Seismic fragility analysis of pile supported wharf for some important port sites in Gujarat

Abstract

In present study, seismic fragility curves are developed for a typical pile supported wharf, for some important port sites in Gujarat i.e. Mundra, Kandla, Navlakhi, Dahej and Hazira, thereby representing highest and moderate level of seismic zones of India (Zone V and III). Curves are developed for three levels of ground shaking i.e. Serviceability Earthquake (SE, 72 years return period), Design Based Earthquake (DBE, 475 years return period) and Maximum Considered Earthquake (MCE, 2475 years return period). The structural model of wharf is prepared in SAP 2000 using Winkler model to represent soil pile system. Pushover analysis is performed to obtain the capacity curve of wharf. Damage states - serviceable, repairable, near collapse and collapse; are established as per PIANC. Site specific spectra is constructed using geotechnical report of port sites with reference to ASCE7-05 and correspondingly 5 pairs of seismic events are selected, normalized and scaled to 0.1g, 0.2g,…1.0g to represent demand. Using Capacity Spectrum Method, maximum displacements at deck are obtained and response matrix is created. Based on the damage states and the response matrix, the fragility curves of the wharf are constructed. It is revealed that port sites Mundra, Kandla and Navlakhi are most susceptible to seismic risk, while Dahej and Hazira are comparatively at lower risk. Further, the specified spectra given in Indian standard underestimates the ground motions, particularly in zone V. Hence, site specific spectrum is essential for seismic design of port structures. At the same time a need is felt to strongly revise the Indian standard.