Nonlinear Modeling of Wood-Frame Shear Wall Systems for Performance-Based Earthquake Engineering: Recommendations for the ASCE 41 Standard

Abstract

Wood shear wall systems are the primary elements of seismic force-resisting system (SFRS) in virtually all light-frame wood buildings. Wood-frame buildings are unique because their nonstructural wall finishes, such as gypsum wallboard and stucco, provide significant strength and stiffness relative to that of the intended SFRS. Given the fact that nonstructural wall finishes can consist of multiple layered materials, it is essential to understand and characterize their behavior. The development of accurate and robust numerical models to capture the inelastic behavior of individual shear wall systems and buildings comprised of these wall systems is a critical step when performing nonlinear analyses for either design, evaluation, or upgrade of existing buildings using standards such as ASCE 41-13 [(ASCE 213). ASCE 41-13: Seismic evaluation and retrofit of existing buildings]. In general, existing modeling approaches do not account for the implementation of residual strength and displacement, which have been observed for light-frame wood buildings during shake-table tests. Furthermore, nonlinear representation of elements in the ASCE 41 standard considers only cyclic envelopes to define the nonlinear response of wood shear wall systems and not full hysteretic properties. To address these challenges, this study was divided into three main parts. The first part focused on the development of an excessive synthesis of wall assembly tests incorporating different wood sheathing materials and material combinations, and the evaluation of their force-displacement response. The second part introduced a new envelope curve proposed for modeling wood-frame wall systems with the parameters of this curve identified for the different material combinations included in the synthesis of Step 1. Finally, the proposed backbone curve was implemented in a case study of a multifamily wood frame building subjected to seismic excitation. Incremental dynamic analyses were conducted considering both the proposed envelope curve and the ASCE 41 modeling recommendations, and the response of the building structure was evaluated for three different performance levels (immediate occupancy, life safety, and collapse prevention) through fragility analysis. The main objective of this study was to introduce a beneficial wall-system level modeling tool for nonlinear analysis of light-frame wood buildings as specified in codes and standards in the United States.