Underwater shaking table test on seismic responses of deep-water bridge pier considering the effect of constraint boundary at pier top

The water-pier interaction remarkably affects the seismic performance of deep-water bridges. There are many studies on the dynamic responses and damage analysis on the water-pier coupling system. However, many studies on the water-pier interaction assumes a free boundary at pier top, while there is a constraint at pier top in the real engineering. The boundary condition significantly affects the responses of the pier under earthquake according to the structural dynamics. In this study, a series of underwater shaking table tests were conducted to investigate the responses of deep-water pier considering the effect of constraint boundary at pier top. The model pier was designed and assembled with a specially-made rubber material. The seismic responses of pier were measured under ground motions with various characteristics. The results declared that the proposed test scheme was effective to provide a displacement constraint at the pier top. The constraint boundary increased the natural vibration frequency, hydrodynamic pressure, acceleration, and relative displacement of pier and decreased the strain of pier. As the constraint stiffness at pier top changed from 0 to 200 kN/m, the natural vibration frequency increased by up to 140.0 % and the responses of pier increased by up to 375.3 %. The earthquakes with pulse effect increased the responses of pier by up to 176.8 % then those without pulse effect. The seismic responses of the pier increased by up to 60.0 % when the water depth changed from 0 to 2.0 m. The effect of constraint boundary at pier top should be considered in the design of deep-water bridge.