Out-of-Plane Dynamic Stability of Unreinforced Masonry Walls in One-Way Bending: Shake Table Testing

Given sufficient anchorage to the diaphragms, an unreinforced masonry (URM) wall subjected to out-of-plane inertial forces will likely develop a horizontal crack at an intermediate height about which the wall will rock as semirigid bodies. The effect of wall slenderness on out-of-plane stability has been demonstrated in past studies, but treatment of the effects of diaphragm flexibility and ground motion variability has been limited. This paper presents an experimental study examining the out-of-plane stability under seismic loading of URM walls connected to flexible diaphragms. Five full-scale unreinforced solid clay brick wall specimens spanning one story were subjected to earthquake ground motions using a shake table. The top and bottom of the walls were independently connected to the shake table through coil springs, simulating the flexibility of diaphragms. Variables examined experimentally included diaphragm stiffness and wall height. Both the amount of rocking observed as well as the ground motion scale causing collapse varied significantly with changes in the diaphragm properties. The test results provided data used for validation of a rigid-body rocking model, enabling an extensive parametric study on wall stability and the development of new assessment guidelines in a companion paper.