Abstract:
The out-of-plane flexural testing of two (02) full scale unreinforced masonry (URM) walls seismically retrofitted using post-tensioning is reported. The selected wall configuration was representative of a common out-of-plane URM wall, achieving a percentage new building standard (% NBS) of 57 when evaluated using the New Zealand Society for Earthquake Engineering (NZSEE) guidelines. The test walls imitated heritage New Zealand URM construction by using recycled clay brick masonry laid in common bond pattern, with one header course after every three stretcher courses, and ASTM type O mortar was used. A low level pre-compression was applied using a single mechanically restrained tendon inserted into a cavity at the centre of the walls. Threaded mild steel bar with a coupler system (with tensile yield strength of 500 MPa) and sheathed greased seven-wire strand (with tensile yield strength of 1300 MPa) were tensioned with an initial force of 50 kN and 100 kN respectively. Behaviour of the seismically retrofitted URM walls using posttensioning was compared to the response of a non-retrofitted URM wall, with the out-of-plane flexural strength of the posttensioned masonry walls observed to range from 2.9 to 7.1 times the strength of the non-retrofitted URM wall. Several aspects pertaining to seismic behaviour of posttensioned masonry walls including tendon stress variation, damage patterns, force-displacement behaviour, initial stiffness, and displacement capacity were investigated. Furthermore, the results for the retrofitted walls were compared with equations developed in previous studies, and it was inferred that current predictive techniques give conservative values of out-of-plane flexural strength for high level of pre-compression.
