Elastic Buckling And Ultimate Strength Of Web Plates In I-girders Under Patch Loading And Shear

Local buckling may occur in web plates in I-girders subjected to bending, shear and patch loading. The local buckling of web plates in I-girders under wheel loading has been rarely investigated, due to the unknown distribution of bearing stresses in the web plates. The recommended method for calculating bearing stresses on the edge of web plates in GB50017-2003 is deviated further from the accepted method in the world than that of GBJ17-88. In fact, no study has been carried out on this recommended method. On the other hand, although much has been done to study the stability of web plates under patch loading and shear, the rotational restraint from the flange to the web plate has not been reasonably accounted for. In order to evaluate this rotational restraint properly, the finite element method was utilized to analyze the elastic buckling and ultimate strength of web plates in I-girders under patch loading, wheel loading as well as shear forces.An extensive parametric study was conducted on the bearing stresses of web plates in crane runway I-girders under wheel loading. It was found that the most important factors influencing the stress dispersion are the web thickness and the inertia moment of the rail, while the inertia moment of the top flange has a minor influence. The depth and length of the girder and its boundary conditions have a negligible effect. Based on the theory of beams on elastic foundation and the numerical results, design equations are proposed to predict the bearing stresses on the edge of the web plates. The distribution of bearing stresses along the depth and the span of the girder was also obtained.The behavior of rectangular plates under patch loading and wheel loading, with all four edges being simply supported and two opposite edges being simply supported and fixed as well as three edges being simply supported and the rest edge being fixed, were analyzed with the finite element method. The regression formulae were obtained to determine elastic buckling coefficients of the forementioned rectangular plates.An eigenvalue buckling analysis was carried out on I-girders under patch loading and wheel loading with ANSYS. A parameter correlating the torsional stiffness of the flange and the flexural stiffness of the web was introduced to quantify the rotational restriction from the flange to the web plate. A formula with good accuracy was suggested to determine elastic buckling coefficients, which accounting for the rotational restraint reasonably.The investigation on elastic buckling coefficients of web plates in I-girders loaded by patch load on top flanges was carried out and the effects from parameters such as aspect ratio and slenderness of web plate, length of patch load were taken into account.The behavior of rectangular plates under shear, with all four edges being simply supported and two opposite edges being simply supported and fixed as well as three edges being simply supported and the rest edge being fixed, were also analyzed with ANSYS. An improved formula was suggested to evaluate the elastic buckling coefficients of the simple-fixed rectangular plates, and another formula for plates with three edges being simply supported and the rest edge being fixed was also brought forth.Based on numerical results of 690 I-girders, a formula accounting for the rotational restraint provided to the web plate by the flange was obtained to calculate the shear buckling coefficients of web plates. Subsequently, a method to predict the ultimate shear strength was suggested. It is worth noting that the effect from the rotational restraint on the elastic buckling strength and the contribution from the flange itself were both considered in the suggested method. The correlation between the experiments and the suggested method is good, especially for web plates with great aspect ratio or slenderness, for which the ultimate shear strength has not been predicted satisfactorily through currently available method.