| The suspension bridge with spatial cables not only has characteristics of large span,but also has strong lateral stiffness,which can improve the dynamic stability of structure.The spatial cables and the large span are two developing directions of suspension bridge in this century.However,there are not enough studies on suspension bridges with spatial cables,especially about the dynamics.Relying on a rail-cum-road-cum-sidewalk suspension bridge with spatial cables,the dynamic characteristics and the dynamic response from comfort degree of pedestrians are studied.Then,the TMD(tuned mass damper)is used to control vibration of the bridge.Main contents of the paper are as follows:Firstly,relying on the bridge nonlinear analysis software BNLAS,the dynamic characteristics of suspension bridge with spatial cables are studied from several aspects,including the inclination of cable plane,the span-rise ratio,the stiffness of tower,the stiffness of main girder and whether the central buckle is installed.Then,the laws are summarized.The results show that spatial cables are helpful to improve the lateral stiffness of suspension bridge.However,when the span is small and the lateral stiffness of the main girder is large,the restraint of the main girder by the lateral bearing will reduce the stiffening effect of the spatial cables on the lateral stiffness of the structure.With the increase of the span-rise ratio,the vertical stiffness increases at 1/4 span of main girder and decreases at 1/2 span of main girder.As the height of the main girder increases,the vertical stiffness of the bridge increases.After the central buckle is arranged,the longitudinal stiffness of the suspension bridge with space cables increases significantly.And the central buckle anchored in the upper deck is more effective than in the lower deck.Secondly,after comparing the regulations on comfort degree of pedestrians in various countries,the dynamic response under road and subway loading is analyzed from the transient nonlinear time-history analysis of the model established in ANSYS.In the model,cars and trains are modeled with a moving mass,and the effects of pedestrians are ignored.The impact of train speed,cars speed,cars mass,cars distance on the dynamic response of the bridge is studied,and the comfort degree of pedestrians is evaluated based on the Germany standars.The results show that the structural vibration gets more intensive with the increasing speed or mass of the vehicles.On the other hand,the structural vibration gets weaker when increasing the distance between the vehicles.Particularly,when such distance is 22.5m,the vehicle excitation,having the frequency close to the third natural frequency of the structural vertical bending,induces the resonance,which significantly amplifies the displacement and acceleration response.Additionally,the dynamic response of the structure is much larger when two way trains passing through.From this study,it can be concluded that the structural vibration can be reduced by several measures,e.g.,controlling the weight of vehicle or the distance between vehicles,avoiding two way trains passing through simultaneously.Finally,considering the effect of track irregularity,the dynamic response of the bridge is studied under the train incentive,which consists of a constant axial load and a simple harmonic load.The STMD(single tuned mass damper)system and the MTMD(multiple tuned mass damper)system are used to control the vibration of structure,enhancing the comfort level from “uncomfortable” to “moderate”.In the course of research,parameter sensitivity analysis is also performed between two kinds of TMD systems.The effectiveness of Single Tuned Mass Damper(STMD)and Multiple Tuned Damper(MTMD)are compared,changing the natural frequency of the structure.The results show that the robustness of MTMD is much better,especially when increasing the number of TMDs.Due to their small stiffness,suspension bridges are prone to vibration and may make pedestrians uncomfortably.The TMD can effectively control structural vibration and improve pedestrian comfort. |
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