| From the current development trend of footbridges,it can be seen that the design and construction of footbridges should not only meet the needs of pedestrians,but also meet new requirements such as novel structural systems,beautiful and soft appearance,and wide view on the bridge deck,which brings new challenges and topics to human-induced vibration analysis and control of footbridges.Based on the engineering background of Xiamen Shanhai Health Trail,the modal parameters identification of the long-span steel footbridge with complex system,the damping identification of human bumping excitation method,the experimental study of human-induced vibration,the human-bridge-TMD interaction system,and the evaluation of vibration control of eddy current dampers were investigated.The main contents of this thesis include the following aspects:(1)The modal parameter identification of long-span steel footbridges with complex system had been carried out.Introduced the theoretical analysis of modal characteristics and the experimental study of the beam string system footbridge(NO.1 Footbridge),the curved basket-handle arch system footbridge(NO.3Footbridge),and the high-pier Z-shaped spiral ramp footbridge(Guanyin Temple Footbridge).The difference between the theory and the actual measurement were compared and analyzed.The modal parameters such as sensitive frequency characteristics and damping characteristics of long-span steel footbridges with complex system of the Xiamen Shanhai Healthy Trail were summarized and counted.There are less than 5 human-induced vibration sensitive modes,most of which are vertical sensitive modes.Only the NO.2 Footbridge(main span is 216.7m)has 2lateral sensitive modes.Research shows that the footbridges of the Xiamen Shanhai Healthy Trail are typical light and flexible steel footbridges with very small damping ratios,and the damping ratios under different amplitudes have significant nonlinear characteristics.The damping ratio of the flat steel box continuous girder footbridge(the approach bridge of NO.1 Footbridge,0.7m beam height)is only 0.1%under small amplitude,and the damping ratio of the beam string system footbridge(NO.1Footbridge)is only 0.17%under small amplitude.Even at large amplitude,most bridges.Therefore,for the light and flexible steel footbridge,the damping ratio in the theoretical calculation should be 0.1%to 0.3%.(2)Damping identification of human bumping excitation method was researched and applied.The damping identification of human bumping excitation method was used to effectively excite 9 steel footbridges,and some bridges were excited to vibrate greatly in vertical direction,and the maximum peak acceleration response was3.05m/s~2.The damping characteristics of steel footbridges under different amplitudes were analyzed.The applicability and influencing factors of the damping identification of human bumping excitation method were analyzed,and the NO.1Footbridge is taken as an example to compare the theory with the actual measurement.Theoretically,the human bumping excitation method can effectively excite the vertical mode of the footbridge with a modal mass within 300t,a modal damping ratio within 0.8%,and a modal frequency within 1.2Hz to 3.8Hz,the peak acceleration response was greater than 0.2m/s~2.(3)The human-induced vibration analysis and influencing factors analysis of the human-bridge interaction system were carried out.Taking the NO.1 Footbridge as an example,analysis of a single(group)pedestrian-bridge interaction system was carried out,and the calculation results were compared with the calculation results of the German EN03 standard method and the Chinese GJJ69-2017 draft method.Furthermore,the changes and influencing factors of the instantaneous modal parameters of the human-bridge interaction system and the influencing factors of the coupled dynamic response of the human-bridge system were analyzed.Research shows that when the mass ratio of the footbridge is 35%,the instantaneous modal frequency of the footbridge decreases by 7.9%,and the instantaneous modal damping ratio increases by 5 times.For steel footbridges with light weight,low fundamental frequency and low damping or other soft footbridges,although crowd action can increase the damping ratio of the coupling system,the impact of pedestrians on the instantaneous frequency of the structure under different crowd densities should still be considered,for providing basis for TMD parameter design.(4)Experimental tests such as single pedestrian walking across the bridge,single pedestrian running across the bridge,group of pedestrians walking across the bridge,and group of pedestrians running across the bridge were carried out on the No.1 bridge,which verified the accuracy of the single(group)pedestrian-bridge coupling calculation method and proved that when the footbridge has a large longitudinal slope,the effect of the longitudinal walking force cannot be ignored.(5)The human-induced vibration analysis considering the human-bridge-TMD coupling effect was carried out.Taking the NO.1 Footbridge installed with TMD as an example,the applicability of the human bumping excitation method was analyzed,and the human-induced vibration under the coupled dynamic action of the group pedestrian-bridge-TMD was analyzed,and the vibration damping effectiveness of the TMD was evaluated.According to the group pedestrian-bridge-TMD coupling dynamic analysis method,the first or second order vertical mode vibration reduction rate of the NO.1 Footbridge were 86.8%or 79.2%.The vibration under extreme conditions can still meet the CL2 moderate comfort standard in EN03.(6)Taking the NO.1 Footbridge installed with EC-TMD as an example,experimental and evaluation were carried out,and various working indicators such as EC-TMD’s ride comfort,starting acceleration,synchronization,and damping efficiency were analyzed.The high reliability and high sensitivity of EC-TMD were verified by engineering applications. |
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