Sensitivity of Wood-Frame Shear Wall Collapse Performance to Variations in Hysteretic Model Parameters

Abstract

This paper presents a numerical investigation of the influence of varying three parameters of the cyclic analysis of shear walls in wood-frame structures (CASHEW) 10-parameter wood-frame shear wall hysteretic model that have distinctly different effects on the shape of the backbone curve. The purpose is to assess the sensitivity of wood-frame shear wall collapse performance to changes from the baseline assumptions used to validate the FEMA P695 collapse performance methodology. The variations in backbone curve shape are intended to reflect observed variations in experimental response due to test methods, test boundary conditions, and shear wall aspect ratio. The paper also investigates the influence of including P-delta effects and the use of assumed equivalent viscous damping of 5% of critical. The baseline assumptions exclude P-delta effects and use 1% damping. A total of 126 unique analyses are conducted for six of the FEMA P695 wood-frame shear wall index models ranging from two to five stories. The results show that improved collapse performance (increased adjusted collapse margin ratio) occurs for hysteretic model assumptions that reduce (less negative) postpeak stiffness, increase displacement at peak strength, and increase peak strength intercept. These hysteretic model changes produce improved collapse performance for cases modeled with and without P-delta and for cases modeled with 1% and 5% damping. The inclusion of P-delta effects reduces adjusted collapse margin ratio by an average of 10% relative to the without-P-delta baseline. Use of 5% damping in these models improves adjusted collapse margin ratio by an average of 13% relative to the 1% damping baseline.