Probabilistic Seismic Behavior Of Medium And Small Span Beam Bridges In High Intensity Mountainous Areas

In the domestic construction of mountain bridges,small and medium span continuous girder bridges are widely used for their cost advantages and the convenience of construction.However,most of the mountainous areas in China are located in high-intensity seismic areas,which exist problems,like high frequency,high intensity,shallow source,wide distribution and strong uncertainty.Therefore,those potential seismic hazards also have higher requirements for the seismic performance of the mountain bridges.At present,there are abundant information about seismic damage of girder bridges.Many engineers have carried out many seismic research results on such bridges.However,these studies mainly consider a single seismic calculation method from the perspective of components or structures,while studying and optimizing the seismic structural measures of a certain component or the seismic performance of a bridge.There is a lack of seismic response analysis of mountain bridges under different conditions,besides,there is also lack of a reasonable and complete seismic evaluation system for the specific bridge.In view of the above problems,the medium-span steel-concrete composite girder bridge in a high-intensity mountain area will be taken as the research object in this paper.Firstly,the aseismic capacity of kinds of components of bridge relying on engineering is analyzed.Then,the seismic response characteristics and the disadvantageous links of seismic design of bridge in mountainous area under the conditions of intensity,structure and topography are clarified.After that,the probabilistic seismic performance evaluation of the bridge is carried out,and the main disadvantageous components of the bridge under high-intensity earthquake are determined,which can provide reference for optimizing the seismic fortification of the bridge.At the same time,the expected formula of time-varying seismic loss of the bridge is deduced to realize the quantitative evaluation of the seismic economy of the bridge relying on engineering.Besides,a complete and reasonable seismic system evaluation process is proposed,and the seismic system of the relying project,the vulnerability analysis,loss expectation analysis and life-cycle cost analysis of six alternative systems are carried out by using the above evaluation process.Finally,a safe,reliable and economical seismic system suitable for relying on engineering is established.Therefore,the main contents of this paper are as follows:(1)Taking a steel-concrete composite beam bridge in a high-intensity mountainous area as the research object,a series of finite element models are established to analyze the seismic time-history response of the bridge structure under high-intensity conditions,determine the seismic response law of the bridge under complex terrain in high-intensity mountainous area and the influence of different bridge design variables on the seismic response,and carry out the adaptability of different bridge structures under complex terrain.Finally,the influence weight of different influencing factors on seismic response of bridges is determined by orthogonal working condition analysis.(2)Based on Opensees source code analysis platform,a refined non-linear dynamic model of engineering bridge is established,and 100 actual seismic waves are input into the model.Nonlinear time history analysis and logarithmic regression analysis are carried out.The vulnerability curves of components and systems of engineering bridge are fitted by matlab,and the seismic performance and dangerous components of the bridge are evaluated from the damage probability.(3)The composition of loss and life-cycle cost of bridges under earthquake is defined.The seismic risk curve is fitted by exponential parabola model,and the timevarying earthquake loss expectation formula of bridges is deduced.The time-varying loss expectation surface and life-cycle cost surface of bridges are established.At the same time,the influence of discount rate change on the calculation results of the model is analyzed,and the quantitative evaluation of seismic economy of the project is realized.(4)The concept of "reasonable seismic system" of bridges and its evaluation process are qualitatively put forward.Six seismic systems are preliminarily drawn up by improving energy dissipation bearings and structural measures.The vulnerability curves of components of each seismic system are analyzed and established through parallel comparison and selection of control variables.On this basis,the seismic cumulative damage expectation surface and life-cycle cost surface of the alternative system are established,and the loss expectation and life-cycle cost of the alternative system are evaluated quantitatively.Finally,the safe,reliable and economical seismic system of the bridge is established.