Seismic Performance of Gypsum Walls - Analytical Investigations

The aim of this study is to develop analytical models to predict the seismic performance of gypsum drywall partitions. The analytical investigation summarized in this report is a companion to a wall panel test program conducted at San Jose State University. These test panels were detailed to represent partition walls, featuring door and window openings to provide data on damage initiation due to cracking around the openings. The tests were configured to represent the boundary conditions of interior wall partitions with corner taping to the adjacent ceiling and walls. Data from seventeen wall tests, together with other published data, are utilized to develop and calibrate models to simulate load-deformation response of drywall panels and cracking damage around door and window openings. Fragility models for cracking damage are useful both for design, e.g., to predict wall damage and the associated repair costs, and for post-earthquake investigations to infer seismic demands from observed wall damage.

Probabilistic fragility models are developed to estimate the length of cracks propagating from window and door openings as a function of the imposed wall drift. Two approaches were developed for predicting cracking damage in gypsum walls. One is a simple empirical approach based on the wall test data. The second method combines the fracture mechanics damage analyses with the wall test data, which permits one to generalize the test results to conditions beyond those considered in the testing program. This method assumes variability in the critical stress intensity factor and modulus of elasticity and relates these to variability in the cracking damage using fracture mechanics. The fragility data indicate that cracks around window and door openings reach 1-inch lengths at wall drift ratios between 0.05 to 0.1% and grow to 12- inches at ratios of 0.3 to 0.7% drift. Generally, the cracks reach their full lengths and stop growing by wall drift ratios of 1% or roughly 1-inch drift in an 8-foot tall wall. Under increasing drifts the crack lengths remain constant while crack widths continue to increase.

Fragility models for other types of wall damage, such as localized failure around connections, wall panel buckling, etc., and information on repair costs are summarized in the companion report on the wall tests by researchers at San Jose State University. Together, these two reports (this report and the companion report) provide important data to characterize the role of gypsum partition walls in resisting earthquake induced-deformations and the damage to the walls resulting from these deformations.