In several upcoming articles in Structural Engineer Magazine, we will be discussing how modeling different types of diaphragms in commercially available software may impact results. The diaphragm types that will be discussed are No Diaphragm/Flexible Diaphragm, Rigid Diaphragm, Semi-Rigid Diaphragm, and Pseudo-flexible diaphragm.
Diaphragms are used to distribute horizontal forces to lateral frames/walls in a building. The type of diaphragm that is modeled impacts how the loads are distributed. Does metal roof deck constitute a rigid diaphragm? A podium slab? What about Concrete on top of metal deck?
In the November 2011 SE University session: Diaphragm Considerations for Structural Engineers, Allen Adams, PE, SE of Bentley Systems discussed how ASCE7-10 defines a rigid diaphragm in Chapter 12 (Seismic Design Requirements for Building Structures). The video below discusses the ASCE7 definition of a rigid diaphragm, and the irregularities that can affect the rigid diaphragm idealization.
Please let us know if you have any questions. We hope you find the information helpful.