Reliability Assessment Of PC Beam Bridge Under Bending And Shear Stress

In recent years,along with economy and society development,the traffic industry has ushered in a strong opportunity for development,but at the same time it has brought some problems.The deterioration of bridges caused by the increase of traffic volume is becoming more and more serious.According to statistics,more than 800,000 bridges have been built in China,of which more than 80%are small and medium span bridges,and the traffic volume is characterized by large flow,overweight and channelization.With the extension of the service life of bridges,these characteristics make higher requirements for the safety and durability of existing bridges.At the same time,along with how to evaluate the durability status,it has become an urgent problem to be solved.In order to study the fatigue performance of concrete girder bridge under bending and shear stress and the reliability performance of PC box girder webs after cracking,a series of experiments and theoretical studies have been carried out in this paper.The concrete work and results are as follows:1、Expanded sample test was carried out on the basis of predecessors,and the fatigue equation of concrete under bending and shearing force was obtained by statistical analysis on this basis.Taking a continuous T-girder bridge with a span of(4 x 40)m as the background bridge,the finite element model is established.The limit state equation of fatigue reliability under bending-shear stress is established based on S-N curve equation and Palmegren-Miner linear cumulative damage quasi-model.The fatigue reliability indexes under different traffic volume growth factors(0,1%,2%,3%)and different overload rates are analyzed.2、Based on the static loading test of 12 PC box girders and the test data of bending and shearing force of existing concrete beams,this paper revises the calculation method of bearing capacity in corresponding codes based on the parabolic calculation model of bending and shearing capacity.The reliability of main girder bearing capacity is checked based on the formula in the revised formula and code(JTG D62-2018 Code for Design of Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts).The results show that the influence of bending-shear correlation on the calculation formula of bearing capacity should be taken into account when designing the section of main girder of Reinforced Concrete Beam Bridge.3、Comprehensive domestic and foreign tests show that the flexural and shear bearing capacity of reinforced concrete beams are correlated under the combined action of bending moment and shear force.The fatigue tests of seven pre-stressed concrete box girder webs after cracking were carried out.The stiffness degradation model of PC box girder after cracking was obtained by statistical analysis.Based on the stiffness degradation model,the function of stiffness degradation fatigue was established,and the variation of reliability index was analyzed with the increase of fatigue load times.