钢箱梁横隔板-U肋交接部位疲劳应力有限元分析

FEA for fatigue stress of diaphragm-U rib connection in steel box girder

为探索钢箱梁横隔板-U肋交接部位疲劳应力（包括焊接接头热点应力以及钢板母材疲劳应力）的有限元分析方法,采用ABAQUS分别建立钢箱梁体壳混合有限元模型和纯板单元模型,计算轮载作用下的构造疲劳应力,分析了单元类型、网格精度及表面外推方法对计算疲劳应力的影响.得到以下结论：1）单元类型与网格尺寸是构造细节计算疲劳应力的主要影响因素,外推方法对热点应力也存在较大影响;2）热点应力计算建议采用高阶的四面体或六面体单元,局部单元网格划分至1/4板厚;3）采用表面外推法计算焊趾热点应力时,应力取值点宜位于距焊趾0.5t（t为板厚）以外,建议采用DNV等船级社推荐的三点二次外推法,该结论对于焊缝a类、c类热点均适用;4）对于弧形切口母材局部应力,采用体单元时单元应划分至1.3mm,采用板单元时应划分至0.3mm,板单元计算应力较体单元普遍偏小,建议采用二阶体单元以准确模拟板厚方向的非线性应力分布.

In order to investigate the FEA method for fatigue stress calculation of diaphragm -U rib connection, including hot spot stress of welding joint and fatigue stress of the base metal, finite element models of block-shell-mixed element and pure shell element of steel box girder are established by ABAQUS to cal- culate fatigue stresses of structural details under vehicle load; and then the effects of element type, mesh size and surface extrapolation method on fatigue stresses are analyzed. Some conclusions are drawn as follow： 1. Element type and mesh size are the main factors affecting the calculated fatigue stress of structural details; the extrapolation method also has some effect on hot spot stress. 2. Higher order tetrahedral or hexahedral element are suggested to calculate hot spot stress of the welded joints; and the grid size should be 1/4 of plate thickness. 3. Extracting position should locate at 0.5t （t is plate thickness） away from the weld toe when using surface extrapolation method to calculate the hot spot stress at the weld toe, DNV quadratic extrapolation method was recommended conservatively. These conclusions are applicable for all hot spots of class A and class C. 4. For local stress analysis of the base metal of the cutout, the grid mesh should be 1.3 mm when using block element, which should be 0. 3 mm when using shell element; the cal culated stress of shell element is generally smaller than that of block element; higher order element is sug gested for accurately simulating the nonlinear stress distribution in the thickness direction.