Have you ever been in a project meeting and needed to make a quick estimation of beam sizes without any reference books?  Experience alone can sometime suffice, but a quick rule of thumb can be helpful to determine the beam weight needed for a given loading condition.

In the September 2023 SEU session, John A, Kennedy, SE, PE, from Structural Affiliates International, Inc.presented Rules of Thumb for Steel Design.  John shared some quick reference approximations for mechanical properties of steel sections.  He also identified some rules of thumb for the design of beams, columns, and trusses, and shared some design examples using these rules. 

John offered a quick, simple equation for determining the beam weight based on the moment and selected beam depth. For 50 ksi steel, the slide below shows this quick, useful equation which results in the beam weight per foot based on the moment in kip-feet and the beam depth in inches.

John walked through an example using this rule of thumb to determine the beam weight needed for a 16 inch beam which is 32 feet long with a dead load of 1 kip per foot.

As you can see, the rule of thumb was quite accurate to make a quick determination for the beam size needed for this given loading condition.  John noted that all rules of thumb are approximations and are not always conservative; however, they can be very useful when an on-the-spot intelligent decision is needed.  A rigorous structural analysis should always follow when more time allows.

Using web based tools can save time and increase efficiency during structural analysis, and often these tools are the most up-to-date resources which include changes and updates to the code.  Are you aware of the many online resources available to assist with calculating the shear strength and stiffness of steel deck diaphragms?

In the July 2023 SEU session, Mike Antici, PE, from Vulcraft, and Thomas Sputo, SE, PE, from Sputo and Lammert, LLC, presented, on behalf of the Steel Deck Institute, Diaphragms Are More Than Just Deck and Fasteners.  Tom and Mike explained how traditional shear mechanics are applicable to diaphragms and how the shear stiffness analysis can be used in lieu of designing a diaphragm as rigid or flexible.  They also reviewed capacities and limitations of  joists, deck, and fasteners.  

During the presentation, Tom and Mike mentioned several online tools and analysis resources for diaphragm and fastener checks.  For example, SDI has a Diaphragm Interaction Calculator which produces deck capacities based on the user’s input of various deck profiles, thickness, and spans, as well as different fastener sizes and spacings.  Tom noted the importance of using the correct number of spans in this online tool since the stiffness of the deck is proportional to the number of spans, while the deck strength is inversely proportional to the number of spans.  This free online tool calculates the shear strength and stiffness of the diaphragm as well as the interactive allowable shear strength under combined loads with uplift.

Mike noted that SDI is not the only tool available; many deck and fastener manufacturers have also developed online tools.  Hilti offers its users PROFIS DM Diaphragm which is offered as a free software download.  Nucor offers its customers a Bare Deck Diaphragm tool as well as a Deck-Slab Diaphragm tool which is available free for registered users.  Also, New Millennium Building Systems offers a web based calculator, Deck Tools,  for deck diaphragm capacities.  This online tool allows for roof deck, composite deck and form deck calculations with various fastener patterns.  Simpson Strong-Tie has developed a Steel Deck Diaphragm Calculator as well, which can be used to produce the necessary diaphragm capacity tables for your deck configuration.

Tom and Mike highlighted a number of recent changes within the code which affect the capacity of deck diaphragms, and Mike strongly recommended using these online tools in favor of published manufacturers tables which may be outdated or not include these new code provisions.  Deck diaphragms are a critical component of the lateral force resisting system, and using these free, available resources can validate that all aspects of the diaphragm are capable of providing a continuous load path for your structure.

If a building consists of bearing walls, shear walls, and braced frames, should the building be classified as a bearing wall system or a building frame system?  While an argument can be made in favor of each side, which system is the most appropriate?

In the June 2023 SEU session, Emily Guglielmo, PE, SE, from Martin/Martin, presented ASCE 7 Frequently Asked Questions (Seismic).  Emily covered many frequently asked questions regarding seismic design according to ASCE7 and explained the rationale for key updates to ASCE 7-16 and ASCE 7-22 seismic load provisions.

Emily addressed a common question encountered by engineers when determining what type of seismic force resisting system is most applicable to their structure.  While a moment frame system is quite obvious, distinguishing the difference between a bearing wall or building frame system can be more challenging. 

A bearing wall system is defined as a structural system with bearing walls providing support for all or major portions of the vertical loads.  Shear walls or braced frames provide seismic force resistance.  A building frame system is a structural system with an essentially complete space frame providing support for vertical loads and the seismic forces are resisted by shear walls or braced frames.  As Emily pointed out, these definitions leave some ambiguity as to how the vertical loads are supported.

How then should an engineer decide between the two for a structure which is comprised of bearing walls, shear walls, and braced frames?  Selecting a system with a higher R value would reduce the seismic base shear, but Emily explained that the intent of the provisions is to prevent a situation where a brittle and catastrophic failure of a lateral force-resisting element also results in the collapse of the vertical load carrying capacity of the building.  Thus, when deciding whether a “major” portion of the vertical load is supported by columns or bearing walls, the engineer may want to consider the intent of the provision rather than adhere to a stringent 51/49 percent determination on how the vertical loads are supported.  Emily advised using a lower R value in cases where shear walls provide a good portion of the gravity loads since this type of system can result in more catastrophic damage in a seismic event if the lateral system is damaged or fails.

While ASCE 7 does leave some room for interpretation, the intent of the code should always be considered when selecting the seismic force-resisting system.  While selecting a higher R value is always tempting, structural engineers should consider the implications of their choices and be able to justify their reasoning.

In July 2023, Mike Antici, PE, from Vulcraft, and Thomas Sputo, PE, SE, from Sputo and Lammert, on behalf of the Steel Deck Institute, presented Diaphragms are More Than Just Deck and Fasteners.  They selected the Miracle League of Florence County (Miracle League of Florence County – Serving Special Athletes in Florence and Surrounding Counties) for the SEU Speaker Inspires donation of the month.

The Miracle League of Florence County aims to offer individuals with special needs the opportunity to participate in the sport of baseball in a community supported, safe, adapted and encouraging environment.

Thank you, Mike and Tom, for helping structural engineers with your SE University session, and for your designation of the Miracle League of Florence County as our SEU Speaker Inspires Organization of the Month!

SE University began the SEU Speaker Inspires program in 2015 as a way to “pay it forward”, enabling our speakers to designate a charity/organization of their choice for SE University to make a donation to help improve our world.

Podium structures have increased in popularity in recent years. Are you familiar with the 2-stage seismic analysis procedure in ASCE 7 and necessary structural considerations with this type of structure?  ASCE offers guidance for this procedure, but some provisions are more straightforward than others.

In the June 2023 SEU session, Emily Guglielmo, PE, SE, from Martin/Martin, presented ASCE 7 Frequently Asked Questions (Seismic).  Emily covered many frequently asked questions regarding seismic design according to ASCE7 and explained the rationale for key updates to ASCE 7-16 and ASCE 7-22 seismic load provisions. 

Emily clarified several questions on the 2-stage seismic design of podium-type structures.  To hear Emily explain the most commonly confused provisions, watch this short 3 minute video:

ASCE 7 has included some changes in the 2022 cycle to clarify past confusion with the 2-stage procedure, and as Emily noted, more work is forthcoming on the 2-stage seismic analysis provisions to clarify this procedure for practicing engineers and code officials in future editions.

Cathleen Jacinto, PE, SE, FORSE Consulting and Steel Tube Institute

In May 2023, Cathleen Jacinto, PE, SE, from FORSE Consulting and the Steel Tube Institute, presented Know Your HSS Welds. She selected the Pancreatic Cancer Action Network (Pancreatic Cancer Action Network – Research, Patient Support, Resources (pancan.org)) for the SEU Speaker Inspires donation of the month.

The Pancreatic Cancer Action Network, or PanCAN, seeks to create a world in which all patients with pancreatic cancer will thrive.  Their mission includes improving the lives of everyone impacted by pancreatic cancer by advancing scientific research, building community, sharing knowledge, and advocating for patients.

Thank you, Cathleen, for helping structural engineers with your SE University session, and for your designation of the Pancreatic Cancer Action Network as our SEU Speaker Inspires Organization of the Month!

SE University began the SEU Speaker Inspires program in 2015 as a way to “pay it forward”, enabling our speakers to designate a charity/organization of their choice for SE University to make a donation to help improve our world.

Are you familiar with the similarities and differences between the various seismic moment frame systems allowed by code?  As the seismic hazard increases, more ductility is required, but how is that accomplished?

In the March 2023 SEU session, Matt Mester, PE, SE, from MiTek, Inc., presented Steel Moment Frames: Design Principles & AISC 341/358 Provisions.  Matt identified the four types of moment frames allowed by the building code, and how to choose a system based on the seismic criteria.  He then reviewed the design provisions contained in AISC 341 for SMF, IMF, and OMF systems.  Matt also reviewed the AISC 358 connection types and why you would choose one for your project.

Depending on your seismic criteria, some moment frame systems are more appropriate than others.  Matt noted that, when allowed, most engineers will select an R=3 moment frame system which is not specifically required to be detailed for seismic resistance.  These R=3 systems are only permitted in Seismic Design Categories A, B, and C with no limits on height, and are typically found in a wind governed structure.  AISC 360 dictates the design of these systems, and the LRFD or ASD load combinations for both wind and seismic must be checked, however drift limits typically control the design.

For areas of higher seismic activity, the design category may push the EOR to select a moment frame system that is specifically designed and detailed for seismic resistance.  The three options include R=3.5 Ordinary Moment Frames, R=4.5 Intermediate Moment Frames, and R=8 Special Moment Frames.  The three systems are required to have explicit deformation capabilities, strength requirements, and connection detailing limitations.  Matt included these helpful slides in his presentation which are a useful quick reference for breaking down the differences in these moment frame systems:

Using these chart comparisons, the EOR can identify the required drift angles, connection shear strength required, and various section references to find connection detailing requirements within the AISC 341 and 358.  Matt noted that as the R value increases, the system ductility must increase, which leads to more stringent bracing and connection details which can be found in Chapter E of AISC 341.  Being familiar with the differences between these systems can help engineers ensure compliance with the system ductility and drift requirements for their seismic moment frame projects.

Renovation projects are often complex endeavors in which engineers often lack pertinent structural information of the original design and any subsequent changes to the building.  Investigating old records from previous owners, historical resources and searching for photographs taken during construction can be helpful; however, engineers typically need more definitive material specifications to ensure the capacity of the system can sustain new intended loads for the structure.

In the April 2023 SEU session, D. Matthew Stuart, PE, SE, P.Eng, F.ASCE, F.SEI, A.NAFE, from Partner Engineering and Science, Inc., presented Adaptive Reuse of the Historic Witherspoon Building.  Matthew reviewed the different types of vintage structural components used at the historic Witherspoon building in Philadelphia, PA.  He explained the different approaches used to determine the load carrying capacity of the existing floor and roof framing and talked about the historical reasons for the development and use of hollow clay tile arch framing systems.

Due to the age of the structure and lack of construction documents, the steel used on the project was tested to determine the actual yield strength to be used in the renovation design.  After the presentation, Matthew was asked for guidance on coupon testing steel from an existing structure, and he provided some tips for successfully determining the yield strength.

Matthew noted that a steel coupon test only needs a sample about 2 inches wide and 6-8 inches long to perform the load test.  Typically, the steel can be safely collected from redundant areas of the structure such as the bottom flange of a simply supported beam near the support or the bottom chord extension of an open web steel joist.  Exploratory demolition may also be necessary to locate structural systems hidden behind walls or ceilings.

Lab testing can then be performed to determine the yield strength of the steel.  Typical testing standards include ASTM A370 Standard Test Methods and Definitions for Mechanical Testing of Steel Products or ASTM E8 Standard Test Methods for Tension Testing of Metallic Materials at room temperature.

It is common during reuse or renovation projects to be without necessary design information from the original construction.  While educated design assumptions based on historical data must be used, material  lab testing ensures designers do not use overly conservative assumptions, and can maximize the capacity of the structural system being repurposed.

D. Matthew Stuart, PE, SE, P.Eng., Partner Engineering and Science, Inc.

In April 2023, D. Matthew Stuart, PE, SE, PEng., F.ASCE, F.SEI, A.NAFE, from Partner Engineering and Science, Inc., presented Adaptive Reuse of the Historic Witherspoon Building. Matthew nominated the United Methodist Committee on Relief (UMCOR) (UMCOR – Global Ministries (umcmission.org)) for the SEU Speaker Inspires donation of the month.

According to it’s mission statement, UMCOR is the humanitarian relief and development arm of The United Methodist Church and it assists churches to become involved globally in direct ministry to persons in need. UMCOR comes alongside those who suffer from natural or human-caused disasters – famine, hurricane, war, flood, fire or other events—to alleviate suffering and serve as a source of help and hope for the vulnerable. UMCOR provides relief, response and long-term recovery grants when events overwhelm a community’s ability to recover on their own. UMCOR also provides technical support and training for partners to address emerging and ongoing issues related to disaster relief, recovery, and long-term health and development.

Thank you, Matthew, for helping structural engineers with your SE University session, and for your designation of the United Methodist Committee on Relief as our SEU Speaker Inspires Organization of the Month!

SE University began the SEU Speaker Inspires program in 2015 as a way to “pay it forward”, enabling our speakers to designate a charity/organization of their choice for SE University to make a donation to help improve our world.

Intermediate Moment Frame systems and Special Moment Frame systems have stringent connection detailing specifications and limits.  Selecting the best prequalified connection for your system can be confusing given the many stipulations and options available.

In the March 2023 SEU session, Matt Mester, PE, SE, from MiTek, Inc., presented Steel Moment Frames: Design Principles & AISC 341/358 Provisions.  Matt identified the four types of moment frames allowed by the building code, and how to choose a system based on the seismic criteria.  He then reviewed the design provisions contained in AISC 341 for SMF, IMF, and OMF systems.  Matt also reviewed the AISC 358 connection types and why you would choose one for your project.

Matt included some very useful slides in his presentation which summarize the limitations for the prequalified connection contained in AISC 358.  The limitations include span/depth ratios, beam and column depth and weight limits, as well as flange thickness limits as shown in the slides below:

These useful charts are a great quick reference when you need to identify which prequalified connection might work best given certain beam and column sizes on your next project.  Click on the slide to print a PDF copy to keep on hand when you start detailing your next IMF or SMF project.