اثر تنش پسماند و اعوجاج در رفتار سازه ای اعضای فولادی استوانه ای دور جوش داده شده

The structural response of girth-welded cylindrical steel members is affected by the weld-induced residual stresses and distortions. This paper presents finite element analyses to clarify the effects of the girth weld-induced imperfections on the structural behavior of the cylindrical steel members with medium diameter-to-thickness ratio. Finite element modeling of the girth weld-induced residual stresses and deformations is first described. Nonlinear finite element analyses in which the behavior of the cylindrical steel members in pure compression and in pure bending is explored incorporating the girth weld-induced imperfections are next discussed. Results showed that the weld-induced residual stresses and distortions should be taken into account in assessment of the structural behavior of the girth-welded cylindrical steel members subjected to pure compression or pure bending since the weld-induced imperfections always induce local buckling near the girth weld, which alters the load–displacement behavior and diminishes the ultimate load-carrying capacity.

The use of structural steel cylindrical sections as compression or bending members has drawn considerable attention from engineers and architects in the construction industry due to their aesthetic appearance and structural efficiency. In the realistic applications, girth welding of the cylindrical members is frequently required owing to the long geometry relative to the diameter and the wall-thickness. When two cylindrical sections are welded together, residual stresses and deformations are produced in the vicinity of the weld region as a result of plastic deformation caused by non-uniform thermal expansion and contraction in the welding process. The presence of welding residual stresses can be detrimental to the integrity and the service behavior of the welded members [1]. Particularly, when combined with service loads, welding residual stresses cause premature yielding and loss of stiffness and may lead to deterioration of load-carrying capacity. Moreover, welding deformations, i.e. weld distortions induced by circumferential shrinkage of the weld region has been founded to have significant effects on the buckling behavior of welded cylindrical shells [2]. Accurate estimation of magnitude and distribution of the weld-induced imperfections, and understanding their influences on the compression or bending behavior of girth-welded cylindrical steel members are therefore very important for the efficient design and safety. The finite element method can be employed to simulate welding temperature field, welding residual stress field and welding deformation [3], [4], [5], [6], [7] and [8]. In the past, a significant amount of finite element models were proposed to predict welding residual stresses and deformations in girth-welded steel pipes [9], [10], [11], [12], [13], [14] and [15], but these models were generally limited to the axisymmetric model. As demonstrated in the work by Lee and Chang [16], the axisymmetric model cannot reproduce the three-dimensional features in the girth welding process. In the available three-dimensional finite element analysis, limited works have been conducted due to the high computational cost [16], [17], [18], [19], [20], [21], [22], [23] and [24]. Many researchers have investigated the behavior of welded cylinders subjected to compression or bending considering the effects of weld-induced imperfections by experimental, theoretical and numerical methods. However, their works have been confined to cylindrical shell structures which normally contain several longitudinal and/or circumferential welded joints or cold-formed sections for the compressive behavior [25], [26], [27], [28], [29] and [30] and have been limited to cold-formed sections for the flexural behavior [31], [32], [33] and [34], and thus they have not considered the girth welding process. As for the analysis of compression or bending behavior of girth-welded cylindrical steel members including the process in which the weld-induced residual stresses and distortions are produced, very little attempts have been made to date due to the truly complex analysis procedures involved in the welding and buckling. Actually, Lee et al. [35] assessed the buckling behavior of girth-welded circular steel tubes exposed to external couples by a FE method taking the weld-induced imperfections into consideration. However, quantitative evaluation of the effects that the girth weld-induced imperfections have on the bending behavior was not attempted. This paper presents finite element analyses which focus on the influence of the weld-induced imperfections on the structural behavior of a girth-welded cylindrical steel member with medium diameter-to-thickness ratio subjected to compression or bending. The base material used here is SUS304 austenitic stainless steel. Finite element modeling of the girth weld-induced residual stresses and deformations is first described. Nonlinear finite element analyses in which the behavior of the cylindrical steel member in pure compression and in pure bending is explored with and without considering the residual stresses and distortions in order to clarify the effects of the weld-induced imperfections are next discussed. Finally, the paper concludes from the discussion of the analysis results, and outlines future works.

In this paper, the influence of the weld-induced residual stresses and distortions on the structural behavior of a girth-welded cylindrical steel member with medium diameter-to-thickness ratio was investigated by finite element analysis method. Finite element simulation of the girth welding process was first performed to predict the weld-induced imperfections employing a sequentially coupled full three-dimensional finite element model. Nonlinear finite element analyses in which the behavior of the girth-welded cylindrical steel member under pure compression and under pure bending was explored taking the residual stresses and distortions into consideration in order to clarify the effects that the weld-induced imperfections have on the structural behavior were next carried out using the layered shell element. Based on the results in this work, the following conclusions can be made. (a) Girth-welded cylindrical steel members with medium diameter-to-thickness ratio in pure compression exhibit non-axisymmetric buckling behavior due to the weld-induced non-axisymmetric residual stresses and distortions and undergo local buckling near the girth weld in addition to the occurrence of local bucking near the ends, which alters the axial load versus end-shortening response and diminishes the ultimate load-carrying capacity to some extent. Nevertheless, the local buckling near the ends governs predominantly the compressive strength of the girth-welded cylindrical members. (b) The flexural behavior of the girth-welded cylindrical steel members involves local buckling near the girth weld on the compression side, which changes the nature of the moment versus end-rotation response curve and deteriorates the limiting buckling moment significantly. (c) The weld-induced residual stresses and distortions should be taken into account in accurate assessment of the structural behavior of the girth-welded cylindrical steel members subjected to pure compression or pure bending. The influence of the welding residual stress and distortion on the structural behavior of girth-welded cylindrical steel members with varying slenderness and aspect ratios will be considered in future work.