Assessment of the material properties of New Zealand's unreinforced masonry building stock

Abstract

Unreinforced masonry (URM) buildings in New Zealand were constructed mainly between about 1880 and 1950. These buildings are regarded as seismically at-risk, and because they represent a significant part of New Zealand’s architectural heritage structures, they are prime candidates for seismic retrofit. Currently a large-scale research project focused on developing retrofit solutions for New Zealand’s earthquake risk URM buildings is being undertaken, and within this programme it was determined that the first task to be completed was the development or adoption of accurate seismic assessment techniques, and that within this task the primary issue was accurate determination of material properties. Material properties of URM in New Zealand are unique, and currently there is a significant lack of adequate and accurate material data. Without accurate material data, overly conservative assessments and correspondingly expensive retrofit interventions are required. The use of accurate material data is essential in ensuring that heritage architecture is maintained, and not demolished. This paper discusses the difficulties in procuring material samples and the findings on both lab and field studies investigating the compression, shear and flexural tension strength of unreinforced masonry. Significant variation in the properties between and within buildings has been encountered. It is determined that due to the highly variable nature of URM, testing must be conducted not only on individual materials, but their interactions with each other, particularly the interaction between mortar and bricks.