Dynamic Response Of Artially Ground-anchored Cable-stayed Bridges With Axial-free Hinge Under The Action Of Cable Loss

The partially ground-anchored cable-stayed bridge with axial-free hinge is a new type of long-span cable-stayed bridge structure.Due to the addition of the axial-free hinge and side-span ground-anchored structure,the mechanical performance and integral stiffness of the structure are different from the conventional self-anchored cable-stayed bridge,the influence of those on the structural response after the cable loss is not to be underestimated.Based on a partially ground-anchored cable-stayed bridge with axial-free hinge,this paper uses finite element analysis to obtain the dynamic characteristics of the structure,which is prepared for the subsequent calculation of the damping co efficient of the broken cable dynamic analysis.Taking the SB24 cable loss of the southern span with the largest cable force as an example,based on ANSYS transient dynamic analysis method,the response of cables,beams and pylons and their influence on dy namic characteristics and integral stiffness of the structure were analyzed,and compare these results with static analysis methods;Then the DCR and the standard methods are used to evaluate the remaining load-bearing capacity of the structure after the c able loss,and the two results are compared and analyzed to determine the feasibility of using the relevant limit of the static calculation in the standard to evaluate the transient impact process of the broken cable;Finally,the influence of different ca ble loss parameters on the structure response is analyzed.The main content and conclusions are as follows:(1)The whole bridge models of Midas and ANSYS were established respectively.Through static analysis of the completed bridge state and modal analysis of the structure using the Lanczos method,the whole bridge cable force value and the frequency and mode shapes of the first 15 natural modes were obtained.From the cable force data,it is concluded that the cable with the largest cable force in the bridge is the SB24 cable of the southern span.(2)Taking the SB24 cable loss of the southern span as an example,the response of cables,beams and pylons and the influence on the dynamic characteristics and integral stiffness of the structure are analyzed by ANSYS transient dynamic analysis method.Then,the difference of response results obtained by dynamic and static analysis methods was compared.In addition,the safety evaluation of each component after the cable loss was carried out based on t he DCR and the standard method.It is discovered that the response of the nearest cable is the largest after the cable loss and the response of the distant cable decreases with the increase of the distance;the stress response of the broken cable to the an chorage section of the girder and the pylons is the most obvious;the influence of individual cable loss on the dynamic characteristics of the structure is very small,so analysis is not necessary.It is also found that the girder showed a downward deflection tendency,and the vertical displacement of the mid-span girder changed significantly,and the maximum value was obtained near the middle span;the broken cables on the side span caused the pylon to fall toward the mid-span.It is suggested that the quasi-dynamic analysis method(DAF=2.0)can be used to approximate the overall calculation,but for local sections,the dynamic analysis method should be used for supplementary verification;the safety of the structure after cable loss can be evaluated by the relative limit of the static force calculation in the standard.(3)The influence of different cable loss positions and the number of broken cables on the structure response is studied by setting different cable loss conditions.It is concluded that the longer cable loss has a greater impact on the structural response;as the number of simultaneously fractured cables increases,the impact on the structural response will increase,rather than the simple superposition of the response values after a single cable breaks separately.The proposed cable-breaking response analysis method and the obtained adverse cable-breaking conditions,and can provide the corresponding basis for the cable design and cable breaking calculation of such cable-stayed bridges,and pay attention to the changes of cable forces in these positions during the operation.