Research On Ultimate Bearing Capacity Of Existing Prestressed Concrete Box Girder

Prestressed concrete small box girder bridges account for a relatively large proportion of the small and medium-span bridges in service.During the service of the bridge,different degrees of disease will occur due to various factors such as environmental and human factors.In addition,the increasing vehicle load will further aggravate the development of disease,and the structure will continue to be damaged due to various factors.The gradual aging of development affects the durability and even safety of bridges.Therefore,research on the ultimate bearing capacity of in-service bridges is extremely important.This paper takes a prestressed concrete continuous small box girder bridge with complex damages of slab concrete damage,prestressed steel strands and steel bar fractures as a background.The ultimate bearing capacity is studied from three aspects: special inspection and evaluation,full-scale load test and numerical analysis.And check the capacity of special vehicles on the bridge based on the bearing capacity results to provide a reference for the operation,maintenance and reinforcement of similar bridges.The main research contents and conclusions are as follows:(1)The undamaged and damaged prestressed concrete box type single beam was tested for its material condition,the thickness of concrete protective layer and the corrosion potential of steel bars.The damage resulted in serious corrosion of steel bars,serious carbonization of concrete and reduced natural vibration frequency of structure.According to the special test results,the bearing capacity of the two kinds of single beams was evaluated by using the current bearing capacity evaluation standard.The bending capacity of the prestressed concrete small box girder was greatly reduced due to the complex damage disease,and the structure had hidden danger.(2)The load test of the undamaged prestressed concrete small box girder is carried out by static loading.The data of deflection,strain and cracks are tracked and collected during the whole test.Based on the test data,the elastic stage and cracks of the prestressed concrete small box girder are tested.The mechanical behavior characteristics of the stage and the failure stage are analyzed.Based on the ABAQUS plastic damage mechanics model,a refined model of the undamaged small box girder is established,and the model is further adjusted based on the field measured data of the box girder.According to the numerical analysis results,the correlation between concrete damage and crack development trend is further discussed,and the numerical analysis of bearing capacity has good applicability.(3)According to the actual disease situation of the damaged prestressed concrete box girder,adjust the placement of various sensors for the load-bearing capacity load test.According to the test results,analyze the deformation and crack development characteristics of the prestressed concrete box girder under different working conditions under the condition of severe damage and disease.The actual bearing capacity of the small box girder is still greater than the design bearing capacity and the testing and evaluation bearing capacity.Based on the refined model of the undamaged test small box girder,considering the influence of steel bar corrosion,steel strand breakage and prestress damage on the structure,the Model Change function is used to complete the numerical analysis of the damaged small box girder.The numerical analysis results are more consistent with the test results It provides a reference for numerical analysis of similar diseases.(4)A finite element girder grid model of a prestressed concrete continuous small box girder bridge is established,and the traffic capacity of different special vehicles under two different conditions,undamaged and damaged,is analyzed from two aspects of different driving lanes and following distances.Although damage and disease have severely reduced the bearing capacity of the bridge,the bridge still has the capacity for special vehicle operation and a certain safety reserve.Combining the law of load effect of different special vehicle traffic schemes,calculate the maximum load capacity of special vehicles under the background of emergency repairs.