Corotational Model for Cyclic Analysis of Light-Frame Wood Shear Walls and Diaphragms

Abstract

This paper presents a new two-dimensional shear-wall and diaphragm model developed as part of a Network for Earthquake Engineering Simulation (NEES) Project entitled NEES-Soft: Seismic Risk Reduction for Soft-Story Woodframe Buildings. A large portion of the older multistory buildings in the California region were constructed with a deficiency that makes them vulnerable to collapse in the first story during earthquakes. This deficiency is referred to as soft-story. The new model presented in this paper was developed using a corotational formulation, which makes it suitable for modeling the side-sway collapse of wood shear walls under large displacement as well as estimating the in-plane stiffness of floor diaphragms. To achieve high computational efficiency, a nodal condensation technique is used to eliminate the degrees of freedom (DOFs) associated with the nail connections from the global DOFs of the model. To verify the validity of the new model, the model was coded into a computer program and was used to analyze selected shear walls and diaphragms tested by various institutions and research programs. Good agreement was observed between the test and model-predicted backbone and cyclic curves for shear walls with various gravity loads and different anchorage conditions. The model is highly flexible and has been shown to be able to model older shear wall construction with horizontal sheathing boards and diagonal bracings.