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Direct measurements and numerical predictions of welding-induced initial deformations in a full-scale steel stiffened plate structure

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Highlights

  • Measurement database of welding-induced initial deformations was developed for a full-scale steel stiffened plate structure which was fabricated using exactly the same welding technology as used in shipbuilding industries.

  • Computational models were developed to predict welding-induced initial deformations.

Abstract

As a sequel to another paper of the authors on welding-induced residual stresses [1], this paper aimed to obtain a direct measurement database of welding-induced initial deformations in a full-scale steel stiffened plate structure and also to study the applicability of computational models to predict them. A full-scale steel stiffened plate structure in association with bottom plate panels of an as-built 1,900 TEU containership was fabricated by exactly the same technology of welding as used in today's shipbuilding industry. The 3D scanner was employed to measure welding-induced initial deformations of the structure. Computational models using the three-dimensional thermo-elastic-plastic finite element method were developed to predict the plate initial deflections. A comparison between direct measurements and numerical predictions was made. Details of direct measurement databases are documented as they are useful to validate the computational models formulated by other researchers.

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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