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Abstract
This thesis concerns with the calculation of stress concentration factors (SCFs) in steel circular hollow section (CHS) joints. SCFs are used for the prediction of the hot-spot stress in order to assess joint structural integrity against fatigue. Thus. to calculate the stresses in the analyzed joints, a three-dimensional model based on the finite element method is presented.
The thesis consists of two studies:
The first study deals with uniplanar CHS joints reinforced by stiffened plates subjected to various types of basic loadings such as axial force. in-plane and out-of-plane bending moments. To verify the numerical results. the results of un-stiffened joints are compared with those of the empirical formulae available in the literature. After the verification. a parametric study is generated in order to evaluate the performance of stiffeners in CHS joints. The parametric study is done by varying the geometrical parameters of the joints such as the wall thickness ratio and the diameter ratio between the brace and the chord members of the joints. Also, the variation of the ratio of thickness of the stiffened plate to the chord thickness is considered in the parametric study. From the results obtained. the stress concentration factors in the stiffened joints were found to be lower than that of the un-stiffened joints. Consequently, the stiffening plate enhances the performance of joints under fatigue loadings.
The second study concerns with multiplanar CHS joints. The results of the finite element model in characteristic locations around the welds at the chord and brace sides correlate fairly well with those of the available experimental and empirical formulae. The important phenomenon of carryover loading. which refers to the interaction between the out-of-plane and the in-plane braces. is examined in detail. The efTect of the geometrical parameters of the joint is examined through a parametric study. The parametric study includes basic geometrical parameters (the thickness ratio between the brace and the chord. the diameter ratio between the brace and the chord, and the slenderness ratio of the chord) and the multiplanar geometrical parameters (the out-of-plane angle between the two braces and the gap angle). Based on the results obtained. the multi-planar parameters seem to be crucial parameters for the evaluation of multiplanar joints for fatigue design.