Calculation Method of Hydrodynamic Forces on Circular Piers during Earthquakes

Abstract

The flow field around a horizontally oscillating bridge pier during earthquakes is characterized by a high Reynolds number and a small Keulegan-Carpenter number. This study aimed at the fluid forces exerted on a circular bridge pier in quiescent water during earthquakes. By scaling the hydrodynamic equations, it is analytically shown that the inertial force dominates the drag force. This characteristic is further demonstrated by performing numerical simulations. A given earthquake is first decomposed into a series of equivalent harmonic components. Then, the hydrodynamic forces are computed in the numerical code. The numerical results confirm that the inertial force dominates the drag force, and the inertial coefficient is essentially equal to 1 for all conditions examined for the monochromatic and two-frequency oscillations as well as the actual earthquakes. This confirmation is crucial, because the dominance of inertial force means that the resultant force can be predicted with the linear superposition of decomposed frequency components, owing to the inertial force being linear in the fluid-flow acceleration.