Paper Number XXX Provisional Seismic Assessment and Improvement of Napier’s Art Deco Buildings 2013 NZSEE Conference K.Q. Walsh University of Auckland J.M. Ingham University of Auckland ABSTRACT: Following the 1931 Hawke’s Bay earthquake, buildings in Napier and surrounding areas were rebuilt in a comparatively homogenous structural and architectural style comprising the region’s famous Art Deco stock. These ‘interwar buildings’ are most often composed of reinforced concrete frames and, while detailed in a fairly ductile fashion for the time, often register as earthquake-prone in preliminary seismic assessments, causing concern to owners, tenants, city officials, and all of those who value the heritage and future use of these iconic structures. The study reported here will address aspects of the seismic hazard, assessment, and potential retrofit solutions for Napier’s Art Deco buildings. The study concluded with provisional recommendations developed in collaboration with the Napier Art Deco Trust and other interested parties regarding a pathway to alleviate the hazard posed by Napier’s Art Deco buildings. 1 INTRODUCTION AND BACKGROUND TO RISKS AND VULNERABILITIES At 10:47 am on 3 February 1931, the infamous Hawke’s Bay earthquake shook Napier, Hastings, and the surrounding areas. The collapsing structures, landslides, and subsequent fires killed 256 people (Lee et al. 2011) including 157 people in Napier (McGregor 2012). The people of Napier rebuilt most of their city in the ensuing two years, and many of the reconstructed buildings were erected as reinforced concrete frames in the Art Deco architectural style. The policies regarding “earthquake-prone” buildings in the Building Act (NZ Parliament 2004) and findings from the Canterbury Earthquakes Royal Commission (Cooper et al. 2012) have caused local Councils, building owners, and tenants alike to consider more keenly the implications of seismic risk and retrofit costs associated with Hawke’s Bay’s heritage buildings, especially Napier’s famous Art Deco buildings constructed during the “interwar” years of 1920-1940, with the majority built in the few years immediately following the 1931 Hawke’s Bay earthquake. Two major active fault lines exist just west of Hawke’s Bay (the Mohaka Fault and Ruahine Fault) and numerous other faults exist in the southern portion of the region. Hence, the hazard factor, Z, for Napier is 0.38, which is amongst the higher values in the country’s major cities when considering Z=0.13 applies in Auckland and Z=0.40 applies in Wellington (NZS 1170.5:2004). The design basis earthquake (DBE) for Napier’s buildings (assuming an importance level of 2 and design working life of 50 years) is expected to occur every 500 years on average with an intensity of ~MM 9.1 (Stirling et al. 2002). Napier, Hastings, and Havelock North are located in a physiographic region known as the Heretaunga Plains and are situated on Quaternary sediments (Dravid and Brown 1997). These surface soils could be at risk of liquefaction when saturated and subjected to seismic waves. However, one sample taken from the foundation of one of the case study buildings in Napier City Centre showed visibly higher cohesion, consolidation, and grain-size heterogeneity than is typically associated with soils having high liquefaction potential. Nonetheless, alluvial soils such as these can vary largely in grain size and consolidation across even a relatively small geographic area such as the region in discussion (Lee et al. 2011).