Application Of Combined Damage Index Based On Entropy Method In Seismic Vulnerability Analysis Of Urban Bridges

As an important hub structure in urban transportation,urban bridges play an important role in urban earthquake resistance and disaster reduction,which requires urban bridges to have strong resilience/reconstruction when earthquakes come,so it is necessary to evaluate the seismic performance of urban bridges.In-depth research,the most effective method is to analyze its seismic vulnerability.Urban bridges often have the characteristics of uneven high and low piers and many curved ramps.Therefore,when quantifying damage to their substructures,different damage indicators are selected with different effectiveness.When the degree of deformation is selected as the damage indicator,the hysteresis of high piers will be ignored.For the energy dissipation capacity,when the elastic-plastic energy dissipation difference is selected as the damage index,the error for the low pier is larger.Therefore,it is particularly important to select a more applicable damage index according to the characteristics of uneven piers in urban bridges.This paper proposes a combined damage index and calculation method based on the entropy method,and applies it to the vulnerability analysis of typical urban bridges.A finite element model of a vase pier of a typical urban bridge is established.After selecting the appropriate ground motion amplitude modulation,it is analyzed by IDA.Based on the entropy method,the combined damage index value is obtained,and it is analyzed that the combined damage index has better applicability than a single damage index.and its effectiveness;it is analyzed that the combined damage index based on the entropy method has good applicability and effectiveness under different site conditions,and the weightpier height relationship of a single damage index under different site conditions is obtained.Taking the column-pier bridge as the analysis object,a full bridge model was established,and the combined damage index based on the entropy method was analyzed to have good applicability and effectiveness in typical urban single-column pier bridges,and the correctness of the weight-pier height relationship was verified.sex.The main research contents and conclusions are as follows:(1)The limitations of using the curvature-ductility ratio and the elasto-plastic energy loss ratio as the damage indicators to analyze the seismic fragility of urban bridges are theoretically explained,and the calculation method of the combined damage indicators based on the entropy method is proposed.Its feasibility is discussed.Based on the dynamic finite element analysis software,a batch of vase-type piers of urban bridges with different heights were established.After selecting the ground motion amplitude modulation suitable for the engineering site conditions,the structure was input for IDA analysis,and the curvature-ductility ratio and elastic-plasticity ratio of five piers with different heights were obtained respectively.The difference rate of energy consumption is calculated,and the weight of the two is calculated according to the entropy method to obtain the combined damage index.The applicability and effectiveness of the combined damage index are analyzed according to the fit index and standard deviation,and each The fragility curve of a bridge pier.The conclusion is: the weight of the elastic-plastic energy dissipation difference index increases with the increase of the height of the bridge pier,and the curvature-ductility ratio is opposite;the combined damage index based on the entropy method is more applicable and effective than the single damage index;The damage excess probability increases with the increase of the pier height.(2)Analyze the applicability of the combined damage index based on the entropy method under different site conditions,select the ground motion records under Class I,II,and III site conditions and adjust the peak acceleration amplitude of the ground motion to be consistent,and perform IDA analysis on the structure.,the weights of a single damage index for piers with different heights under different site conditions are obtained,the applicability and effectiveness of the combined damage index under different site conditions are analyzed,and the vulnerability curves under different site conditions are calculated.The results show that: the weights of the elasto-plastic energy dissipation difference index under the site conditions of I,II and III increase in turn,and show a significant difference when the pier height is greater than 10.4m;the applicability of the combined damage index under any site conditions and effectiveness are better than a single damage index;the damage transcendence probability under the conditions of Class I,II,and III sites increases sequentially,and for Class II and III sites,the difference between the damage transcendence probability of bridge piers at heights between 6.9m and 17.4m is small..(3)A typical urban single-column pier ramp bridge was selected to establish a full bridge model,and IDA analysis was also performed on it.The weights calculated from the relationship between the pier height and the pier height are compared.The weightpier height relationship is effective,and the damage index weight of piers within a certain height can be easily calculated according to this relationship.