Experimental Investigation of In-Plane Cyclic Response of Unbonded Posttensioned Masonry Walls

Abstract

This paper reports on an experimental study on four unbonded posttensioned masonry walls (PT-MWs). All walls had identical thickness, height, and length of 190, 2,000, and 1,400 mm, respectively, and were constructed using concrete masonry units (CMUs) and mortar type N, and were fully grouted. Different horizontal spacing values of 400, 600, and 1,200 mm were used between the posttensioning bars in the walls. Only Wall W4 had horizontal bonded reinforcement, located in the fourth and seventh courses. Two different levels of posttensioning force corresponding to an average posttensioning compressive axial stress on the masonry of 1.35 and 2.7 MPa were applied to the walls. Different initial posttension stresses in the bars ranging from 0.32 to 0.63 of the yield stress of each bar were applied to the walls. The walls were subjected to incrementally increasing in-plane lateral displacement cyclic load applied to the top of each wall. The experimental results including damage pattern, force displacement response, residual drift ratio, masonry compressive strain, wall rotation, damping, stiffness, stiffness degradation, and displacement ductility of the tested walls are presented and discussed in detail. The accuracy of ignoring the elongation of post-tensioning bars in predicting the strength of the tested walls is investigated based on the experimental results. The experimental tests showed that PT-MWs having the same total initial PT force but different stress levels in the PT bars displayed different lateral strengths. Doubling the total initial PT forces in the bars resulted in insignificant increases in the wall lateral strength. Finally, using bonded horizontal steel improved the lateral displacement capacity of the test specimen. Specimens that had horizontal reinforcement did not suffer postpeak shear cracking and hence were able to reach higher level of lateral displacement.