Earthquake performance of shopfront canopies connected to URM buildings

Abstract

New Zealand’s main streetscapes are characterised by a prevalence of one and two storey commercial unreinforced masonry (URM) buildings which commonly feature an extended covering of the adjacent pedestrian walkway. An integral aspect of the historic use of these coverings was to provide shelter and to attract passers-by to stop and view the items on display inside shops. Shopfront canopies were a characteristic feature of late nineteenth century and early twentieth century streetscapes in New Zealand, as well as throughout the British Empire. Changing architectural styles and increases in motor traffic volume resulted in evolving canopy styles that included supported, suspended, and cantilever typologies. Field and archival studies reveal that during the twentieth century many building canopies underwent changes from supported to suspended forms. After the 2010-2011 Canterbury earthquakes (CE) an international team of researchers documented the observed earthquake damage to unreinforced masonry (URM) buildings in the Christchurch Central Business District. As part of the archived documentation a dataset was compiled that enables quantitative studies on different attributes associated with the performance of URM buildings when subjected to earthquake loading conditions. As has been previously observed on various occasions, URM buildings were found to be highly vulnerable to seismic activity during the CE (Dizhur et al., 2011, Leite et al., 2013). Parapet and façade overturning were identified as the most frequent collapse mechanisms (Dizhur et al., 2015), causing 83% of deaths due to URM buildings and hence demonstrating a significant urban safety risk (Dizhur et al., 2010). In addition, key architectural elements were destroyed. Despite being the only structure present between pedestrians and any falling debris associated with collapse of URM parapets and facades, little research has been undertaken to examine the performance of shopfront canopies during earthquakes. This lack of quantitative research associated with canopy behaviour has led to some engineers postulating that canopies are likely to contribute to the range of seismic damage mechanisms attributable to URM buildings. With the intent of providing quantitative evidence, the aim of the reported study was to document the observed response during the CE of hundreds of canopies that were connected to URM buildings.