Analysis Of Seismic Fragility And Seismic Resilience Of Simple Supported Beam Bridges Under Environmental Erosion Conditions

Generally speaking,the service environment of bridges is complicated,and they will be subjected to various environmental erosions in the service process,which directly or indirectly affect the mechanical properties of the bridge,and then affect the performance of the bridge structure under the action of earthquakes.The structures seismic fragility reflects the degree of vulnerability to damage,and the seismic resilience further reflects the ability of the structure to recover from damage.As one of the countries with frequent earthquakes,China has important practical significance in researching the seismic fragility and seismic resilience of highway bridges under the condition of environmental erosion in our country.Based on the collation and summary of the mechanism of environmental erosion,this paper studies the time-varying seismic resistance of simple supported beam bridges under single environmental erosion and multiple environmental erosion in combination with seismic fragility analysis methods,and proposes a bridge seismic resilience analysis method based on maintenance mode according to the possible maintenance situation of bridges after earthquake,aiming to better serve the research of earthquake damage prediction,loss assessment and post-earthquake recovery,and help the formulation and improvement of emergency relief decisions.So as to achieve the purpose of reducing the earthquake damage of bridge structures and improving the efficiency of rescue and relief work.The thesis mainly completes the following work:(1)This paper reviews and summarizes the research status of seismic fragility of bridge structures under scour,chloride ion corrosion and freeze-thaw cycles,as well as the research status of seismic resilience of structures,points out the main problems existing in the current research,studies the influence of various types of erosion on the mechanical properties of bridge structures,summarizes the mechanism and characteristics of various types of erosion.(2)Based on the results of structural mechanical performance degradation analysis,considering the uncertainty of the initial corrosion time,corrosion speed,corrosion depth,freeze-thaw cycles times and other factors of the reinforcement,combined with the finite element model of the bridge,a similar field ground motion was selected from the strong seismic record database,and the seismic fragility analysis of the bridge structure under chloride ion corrosion,freeze-thaw cycles,scour was carried out,and the seismic fragility model of the bridge structure under different service times was obtained.The influence of uneven degradation of mechanical properties of pier under the action of chloride ions corrosion and freeze-thaw cycles on the seismic fragility of simple supported beam bridges was discussed.(3)According to the corrosion depth prediction model,chloride ion corrosion model,and freeze-thaw cycles mechanical degradation model,and guided by the performancebased seismic design concept,the analysis framework of time-varying seismic fragility under different erosion combinations was established.The time-varying seismic vulnerability of bridges under different erosion combinations(scour+chloride ion corrosion,scour+freeze-thaw cycles,chloride ion corrosion+freeze-thaw cycles,and scour+chloride ion corrosion+freeze-thaw cycles)were calculated separately.(4)Based on the residual traffic capacity coefficient and mechanical property degradation coefficient of bridges under different earthquake damage levels,the residual traffic capacity analysis model of bridges after earthquake is established.A bridge recovery time model based on maintenance mode is established,and the calculation results based on component-based recovery time are compared.The seismic resilience index of the bridge has been graded,and a macroscopic description of the corresponding grade is given according to the post-earthquake recovery time and the degree of postearthquake function reduction of the bridge.Taking the bridge model as an example,the seismic resilience of the bridge under various kinds of erosion is evaluated.