Full length articleDirect measurements and numerical predictions of welding-induced initial deformations in a full-scale steel stiffened plate structure
Introduction
Welding-induced initial deformations are unavoidable in fabrication of steel structures, as shown in Fig. 1, and they significantly affect the buckling and ultimate strength which are primary criteria for structural analysis and design [2,3]. Structural analysis and design need to start with an adequate definition of such initial imperfections. As would be expected, the welding-induced initial deformations in thin-walled structures are greater than in thick-walled structures. Thin-walled structures are likely to subject to thermal plate buckling in the process of fabrication, as shown in Fig. 1, Fig. 2, Fig. 3, resulting in costly fairing works to remove distortions.
A number of studies on this topic are available in the literature, and their survey is found in Ueda [4] and Paik [2], among others. The previous studies include both direct measurements and numerical predictions. A few measurement studies were performed with full-scale structure models [5]. Most of previous studies used small-scale models which were far different from the actual welding in practice, which would significantly affect the resulting measured initial deformations in magnitude and pattern. Therefore, the development of direct measurement databases of welding-induced initial deformations in full-scale steel stiffened plate structures is highly demanded. A number of studies in numerical predictions of welding-induced initial deflections are also available in the literature [[6], [7], [8], [9], [10], [11], [12], [13]].
The objective of the paper is to contribute to the development of direct measurement databases of welding-induced initial deformations in full-scale steel stiffened plate structures, and also to study the applicability of numerical predictions using the three-dimensional thermo-elastic-plastic finite element method models formulated by the authors [12,13]. This paper is a sequel to another article of the same authors on welding-induced residual stresses of a full-scale steel stiffened plate structure which is an identical structure used in the present paper [1].
Section snippets
Design of a full-scale steel stiffened plate structure
In this paper, plate panels in bottom structures of an as-built containership carrying 1,900 TEU were chosen as the reference vessel, as shown in Fig. 3. Note that containerships in full load condition are in hogging and thus bottom plate panels are subjected to axial compressive loads [3,14,15].
Details of the scantlings for the test structure made of high tensile steel with grade AH32 are provided in Paik et al. [16], and a summary of the structural design is presented here. Fig. 4 shows the
Fabrication of the structure
The structure is made of high tensile steel with grade AH32. After the material procurement, tensile coupon test specimens were extracted from the steel sheet as per ASTM E8 [17], as shown in Fig. 6(a). The universal test machine together with an extensometer was used for the tension tests as shown in Fig. 6(b). The failure pattern of the tensile coupon specimens was similar, as shown in Fig. 6(c). Fig. 7 shows one of typical engineering stress-engineering strain curves of the material obtained
Measuring methods of initial deformations
Three kinds of welding-induced initial deformations are relevant in stiffened plate panels, namely plate initial deflection, stiffener's deflection and sideways deformation. Appendix presents all of the three types of measured databases, but this section focuses on the measurements of plate initial deflection.
A 3D scanner as a non-contact method is employed to measure the welding-induced initial deformations. Table 4 provides the specifications of the 3D scanner used for the measurements.
Computational models using the thermo-elastic-plastic finite element method
The shape of welding-induced initial deformations in plate panels is very complex [4]. Thinner plate panels may show more complex patterns of initial deformations. The shape of welding-induced initial deformations in plate panels is often modeled as a combination of multiple sinusoidal waves [2,4,5], but an accurate prediction is sometimes required unless direct measurements are realistic.
In this paper, computational models are developed to predict welding-induced initial deformations of plate
Results and discussions
Fig. 15 presents the results of computational predictions for welding-induced initial deflections in the structure. Fig. 15 compares the direct measurements and numerical computations of plate initial deflections at cross sections A-A’ and B-B’ of the test structure.
It is seen from Fig. 15, Fig. 16 that plate initial deflections happened to one side, i.e., support member side of the structure. Not only plating but also transverse frames deflected by welding. During fabrication, four edges of
Concluding remarks
The aim of the paper was to obtain direct measurement databases of welding-induced initial deflections in a full-scale steel plate structure, and also to compare them with computational predictions. Based on the study, the following conclusions can be drawn.
- (1)
A full-scale steel stiffened plate structure was designed and fabricated in a shipyard using exactly the same technology of welding as used in today's shipbuilding industry.
- (2)
3D scanner was used for measuring welding-induced initial
Declaration of competing interest
This article is not in conflict of interests at all.
Acknowledgements
This work was conducted at the International Centre for Advanced Safety Studies/Korea Ship and Offshore Research Institute (www.icass.center) which has been a Lloyd's Register Foundation Research Centre of Excellence since 2008.
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