Analysis On Seismic Vulnerability Of Suspension Bridge In Deep Cutting Gorge Area

With the rapid development of the national economy,the construction of large-span bridges is increasing day by day.Most west areas in China feature high mountains and deep valleys where the topography is undulating and the terrain is steep,so the bridges need to cross the deep-cutting gorge.Suspension bridges are characterized by their load-bearing characteristics of main span,which makes it superior to other load-bearing structures for the technology and economy in large-span bridge,and is therefore widely favored.The earth-anchored suspension bridge with single tower that the thesis relies on is located in a special gorge area.The 766 meters of the main span is the largest span of this type of structure in the world.It is the first time that the roller composite cable saddle structure is used on large-span suspension bridges in the word.In addition,earthquakes with high intensity at the bridge site are relatively frequent.At present,there is no seismic study on similar structural systems.Therefore,the seismic performance of the practical project is analyzed based on the finite element platform to provide technical support for the design.The main work and achievements are as follows:(1)A method for simulating the structure of a roller composite saddle based on the Midas Civil platform was proposed,and a full bridge model considering the nonlinear behavior of the roller composite cable saddle,bearings and dampers was established.The results of static calculation are compared with those from "BNLAS of Bridge Nonlinear Analysis System" and they turn out to be in good agreement.The results show that the model is in good condition and can be used for subsequent calculation.(2)A systematic comparative analysis about the seismic response of composite saddles,rock anchors hangers,bearings,and towers under spatial variability of ground motion effect was performed.The results show that the displacement amplitude which was outputted from the plane strain model at the same bearing point increases with the elevation,while,the variation trend of the acceleration amplitude is telated to the local topography in the canyon.The different propagation speed of the seismic wave leads to the different dynamic response of the structure.Compared to uniform excitation,the site effects have more obvious effects on the remain structures than on the ordinary hangers and the axial force at the bottom of the tower.The effect of site effects should be considered in the seismic response analysis of this thesis so as not to underestimate the dynamic response of the structure.(3)Using the ground-peak acceleration as the ground motion intensity,then the thesis select 15 groups of artificial time-waves and real-recorded waves,and adjusts each group of waves to 10 intensity levels.The influence of different damage indexs on the vulnerability of critical structures and the structural vulnerability of the system are investigated by using the incremental analysis(IDA)method.The results show that the composite saddle system and the rock anchor hingers are in a safer state.The main cable anti-slip and the bearings are more likely to be damaged under the action of the space ground motion.When the values of K and ? given by the specification are adopted,the exceeding probability of the main cable anti-sliding damage is nearly 100% at the E1 level.Under the action of longitudinal and vertical ground motion,the exceeding probability about the bearings on the mountain are relatively high.Under the action of horizontal and vertical ground motion,the exceeding probability about the bearings on the tower are relatively high.The limit of tension is a major factor damaging the bearing system.The bottom of the tower is the location with the highest exceeding probability of damage.