|CUREE-Caltech Woodframe Project
Element 1 - Testing & Analysis
Task 1.4.6 Wall Finish Materials
PI: Gregory G. Deierlein (Stanford University) - Analysis
PI: Kurt McMullin (San Jose State University) - Lab Testing
This task involves investigations of seismic response and damage to gypsum drywall.
Main Objectives and Methodology
The overall aim of the investigation is to understand the damage characteristics and to accurately relate seismic response to wall repair costs. A related component of the study is to improve understanding of the shear strength and stiffness gypsum drywalls and to develop response models that can be incorporated in simulation studies to look at the performance of overall woodframe systems.
This investigation includes two related efforts. One is a wall testing program being conducted under the direction of Prof. K. McMullin at San Jose State University, and the second is an analytical portion being conducted by Deierlein and Kanvinde at Stanford University. A summary of the testing portion is provided in a separate write-up by McMullin. This summary deals with the analytical portion.
The overall objective of the analysis study is to enable one to generalize results and behavioral observations from the wall tests. The study has two main aspects. One is to develop a nonlinear strut model (single degree of freedom spring) of the lateral load-deformation response of the wall. This model incorporates a backbone curve that describes the envelope of load-deformation response, including expressions to calculate the initial stiffness and ultimate strength of the wall. The backbone curve is then combined with a hysteretic expression that accounts for stiffness and strength degradation (including pinching response).
A second aspect of the study deals with modeling wall cracks that initiate and propagate from door and wall openings. These are only one of several damage modes in the walls, but it is a mode that is very common and is a good indicator of the level of damage and deformation that the walls have experienced. The damage modeling begins with detailed finite element fracture mechanics models to relate interstory drift to crack propagation. Data from these analyses are combined with empirical test observations to develop fragility expressions that provide a probabilistic relationship between seismic demand (interstory drift) and crack length. A key advantage of this approach, over a purely empirical one, is that it provides the means to generalize the observations beyond the specific wall configurations that were tested.
Lab Testing Methodology
Seventeen tests will be conducted to meet the required test objectives. Specimens are 8-foot high and 16-foot long, double-sided with _" gypsum wallboard. Test variables include: fastener type and spacing, loading protocol, top-of-wall boundary condition, method of attaching top of wallboard to top sill, wall penetration style, innovative construction methods, influence of door and floor trim, and repair and retrofit strategies.
Instrumentation was designed to measure applied load, lateral deflection at the top of the wall, lateral deflection at the bottom of the wall, shear distortion of the piers, and uplift at the door jambs.