Published works

As reported in the previous project reports “Fragility Curves for URM Buildings” (Derakhshan and Griffith, 2018) and “Fragility Curves for Retrofitted URM Buildings” (Vaculik and Griffith, 2018), fragility curves are an important tool for estimating the economic loss due to earthquakes. In this report, Fragility is used as a proxy for Vulnerability.  As a follow-up to the work presented in the previous two reports, this report presents fragility curves for ‘as-is’ and ‘retrofitted’ URM buildings in terms of ‘probability of exceedance’ versus ‘peak ground acceleration’ (PGA) for four damage ratios, D1 – D4. With this additional information, it will be possible to estimate the reduced damage due to seismic retrofit for cost-benefit analyses for a range of earthquake scenarios in order to ensure cost-effective seismic strengthening policy.

With this in mind, the remainder of this report should be treated as an addendum to the previous two project reports (Derakhshan and Griffith, and Vaculik and Griffith, 2018), hereafter referred to as the August and October 2018 reports.

In the October 2018 report, we described the methodology used to produce empirically-based fragility curves for seismically strengthened URM buildings on the basis of performance reported for 78 heritage-listed buildings in Christchurch during the 2010 and 2011 earthquake sequence. 

Empirical fragility curves for the global damage of strengthened buildings have been derived using the simplifying assumption that the PGA to cause a particular probability of a given damage state in a strengthened building can be obtained as a scalar multiple of the probability to cause the same damage state in the unstrengthened building. On the basis of this assumption, PGA scaling multipliers are calibrated which can be used to apply a rightward shift to the unstrengthened building curves (from the August 2018 report) to produce the corresponding curves for strengthened buildings. These multipliers were calibrated using the Christchurch earthquake damage data for two levels of retrofit. It was found that a multiplier of 1.4 produces good agreement for buildings with a full building strengthening level of retrofit, and a multiplier of 1.1 for buildings with partial or incomplete strengthening.  These relatively low values are a result of the fact that the unreinforced masonry buildings in Christchurch were retrofitted as many as 50 years ago when seismic strengthening technologies for URM buildings were in their infancy.  With advances in our understanding and improved retrofit technologies of today, where the seismic strengthening techniques have been experimentally validated, slightly higher scaling multipliers of 1.25 and 1.6 are justified and were used to generate the fragility curves for partial and full seismic retrofit, respectively.