Date of Award

Spring 1-1-2011

Document Type


Degree Name

Master of Science (MS)

First Advisor

Keith A. Porter

Second Advisor

Abbie Liel

Third Advisor

Ross Corotis


Often building decision-makers make decisions regarding the seismic risk to existing buildings, sometimes considering the effect of specific building features, such as geometric irregularities. Alternatives for quantifying the effect of a building feature on vulnerability are to use expert opinion, analytical methods, or empirical data from past earthquakes to quantify the effect. This work presents an analytical methodology to quantify the effect of a readily observable building feature on the seismic performance of a building class using 2nd-generation performance-based earthquake engineering (PBEE-2). Such a methodology does not appear to have been developed. The methodology begins by creating index buildings designed to span the observed range of values of the features with the greatest effect on vulnerability, to reflect variability within the building class. One set is designed with the feature of interest and another without. Each building is analyzed for collapse probability using PBEE-2 procedures. The effect of the feature is estimated as the ratio of the weighted-average vulnerability of the set with the feature to the weighted-average vulnerability of the set without the feature. I will call this ratio a seismic performance modification factor (SPM), a scalar value that varies with shaking severity. Illustrating the methodology, I quantify the effect of plan irregularity on the vulnerability of tall, steel-moment-frame buildings. It was impractical to fully illustrate the methodology, since doing so requires PBEE-2 models of several buildings, so I used Muto and Krishnan’s (2011) models as proxies, and evaluated their PGV-based fragility functions. At Sa(1.0 sec, 5%) = 0.533g (2/3 MCE shaking for an area of Los Angeles County), I found a SPM = -0.488 (DSa = 0.31), compared to -0.50 from FEMA 154 (ATC 2002a). Considering the simplifications, these two values are surprisingly close, but perhaps a coincidence. However, comparing the result to what the FEMA 154 (ATC 2002a) authors produced by expert opinion shows that the methodology can result in a reasonable SPM for use in practice.