Out-of-plane shaketable testing of unreinforced masonry walls in two-way bending

Abstract

Five half-scale unreinforced clay brick walls were subjected to out-of-plane shaketable testing, in order to verify whether wall behaviour observed in a previous test campaign involving quasistatic cyclic loading of full-scale walls could be considered representative under dynamic loading. The walls tested in the present study all had identical dimensions and support conditions which included translational support at their top and bottom edges and fixed support at their vertical edges. Three of these walls contained a window opening, and three were subjected to vertical precompression. An extensive number of individual runs were performed on every wall, comprising three basic types of input motion: pulses, harmonic excitation and realistic earthquake motions. The tests confirmed the main behavioural trends observed in the quasistatic cyclic test study, including attainment of a peak load capacity during the initial sequence of cracking, good post-cracking strength, substantial hysteretic energy dissipation, degradation of strength and stiffness with increasing size and number of cycles, and agreement between the overall cracking patterns. A discussion of the observed behaviour is provided by considering similarities and, where observed, the differences between the two studies and also between the five walls tested in the present study. As a means of standardising comparisons of key features of the measured force–displacement response of the half-scale shaketable test walls versus the full-scale cyclic test walls, theoretical predictions of ultimate strength and post-cracking strength are undertaken using simplified analytical methods utilising idealised collapse mechanisms. Predictions of the ultimate strength which allow for the tensile bond strength of the masonry show good correlation with the results of both test studies. The predicted post-cracking strength envelope is shown to be conservative within the range of deformations achieved in both sets of tests.