Research On Fatigue Performance Of Box Girder Bridges In Heavy Highway

The prestressed concrete beam bridge is a common highway bridge type. With the rapid development of economy and traffic vehicles in China, highway traffic volume and vehicle load show a growth trend, especially in Inner Mongolia where produce the major coal resources for our country. Serious damage would be made to the bridge when more and more coal vehicles go through the bridge. At the same time the bearing capacity and the service life of the bridge will be descend as the damage accumulate. Even one bridge maybe collapse when there is a heavy vehicle on the bridge. All of this would be bring a great number of economic loss to our country and caused a serious threat to the lives and property of the people. This paper selects the common prestressed concrete gird bridge type which span is twenty meters long to research its carrying capacity change under heavy load. The main contents are as follows:(1) Based on the similarity theory, designed a prestressed concrete model beam with a scale ratio of 1:3. And the ultimate carrying capacity load of this model beam is tested in laboratory. At the same time, the finite element model of the model beam is established by the large-scale finite element software ABAQUS, and the ultimate bearing capacity of the model beam is calculated by numerical simulation. Then compared with the experimental results to adjust the finite element model.(2) Based on the investigations of the vehicle loads on the highway in Inner Mongolia section which belongs to G6. Combined with the three kinds of fatigue calculation load model in the "general code for design of highway bridges and culverts" (JTG D60-2015) and three overload models from Chao Wang's fatigue load model( 20%, 50% and 70%); Use the influence line to find the most unfavorable load position of the beam. After this step, to use the software ABAQUS to calculate the Stress Amplitude of the beam that under every type loads.(3) There is the stress-life computational model of regular reinforcement and of prestressed reinforcement. To calculate the Stress Amplitude of the model beam under every type of fatigue load by these equations. The results show that the greater the stress amplitude is, the shorter the fatigue life of the model beam is. And the bridge can meet the design life,but heavy traffic seriously reduces the service life of the bridge.(4) In the process of fatigue deformation, the prestressed concrete beam shows three distinct stages. The fatigue constitutive relation of each component material of the beam at different stages is summarized. Numerical simulation of full fatigue process of prestressed concrete model beam is carried out using finite element ABAQUS. To calculate the residual carrying capacity of the beam under different stress amplitudes after 10, 30, 50, 70, 90 and 100 years fatigue load cycles. The results show that the greater the stress amplitude is, the faster the residual carrying capacity of the model beam decreases, and the greater the descender is.