The Analysis Of Spatial Static And Time Effect About Curved Thin-walled Box-girder Bridges

Due to the excellence of torsional stiffness, economy and aesthetic appearance, curved box-girders are widely used in modern highway bridges, interchanges and urban viaduct systems. Because of curvature, the mechanical behavior and the calculation of curved girder are more complex compared to the straight girder. Box-girder bridge has become increasingly popular in construction of curved bridge, the conformation of it has been presented the characteristic of variable curvature and variable height. Practical design of curved box-girder bridges requires an analytical method which can be applied to analysis of construction process and the finite element formulas about analysis of creep effect and shrinkage effect. In this dissertation, spatial static linearity analysis and time effec(tcreep effect and shrinkage effect) for curved thin-walled box-girder bridge were studied. According to those, the main contents and results are as follows:1. In this dissertation, considering the influence of transverse shearing deflection and noncoincidence of torsion center and gravity center, the equilibrium formulas of variable-curvature box-girder with rectangular cross section were established. Based on deformation expression of arbitrary point on the girder and relationship between inner forces and displacement equations, considering noncoincidence of torsional center and gravity center, the governing differential equations for variable-curvature box-girders were generalized. The results of research indicates: the shorter the radius is, the greater influence of the noncoincidence of the torsion center and gravity center for torsion angle will be.2.The causes why normal stress of curved-box girder vary with transverse axis are as follows。Besides the normal stress of torsion and distortional warping,bending normal stress brings asymmetrical distributing. Because curvature varying on width of curved girders have effects on the vertical bending deflection angle, the displacement assumption which plane surfaces of girder remain plane after bending is canceled. The bending normal stress of arbitrary point on the cross section are in inverse proportion to square of radius of this point. And the inner portrait bending stress of curved box-girder are stronger than outer portrait stress. The effects of above-mentioned are usually opposite. If the ratio of axis-radius to width is less than 10, the effect of curvature varying on width of curved girders must be considered. 3. A curve coordinate system which is suitable for variable height curved box-girder were established. The flexure, torsion and distortional warping displacement functions were established, and the strain-deformation equations were obtained, a spatial finite element analysis method of trapeziform cross section variable-curvature box-girder with vertical symmetrical axis was also presented. During the process, following were considered:the effects of variable radius of cross section on the vertical bending deflection angle, noncoincidence of torsional center and gravity center, the effect of transverse shearing strain on energy of strain. In order to calculating the curvature and height in the element, the shape functions were also used for the variable expression of curvature and height.4. Applying integral intermediate value theorem, new effective elasticity modulus expressions were presented, which creep aging coefficient can be calculated by the creep coefficient of intermediate time of incremental time segment. Creep and shrinkage strain were treated as a kind of compulsive strain. Compulsive strain methods were used for the analysis of creep effect and shrinkage effect about concrete curved box-girder bridge. A group of finite element formulas about analysis of creep effect and shrinkage effect were deduced.5. Based on the facts mentioned above, the curved boxed-girder bridge program was programmed, which can be applied to the analysis of bridge construction process. Some examples were proved to the validity and the accuracy of these proposed methods and analysis programs.