Report - PEER - University of California, Berkeley

BUILDING VULNERABILITY ASSESSMENT USING PUSHOVERMETHODS — A TURKISH CASE STUDYEdmund BOOTH 1 , Juliet BIRD 2 and Robin SPENCE 3ABSTRACTNon-linear static pushover analysis forms one key element of current methodologies ofperformance-based seismic design. It is also central to the estimates of building vulnerabilityused by the HAZUS earthquake loss methodology. However, despite the theoretical appeal ofthe methodology, recent comparisons of predictions using HAZUS with damaged recorded inthe 1999 Kocaeli earthquake have shown poor agreement, not significantly better than thoseusing intensity based methods. This paper examines further the reasons for this poorcorrelation, and uses a series of simple Monte Carlo simulations to examine the effect ofvarying degrees of brittleness and ductility on predicted damage distributions. These MonteCarlo simulations used the capacity spectrum method, and found that in allowing for therandomness of demand and capacity, the degree of brittleness markedly affected damagedistributions in a way that appears plausible by comparison with observed data. Thisdependence on brittleness cannot be directly obtained from the original HAZUS methodology,nor from intensity based methods.Keywords: Capacity spectrum; Insurance loss; Earthquake loss; HAZUS; Monte Carlosimulation.1. INTRODUCTIONPredictions of the scale of future losses in earthquakes are vitally important to theinsurance industry; inter alia, they are needed to set premiums and the size offinancial reserves the industry should maintain. In the past, these predictions usedempirical data, based on intensity. The methodology introduced by HAZUS (FEMA1999), using the capacity spectrum method, offered a radical change in approach; theground motion measure was a response spectrum, and so could be based directly oninstrumentally recorded strong motion data, allowing a much more rational approachto the influence of factors such as frequency content and soil conditions on response.Moreover, structural vulnerability was expressed by a capacity curve, which could bedirectly related to fundamental structural parameters like yield strength, stiffness andductility in a way that was impossible in an intensity based approach. However, anintensity based approach has its advantages, too. The data are very clearly based on1 edmund@booth-seismic.co.uk 2 Imperial College, London3 CAR Ltd, Cambridge, UK397