Human-Induced Vibration And Vibration Reduction Of Aluminum Alloy Truss Footbridge

As new materials(aluminum alloy,CFRP,glued laminated wood,etc.)are continuously applied to footbridges,some light material footbridges are emerging,and more complex interaction problems between people and footbridges arise.In this paper,the dynamic characteristics and human-induced vibration response of the coupled human-bridge system under the action of static single person,static crowd concentration and uniformity,dynamic single person,and dynamic crowd are measured and analyzed for a high fundamental frequency light material footbridge-aluminum alloy truss glass footbridge.Finally,based on the comfort evaluation results of the footbridge,the vibration control of the footbridge is carried out by applying the combined vibration damping system of Viscous Fluid Damper(VFD)and Tuned Liquid Damper(TLD).The main research contents and results of this paper are as follows:(1)The dynamic characteristics of the coupled system of human and high fundamental frequency aluminum alloy truss footbridge were measured.A high fundamental frequency aluminum truss footbridge was used as a platform to test the dynamic characteristics of the bridge itself under three excitation modes: environment,single person jumping and weight impact;and the dynamic characteristics of the human body of 12 testers were measured based on the human body transfer rate method,and the average intrinsic frequency of the human body was 5.4Hz and the average damping ratio was 0.28;the effects of static and dynamic crowds on the dynamic characteristics of the bridge were analyzed and compared with the human body with equal weight.and compared with the human equivalent weight.The results show that the dynamic characteristics of the footbridge are influenced by the position,distribution and motion of the human body,as well as the human-to-structure mass ratio and frequency ratio.Compared with the no-load fundamental frequency of the footbridge,the vibration frequency of the footbridge increased slightly with a single person standing still,while the vibration frequency of the footbridge decreased with both the standing crowd and the weights.The damping ratio of the footbridge was significantly increased by the stationary human body,and the equal weight had almost no effect on the damping ratio of the footbridge.Compared with the stationary human body on the bridge,the pedestrian on the bridge causes a slight increase in the vibration frequency of the footbridge,and the human body on the bridge is more likely to increase the damping ratio of the structure in the walking condition.Therefore,when calculating the dynamic characteristics and human-induced vibration response of the high fundamental frequency aluminum alloy truss footbridge,the human body cannot be equated as an equal weight mass block,and the human-structure interaction should be considered.(2)The dynamic response of the coupled system of human and high fundamental frequency aluminum alloy truss footbridge is studied.The effects of different numbers of pedestrians walking in unison,walking randomly and stepping in place on the vibration response of the footbridge were analyzed by human-induced vibration measurements.The human induced vibration response of the bridge and the stationary human body on the bridge was tested.The results showed that the maximum human induced vibration response of the bridge was tested by using fixed-point in-situ stepping instead of pedestrian movement,which can simplify the testing process and make the results slightly safer.Under the human-induced vibration of the footbridge,the vibration acceleration of the stationary human body on the bridge is about 1.08～1.40 times of the vibration acceleration of the footbridge at the stationary human body,and the acceleration response of the footbridge can no longer accurately assess the human comfort.(3)The vibration damping study of high fundamental frequency aluminum alloy truss footbridge.Based on the results of the comfort analysis,a joint damping system of viscous dampers and self-made TLD was designed,and the feasibility of the damping system was verified by human-induced vibration measurements.The results show that when the main and sub-harmonic components of pedestrian walking frequency are close to the vibration frequency of the human-bridge coupling system,the high fundamental frequency aluminum truss footbridge will produce a large human-induced vibration response and affect the pedestrian comfort.The viscous dampers and the TLD water tank have good damping effect on the bridge in vertical and lateral directions respectively,with the maximum damping effect reaching about50% and 30%,and the best damping effect is achieved when the fundamental frequency of the TLD water tank is similar to the lateral excellence frequency of the human-bridge coupling system.