Influence of loading protocol on the structural performance of timber-framed shear walls

Timber-framed shear walls are designed to resist the lateral loads on a building from wind and earthquake. Many regions around the world have developed standard test methods for evaluating the performance of timber-framed shear walls. Currently, Australia has no such standard test method for timber-framed shear walls. The aim of this study is to develop a standard loading protocol for evaluating the performance of timber-framed shear walls in Australia that is informed by the concerns of both earthquake engineers and wind engineers. To achieve this aim, the key objective of this study is to compare the performance of a standard timber-framed shear wall under three different monotonic (groups M1, M2 and M3) and four different cyclic (groups C1, C2, C3 and C4) loading protocols according to their respective standards. The number of test panels in each group was three (3) for a total number of 21 individual tests. Structural performance characteristics of the standard test panel, such as ultimate and yield strength and global stiffness, were found to be strongly dependent on the loading protocol. For example, ultimate strength was lower for test panels subject to monotonic loading (i.e., 5.99, 6.41 and 6.34kN/m for groups M1, M2 and M3 respectively) compared to test panels subject to cyclic loading (i.e., 6.70, 6.73, 8.03 and 8.11kN/m for groups C1, C2, C3 and C4 respectively). Internal stiffness was found to be relatively consistent regardless of loading protocol. The higher ultimate and yield performance of group C3 (CUREE protocol) and C4 (Cyclone Testing Station protocol) is statistically significant, at the 5% significance level, compared to results from all other test methods (i.e., AS1720.1, EN 594, ASTM E564, BRANZ P21 and ISO 16670). Differences in boundary conditions between the loading protocols might explain some of the differences in results; however, this hypothesis is not strongly supported by the evidence. These results are used to inform our recommendations for developing an Australian standard test method for evaluating the structural performance of timber-framed shear walls.