NONLINEAR FINITE-ELEMENT MODEL FOR LIGHT-FRAME STUD WALLS

Considerable attention has been given to the performance and modeling of wood-frame stud walls in the past two decades, and linear and nonlinear models were presented. Linear models do not truly describe the wall behavior. They either underestimate or overestimate the wall stiffness, depending upon load applied. In this presentation, the writers use load-deflection characteristics to transform a three-dimensional detailed model of a wood-frame stud wall into a simple two-dimensional model made equivalent to the original substructure by energy concepts. The detailed model is represented in three dimensions by linear and nonlinear finite elements, where each nail joint is included via its translational stiffness. Gaps and discontinuities in the sheathing are also considered. The model is loaded in shear, torsion, X-, and Y-bending, simulating simple tests of the real substructure. Results are used to identify properties of an "equivalent" orthotropic continuum. The application of equivalent models in a full-structure nonlinear analysis yields the global behavior of the structure (deflections and reactions), in reasonable computer times. The approach can be used for wood-frame stud walls with or without openings. The method may be particularly useful to those evaluating alternative designs in manufactured structures or for structures with redundant substructures.