Robustness Quantification Of Cable-stayed Bridges For Accidental Loads And Seismic Loads

The ability of bridge structure to resist continuous collapse under partial failure will be reflected by the robustness of the bridge.At present,there is little accepted and feasible robustness quantification method in domestic and foreign codes and literatures.In order to quantify robustness,the type of cable-stayed bridge is selected for investigation,robustness quantization methods are designed based on accidental loads and seismic loads.Accidental load is a statement of relative seismic load,which refers to sudden loads such as car collision,explosion,and fire.Taking BaiTanHu Bridge for example,the related bridge models based on Midas Civil and Sap2000 was modeled to illustrate the application of robustness quantization in accidental loads and seismic loads.1.For accidental loads,an evaluation index based on component importance robustness is proposed.The stay cable is selected as the most important components,the ultimate bearing capacity differences(before and after the failure of stay cable)serves as the influence of integral performance.The deflection and stress of its main girder and main tower,as well as the force of the cable,serve as the influences of partial components.In order to evaluate the 5 points above,the method of drawing a radar map is used to quantify the influence of the radar map area on five aspects.A formula for calculating the importance of components is proposed,by considering the integral influence and partial-componentsinfluence.A deterministic evaluation index for robustness of cable-stayed bridges is proposed based on the negative correlation between components importance and robustness.2.For seismic loads,a seismic robustness assessment index based on seismic sensitivity is proposed.The main tower is selected as the research object of seismic robustness.Considering the uncertainty of seismic load,the probability method for finding the expected value of discrete random variables in statistics is used to calculate the expected value of seismic sensitivity of different sections of bridge tower.Firstly,the damage level of the main tower section is determined,and the damage probability and damage degree of the main tower section at each damage level are obtained.Its product is the different cross-section earthquake sensitivity expectations.A probabilistic robustness cable-stayed bridge seismic evaluation index is proposed based on the characteristic that seismic sensitivity is negatively related to the seismic robustness.3.Calculation of robustness under accidental load,static analysis and dynamic analysis of single cable failure and combined failure are carried out respectively.According to the results,partial components were not fatally damaged under the static analysis,and the structure could still be used normally.Dynamic analysis result shows that the 13+14# model has the highest importance coefficient.The deflection of the main beam of the 13+14# model is 31.322 cm,exceeding the limit of the specification(30cm).The main beam fails according to the deformation principle.Comprehensively analysis,the 2 lower limit of the robustness(S13 and S14 cables)lose their dynamics simultaneously,and the lower limit of the robustness of the bridge is 1.4.The calculation of seismic robustness under earthquake load,the IDA analysis of the main tower section is carried out separately,and the calculation results show that the seismic sensitivity of section E is the highest,which needs special attention.In the case of rare occurrence earthquakes,the seismic capacity of tower bottom will lose 21.6%,and the seismic robustness data of the whole bridge is 4.63.