Seismic Analysis of Woodframe Structures. I: Model Formulation

A simple numerical model to predict the dynamic characteristics, quasistatic pushover, and seismic response of woodframe buildings is presented. In this model the building structure is composed of two primary components: rigid horizontal diaphragms and nonlinear lateral load resisting shear wall elements. The actual three-dimensional building is degenerated into a two-dimensional planar model using zero-height shear wall spring elements connected between adjacent diaphragms or the foundation. The degrading strength and stiffness hysteretic behavior of each wood shear wall in the building can be characterized using an associated numerical model that predicts the walls load-displacement response under general quasistatic cyclic loading. In turn, in this model, the hysteretic behavior of each shear wall is represented by an equivalent nonlinear shear spring element. With this simple approach the response of the building is defined in terms of only three degrees of freedom per floor. This numerical model has been incorporated into the computer program SAWS (seismic analysis of woodframe structures). This paper discusses model formulation. In Part II, the predictive capabilities of this program are compared with recent shake table tests performed on a full-scale two-story woodframe house.