Reinforced Concrete Wall Response under Uni- and Bi- Directional Loading

During an earthquake, structures are subjected to both horizontal and vertical shaking. Most structures are rather insensitive to variations in the vertical acceleration history and primary considerations are given to the impact of the horizontal shaking on the behavior of structures. In the laboratory, however, most component tests are carried out under uni-directional horizontal loading to simulate earthquake effects rather than bi-directional loading. For example, biaxial loading tests of reinforced concrete (RC) walls constitute less than 0.5% of all quasi-static cyclic tests that have been conducted. Bi-directional tests require larger and more complex test setups than uni-directional tests and therefore should only be pursued if they provide insights and results that cannot be obtained from uni-directional tests. To investigate the influence of bi-directional loading on RC wall performance, this paper reviews results from quasi-static cyclic tests on RC walls that are reported in the literature. Results from uni-directional tests are compared to results from bi-directional tests for walls of different cross sections including rectangular walls, T-shaped walls, and U-shaped walls. The available test data are analyzed with regard to the influence of the loading history on stiffness, strength, deformation capacity and failure mode. Walls with T-shaped and Ushaped cross sections are designed to carry loads in both horizontal directions and thus consideration of the impact of bidirectional loading on behavior should be considered. However, it is also shown that the displacement capacity of walls with rectangular cross sections is typically reduced by 20 to 30% due to bi-directional loading. Further analysis of the test data indicates that the bi-directional loading protocol selected might impact wall strength and stiffness of the test specimen. Based on these findings, future research needs with regard to the response of RC walls subjected to bi-directional loading are provided.