for those not already performing it.

Another common misunderstanding is seeing mental load as mere support rather than leadership. Individuals who take on this work are viewed as “reliable” helpers instead of recognized for their highlevel oversight and ability to guide project flow. Consequently, their contributions are treated as supplementary to technical work instead of foundational to success. This perception limits advancement into formal leadership roles despite these individuals already performing many leadership functions.

Additionally, mental load can be mistaken for low-value or administrative work. Because it doesn’t always involve direct technical output, it’s sometimes perceived as overhead or outside project scope. This not only devalues the work but reinforces a flawed system where critical coordination efforts go unrecognized in reviews, promotions, and planning. In reality, mental load is strategic work that reduces risk, improves communication, and enables efficient delivery. Misidentifying it as peripheral contributes to its uneven distribution and undervaluation in many firms.

Mental Load Is a Learnable Skill Like structural analysis or project management, carrying mental load is a teachable skill that can be broken down, practiced, and

improved. By treating it as a core competency, firms can intentionally train younger engineers to anticipate needs, track progress, and manage interdependencies across teams and disciplines.

The Role of Junior Engineers

What People See • Visible deliverables: drawings, calculations, deadlines, milestones.

• What gets measured and credited.

Junior engineers can begin cultivating mental load by expanding their perspective beyond What People Don't See individual tasks and building habits that 1. Tracking Interdependencies develop system-level awareness. This starts Knowing how parts relate and anticipating the with small but intentional shifts—asking quesdownstream effects. tions like, “Who uses this next?” or “What • Asking “What else does this decision affect?” else depends on this decision?” Instead of • Keeping a mental map of design stopping at a completed beam calculation, a dependencies. junior engineer might consider how that beam • Watching for cross-discipline coordination risks connects to a moment frame, whether its depth 4. Maintaining Big-Picture Awareness (e.g. MEP/arch conflicts). affects ceiling coordination, or if a last-minStaying oriented to the whole project even • Reviewing related drawing sheets after a while deep in details. ute architectural change will impact its span. change.

• Regularly revisiting milestones and After coordination meetings, they can practice deadlines. reflecting on what decisions were made, what 2. Anticipating Risks • Asking how today’s task fits into the bigger Foreseeing what might go wrong and preparing wasn’t discussed, and who might be affected goal. in advance. but wasn’t in the room. Keeping a personal log • Noting when small issues could delay the • Maintaining a mental list of fragile items of recurring issues, near-misses, or things that whole. (permits, long-lead materials). slowed progress is a simple but powerful way • Mentally updating status across teams, not • Learning from past near-misses or delays. to build pattern recognition over time. These just your own.

• Checking with others about what might be habits create a mindset that sees beyond the missing. immediate task to the larger project flow—an • Watching for ambiguous instructions or scope 5. Coordinating Without Authority Informal leadership to keep things moving. essential foundation for leadership growth. creep.

• Keeping a shared checklist or calendar.

Carrying mental load also means taking own• Reminding teammates of upcoming needs. ership of small but meaningful coordination 3. Bridging Communication Gaps • Stepping in to clarify when handoffs are Ensuring the right people are aligned and responsibilities. Junior engineers can build fuzzy. informed. this capacity by offering to track RFIs, moni• Encouraging accountability by example, • Following up with summaries after meetings. tor submittal schedules, or manage internal not directive.

• Clarifying next steps when no one else does. checklists in support of milestone readiness.

• Looping in someone who was absent but These tasks aren’t glamorous, but they teach affected. engineers to think ahead, follow dependencies, • Proactively checking on dependencies or RFIs. and anticipate where gaps might appear. When a senior redlines a lateral revision, a junior can take the initiative to review related holdown placement, slab edge coordination, or notes that may affect permit awareness and intention. documentation. These are opportunities to practice connecting details Equally important is the willingness of senior staff to let go of total to the bigger picture. Observing how senior engineers manage meet- control. Handing off parts of the mental load can feel risky—projects ings, communicate decisions, or summarize action items offers daily may slow down or encounter hiccups—but this discomfort is part of the examples of mental load in action. Emulating these behaviors—like learning curve. The short-term imperfection is a necessary investment in following up with a quick summary email after a discussion or check- long-term team capacity. Letting go doesn’t mean disengaging; it means ing in before a handoff—helps junior staff begin practicing leadership shifting from doing to guiding, from managing every detail to developthrough awareness, not authority. Over time, these efforts compound ing others who can. into trust, influence, and readiness for more complex responsibilities.

When senior engineers pair modeling with intentional delegation, they create an environment where mental load is shared more evenly and becomes part of the firm’s collective skillset. In turn, this cultivates The Role of Senior Engineers stronger teams, reduces burnout, and strengthens the leadership pipeline for the future.

Junior engineers won’t gain this fluency by diffusion. Senior staff play a pivotal role not only in mentoring, but in actively modeling mental load behaviors. This means narrating their thought processes, explaining how they anticipate coordination issues, and demonstrating how they track Attend This Session at the NCSEA Summit dependencies or manage communication across teams. By making the Author Angelina Stasulis will be presenting on the topic of mental load at the NCSEA invisible visible, experienced engineers help demystify this skill set and Summit held October 14-17 in New York City. For more information about the Summit, show that it’s not about instinct or engineering judgment—it’s about visit www.ncseasummit.com.

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Mental Load in Practice Takeaways for Junior Engineers

Takeaways for Senior Engineers

Start with Curiosity • Ask: “What happens after my task?” or “Who relies on this next?”

• Look beyond your assignment to see how your work fits into the broader project system.

Build Awareness Habits • Reflect after meetings: What was decided? What was missing?

Who else might be impacted?

• Keep a running list of coordination gaps, recurring issues, or unexpected delays to sharpen foresight over time.

Take Ownership of Small Systems • Volunteer to track RFIs, manage internal milestone checklists, or coordinate submittals.

• These roles teach you to anticipate needs and follow through on cross-team dependencies.

Practice Upstream Thinking • When a change occurs, consider how it ripples outward—drawing updates, schedule shifts, permitting implications.

• Anticipating the second- and third-order effects shows leadership thinking early.

Observe and Emulate • Watch how senior engineers manage flow: Do they recap meetings? Flag gaps early? Delegate clearly?

• Try adopting similar behaviors, even on a smaller scale—like following up after a discussion or clarifying next steps.

Communicate with Intention • Share progress with context: not just what you did, but why it matters and what’s next.

• Thoughtful updates build trust and demonstrate system-level thinking

Model the Invisible Work • Narrate your thinking: explain how you spot coordination risks, track dependencies, or anticipate bottlenecks.

• Make mental load visible by talking through decisions, tradeoffs, and early warnings—not just outcomes.

Mentor Through Context, Not Just Correction • When reviewing work, explain why something matters, not just what to change.

• Help junior staff connect their tasks to the bigger picture—system behavior, project phasing, or client expectations.

Let Go to Level Up • Delegate small pieces of coordination—checklists, meeting followups, or schedule tracking—and coach through mistakes.

• Trust-building comes from support and stretch, not perfection.

Letting go enables others to grow.

Create Space for Foresight • Invite junior engineers into planning conversations early—scope reviews, milestone prep, or client discussions.

• Give them a front-row seat to how mental load is carried across project phases and roles.

Recognize and Name Mental Load • Acknowledge team members who anticipate needs, catch misalignments, or keep others moving—even if they aren’t in formal leadership roles.

• Elevate this work in reviews, promotions, and team debriefs. What gets named gets valued.

Build a Culture That Shares the Load • Mental load shouldn’t default to the most organized or overburdened team member.

• Distribute responsibility intentionally and check in regularly to prevent silent burnout and uneven labor.

Consequences of Unrecognized Mental Load

Conclusion

When mental load is neither modeled, taught, nor shared, the burden falls on a few individuals—often without support or recognition. This concentration leads to burnout, as these key contributors become default problem-solvers and culture-builders, bearing heavy emotional and professional tolls.

Over time, invisible labor breeds resentment. Those carrying the load feel undervalued and overextended, stuck in a cycle where competence brings more burden but not more recognition. Others miss growth opportunities, appearing capable only because someone else maintains the mental scaffolding.

This imbalance creates systemic inequities. Those always in support roles have less time for visible work that drives promotion, while those shielded from responsibility may rise without learning leadership or coordination skills.

Firms suffer too. Projects become reactive, bottlenecks unnoticed until problems arise, and teams get caught off guard by lack of foresight.

Workflow becomes fragile, dependent on a few linchpins who, if unavailable, cause collapse.

Critically, when these linchpins leave—due to burnout, better opportunities, or life changes—the firm faces sudden knowledge gaps, coordination breakdowns, and leadership voids. Without a culture that shares and supports mental load, firms risk not just short-term disruption but lasting damage to institutional memory, client relationships, leadership pipelines, and performance.

By failing to intentionally teach and distribute mental load, firms limit their own resilience. They reduce their leadership pipeline and risk losing valuable contributors who burn out from shouldering too much—or walk away altogether.

Mental load is not a fixed personality trait or an extra burden to be shouldered by the most conscientious. It is a skill—teachable, learnable, and essential. Junior engineers can develop it through structured habits and mentorship. Senior engineers can model it, delegate it, and normalize its value through everyday practice. Firms that cultivate this competency create more effective project teams, strengthen their leadership pipeline, and reduce long-term risk.

To build stronger teams and healthier cultures, we must move beyond celebrating visible output alone. Recognizing and cultivating mental load is not just a matter of fairness—it’s fundamental to engineering integrity. ■

66 STRUCTURE magazine

Angelina V. Stasulis, PE, SE is a Senior Structural Engineer with Shear Structural in Atlanta, GA and has over 15 years of experience in complex building projects. With a background in education, she has a lifelong passion for teaching and sharing knowledge, which inspires her work mentoring and supporting others. She encourages everyone to actively develop mental load as a fundamental skill—one that is essential not just at work, but in all areas of life.

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