Horizontal wood diaphragm systems, whether decked with conventional or mass timber panels, transfer wind and seismic loads to vertical elements of the lateral force-resisting system (LFRS), in flexible, rigid, or semi-rigid fashion. Characterizing and calculating the resulting diaphragm deflections determines the distribution of forces to critically loaded components and a significant portion of lateral building translations and rotations. Deflection equations for sheathed wood structural panel (WSP) diaphragms are well established in U.S. design standards in a 4-term expression that models flexural, shear, and fastener-slip deformations, but similar equations for cross-laminated timber (CLT) diaphragms have yet to unfold, despite growing industry consensus that CLT panels make efficient slabs and decks. Building code standards require CLT diaphragm deflections be computed using principles of engineering mechanics. The current 3-term and 4-term deflection equations for WSP diaphragms are based on various assumptions that are often outpaced by current design practice. This is the second of two companion papers, where the first paper (Lawson et al. 2023) provides the full generalized derivation of the current 4-term WSP diaphragm deflection expression with a mechanics-based expansion to unify both potential WSP and CLT applications. This second paper builds on the first paper by expanding the generalized equation with implementation insights unique to WSP and CLT diaphragms. Various challenges of calculating diaphragm deflections associated with current design practices are discussed with suggestions to assist in implementation.


Architectural Engineering

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Full Citation: Lawson, J., S. Breneman, and M. Lo Ricco. 2023. "Wood diaphragm deflections. Part II: Implementing a Unified Approach for Current CLT and WSP Practice." Journal of Architectural Engineering. Vol. 29, Issue 3, Sept. 2023, Reston, VA: ASCE. https://doi.org/10.1061/JAEIED.AEENG-1574



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