Prestressed Concrete Cable-stayed Bridge Considering Time-varying Factors Structural State Prediction

Prestressed concrete cable-stayed bridge has been widely used because of its good structural performance and beautiful shape.However,the time-varying factors such as concrete creep,prestress loss of steel bundle,cable damage,cable relaxation and so on lead to the continuous deterioration of the force and linear shape of the bridge structure,which affects the normal use of the bridge structure and even endangers the safety of the bridge structure.Therefore,this paper takes a prestressed concrete cable-stayed bridge in service as the engineering background to study the influence of the above time-varying factors on the structure stress and linear shape of the bridge.Combined with the inspection data over the years,a reasonable prediction model is determined to predict the structure stress and linear change of the cable-stayed bridge,so as to provide theoretical support for the bridge maintenance and management.The main research contents and results are as follows:The finite element analysis model of the cable-stayed bridge was established based on the finite element software MIDAS/Civil.Taking the measured cable forces as the objective,the formal iteration method was adopted to carry out the construction phase analysis,and the initial finite element analysis model was obtained.According to the test data of bridge load,the finite element model correction method is adopted by combining static and dynamic methods,and the non-dominated sorting genetic algorithm NSGA-II is used to solve the problem.The results show that the modified finite element model can better reflect the actual state of the structure.Based on the modified finite element model,different calculation modes are selected to analyze the influence of time-varying factors of concrete creep and steel bundle prestress loss on the stress and alignment of the bridge structure.For different calculation model calculation value differences,but different model calculation of creep of concrete and steel beam loss of prestress time-varying effect law is consistent,are all increased with the increase of operating time,main girder down warping unceasingly,across the middle girder down warping quantity,cable tower to cross direction,on the whole hanger forces appear less phenomenon,and the early change fast,slow.Based on the analysis of the time-varying effect of the prestress loss of the steel bundle,it is concluded that the time-varying factors of the prestress loss of the steel bundle have great influence on the stress of the main beam.By analyzing the time-varying effect of cables,it is found that the deeper,the more and the longer the cables are damaged,the greater the influence on the force and linear shape of the bridge structure,and the greater the influence on the force and linear shape of the structure near the damaged cables,and the less the influence on the force and linear shape of the position far away from the damaged cables.Cable relaxation has great influence on the deflection of main girder.Based on time-varying effect analysis and bridge inspection data over the years,the prediction model of cable-stayed bridge is established.It is predicted that with the increase of the service time,the main girder will keep buckling,and the buckling is the largest in the mid-span,and the tower keeps tilting to the mid-span direction.The top of the tower has shifted about 13 cm to the mid-span direction after 20 years of operation,and the cable-stay force is generally reduced.At present,the cable-stayed bridge has been in operation for 20 years.In the next 20 years,the main girder will continue to bend downward,with the largest deflection at the mid-span position,which is 5.5cm.The cable tower will also continue to shift in the mid-span direction,with the top offset of 3 cm and the cable force will not change much.