The Effects of Diaphragm Flexibility on the Seismic Performance of Light Frame Wood Structures

Abstract eng:
Several experimental and mathematical studies on light frame wood structures (LFWS) have been performed in the last few decades. The current residential design guideline still does not consider the actual flexibility of diaphragm in analyzing LFWS when they are subjected to lateral loads. For lateral force distribution, the guideline assumes the in-plane stiffness of diaphragm as either negligible or infinite. This paper presents work targeted to study the effects of diaphragm flexibility on the seismic performance of LFWS. Finite element models of various LFWS are created and nonlinear response history analyses are performed using the Imperial Valley and Northridge ground motions. These analyses encompass the parametric study on the LFWS with varying aspect ratios, diaphragm flexibility and lateral force resisting system. Torsionally irregular house models showed the largest range of variation in peak base shear of individual shear walls, when corresponding flexible and rigid diaphragm models are compared. It is found that presence of an interior shear wall helps in reducing peak base shears in the boundary walls of torsionally irregular models. The presence of interior wall was also found to reduce the flexibility of diaphragm. A few analyses also showed that the nail connections are the major source of in-plane flexibility compared to sheathings within a diaphragm, irrespective of the aspect ratio of the diaphragm.

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