水流作用下双圆柱墩混凝土梁桥的动力响应实测与数值模拟

西藏达林大桥为一座7跨桥面连续的混凝土梁桥，下部结构采用双圆柱桥墩。2018年7月，在水流作用下达林大桥桥墩及桥面出现了显著的顺桥向振动。该文报道了水流作用下大桥的动力响应实测与数值模拟研究。实测表明:桥梁顺桥向振动表现为桥梁一阶纵向模态为主的拍振，横桥向为随机微振动；顺桥向最大加速度约为0.08 m/s2，梁端最大位移约为1.56 mm。基于一阶纵向振动模态参数，将双圆柱墩梁桥简化为单自由振动体系，在2 m/s~10 m/s流速范围内(折减流速U_r=1.69~8.45、雷诺数Re=2.6×106~1.3×107)进行了二维流固耦合数值模拟，得到了桥墩双圆柱升阻力系数以及不同结构阻尼比时的涡振响应。并对桥墩振型与水流流速剖面等三维效应进行修正，得到了墩顶位移随流速变化的关系。结果表明:上游柱尾流对下游柱的脉动涡激升力有显著增强作用，在3 m/s~6 m/s流速范围内双圆柱桥墩出现了涡激振动。在考虑三维修正后，ζ=0.01工况下墩顶位移数值模拟结果与实测值较为吻合。随着阻尼比ζ的增加，涡振最大振幅变小，锁定区间基本不变。

NUMERICAL SIMULATION AND FIELD MEASUREMENT OF DYNAMIC RESPONSES OF BRIDGES WITH TWIN CIRCULAR-CYLINDER PIERS SUBJECTED TO WATER FLOW

The Dalin Bridge in Tibet is a 7-span concrete beam bridge with a continuous bridge deck,supported with several twin-circular cylinder piers.In July 2018,pier and deck of Dalin Bridge suffer from significant vibration along the bridge direction under the action of water flow.This paper described the field measurements and numerical simulations of dynamic response of the bridge system subject to water flow.The field measurement showed that:the longitudinal vibration of bridge deck is a beat vibration dominated by its fundamental mode while the lateral vibration is random vibration;the longitudinal maximum acceleration is about 0.08 m/s^2,maximum displacement is about 1.56 mm.Based on the first-order longitudinal fundamental mode,the bridge is simplified as a SDOF system,two-dimensional numerical simulation of twin-circular cylinders is carried out for flow velocity 2 m/s~10 m/s(reduced flow velocity Ur=1.69~8.45,Reynolds number Re=2.6×10^6~1.3×10^7),and the lift and drag forces,and the dynamic responses of piers under different damping are obtained.After incorporating a correction accounting for the pier vibration mode and velocity profile of water flow,the vortexinduced vibration amplitude at pier top is derived.The results indicate that the interference effect of upstream cylinder will increase the lift force of downstream cylinder.Vortex-induced vibration(VIV)is observed from flow velocity 3 m/s~6 m/s.The three-dimensional effect has a significant impact on the displacement of pier top in two-dimensional numerical simulation and the numerical simulation result matches well with the measurement when damping ratioζ=0.01.The maximum VIV amplitude will decrease with the increase of structural damping,but the velocity regime of VIV remains unchanged.