Overstrength for Diaphragm in Precast Building

[ChrisNYCEng]

Hi, I have a question regarding the use of the overstrength factor for diaphragm and chord reinforcement. The building is a precast parking garage and is classified as seismic design category C. The latest edition of ASCE7 indicates overstrength is required in the design of collector elements. However, both the 6th and 7th edition of PCI state that overstrength is not recommended in the design of these elements for SDC A, C AND C (PCI Design Handbook, 7th Edition, Section 4.2.6.1). I know IBC/ASCE govern over PCI, I am just looking for some sort of reasoning or explanation as to why PCI contradicts IBC, and if there is anyway to avoid the use of this overstrength factor.

Best,
Chris

 

[tdoung]

The system overstrength factor (omega) is required by code. The PCI handbook introduces a diaphragm overstrength factor. The diaphragm overstrength is a recommendation that applies the structure even when the system overstrength is not triggered. In other words, the PCI Hndbk 7's recommendation is above & beyond the code.