Experimental testing to determine failure patterns in URM pier/spandrel sub-structures

Abstract

The seismic assessment and retrofit of unreinforced masonry (URM) buildings in New Zealand is important due to their prevalence and their historical significance, and the requirements of the Building Act (2004) have motivated extensive research into the seismic strength of these historical buildings. Current analysis methods employ a simplified model to assess the lateral resistance of perforated URM shear walls. The strong-spandrel weak-pier model assumes that the spandrel is a rigid body of infinite strength and stiffness, and this assumption has justified the use of equations for pier shear strength to assess the lateral response of the wall. Previous pseudo-static testing of two coupled unreinforced masonry pier sub-structures indicated that their lateral response was governed by pier rocking and substantial spandrel damage due to flexure and shear. Subsequent testing has been carried out on a series of pier/spandrel joint sub-structures to further investigate the effects of pier and spandrel geometry on the performance of the joint region. The sub-structures were constructed in the common American bond formation using solid clay bricks and 1:2:9 composition lime mortar, consistent with the current state of historical New Zealand unreinforced masonry buildings. It is concluded that the crack propagation in the pier/spandrel interface region strongly influences the lateral strength of a perforated wall as the crack pattern dictates the effective height and boundary conditions of the piers.