Seismically inadequate buildings are often demolished without due consideration for unique retrofit solutions which may provide the necessary strength and ductility to the existing structure.  Buckling restrained braces are one solution which can be used in buildings with weak lateral systems, seismic irregularities, or load path discontinuities, and there are many creative ways to incorporate these braces to add strength and ductility to the existing lateral system.

In the August 2023 SEU session, Kimberley Robinson, SE, PE, from EVER Seismic, presented It’s Better to Bend than Break: Retrofitting with Buckling Restrained Braces and Steel.  Kim identified frequent problems with seismically inadequate buildings and explained how Buckling Restrained Braced Frames are used to address inadequacies in buildings.She also covered some of the requirements for retrofits that are included in ASCE 7-22 and ASCE 41-17.

Kim offered some unique solutions to retrofitting buildings with buckling restrained braces, especially for buildings which are very complicated, congested, or cannot be out of use for long periods of time for construction.  One example could be working from the exterior of the building by removing the facade to install new BRBs within the existing wall so that there is minimal disruption to the facility.

Another option might be to install BRBs on the exterior of the building which are attached to new elastic buttress frames.  This is especially useful for buildings that are congested with existing equipment and piping.  These new steel buttress frames are designed to be stronger than the BRBs to limit the seismic drift of the existing building.

For buildings with existing braced frames, elements of the existing frame can be replaced with BRB “fuse” elements which protect the other existing frame elements which remain elastic.  Some existing connections may need to be modified to accommodate the additional demand on the frame, but this option results in minimal change within the building layout.

BRBs can also be installed with a rocking frame or wall within the building.  The wall or frame remains elastic, while the BRBs take the inelastic demand to strengthen the seismic lateral system.

Kim also provided a solution for two buildings which were anticipated to pound during a seismic event.  With BRBs installed across the joint of the two buildings, and an additional BRB running laterally along the joint to combat the shear between the buildings, the anticipated movement between the buildings is reduced.

Many creative solutions exist, but some require a “thinking outside the box” mentality to incorporate in congested or complex structures.  These examples are just a few of the possibilities for using buckling restrained braces to retrofit existing structures which do not meet the requirements of current seismic building standards.

Emily Guglielmo, PE, SE, Martin/Martin

In June 2023, Emily Guglielmo, PE, SE, from Martin/Martin, presented ASCE 7 Frequently Asked Questions (Seismic). She nominated LeaderFlow (LeaderFlow – Leadership for AEC professionals) for the SEU Speaker Inspires donation of the month.

Emily shared “I chose LeaderFlow because Structural Engineering has been significantly underrepresented by diverse leadership, and there are still challenges with retaining diverse talent. One large gap in this career pipeline is the opportunity for mid-career professionals, especially those of color to access vital leadership development training and LeaderFlow is working to close that gap.”

Thank you, Emily, for helping structural engineers with your SE University session, and for your designation of LeaderFlow 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.

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.

Matthew Mester, PE, SE MiTek, Inc.

In March 2023, Matthew Mester, PE, SE, from MiTek, Inc., presented Steel Moment Frames: Design Principles & AISC 341/358 Provisions. In 2017, he nominated the Structural Engineers Association of Southern California Foundation (http://www.seaosc.org) for the SEU Speaker Inspires donation of the month, and he has chosen to do the same in 2023.

The Structural Engineers Association of Southern California Foundation, in its goals to further the development of the structural engineering profession, looks for partners, be it individuals, companies or corporations, to pursue structural engineering innovation and research for use in the public domain. The foundation can assist in the development process of specific structural engineering research projects and publishing of any findings.

The foundation is dependent upon donations for its operation and funding of research projects and annual student scholarships.  Matthew chose to donate to the SEAOSC Foundation for student scholarships to “help the next generation of structural engineers.”

Thank you, Matthew, for helping structural engineers with your SE University session, and for your designation of the Structural Engineers Association of Southern California Foundation 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.