Analysis Of Shear Lag Effect In Thin-walled Curved Box Girder With Special Support

Curved box-girder bridge, with its excellence torsional stiffness, smooth traffic and aesthetic appearance, is widely adopted in modern bridge design and construction. In order to make construction convenient, box girders have trended to one-cell single box girders of long cantilever and wide web spacing, which results in the shear lag effect becoming increasingly seriously. Many scholars commit to the shear lag effect of box beam and has gained many positive achievements, however, many of which are based on the straight-line one. Due to the presence of curvature, only the role of symmetric vertical load can cause both bending and torsion coupling. At the same time, if consider the skew structure used to adapt linear in box girder, the analysis of the shear lag effect of curved box girder is much more complex than the straight one. Even if the shear lag effect based on the thin-walled bar theory was taken into account later, the mechanical properties of curved box girder have still been difficult to reflect objectively, if the warping displacement effect from the second shear deformation in constraint torsion would have be omitted, that is to say, the constrained torsion warping generalized displacement is taken as the first derivative of the torsional angle. Therefore, it remains to be a further in-depth and detailed study of curved box girder.In this paper, the research mainly studies on the shear lag effect for the curved box girder bridge, proposing an analysis method of thin-walled curved box girder. The method is based on the assumption of rigid peripheral rims, and shear lag deformation is added to the basic deformation, considering the shear lag effect of curved box girder and merging into the effect of the secondary shear deformation on torsion warping displacement from the constraint wrap. Based on the axial force equilibrium condition, the appropriate shear lag warping displacement mode is chosen. As for the representative single-box-single-cell trapezoidal girder, the general formulas of the geometrical properties on shear-lag-warping cross section are derived according to the chosen displacement functions. Energy variational method is adopted to establish the governing differential equations and corresponding boundary conditions in controlling the flex and torsion of thin-walled curved box girder. According to the principle of force-method in structural mechanics, the curved beam bridge with one skew end and anti-torque along the direction of the skew are taken as the basic system and excess force respectively. Then, the canonical equation can be established based on the condition of coincident deformation that the rotatory angle around the skew support line perpendicular is zero.1. The mechanical characteristics of thin-walled box beam are analyzed and the concept of shear lag effect is described. Besides, the main theories and methods to solve the shear lag problem are introduced and its applicability and limitations are to be explored.2. Based on the finite element theory, the shell element in ANSYS program are used to model and analyze the curved box girder under different constraint conditions, and comparative analysis of the shear lag effect in the different models are analyzed.3. The plexiglass models of simply supported, cantilever and two-span continuous curved box girder are solved using the finite difference method. The results show that, the theoretical and measured values are in good agreement with each other, verifying the correctness of the calculation method and equations in this paper.4. Based on the principle of the force-method in structural mechanics, the mechanical properties of skew curved beams are discussed and the formulas for internal forces of the skew curved beam bridges with arbitrary degrees of skew are gained. The impact of the skew girder bridge by load type and degree of skew is discussed.