Study On Vibration Response Of Upper Span Railway T-structure Turnaround Bridge Under Train Operation Excitation

With the large-scale rollout of China’s high-speed railway construction,cross-railway line bridges often appear in transportation line planning,As a widely used construction process in bridge construction,turnaround construction shows great advantages for the construction of railway cross-line bridges in very heavy traffic,and it will not hinder railway transportation and pose safety threats.However,the turnaround bridge is close to the railway line,and the construction phase is inevitably affected by train-induced ground vibrations.It is easy to generate forced vibration on the bridge structure.And it may adversely affect the safety of bridge structures and the comfort of personnel who build rotating bridges.Therefore,it is of great practical significance to study the vibration characteristics and vibration propagation laws of the rotating bridges along the railway line under train excitation.In this paper,The new cross-Shanghai-Kunming railway turnaround bridge will be the research object.The vibration characteristics and propagation laws of the bridge structure under train excitation in different construction stages of the turnaround bridge were analyzed.The vibration response of the vehicle-induced structure was also evaluated.The research content of this paper mainly includes the following three aspects:(1)Vibration tests were carried out for three typical construction stages of rotating bridges:1/4 bridge stage,maximum cantilever stage and bridge stage.The dynamic test was carried out for the key parts of the structure of the bridge structure along the line induced by train operation.The analysis compares the differences in the time and frequency domains of different construction phases.From the three aspects of peak,energy spectrum and response spectrum,the influence of vehicle-induced vibration on the vibration characteristics of bridges in different construction stages was analyzed.(2)A refined dynamic prediction model for the maximum cantilever state of the rotating bridge is established.In addition,according to the principle of impedance equivalence in structural dynamics,the complex geometry of the rotating structure is simplified.The measured acceleration is used as the load input to solve the dynamic response of the structural model.Combined with the vibration test,the calculation accuracy and calculation efficiency of the two sets of models are compared,and the dynamic prediction of the vibration response under unfavorable train excitation is carried out.The results show that the equivalent dynamic model of the rotating structure proposed in this paper not only has good accuracy,but also has the advantages of fast modeling and fast calculation.It has a good alternative effect on refined dynamic prediction models.(3)The environmental vibration control standards of various countries were compared,and GB50868-2013 "Allowable Vibration Standards for Construction Engineering" was used to evaluate the vibration safety of different construction stages of rotating bridges.The Chinese standard "Environmental Vibration Standard" and ISO10137:2007 were used to compare and evaluate the vibration comfort,and the applicability of the two sets of standards to the construction environment of the rotating bridge along the line was analyzed.