Vulnerability Analysis Of The Mid-span Steel-box Basket Arch Bridge

The mid-span steel-box basket arch bridge fully embodies the advantages of arch ribs in compression and a strong spanning capability of the conventional arch structure.The lateral rigidity of the structure is increased and its stability is improved because of the inward tilt of arch ribs.In addition,it is easy for the mid-span steel-box basket arch bridge,with beautiful shapes,to coordinate with the surrounding environment.Therefore,the mid-span steel-box basket arch bridge has been widely applied and developed in the municipal administration,highway and rail transportation in recent years.As a kind of cable structure,the mid-span steel-box basket girder arch bridge suspender has a shorter working life,and the destruction of the whole structure occasionally happen because of suspender fracture and the earthquake.In this thesis,by using finite element analysis software ANSYS and taking,the dynamic analysis for suspender fracture is implemented,and vulnerability of suspender fracture and seismic vulnerability are analyzed The main study is summarized as follows:(1)The spatial finite element models for the above background bridge are established respectively by using the large-scale finite element analysis software ANSYS and Midas/civil.The cross-sectional properties calculated by the two software are compared with the theoretical calculation values of the material mechanics method,and the static response and dynamic characteristics of the bridge are calculated.Calculation results are verified each other in order to ensure the accuracy of the finite element model as a basis for follow-up work.(2)The applicability of the static amplification coefficient method,the semi-dynamic analysis method and the full dynamic analysis method to the suspender fracture problem are discussed,respectively.Firstly,the static response method is used to calculate the structure responses of a single short suspender fracture and double long suspenders fracture.Secondly,the effects of the breaking cable under these two conditions on the whole dynamic performance of bridge are analyzed by means of semi-dynamic method based on the transient dynamics.The static amplification factor is calculated and the reasonable range of the amplification factor is discussed.(3)In terms of the theory of vulnerability analysis,the quantitative analysis of vulnerability under a single short suspender break and two long suspenders break is conducted,respectively,which is combined with the impact parameter M of the damage scene on the overall performance of the structure and the size parameter C of the damage scene in the entire structural system.And then,the vulnerability index curves of the suspender stress and the longitudinal beam bending stress are obtained.(4)Based on the response surface method,the suitable seismic wave and eigenvalue parameters are selected,the orthogonal test is designed,and the response surface equation is built instead of the complex finite element model.And the seismic vulnerability on the basis of sampling results of Latin hypercube is analyzed,and the vulnerability curves of every support and the whole bridge system are drawn.