Benchmarking the Seismic Risks Associated with Clay Brick Unreinforced Masonry Buildings in New Zealand

Abstract

The structural performance of URM buildings in earthquakes has immediate and long term social and economic consequences for the affected community. The accurate forecasting of risks associated with both retrofitted and unretrofitted URM building seismic performance can provide decision-makers with information to pre-emptively take measures to mitigate the adverse effects of URM building damage. Thus, the primary objective of the research presented herein was to advance engineering, social science, and risk knowledge related to URM building seismic performance through the analysis of empirical earthquake data. An in-depth analysis of the context and cause of all known fatalities associated with New Zealand earthquakes was undertaken. URM building damage was identified as the leading cause of earthquake-related deaths in New Zealand. Case studies were undertaken to evaluate the overall success of retrofitted URM buildings with satisfactory in-field seismic performance during the 2010/11 Canterbury earthquakes. Case study buildings were assessed in terms of the seismic design, architectural appeal, heritage preservation, economic viability, and observed performance of the seismic retrofit. A Canterbury masonry building dataset and post-earthquake damage photographs and satellite images were analysed to determine where masonry debris fell, be it inside or outside of the damaged building, and to measure the extent of the fallen masonry debris. Approximately 25% of the evaluated URM buildings experienced volume loss, and 67% of the buildings had debris that fell outside of the building footprint. Probability functions to predict earthquake-induced volume loss and debris extent for commercial clay brick URM buildings were developed. Finally, the volume loss and debris extent probability functions were used to develop indoor and outdoor casualty models for clay brick URM buildings. Though derived solely from New Zealand earthquakes, the proposed models are thought to be applicable to other countries with comparable stocks of commercial clay brick URM buildings.