| With the rapid development of China’s economic construction,the demand for long-span railway cable-stayed bridge is growing,and the railway transportation presents high-speed,heavy-load and large flow development trend.Therefore,the dynamic performance of long-span railway cable-stayed bridge has attracted much attention.Considering the corrosion of existing steel cables and the fatigue problem of railway bridges,the application prospect of new CFRP cable which has the characteristics of light weight,high strength,corrosion resistance and anti-fatigue is worth exploring.In this thesis,the research work is carried out from the aspects of material fatigue test,structural static and dynamic test and numerical simulation,focusing on the vehicle-bridge coupling dynamic performance of railway cable-stayed bridge and the vehicle-induced fatigue damage of stay cable.The main research contents and conclusions of the thesis are listed as follows:(1)Experimental and theoretical study on fatigue performance of CFRP tendonThis thesis carried out constant-amplitude tension-tension fatigue tests of CFRP tendons at five stress levels.During the fatigue loading process,the residual stiffness of CFRP tendons was tested to study the fatigue life and residual stiffness degradation regularity at different stress levels.A residual stiffness model suitable for different stress levels and a cumulative fatigue damage model suitable for multi-level fatigue stress were proposed.In order to verify the accuracy and applicability of the proposed model,some recommended residual stiffness models and related experimental data were cited.The results show that the residual stiffness of CFRP cables presents a three-stage degradation regularity can be observed at each stress level.When the stress range becomes smaller,the degradation degree of residual stiffness at stage I becomes higher,the proportion of stage II to fatigue life become larger,and the three-stage boundary becomes more obvious.Both the modified residual stiffness model based on W.X.Yao’s model and the cumulative damage model based on the residual stiffness model have good accuracy and applicability.The proposed residual stiffness model can accurately predict the residual stiffness degradation of CFRP tendons at different stress levels,and the proposed cumulative damage mode can better prediction the damage development under multi-level fatigue stress than the Palmgren-Miner rule.This proposed fatigue model provides a theoretical basis for the damage assessment of CFRP cables in cable-stayed bridges under different dynamic excitation.(2)Numerical analysis of vehicle-bridge dynamic interactionThe dynamic equilibrium equation of bridge structure and vehicle are respectively established based on the finite element method,and coupled according to the wheel-rail contact relationship.In order to complete the vehicle-bridge coupling vibration analysis of bridge structure,the Newmark-b method is adopted to solve the coupled equations.This coupling vibration numerical model is verified by the analytical solution of a non-gravity simply-supported beam subjected to moving sprung mass.Meanwhile,the simulation of the numerical model are in good agreement with the coupling vibration measurements of the cable-stayed girder,which further verifies the accuracy of the establishment and solution of the numerical model for the vehicle-bridge coupling vibration.Furthermore,in order to investigate the natural vibration characteristics of the bridge structure,the subspace iteration method is adopted to solve the free vibration equation of the bridge structure.(3)Experimental study on vehicle-bridge dynamic interaction of cable-stayed model bridgeIn order to carry out the coupling vibration study of cable-stayed bridge,a cable-stayed model bridge is designed and manufactured.And in order to perform the experimental study on coupling vibration of the cable-stayed model bridge,the vehicle excitation on bridge structure is simulated by a moving model vehicle.In addition,the static performance and natural vibration characteristics of the cable-stayed beam are tested.The influence of cable stiffness,axle load and suspension stiffness on the static and dynamic displacement,cable stress and bending moment is tested.Meanwhile,the influence of different cable stiffness on the natural vibration characteristics of cable-stayed model bridge is observed.The experimental study shows that the dynamic peak response of the cable-stayed model bridge is generally higher than the static peak response at the same location,and the loading position corresponding to peak response changes.Axle load of model vehicle and cable stiffness are important factors affecting the dynamic peak response of the cable-stayed model bridge,and affecting the loading position and generated location where the dynamic peak response occurs.The dynamic peak response of the cable-stayed peak shows a monotonically increasing trend with the increase of the axle load,and a nonlinear monotonically decreasing trend with the increase of the cable stiffness.The change of dynamic response with suspension stiffness is not obvious,but there are differences at each position.(4)Theoretical study on vehicle-bridge dynamic interaction of cable-stayed model bridgeThe dynamic amplification factor analysis of displacement,bending moment and cable stress of the cable-stayed model bridge is carried out through combining static and dynamic measurements and numerical model.And the range of the cable stiffness,speed,axle load and suspension stiffness is further expanded,in order to investigate the influence of different factors onthe dynamic amplification factor of displacement,bending moment and cable stress in the cable-stayed model bridge.The results show that the vehicle speed has a significant impact on the dynamic peak response of the cable-stayed model bridge and the loading position where generates the dynamic peak response.In the range of V=0.2~2.0 m/s,the dynamic amplification factor of displacement,bending moment and cable stress show a fluctuating growth with the increase of the vehicle speed.The axle load of vehicle and the cable stiffness are also important factors affecting the dynamic response of the cable-stayed model bridge.In the range of M=5~50 kg,the dynamic peak response increases linearly with the axle load,but the dynamic amplification factor keeps constant.The dynamic peak response of the cable-stayed model bridge shows a fast-to-slow nonlinear decreasing trend the increase cable stiffness.In the range of 0.1~1.0EA,dynamic amplification factors of the cable-stayed model bridge are different at different locations,and the variation regularities with the cable stiffness at different locations are different.When the suspension stiffness in the range of 0.1~1.0 K,dynamic responses of the cable-stayed model bridge are less affected by the change of suspension stiffness.(5)Investigation on mechanical behavior and cable fatigue damage of railway cable-stayed bridge using CFRP cables subjected to vehicle-bridge dynamic interactionIn this thesis,a case study is presented focusing on a railway hybrid box girder cable-stayed bridge using steel cable which has a main span of 468 m.The original steel cable in the cable-stayed bridge is replaced by CFRP cable based on the principle of equal axial stiffness.The numerical model of cable-stayed bridge using steel cable or CFRP cable is respectively established to conduct the modal analysis,static analysis and vehicle-bridge coupling dynamic analysis.The differences in modal,static response,dynamic response and dynamic amplification factor of these two cable-stayed bridges are compared.Based on the vehicle-bridge coupling vibration analysis of cable-stayed bridge,this paper proposed a method for assessing vehicle-induced fatigue damage of stay cables.Fatigue damage of two kinds of cables caused by train excitation was evaluated,so as to compare the fatigue performance of steel cables and CFRP cables.Furthermore,the effects of train speed and axle load on dynamic performance of cable-stayed bridge and fatigue damage of cables were investigated.The results show that the equivalent elastic modulus of CFRP cable is higher than that of steel cable,and the vertical support stiffness of CFRP cable is better than that of steel cable.The first vertical bending frequency of CFRP cable-stayed bridge is higher than that of steel cable-stayed bridge.Under the same loading condition,dynamic peak values of mid-span displacement,pylon top displacement and cable stress of CFRP cable-stayed bridge are smaller than those of steel cable-stayed bridge,and the coupling dynamic peak response is generally larger than that of static peak response.The dynamic peak response of cable-stayed bridge shows anapproximately linear increasing trend with the increase of axle load,while it shows a fluctuating increasing trend with the increase of vehicle speed.The change of axle load and train speed will also cause the change of the position where the dynamic peak response occurs,and also cause the change of the loading position where excites the dynamic peak response.The dynamic amplification factor of the mid-span displacement of the main girder and the cable stress approximately keep constant with the axle load.The dynamic amplification factor shows a fluctuating increasing trend with the increase of vehicle speed,and reaches local peaks at some speeds.The dynamic amplification factors of cable-stayed bridge using different cables are different under different axle loads and/or vehicle speeds.The train running condition is also an important factor affecting the dynamic amplification factor of cable-stayed bridge.The fatigue damage of stay cables shows a nonlinear increasing trend with the increase of axle load,and the growth rate increases gradually.The fatigue damage of stay cables shows a fluctuating growth trend with the increase of vehicle speed,and reaches local peaks at some vehicle speeds.Under the same loading condition,the fatigue damage of CFRP cables is smaller than that of steel cables at the same position.Train running conditions affect the fatigue damage distribution of stay cables and the position where the maximum fatigue damage occurs.In general,the fatigue damage of stay cables close to the pylon is the smallest,and the fatigue damage of mid-span cables is higher than that of side spans.The fatigue damage distribution uniformity of CFRP cable-stayed bridge is better than that of steel cable-stayed bridge. |
PDF Full Text Request