Cause Analysis And Treatment Of Prestressed Concrete Continuous T-beam Bridge Disease

Prestressed concrete continuous T-beam bridge(simply supported and transferred structure continuous)realizes the factory construction,standardization and assembly of bridge construction,which has been developed rapidly in the construction of freeway bridge in our country.However,through the field investigation of dozens of prestressed concrete continuous T-beam bridges,it is found that there are a lot of cracks in the beam section of prestressed concrete continuous T-beam bridge.For the reason of the cracks,this paper takes the Pujia Bridge as an example to analyze and study from the aspects of design,construction and operation so as to provide the basis for crack prevention and control.1.The general situation of the prestressed concrete beam bridge at home and abroad is fully understood and the common diseases and causes of such bridges are analyzed and summarized.Using the advanced bridge theory and finite element software of bridge,the factors influencing the cracking of concrete are studied in detail.2.Based on finite element analysis theory,the solid model of prestressed concrete continuous T-beam bridge is established by finite element software MIDAS / CIVIL.The prestressed concrete continuous T-beam bridge is simulated.And the measured results are compared with the theoretical calculation results.It is found that the longitudinal cracks in the early stage of the bridge are non-structural cracks,and only the cracks can be closed.3.Taking the Pujia Bridge as an example,firstly,the influence of the effective prestress loss of the prefabricated beam and the effective prestress loss of the short pier on the mid-span deflection and the control section stress are analyzed.Secondly,the influence of single bearing arrangement and double row bearing arrangement on the structural force is analyzed.Finally,the influence of the length of different cast-in-place segments on the bending,shear and tension(compression)of the structure was studied.Concluded as follow:(1)When the effective prestressing loss of the prefabricated beam is as follows:the mid-span L / 4 and the mid-span deflection decrease linearly with the effective prestress loss;When the effective prestress loss value is between 15% and 20%,the edge of the 0-L / 2 section of the mutation occurred,the edge of the bridge was linear S-shaped,fulcrum sections 36 and 116 on the edge of the tensile stress,visible The effect of effective prestress loss on the span is much higher than that of the midspan,which is very disadvantageous to the force of the cross-span structure,which may cause structural damage.(2)The effective prestress loss has little effect on the deflection of the continuous girder bridge when the effective prestressing loss of the dome is short,which has great influence on the stress of the fulcrum and the section of the frigid section.When the loss value reaches 20%,the compressive stress on the section of the fulcrum is reduced by about 20%,and the tensile stress of the section at the pier is increased by about 50%.The stress in the section of the middle pier is increased by the pressure.It is suggested that the prestress loss should be strictly controlled during the construction phase,which may increase the tension control stress(1.01-1.05 times),and the reinforcement ratio of the top of the pier should be improved.(3)Through the analysis of bending moment,deflection and stress,it can be seen that the bending moment,deflection and stress of the double row bearing arrangement and the negative moment and stress value of the pier are smaller than the single row bearing.The effect of double row bearing arrangement on the negative moment and stress of the pier top is especially obvious(which can weaken about 18%),and the weakening effect on the bending moment and stress is more significant(about 10%),The role of weakening the deflection is also more obvious(can weaken about 15%).It is suggested that the double-row bearing arrangement should be adopted at the time of design,which not only reduces the difficulty of construction,but also can improve the working condition of the structure and improve the crack resistance of the structure.(4)The length of the cast-in-section(in the range of 20-80cm)has little or no effect on the structural bending,shear,tensile and compressive design.