Analysis Of Creep Effect On PC Continuous Box Girders Considering The Effect Of Shear Lag

The shear lag of prestressed concrete (PC) box girder will cause uneven distribution of bending stress in sections along the transverse direction of the girder, and also it will cause additional deformation of the girder. The concrete creep will generate the time-dependent deformation of the girder and the redistribution of stresses between the steel and concrete in sections, and it will produce the creep secondary inernal force for system-conversed statically indeterminate structures. As to characteristics of the construction method of cantilever, in this thesis, the effect of shear lag on creep effect in prestressed concrete (PC) continuous box girders constructed through conversing system is studied.First of all, the energy variational method is adopted to establish the governing differential equations of shear lag with the consideration of the steel effects. And also, equivalent section method is introduced to deduced the stress, deflection and shear lag coefficient computational expressions of variable cross section cantilever girders and continuous girders under dead load and pre-tension.Secondly, on the bases of the new governing differential equations of shear lag, by introducing the time-dependent constitutive equation of concrete, the internal force equilibrium and deformation compatibility of cross section at any time are utilized to obtain a novel analysis approach of creep effect of PC box girders with variable cross sections. This analysis approach considers about the effect of shear lag, concrete shrinkage and creep, relaxation of prestressed reinforcement and also the steel ratio of the girders. For statically determinate structure with a system conversion, shear lag is considered to derive the creep secondary internal force formula. By introducing the T-B function, the internal force equilibrium and deformation compatibility of cross section are used to obtain the analysis method of analyze the effect that the shear lag poses on creep of PC continuous box girder with variable cross section. Also, the formulas utilized to calculate the stress and strain of concrete and reinforcement at any time and the deformation of the girder are derived. At last, matlab is utilized to develop and calculate all the formulas derived above and finite element software is used simultaneously. Comparison with rusults obtained from the presented method in this thesis as well as the results obtained from the finite element software shows that the presented method in the thesis is feasible and reasonable to analyze the effect that the shear lag poses on creep of PC continuous box girder with variable cross sections.The analysis method of analyze the effect that the shear lag poses on creep of PC continuous box girder and the relative derived formulas provide a new approach for the study of synthetic effect of the shear lag and the creep.