Seismic Vulnerability Analysis And Structure Optimization Of Cable-stayed Bridges

The long-span cable-stayed bridge is a high-order statically indeterminate structure with complex design and calculation,seismic response.Since China is a country with many earthquakes,it is of great significance to evaluate the damage degree of cable-stayed bridges in order to ensure the smooth relief work after the earthquake.The seismic vulnerability of bridge structures quantitatively describes the seismic performance of bridge structures from the perspective of probability.Therefore,the study of seismic vulnerability of cable-stayed bridges is of great significance to the practical engineering guidance and the evaluation of the structure of the capacity after the earthquake.A concrete beam single-tower cable-stayed bridge(with a main span of 188 meters)was taken as engineering background.A finite element model was established to simulate each component of the cable-stayed bridge in detail based on OpenSEES.In addition,the Midas/Civil finite element software was used to check the self-vibration characteristics.Based on the structural characteristics and site characteristics,20 pieces of natural seismic wave data were selected from PEER Strong Motion Databases as the ground motion input.And the peak ground acceleration(PGA)was modulated to form multiple sets of seismic wave data.The curvature and strain distribution of the main tower and pier along the pier height as well as the longitudinal and transverse displacement distribution of the bearings were analyzed by incremental dynamic analysis(IDA)under 10 seismic waves.In this way,the bottom of the main tower,the consolidation position between the tower and beam,the joint areas between pylons and beam,the joints of the variable sections and the bottom and top sections of the piers were selected as vulnerability parts.Based on the previous analysis,the curvature was selected as the damage discrimination index for the main tower and the bridge pier,and displacement was selected as the damage discrimination index for the bearing.In addition,the damage states were classified.The vulnerability parts were anayzed in P-M-φ method.And the index values of each control section under different damage limit states were quantified.Based on that,the nonlinear analysis of single tower cable-stayed bridge under the 20 seismic waves was carried out.Meanwhile,the regression analysis of the logarithmic mean of curvature demand,logarithmic mean of displacement demand and standard deviation of each control section were carried out under the action of longitudinal and transverse earthquakes.The vulnerability curves of each damage state were given and the comparative analysis of the vulnerability of each component was made.Finally,based on the ductility seismic design,the ECC(Engineered Cementitious Composites)material was used in the most vulnerable part of single tower cable-stayed bridge,and the effect of high ductility materials on seismic vulnerability was studied.In the longitudinal direction,the probability of serious damage to the main tower was reduced by more than 30%.The probability of moderate damage,the probability of severe damage and the probability of complete damage of the bridge pier were reduced by more than 60%,70% and 90%.In the transverse direction,the probability of moderate damage to the main tower was reduced by more than 50%,and the probability of severe damage and complete damage was reduced by more than 60%.The results show that ECC can reduce the vulnerability of the main tower and the bridge pier to different degrees,but it has a negative effect on the reduction of the bearing vulnerability.