Effect Of Creep On Shear Lag Effect Of Prestressed Concrete Box Girder

The shear lag effect is one of the important mechanical properties of thin-walled box girder,and creep is a characteristic of concrete that cannot be ignored under long-term development.For prestressed concrete box girder,creep must have an effect on the shear lag effect.In this paper,the finite beam segment method based on the energy variation method is used to comprehensively consider the influence of the prestressed steel beam and creep on the shear lag effect of the prestressed concrete box girder.The corresponding calculation theory is established to study the prestress in detail and in detail The idea of the influence of steel beam and creep on the shear lag effect of box girder.The main research contents are as follows:(1)Using the warpage displacement function defined based on the shear deformation law,the shear lag effect of thin-walled box girder is studied by the finite beam segment method.Taking the homogeneous solution of the basic differential equation of thin-walled box beam shear lag as the displacement mode of the beam segment element,the energy variation method is used to derive the stiffness matrix and load matrix of the corresponding beam segment element.After programming in MATLAB,the simple supported and continuous box beams are analyzed,and the longitudinal stress of the section under the equivalent load of the prestressed steel beam is calculated,and compared with the corresponding numerical simulation and field measurement results,the results are in agreement good.The analysis shows that the finite beam segment method can be used to analyze the shear lag effect of thin-walled box girder,and the shear lag effect has a significant effect on the longitudinal stress of the thin-walled box girder.(2)For the prestressed concrete simply supported box girder,considering the loss of prestressed steel beam load caused by creep,the shear lag effect under the influence of creep is analyzed.The results show that the shear lag effect of the mid-span section is not obvious.Compared with the case where creep is not considered,the compressive stress of the upper wing plate increases by 24.5%,and the compressive stress of the lower wing plate decreases by 14.1%.At the same time,the shear lag effect and creep Under the combined action,the mid-span deflection is increased by 1.73 times.(3)For the prestressed concrete continuous box girder,the creep secondary internal force is generated due to the conversion of the construction system,resulting in the redistribution of the internal force,and then the stress redistribution.First,the calculation expression of creep coefficient in the Design Code for Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts is fitted to an exponential function.Based on the Dishinger method,the calculation formula of creep internal force is proposed;Equivalent to external load,the shear lag effect under creep is calculated.The analysis shows that under the influence of creep,the shear lag effect of the mid-span section is not prominent,but the shear lag effect of the section at the bearing is obvious.Compared with the case without considering the creep,the compressive stress of the upper wing plate increases by 16.5% The compressive stress of the lower wing plate is reduced by 25.3%.At the same time,the shear lag effect and creep together make the mid-span deflection increase by a maximum of 1.58 times.(4)Using the secondary development tool of ANSYS UPFs,numerical simulation of the prestressed concrete box girder considering creep is carried out.The user creep subprogram USER.CR provided by ANSYS has been modified so that it can calculate the creep of concrete.The numerical model analysis shows that the calculation results of the secondary development of ANSYS UPFs are in good agreement with the calculation results in this paper,and can be used in the calculation of actual engineering.