The Effect of the Boundary Conditions on the Out-of-Plane Behaviour of Unreinforced Masonry Walls

Abstract eng:
To prevent the out-of-plane failure of unreinforced masonry (URM) walls during earthquakes, most design codes prescribe a minimum wall thickness and a maximum slenderness ratio. These requirements are typically independent of the boundary conditions of the wall, i.e. the design guidelines do not take into account important parameters affecting the lateral stability of the walls like the level of applied axial load or the restraints of the wall. To investigate the effect of different top and bottom boundary conditions on the out-of-plane behaviour of URM walls, a series of slender wall units were tested dynamically. The test units were 2.4 m high, 1.2 m wide and had thicknesses between 12.5 and 20 cm yielding wall slenderness ratios between 19.2 and 12, respectively. Different top boundary conditions ranging from fully fixed to simply supported, as well as different levels of initial axial load were applied. The walls were tested on the shaking table of the ETH Zurich using a ground motion representing the level of shaking that can be expected on the fourth floor of a URM building located in a region of moderate seismicity. For each wall, the intensity of the ground motion was stepwise increased until the test unit collapsed. The paper presents selected test results showing that the boundary conditions can have a larger effect on the lateral stability of a URM wall than the slenderness of the wall.

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