Research On Static And Aseismic Behavior Of Long Span T-Frame And Tied Arch Combination Bridge

In the conceptual design of the Dalian Tiger Beach cross sea bridge,in order to meet the requirements of the bridge position environment,the cost of the project and the performance of the bridge,the new bridge structure of the T frame and tied arch combination system is conceived on the basis of the tied arch bridge by cooperating with T frame.The system has the advantages of new beauty,construction convenience,low cost and high crossing ability,so it has very good application prospects.In order to understand the structural performance of the T frame and tied arch combination bridge and promote this kind of bridge to be applied appropriately in practical engineering,this paper studied the static and dynamic performance of the system by means of numerical analysis and experimental research.The main contents are as follows:(1)Firstly,this paper introduces the conception process of the T frame and tied arch combination system,and expounds the structural features,general layout,component design,key construction and construction methods of this kind of structure.Secondly,by changing the internal connection mode and external constraint form of the bridge system,the stress characteristics of different systems are compared,then the rational structural connection and force form of the system are determined,and the structure characteristics of the T frame and tied arch combination bridge are mastered.Subsequently,the influence of setting of the hanger,length of the side span,length of the T frame cantilever and stiffness of the pier column on the mechanical properties of the structure are discussed,and the reasonable range of the paremeters of the structure is obtained.Finally,the static model test of the optimized structure system is carried out,the test results are in good agreement with the finite element calculation results,it shows that the calculation method and parameters of the finite element method are reasonable,the model test also validates the reliability of the key force parts of the bridge and the feasibility of the bridge scheme.(2)Taking the Dalian Tiger Beach cross sea bridge scheme as an example,firstly,the response spectrum method and geometric nonlinear time history method are used to analyze the seismic response of the bridge,and the stress characteristics and weak links of the bridge type under the earthquake action are obtained.Comparison of the two methods show that:because the first order vibration mode of the bridge is the longitudinal drift of the middle span steel girder,and the longitudinal natural vibration period is longer than the maximum period of the standard response spectrum,therefore,the response spectrum displacement result under longitudinal seismic excitation is not accurate enough.Secondly,the influence of different damping forms and damping ratio on the seismic response of the hybrid T frame and tied arch combination bridge with different materials is studied.When the vibration mode superposition method is used,it is suggested that the vibration damping is chosen,the calculation precision is high and the time is short;when the direct integration method is used,it is suggested to choose Rayleigh damping.When adopting Rayleigh damping,suitable mode shapes and damping ratios should be chosen for the seismic response calculations of different components.Subsequently,based on the finite element model with reasonable damping form,the influence of the rise to span ratio and the angle of the arch rib on the seismic response of the structure is studied,and the influence of the traveling wave effect is discussed.On the basis of the above research results,in view of the shortcomings of the large longitudinal displacement of the steel girder under earthquake,the damping measures for setting Fluid Viscous Damper on the joint of the steel and concrete girder are given,and the parameters of the Fluid Viscous Damper are optimized.The optimized shock absorption scheme can effectively reduce the harm of earthquake to the structure without changing the static performance of the structure.Finally,through the shaking table test,the dynamic characteristics of the bridge type are further grasped,the weak links of the system are finded out,and the reliability of the finite element calculation and the rationality of the parameter values are verified.(3)Firstly,the Pushover analysis for the background project is carried out using uniform loading and mode combination distribution loading,which can not or can consider the influence of high order mode.The results show that both the two loading ways can not accurately evaluate the seismic performance of the T-frame and tied arch combination bridge,and the result is quite different from the dynamic elasto-plastic time history analysis.Secondly,the background project is analyzed using the MPA method,and several methods for solving the performance points are compared.The following conclusions are obtained:the results of ATC capacity spectrum method are minimal,and the results of Krawinkler-Nassar and Lv Xilin models are larger;the vibration mode of the maximum mass participation coefficient in Zhai Changhai model is abnormally large when the earthquake intensity is large;the results of Vidic-Fajfar model and Fan Lichu model are most close,and the error is minimal compared with the result of time history analysis.Considering the factors of site category and seismic grouping,it is suggested that Fan Lichu model is more suitable for this type of bridge;Compared with the previous Pushover loading mode,the MPA method takes into account the influence of high order modes,the seismic response calculated by it are close to those by time history analysis,and it can greatly shorten the calculation time compared with the nonlinear time history analysis method.Finally,the IDA analysis and MPA analysis are carried out on the background project with various height of pier,the seismic response is calculated by MPA method using Fan Lichu model under a series of seismic wave acceleration peaks used in the IDA analysis.The comparison of the two methods shows that:the structural capacity curve calculated by MPA method and the time history analysis are relatively close,that means they have a consisten judgment on the elasto-plastic mechanical behavior of the structure.Therefore,the MPA method can replace the time history analysis when calculating the seismic response under the specific earthquake intensity or evaluating the seismic performance of the background project,it can satisfies the accuracy of practical engineering application,also it can greatly reduced the computational cost.