EFFECT OF MAJOR SEISMOLOGICAL PARAMETERS ON DIRECTIVITY DOMINANT SPECTRAL AMPLIFICATION

Abstract eng:
One of the most important features of directivity-dominant near-fault ground motions is the existence of impulsive signals in the beginning of ground velocity. Directivity is observed when rupture propagates toward a site at a velocity close to particle shear-wave velocity. Such ground motions with large-amplitude and long-period velocity pulses amplify the response spectrum in medium to long period ranges. As such, they have the potential to impose severe inelastic demands on the medium to high-rise buildings. In this study we discuss the differences between the directivity models proposed in NGAWEST2 [i.e., Shahi and Baker and Chiou and Spudich presented in Spudich et al. (2013)] and Shahi and Baker (2011). Deterministic and probabilistic seismic hazard analyses are done with and without considering directivity effects for different earthquake scenarios as well as 475-year and 2475-year return periods. The response spectrum amplification due to directivity is extracted from these hazard analyses and the effects of major seismological parameters on the computed spectral amplifications are investigated. The observed results suggest some differences in the investigated directivity models for deterministic and probabilistic earthquake scenarios. The characteristic magnitude and fault-site geometry play an important role in all models within probabilistic hazard framework. The Shahi and Baker directivity models also bring forward the significance of slip rate and return period in spectral amplifications. The slip rate and return period do not prominently affect the spectral amplifications in Chiou and Spudich directivity model. The observations suggest a need for the consideration of forward directivity on code-based design spectrum via some practical rules.

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