Wood Diaphragm Deflections. II: Implementing a Unified Approach for Current CLT and WSP Practice

AE1574 Wood Diaphragm Deflections. Part II: Implementing a Unified Approach for Current CLT and WSP Practice By John Lawson S.E., M.ASCE1, Scott Breneman Ph.D., M.ASCE2 and Marco Lo Ricco Ph.D., M.ASCE3 Abstract 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