Experimental Study On Long-term Mechanical Properties Of Three-span Prestressed Concrete Continuous Box Girder

Prestressed concrete continuous beam bridges are widely used in the construction of transportation infrastructure.However,with the gradual aging of a large number of prestressed concrete bridges built in the past,coupled with the frequent occurrence of construction design defects and overloading operations,the problems of cracking and long-term excessive deflection and deformation have become increasingly prominent,and urgent attention is needed.At this stage,most of the experimental studies on the long-term mechanical properties of prestressed concrete continuous beams focus on the uncracked stage,and the cross section is often rectangular,and the number of spans is mostly two spans.For multi-span prestressed concrete continuous box girder cracking The long-term mechanical performance research at the stage is mainly based on numerical simulation,and there is a lack of corresponding experimental research.Therefore,the long-term mechanical performance test study of the prestressed concrete continuous box girder in the cracked state can more truly and reliably reflect the actual long-term force state of the bridge structure,verify and improve related theories,and determine the long-term mechanical performance degradation law of the dilapidated bridge The research has important theoretical significance and provides reliable research data and theoretical guidance for the detection and reinforcement of related bridges.In view of the current operating status of prestressed concrete box girder bridges,with the background of large traffic or overload conditions causing the bridge structure to crack,this paper conducted a 558 d long-term mechanical performance test on the three-span prestressed concrete continuous box girder with cracks.To study the long-term mechanical performance degradation of the prestressed concrete continuous box girder in the cracked state.The following main tasks are completed jobs:(1)The 558 d long-term test of three span prestressed concrete continuous box girder is carried out,and the mechanical properties of the cracked model box girder under long-term stacking load,such as long-term deflection development,concrete strain time history change,control section crack development,and prestress loss,were analyzed.The law of change;the creep coefficient function is obtained by fitting the measured data from the concrete shrinkage and creep test.(2)The effect of cracks on the long-term deformation of the structure is analyzed,and the moment amplitude modulation method is used to solve the internal force redistribution problem that occurs when the prestressed concrete continuous box girder enters the nonlinear stage.By considering the height of the relative compression zone,the stiffness ratio of the mid-span section of the structure to the section of the middle support,and the damage coefficient,the formula of the bending moment amplitude modulation coefficient is obtained.(3)Based on the long-term mechanical test results of the three-span prestressed concrete continuous box girder,the superposition principle is used to analyze,considering the influence of factors such as concrete cracking,shrinkage and creep,and bending moment redistribution,the long-term uniform force is obtained by compiling related analysis and calculation programs The long-term deflection coefficient of the side support and the long-term curvature of each section are used.The long-term deflection of the test beam is obtained by the conjugate beam method,and the calculated results are compared with the measured results.It is found that the theoretical calculation value of the long-term deflection of the mid-span section of the test beam is equal to The test results are in good agreement.