Effect of Moored Vessels on Seismic Response of Structures

June 3, 2016
Effect of Moored Vessels on Seismic Response of Structures

In current design practice any vessel at berth during an earthquake event is ignored. This is rationalized based on the frequency of vessel calls in combination with the infrequency of significant earthquakes and the long response periods of vessels relative to earthquake motions. The ASCE 61 Standards Committee for Seismic Design of Piers and Wharves has formed a Task Committee to investigate whether facilities with high occupancy rates in high seismic regions should consider the effects of a vessel being present as part of the wharf seismic design. As no quantitative analysis of the combined vessel-structure seismic interaction has previously been performed, this paper presents original studies currently being performed by the Task Committee as part of their investigation. This paper highlights a simplified case considering a single vessel moored at a typical wharf during a significant earthquake. The intent of this evaluation is to determine effects on the mooring system and structure. Analysis is performed in AQWA (an industry standard diffraction/radiation analysis program with time domain analysis capabilities) using selected typical marine structure stiffnesses, mooring lines, and fenders as well as typical vessel parameters. Multiple time history events are passed through a simulated marine structure into the vessel (via mooring lines and fenders) and capacities of all system elements are examined. This evaluation allows for the establishment of a methodology to identify key parameters in the analysis, and to provide a better understanding of the actual risk and performance likely to be seen during a significant earthquake with a vessel at berth.

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