Distortional Researches For Off-track Box Girders Of Cranes Considering Variable-distance Diaphragms

With the scale of modern logistics industry becoming more and more larger, design theory of crane structure has been extensively applied into the manufacturing procedure with the aim being bigness and lightweight. Only decreasing the thickness of each plate element will reduce the local stability of girder's grid and improve the transversal and longitudinal deformations of cross sections, which may be unsafy for production. Diaphragms welded in box girder at some distance will effectively improve the local stability of every grid and increase the overall torsional rigidity and anti-distortional rigidity simultaneously, with transversal and longitudinal deformations reducing under eccentrical loadings. Consequently, rationally distributing the distance between adjacent diaphragms can optimize the distribution of stresses and straines on cross section and improve the ratios of steel utilization, realizing the lightweight design of box girder structures.Closely surrounding the key questions of the distortional deformations of cross section of box girders with varable-distance diaphragms, models of distortions of box girders under stiff (flexible) diaphragms assumptions, were both constructed in this dissertation, which the effects of postion and quantity of diaphragms on distortional deformations of box girders were systematical analyzed.The main contributions of this dissertation are listed below:(1) For box girders with diaphragms, the interactive reactions between diaphragms and girders were regarded as the distributed distotional moments in range of thickness of diaphragms. Based on the assumptions of inplane infinite stiffness of disphragms and coordinations of shearing deformations between girders and diaphragms, distortional initial-parameter methods of simple-supported beam (cantilever) with stiff (flexible) diaphragms were both proposed considering distortional shear defortions of cross sections, resulting in the initial-parameter solutions of distortional angles and warping fuctions of girder's cross sections. Compared the distortional initial-parameters solutions and FEA simulated ones of distortional angle, warping displacements and stresses of sample points, the correctness of distortional initial-parameter solutions of girders was testified based on stiff (flexible) assumptions considering different numbers and thicknesses of diaphragms.(2) Based on the initial-parameter method of box girders with flexible diaphragms, parametrical studies were developed considering the effects of parameters-ratios of height to span, number and thickness of diaphragms on distortional angles, warping stresses, transversal flexural angles for some keypoints located in mid and ending of beams. Results show:the increments of ratios, number and thickness of diaphragms can effectively restrain distortional angles, warping stresses, transversal flexural angles of sample points of wheel loadings.(3) Optimizations of diaphragm positions for symmetrical triple-diaphragm strengthened simple supported beams, were developed with the aim of distortional warping displacements and stresses of wheel loading under symmetrical distortional loadings. This optimization belongs to continuously single-parametical problem, the restrained conditions of which include local shearing stability of diaphragm in mid and local mixed flexural-shearing stability of loading plate element. Results show:the optimized position of moving diaphragm I locates at the cross section where external distortional loading lies, the optimized aims of which are distortional warping stress, warping displacements and two above mixed one of nodes located at wheel loading points under different symmetrical distortional moment Md. And at this point the local critical buckling load is the biggest for both middle diaphragm and loading plate element.(4) Taking aims of the first and second differentiations of distortional warping functions at wheel loading points, analysis were accomplished for the relationships of height and width coefficients between unevenly symmetrical triple-diaphragms simply beams and the equivalent triple-diaphragms simple supported beams. Results show:linear correlations indeed existed between two above coefficients based on least square method. Moreover, the distortional warping rigidity and frame rigidity were both fully investigated between equivalent triple-diaphragms simple supported beams with even distance and the original one with even distance under different coefficients of cross section. Results show:the distortinal warping rigidity of symmetrical triple-diaphragm simple supported beam with uneven distance becomes larger and the frame one smaller by compraring with the original beams with evenly distributed diaphragms.(5) For simple supported beam with or without diaphragms, symmetrical concentrated distortional loadings were directly made by loading platform of FCS four-passes hydraulic servo. The distortional displacements and stresses of sample points were observed by dialgages and static strain gauge. The correctnesses of distortional initial-parameter method and the flexible-diaphragms assumptions (deformed coordination) were both fully verified by comparing distortional tested datum and initial-parameter solutions. Meanwhile, considering the uncentainty of every testing portions in loading procedure, there existed permissible errors in some range for displacements and stresses of sample points, mainly produced by low accuracy of manufacturing, installing and residual deformations induced by welding.Above all, the systematical analysises were developed for distortional property of cross section of box girders with diaphragms, including all three parts- theoretical analysis, FEA simulation and experimental testing. The researches in this dissertation enrich the design of distortions of cross section in girder structures, having an important meaning for improving the theoretical system of structural lightweight of girders.