The Seismic Fragility Analysis And Anti-Seismic Performance Evaluation Of Concrete Bridge In Service

Transportation network serves as a very important role in the whole response system of protection against and mitigation of earthquake, a huge damage threatening both human life and economic development. As to public transportation network, the most common used bridge type is prestressed concrete continuous rigid frame bridge to cross shallow sea and ravines. Chloride penetration is the most severe and common erosion of various corrosion media to the reinforced concrete bridge used in shallow sea and ravine. The corrosion of reinforcement in this case can severely degrade the structure durability and anti-seismic performance. Therefore, it is of great theoretical significance and application value to make seismic fragility analysis and performance evaluation research in the anti-seismic field of bridge engineering.Material mechanics property, geometric features and earthquake load of concrete bridge are all obvious spatial randomness and random process, so probabilistic method is a more suitable one for actual projects in anti-seismic performance analysis and evaluation. Based on probabilistic theory, considering randomness of seismic input, material durability damage and stochastic structure dynamic response, under chloride erosion environment, the dissertation makes systematic research on seismic fragility analysis and anti-seismic structure performance evaluation of concrete bridge in service. The main research contents are as follows.On the basis of existing research result and following the principle of whether comparatively bigger sensitivity parameter is included in the models, the rusting rate computing formula of regular reinforcement and pre-stress wire is selected. Sensitivity analysis to 10 concrete cracking time models is made with 3 kinds of relative sensitivity analyzing methods concerned with single parameter, multi-parameter and sensitivity targets. The principle of the model with greater sensitivity parameters is followed, and more reasonable concrete corroded expansion cracking time prediction model is selectedBased on probabilistic theory, the dissertation gets random samples and probability distribution of durability damaged material’s mechanical property and geometrical characteristic variable with the change of time and space. Based on one-dimension-random-field Gaussian function and unit material space coherence distance, using random sampling method, the time-spatial varying random samplings are gotton of reinforced steel bar rustingrate icorr, steel comparative area As/A0, comparative ultimate strain εs/ε0, concrete comparative compressive strength fc/fc0, makes analysis of the samples, and comes to the probability distribution pattern satisfying to the material samples.Simulation method of random ground motion for large-span bridge in service is proposed. Considering the influence of bridge structure service period on earthquake loading, equal exceeding probability method was applied to reduce earthquake load, and two fortification criterions of current anti-seismic code for highway bridge were supplemented to three levels. The probability theory was used to randomize target response spectrum by considering the randomness of ground motion. Combined with coherence function and phase difference spectrum theory, the non-stationary random ground motions of spatial correlation multi-points for exiting bridge structure were generated.The dissertation takes prestressed concrete continuous rigid frame bridge as an example to make analysis to anti-seismic performance of in-service bridge structure. Based on material durability degradation rule, the stochastic finite elemnt model of bridge structure in-service is established. In the light of increment dynamic analysis method, the dynamic response of bridge structure is got. Reflecting displacement and hysteretic energy two –parameter damage criterion DM is used to describe bridge damage under seismic load, and the relation curve of IDA between damage index DM and ground motion peak value PGA is got. IDA probability line is got after making statistical analysis to IDA curve. Through comparing IDA probability line and damage grade, the seismic performance of exising bridge structure is analyzed.Considering durability damage, structure seismic fragility analysis and risk analysis methods are put forward. Based on not regarding to durability damage structure fragility analysis and risk analysis models, time-and-spatial varying law of steel area, ultimate strain, and concrete compressive strength should be regarded. The seismic fragility analysis and risk analysis are made, so the seismic damage probability curve and seismic risk probability curve is got, and the seismic performance evaluation of the bridge structure is completed.