The Model Test Research On The Mechanics Capability Of PC Beams With The Effect Of Cyclic Loading

With the rapidly development of transportation and economy, the prestressed concrete girder bridges gain wide application in the road with the advantages of its high stiffness, comfortable, mature technology.It has a considerable proportion in china's highway bridges. However, due to various reasons,prestressed concrete girder bridges have a common phenomenon about excessive midspan sag across the service stage.The structure's design of long-term deflection is much higher than it's calculated result. It will have negative effect on the service performance and structure safety of the bridges which has already become a serious obstacle of this kind of bridges'development. Research and analysis of long-span prestressed concrete bridges about the reasons of downwarping and the method of long-term deflection calculation, proposed the design and construction measures of the prestressed concrete girder downwarping, searching the method of deflected prestressed concrete beam which has became the urgent problem of china's bridge engineering field. This paper is based on the transportation construction projects in Western Traffic which called "long span prestressed concrete girder bridge role of repeated effect of moving load,"is the sub-project 3 of'large span prestressed concrete bridge beam Deflection Analysis and Countermeasure"。It is on the the changes of mechanical properties repeated loading on prestressed concrete beamsBased on the two different types of T-shaped beam model which were all concrete, according to of different loads experiments,which included normal state, the lower edge appeared the tensile stress without cracking, the state with cracking in the lower edge and under normal load in the contions of less than 0.1mm edge cracking under the four different loading conditions of cyclic loading, Then it exerted static loading of the beam cross section to test the changes ofthe strain, the deflection of a typical cross-section and the effective prestress prestressed forces. Test results showed that in all conditions the strain of cross-section with repeated loads remained stable; residual deflection of prestressed concrete beams with the increase in the number of cyclic loading is increasing; load deflection changes, the number of repeated loading and prestressing degreeλwere with a certain correlation.With the degree ofλdecreaseings,the correltaion in the three parameters is more obvious; PC beams prestressed forces with residual strain increase with the frequency of cyclic loading is increasing; prestressing tendon strain, load time andλhas some degree of correlation.With the degree ofλPC decreases, the cyclic loading frequency on the load deflection impact is more significant. Tendons between changes of strain and deflection showed a strong correlation.According to the analysis of test results that the repeated loading on prestressed beams has some impact. And according to test results, the role of frequency and deflection of the repeated regression analysis of the prestressed beams under repeated loading variation of the residual deflection, and made a cracking of prestressed concrete beams in the deflection correction method.