Are wood diaphragms presumed to be non-rigid in the 2015 International Building Code (IBC)?


The 2015 IBC references the 2015 Special Design Provisions for Wind and Seismic (SDPWS). There's a paper on our website outlining changes to the 2015 SDPWS to clarify flexible, rigid, and semi-rigid diaphragms: http://www.awc.org/pdf/codes-standards/publications/sdpws/StructureMag-SDPWS2015-Changes-1507.pdf

In Section 4.2.5, diaphragm flexibility terminology was revised to utilize the terms “idealized as flexible”, “idealized as rigid”, and “semi-rigid”, consistent with ASCE 7-10 Minimum Design Loads for Buildings and Other Structures. The condition for which a wood diaphragm is permitted to be idealized as rigid (e.g. in-plane deflection of the diaphragm is less than or equal to two times the average deflection of adjoining vertical elements) remains unchanged from prior editions of SDPWS. The significance of “idealized” is to recognize that wood diaphragms always have some rigidity, and are neither truly flexible nor truly rigid but can be idealized as such where certain conditions are met. These idealizations are employed to simplify structural analysis for distribution of horizontal diaphragm shear loads