Strength-Based Seismic Reliability of Wood Shear Walls Designed According to AF&PA/ASCE 16

In the United States the vast majority of single and multifamily homes are constructed using light-frame wood construction which typically consists of dimension lumber sheathed with plywood or oriented strand board. These structures resist lateral loads such as those produced by wind or earthquakes by a system of wood shear walls. One widely used design standard that governs the design of wood shearwalls is the specification provided by American Forest and Paper Association/American Society of Civil Engineers 16 (AF&PA/ASCE-16). This load and resistance factor design (LRFD) design standard (released in 1996) was soft calibrated from the existing allowable stress design code for wood structures, and thus the reliability of wood shear walls designed using AF&PA/ASCE 16 is not explicitly known. To date, no study has evaluated the level of reliability provided by wood shear walls built using accepted design values or prescriptive (deemed-to-comply) procedures. The objective of this study was to examine the strength-based reliability of a portfolio of wood shear walls subjected to earthquake loading. This was one specific task of an ASCE/SEI Special Project entitled Re-evaluation of LRFD for Engineered Wood Products: Keeping Pace with Changes in ASCE 7. The reliability indices were calculated by examining the performance of a portfolio of 12 different wood shear walls, each designed according to AF&PA/ASCE 16. An existing suite of earthquake ground motions for Los Angeles was used to determine seismic demand through a series of nonlinear hysteretic time domain analyses. The results presented herein may be useful in reevaluating existing design codes and can provide guidance to technical committees responsible for maintaining and updating codes and standards.