A Study On Seismic Fragility Of Highway Bridges Based On Wenchuan Earthquake Damage

With the rapid development of comprehensive national strength,China has carried out a large scale of highway network construction.In this period,tens of thousands of highway bridges have been built,which provide a strong support for the sustainable development of the whole economic society.However,during large earthquakes,every time,large numbers of highway bridges were destroyed,which greatly reduced the traffic capacity and seriously hindered the emergency rescue and daily life of city.China is one of the countries with the greatest number of earthquake disasters.Therefore,it is of great practical significance to investigate seismic fragility of highway bridges in our country.Based on a thorough excavation and comprehensive summary of highway bridges survey data in Wenchuan earthquake,seismic vulnerability of contemporary highway bridges was systematically studied by using various methods in this dissertation.Meantime,a study on intensity assessment based on earthquake damage of highway bridges was also carried out.The results of all above works can be used in the following works: seismic damage prediction and economic loss assessment of highway bridges,post-earthquake recoverability research,seismic risk analysis of the traffic system,emergency relief decision-making,as well as improvement of seismic design theory of highway bridges,etc.Eventually,all the research works can be help in reducing seismic damage of highway bridges and promoting rescue efficiency during earthquakes.The main contents are summarized as follows:1.The survey data of highway bridges in low intensity areas of Wenchuan earthquake is incomplete,large numbers of undamaged bridges were omitted.In view of the fact,the survey data in low intensity regions is approximately supplemented,based on the criterion that the number of highway bridges is proportional to the area in which they are located.Subsequently,several common empirical distribution functions were utilized to fitting the damage probability histogram under various intensities.So fragility matrices of arch bridge and girder bridge were both improved.Also,the influence of seismic geological disasters was analyzed.2.For the supplementary bridges,the peak ground acceleration(PGA)of each one at its location was estimated reasonably.Then a series of "bridge name-damage level-PGA" sample pairs were established.The maximum likelihood estimation method was used to determine the undetermined parameters in the fragility function,and consequently the empirical fragility curves of highway bridges in Wenchuan earthquake were obtained.In this process,the seismic vulnerability of arch bridges was compared with that of girder bridges.The influence of bridge size on seismic vulnerability is also discussed.3.The finite element models of continuous girder bridges under 9 working conditions were established by using SAP2000,and 36 typical ground motion records are selected as inputs.Considering the nonlinear behavior of bearings and piers,nonlinear time history analysis of beam bridges was carried out.Firstly,fragility curves of bearing and pier in a bridge were developed.On this basis,fragility curves of the whole beam bridge were synthesized by using the first-order boundary method.The influence of various bearing ways on seismic vulnerability of the whole bridge was discussed.At the same time,the influence rule of bridge size on seismic vulnerability given previously was further verified.4.Through a comprehensive statistical analysis of about 2000 highway bridges with detailed damage information,main seismic damage types of arch bridges and girder bridges were summarized.Meantime,the variation rule of damage level of key components in bridges with the seismic intensities was analyzed.Finally,two sets of index assessing seismic intensity were proposed,one in terms of damage levels,the other typical damage types.Furthermore,a comparative analysis and verification were carried out.