Simplified Nonlinear Model of Straight-Sheathed Wood Diaphragms in Unreinforced Masonry Buildings

Abstract

A simplified nonlinear numerical model is proposed to predict the full dynamic response of straight-sheathed wood diaphragms in unreinforced masonry buildings. The straight-sheathing system is replaced with an equivalent Bernoulli beam element at the center of the diaphragm and parallel to the joists. Nonlinear rotational springs are used to simulate the moment couple generated by nail pairs at the wood-board-to-joist connections. The reduced multidegree of freedom model is able to capture the distributed properties of the diaphragm and maintain compatible out-of-plane displacements with supporting masonry walls. The versatility of the model is demonstrated through implementation in the research software OpenSees and commercial software SAP2000 to conduct modal, cyclic, quasi-static, and nonlinear response history analyses. Comparison to previously proposed numerical models for wood diaphragms including detailed finite element models and experimental results from the literature indicates that the reduced multidegree of freedom model accurately predicts the seismic response of wood diaphragms with computational efficiency. Finally, the reduced multidegree of freedom model is implemented within the numerical model of a large unreinforced masonry building to demonstrate its practical use and integration with masonry walls.