Preliminary Study On Seismic Performance Evaluation Method Of Existing City Beam Bridges

This paper takes existing bridges as the research object,According to the principle of consistency of seismic risk level of existing bridges and the new bridges,the seismic performance fortification standards of existing bridges are studied and determined.According to the importance of lines and bridges in earthquake relief and the seismic vulnerability of bridges,a multi-scale step-by-step screening method is proposed to determine the quantitative index of seismic performance reinforcement priority.The process and method of seismic performance evaluation are studied and put forward.The main research contents and conclusions are as follows:1)Research on seismic fortification standards of existing bridgesAccording to the expected service life of existing bridges,the variable design reference period is determined.The seismic fortification standards of existing bridges with different expected service life are determined according to the principle that the exceeding probability level of existing bridges within the design reference period(less than or equal to 100 years)equals to the exceeding probability of new bridges within 100 years.According to the expected service life,seismic fortification standards are divided into five categories:0-15 years without fortification;15-35 years with fortification standard as design reference period 35 years;35-60 years with fortification standard as design reference period 60 years;60-80 years with fortification standard as design reference period 80 years;80-100 years with fortification standard as new bridges.2)Research on Fast Assessment Method Based on Seismic Design SpecificationsAccording to the common problems of design codes and seismic hazards,a rapid assessment method based on common problems of specifications and empirical vulnerability assessment is proposed.Common problems assessment is based on the comparison of old specifications and the new specification;empirical vulnerability assessment is based on the establishment of empirical prediction formula to calculate bridge damage grade according to bridge seismic damage.This paper adopts the Japanese Civil Engineering Association method and Zhu Meizhen method.When the damage index satisfies both D1?60 and D2?4.4,it is evaluated as the bridge to be strengthened.3)Research on traditional seismic performance evaluation methodBased on the capacity/demand ratio,the traditional seismic performance evaluation is divided into two stages: preliminary evaluation and detailed evaluation.The preliminary evaluation mainly evaluates the contents(seismic fortification standards,structural measures,etc.)that do not require complex seismic analysis.Detailed evaluation,through complex seismic analysis,the bearing capacity and deformation capacity of components are evaluated.4)Research on the Classification of the Importance of Traffic Network LinesConsidering the social attribute level,traffic network topology structure and traffic network redundancy,route classification calculates the node index by Pajek complex network analysis software,and determines the key node by grey relational degree analysis method.The concept of "node set" is proposed,and the ranking of "node set" is taken as the criterion of line importance classification.5)Study on Seismic Performance Grade R of BridgesAccording to bridge vulnerability,importance and seismic risk level,the product of expected damage grade V and seismic risk grade E is taken as seismic performance grade R.E is calculated by spectral acceleration and site amplification factor,V is determined by damage probability under given earthquake action and corresponding weight coefficient,and damage probability is determined by structural vulnerability analysis.6)Research on Multi-scale Stepwise Screening MethodThis paper put forward a multi-scale step-by-step screening method to determine the priority of seismic reinforcement of existing bridges.First,the importance of the line is graded,then the seismic performance of bridges on the same level of line is analyzed,and the seismic performance grade R index is given.Finally,the priority of seismic reinforcement is determined.The priority of seismic reinforcement of the same grade line bridges is determined by the seismic performance level R;the priority of seismic reinforcement of different line bridges is determined by the line level and the seismic performance level R,and finally determined by expert evaluation.