Analysis And Assessment Of Structural Robustness Of Cable-Stayed Bridges

Cable-stayed bridges are the strategic passage of transportation lifeline.It will cause serious economic losses and severe social impact when the safety of bridges is threatened.As the course of modernization progresses rapidly,the cable-stayed bridges are facing increasingly sophisticated risks from both inside and outside,and the unconventional safety problems including disproportionate failure are starting to turn up.Under this situation,the conventional safety design procedures of bridge structures are facing with serious challenges.Currently,the safety design procedures of cable-stayed bridges are primary based on the checking calculation of ultimate state under ideal nondestructive status,while barely considering structural performance after suffering unexpected interferences or local damages.Therefore,systematic study on the structural robustness of cable-stayed bridges is imperative,which means significant value for theory and engineering of enhancing the capacity to resist disproportionate failure.The research was carried out from several aspects including assessment of sensitive risk sources of cable-stayed bridges,structural robustness of construction stage,seismic robustness of service stage and assessment method of structural robustness.The sensitive risk sources were recognized and classified in the construction stage and service stage of cable-stayed bridges.Then they were graded by risk-matrix assessment method,which is based on the ALARP criterion.In order to enhance the structural robustness of cable-stayed bridges,the applicability of four measures was discussed.The measures included reducing the occurrence of unexpected interferences,improving the strength and ductility of primary components,increasing the alternative paths for delivering loads and setting up more energy dissipators.For muti-tower cable-stayed bridges with high piers,the structural robustness of construction stage was researched by taking Chishi Bridge as an example.Based on the characteristics of construction stage of Chishi Bridge,the static responses of the longest double cantilever construction stage was analyzed after suffering local cable fracture.Then the optimization effect of static responses of rest structure was compared under different schemes of spare cables.The results showed that,the spare cables of cantilever construction stage could provide redundant paths for delivering loads,and assist the rest structure to redistribute the internal force preferably,which could guarantee the rest structure of cable-stayed bridge to be still robust after suffering local cable fracture.For cable-stayed bridges with mono-plane and single tower,the seismic robustness was researched by taking 2nd Daxing Bridge as an example.Based on the seismic responses of 2nd Daxing Bridge after setting up longitudinal dampers,lateral dampers and aseismatic piers,the optimization effect of seismic robustness was analyzed by taking the measures of increasing redundant paths for energy dissipation and enhancing key components' ability of energy dissipation.Then an assessment index of seismic robustness was put forward,which based on the bending moment of tower bottom.The results showed that,the index could preliminarily assess the seismic robustness of cable-stayed bridges.Considering the status and predicament of structural robustness quantitative analysis of cable-stayed bridges,the static responses of key components or key joints were taken as the foundation of structural robustness assessment system by referring to the works of structural robustness of architectures.Then five fundamental sub indexes including the cable stress,girder compressive stress,displacement,bending strain energy of towers and robustness of key joints,were chosen to form a omnibus structural robustness assessment index of cable-stayed bridges through radar graphs.At last,through two examples of concrete deck and steel deck cable-stayed bridge,the rationality and applicability of assessment index were sufficiently verified.