Simulation And Statistical Analysis On The Characteristics Of Near-Fault Ground Motions And Its Damage Potential On The Seismic Performance Of Isolated Bridge

The damage potential of near-fault ground motions(GMs)is mainly due to the velocity pulses applied on the structures,which often leads to more serious damage to the near-fault engineering structure.Because the limitations of geometry of terrain,economic condition and interconnection situation,some bridges are inevitably built in the near-fault area,and sometimes even crossing an active fault.Studies have shown that vertical earthquake GMs possess more damage potential for long-span structures.Therefore,it is necessary to study the characteristics of near-fault GMs,especially for the vertical earthquake GMs.In this paper,the mechanism of generation of velocity pulse and forward directive effect in finite fault model is analyzed.The vertical GMs distribution in near-fault region are analyzed,and the damage potential for bridges due to horizontal and vertical GMs are analyzed.The main research results are as follows:1.Simulated and analyzed the mechanism of generation of the near-fault horizontal velocity pulses.Using the discrete wavenumber finite element method,semi-empirical formula and the uncertainty of the source,30 sets of finite source models with a same magnitude are established,and the forward directive effect and velocity pulse are simulated.Compared with the existing empirical formula of pulse parameters,the rationality of the calculation results is verified,and the distribution and generation mechanism of the pulse parameters are analyzed.2.Statistical analysis of characteristics of vertical GMs in near fault region.There are 890 sets of near-fault seismic records were selected to analyze the relationship between the acceleration peak ratio of vertical and horizontal GMs(a_V/a_H)and the moment magnitude,fault distance,site condition,and fault mechanism.A reasonable value of a_V/a_H was given.The energy-based identification method is used to identify the velocity pulses of horizontal and vertical GMs.The distribution of horizontal and vertical pulses and the attenuation of horizontal and vertical pulses are proposed.3.The damage potential of near-fault seismic action on isolated bridges is analyzed.Using OpenSees software and establishing a three-span reinforced concrete continuous beam bridge model,the near-fault horizontal pulse-like GMs,non-pulse-like GMs,and the vertical GMs are analyzed and compared.The hysteretic energy,shear force and deformation demand of the friction pendulum bearing were analyzed.The damage potential of near-fault GMs on the bending moment and shearing force of the pier were compared.