Report - PEER - University of California, Berkeley

Figure 4. Recorded damage from RMS ‘beskat’ survey.3.2 ‘Type I’ and ‘Type II’ Damage DistributionsThe term ‘damage distribution’ refers to the distribution of the different damage statesof none through to complete for a particular building class. Generally it is assumedthat such distributions will have only one peak, with a roughly symmetrical spreads toeither side of the peak. HAZUS (FEMA 1999) generally predicts such distributions(termed here ‘Type I’), found also in the damage probability matrices used inintensity-based methodologies such as ATC-13 (ATC, 1985). However, a numberof damage datasets from the 1999 Kocaeli earthquake collated for this paper displaydamage distributions that did not follow this trend. Of the ten distributions presentedin Figure 5, four have distributions defined here as ‘Type II’; they have two peaks,one at complete damage, and the other at a lower damage level. The salient features ofthe sites summarized in Figure 5 and the others considered in this paper, are presentedin Table 1; no obvious reasons for the Type II distributions emerge.One solution for the prediction of these variable distributions, as well as thevariability in recorded damage at similar sites noted in the previous section would beto consider the mean damage ratio (MDR) only, and to focus calibration efforts etc.onto this composite parameter, on the basis that the complexity of actual damagedistributions cannot be reproduced using simplified methods. Whilst this may beappropriate for some cases, such as those where only the overall loss ratio is ofinterest, it is not conducive to improving damage estimation approaches andunderstanding the variables that influence the distribution of earthquake damage.This study therefore devotes itself to improving the understanding of why thesedifferent damage distributions occur and thus how to predict them in futureearthquakes.Two causes for ‘Type II’ damage distributions are now discussed. The first isthat they represent damage caused by two independent, superimposed mechanisms.401