The Improvement of Structural Adequacy Against Large Demands of Near-Fault Ground Motions

Abstract

Near-fault ground motions impose large demands on structures compared to ordinary ground motions. Recordings suggest that near-fault ground motions with ‘forward’ directivity are characterized by a large pulse, which is mostly orientated perpendicular to the fault. The maximum velocity direction (MVD) component is calculated by finding the angle that the maximum velocity resultant of the original longitudinal and transverse components will be occurred. The MVD component has larger PGV and PGD values compared to other components of near-fault ground motions. The spectral values of the MVD component are an envelope of the other decomposed components. The improvement of structural adequacy against large demands of near-fault ground motions has been the subject of research for the last decade. This study intends to provide quantitative knowledge on the near-fault ground motion demand and corresponding structural capacity requirements. The spectral quantities were computed through an attenuation relationship that is based on the near-fault ground motion records. New findings in this study are compared with the Uniform Building Code provisions and other attenuation relationships. The results demonstrate that for large magnitude events M w > 7, the UBC97 near-source factors (N a , N v ) have more conservative values compared to the study estimates. Hence, seismic coefficients of UBC97 have serious concern for estimating strength when short distances and large magnitude events are considered.