Brief
Major changes to the seismic design of diaphragms and their chords and collectors are contained in the 2022 edition of the ASCE/SEI standard “Minimum Design Loads and Associated Criteria for Buildings and Other Structures.” Kelly Cobeen gives a rundown of the changes and why they necessitate choosing among three methods of diaphragm seismic design, as well as the need to include other updates.
Insight
Using ASCE/SEI 7-22
Designers using the 2022 Edition of the ASCE/SEI standard Minimum Design Loads and Associated Criteria for Buildings and Other Structures (ASCE/SEI 7-22, ASCE, 2022) will find significant changes to the seismic design of diaphragms and their chords and collectors:
A new diaphragm design methodology added, an existing methodology expanded, significant changes affecting bare steel deck diaphragms, and more. This leaves the user needing to choose between three methods of diaphragm seismic design and needing to incorporate other updates into their designs.
The changes were generated from research and code development efforts that go back years, with contributions from many, including research and guideline development teams and the NEHRP and ASCE 7 update participants. This article provides an overview of these changes to diaphragm seismic design from the designer’s perspective.
Three Methods
The three diaphragm design methods found in ASCE/SEI 7-22 are the traditional design method of Section 12.10.1 and 12.10.2, the Alternative Design Provisions for Diaphragms including Chords and Collectors (alternative design provisions) of Section 12.10.3, and the Alternative Diaphragm Design Provisions for One-Story Structures with Flexible Diaphragms and Rigid Vertical Elements (alternative RWFD design method) of Section 12.10.4.
The traditional design method of Section 12.10.1 and 12.10.2 has been used with only minor changes since the 1980s;
This was the only diaphragm design method available in building codes until ASCE/SEI 7-16 (ASCE/SEI, 2017). When using the traditional design method, diaphragm design forces are determined based on the seismic design parameters for the vertical elements of the seismic force-resisting system without consideration of the effect of the diaphragm system on the response of the structure. This method is permitted for all structures, except precast concrete diaphragms in Seismic Design Categories (SDCs) C through F.
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