STUDY ON THE ASEISMIC PERFORMANCE OF EMBEDDED STEEL CYLINDER BREAKWATER FOR BACKFILL SAND FOUNDATION BASED ON NORMALIZED RESIDUAL HORIZONTAL DISPLACEMENT

It was defined that normalized residual horizontal displacement was the aseismic performance index of an embedded steel cylinder breakwater according to aseismic design guidelines for port structures (PIANC), as well as to the statistical results of seismic damage for port structures in Japan and to the characteristics of a steel cylinder structure. Meanwhile, the dynamic characteristics of breakwater for backfill sand foundation were studied by a shaking table test and numerical simulation, and the aseismic performance of a breakwater was evaluated. The study results show that a breakwater is serviceable under design earthquake motion 1.7 m/s² and repairable under design earthquake motion 3.2 m/s², which do not satisfy the demand of grade S for the breakwater, and it is suggested that the effect of far-field and near-field earthquakes is considered in the design of aseismic performance for a breakwater. The slip phenomenon is obvious for backfill sand outside the cylinder under the peak ground acceleration 3.2 m/s² through a shaking table test, and the breakwater model tilts by the reason of the change of the lateral force due to liquefaction of backfill sand outside the cylinder, it is thusly advised that backfill sand outside the cylinder should be considered in the process of design for foundation reinforcement. The stress maximum for the wall of a steel cylinder both decrease gradually with increasing height for the peak ground acceleration 1.7 m/s² and 3.2 m/s², and there are two weak points on the bottom and mudline of the cylinder wall, structural design should be thusly considered as priority.