The effect of near-fault directivity on building seismic collapse risk

Forward directivity can cause large amplitude velocity pulses in ground motion time histories that can be particularly damaging for buildings and may increase seismic collapse risk. Past research has shown that these pulse-like ground motions can induce large strength and deformation demands on structures. This study seeks to quantify the effects of forward rupture directivity through dynamic analysis of complex, building simulation models that are capable of capturing the key aspects of strength and stiffness degradation associated with structural collapse.;A representative set of reinforced concrete frame building models that are designed based on both past and present building code provisions are subjected to a database of 91 near-fault ground motions with varying pulse periods. The collapse capacity of these building models is predicted using incremental dynamic analysis methods, which consists of scaling earthquake records to increasing levels of intensity until global dynamic instability occurs. Such predictions allow for the development of collapse fragility functions that can be used to predict the probability of collapse as a function of ground motion intensity and, in this study, ground motion pulse periods.;Results from nonlinear dynamic analysis show that the predicted collapse capacity is largely influenced by variations in pulse period and building ductility. In addition, a comparison of results for near-fault and far-field earthquake records demonstrates a significant difference in calculated collapse metrics for the two types of ground motions. Probabilistic seismic hazard analysis for a representative nearfault site also illustrates the potential increase in seismic collapse risk when the effects of forward directivity are included.;Assessment of building collapse risk in the near-fault region is essential for the continued improvement of seismic hazard maps and building code provisions. A key advantage of this study is the assessment of building simulation models that were developed to represent real designs and details. This allows for a direct examination of the performance of code-compliant buildings when subjected to pulse-like ground motions. Furthermore, this study provides valuable data for the recently adopted, risk-targeted seismic design maps that are to be included in the 2012 International Building Code (IBC).