Steel Stiffened Plate Structures Research Articles

Analysis of fire-induced progressive collapse for topside structures of a VLCC-class ship-shaped offshore installation

ABSTRACT This study extends the authors’ previous numerical and experimental studies simulating the progressive collapse of steel stiffened-plate structures in fire events (Paik JK, Ryu MG, He KH, Lee DH, Lee SY, Park DK, Thomas G. 2021a. Full-scale fire testing to collapse of steel stiffened plate structures under lateral patch loading (part 1) – without passive fire protection. Ships Offsh Struct. 16(3):227–242; Paik JK, Ryu MG, He KH, Lee DH, Lee SY, Park DK, Thomas G. 2021b. Full-scale fire testing to collapse of steel stiffened plate structures under lateral patch loading (part 2) – with passive fire protection. Ships Offsh Struct. 16(3):243–254; Ryu MG, He KH, Lee DH, Park SI, Thomas G, Paik JK. 2021. Finite element modeling for the progressive collapse analysis of steel stiffened-plate structures in fires. Thin-Walled Struct. 159:107262). Specifically, this study demonstrates that the computational models developed in the earlier studies can be applied to the analysis of the heat transfer and fire-induced progressive collapse behaviour of the topside structures of a ship-shaped offshore installation. To this end, a hypothetical VLCC-class floating, production, storage and offloading (FPSO) unit hull structure is considered, and transient thermal elastic-plastic large-deformation finite element models are used. The novelty of this study and its contribution to industry are the development of a practical procedure to ensure the fire safety of large-scale steel-plated structures with complex geometries.

FULL-SCALE MEASUREMENTS OF WELDING-INDUCED INITIAL DEFLECTIONS AND RESIDUAL STRESSES IN STEEL-STIFFENED PLATE STRUCTURES

Plated structures such as ships and offshore structures are constructed using welding techniques that attach support members (or stiffeners) to the plating. During this process, initial imperfections develop in the form of initial deformations (deflections or distortions) and residual stresses. These initial imperfections significantly affect the buckling and ultimate strength of these structures. Therefore, to assess the strength of welded plate structures, it is very important to predict the magnitude and pattern of welding-induced initial imperfections and their effects on buckling and ultimate strength. To determine the reliability of the prediction methods, it is desirable to validate the theoretical or numerical predictions of welding-induced initial imperfections through comparison with full-scale actual measurements. However, full-scale measurement databases are lacking, as they are costly to obtain. This study contributes to the development of a full-scale measurement database of welding-induced initial imperfections in steel-stiffened plate structures. The target structures are parts of real (full-scale) deckhouses in very large crude oil carrier class floating, production, storage and offloading unit structures. For parametric study purposes, four test structures by varying plate thickness are measured while the stiffener types and weld bead length are fixed. Modern technologies for measuring initial deformations and residual stresses are applied. The details of the measurement methods are documented for the use of other researchers and practicing engineers who welding-induced initial imperfections.

Ultimate Compressive Strength Computational Modeling for Stiffened Plate Panels with Nonuniform Thickness

The aim of this paper is to develop computational models for the ultimate compressive strength analysis of stiffened plate panels with nonuniform thickness. Modeling welding-induced initial deformations and residual stresses was presented with the measured data. Three methods, i.e., ANSYS finite element method, ALPS/SPINE incremental Galerkin method, and ALPS/ULSAP analytical method, were employed together with existing test database obtained from a full-scale collapse testing of steel-stiffened plate structures. Sensitivity study was conducted with varying the difference in plate thickness to define a representative (equivalent) thickness for plate panels with nonuniform thickness. Guidelines are provided for structural modeling to compute the ultimate compressive strength of plate panels with variable thickness.

Finite element modeling for the progressive collapse analysis of steel stiffened-plate structures in fires

This paper is a sequel to the authors’ articles which provided the test data on the progressive collapse of full-scale steel stiffened-plate structures without and with passive fire protection (PFP) under lateral patch loading in fires [1,2]. This paper presents new computational models for the analyses of heat transfer and fire-induced progressive collapse behaviour of steel stiffened plate structures without or with PFP. For this purpose, transient thermal elastic-plastic large-deformation finite element models were formulated. The developed computational models were validated by a comparison with the test data. The novelty of the paper is associated with a new procedure for the fire-induced progressive collapse analysis of steel stiffened-plate structures which is critical for a contribution to fire safety engineering of steel plated structures.

Full-scale collapse testing of a steel stiffened plate structure under axial-compressive loading at a temperature of −80°C

ABSTRACT The aim of the paper was to develop a test database of the ultimate strength characteristics of full-scale steel stiffened plate structures under axial compressive loading at a temperature of −80°C. This paper is a sequel to the authors’ articles (Paik et al. 2020a, https://doi.org/10.1016/j.istruc.2020.05.026 and Paik et al. 2020b, https://doi.org/10.1080/17445302.2020.1787930). In contrast to the earlier articles associated with room temperature or cryogenic condition, this paper investigated the effect of a low temperature at −80°C which is within the boundary range of temperature of the ductile-to-brittle fracture transition for carbon steels. A material model representing the test conditions was also proposed to capture the characteristics of carbon steels at low temperatures both in tension and in compression, and it was used in finite element method simulations of the full-scale experiment. A comparison between numerical analyses and experiments showed that the proposed model could successfully predict the failure modes and ultimate strength characteristics at low temperatures for stiffened plate structures under axial compressive loading conditions.

Full-scale collapse testing of a steel stiffened plate structure under axial-compressive loading triggered by brittle fracture at cryogenic condition

ABSTRACT This paper is a sequel to the authors’ earlier article Paik et al. [2020a. Full-scale collapse testing of a steel stiffened plate structure under cyclic axial-compressive loading, Structures, https://doi.org/10.1016/j.istruc.2020.05.026]. The aim of the paper was to present a test data on the ultimate compressive strength characteristics of a full-scale steel stiffened plate structure at cryogenic condition which may be due to unwanted release of liquefied gases. The test structure was fabricated in a shipyard using exactly the same welding technology as used in today’s shipbuilding industry. It is observed that the test structure reaches the ultimate limit states triggered by brittle fracture, which is totally different from typical collapse modes at room temperature. Details of the test database are documented as they can be used to validate computational models for the structural crashworthiness analysis involving brittle fracture at cryogenic condition.

Direct measurements, numerical predictions and simple formula estimations of welding-induced biaxial residual stresses in a full-scale steel stiffened plate structure

As a sequel to another paper of the authors on welding-induced initial deformations [1], this paper aimed to obtain a direct measurement database of welding-induced biaxial residual stresses 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 plate panels in bottom structures of an as-built containership carrying 1900 TEU was fabricated using exactly the same welding technology as used in today’s shipbuilding industry. The X-ray diffraction method was employed to measure the biaxial residual stress distributions in the plating. In addition to simple formula estimations, computational models using the three-dimensional thermo-elastic-plastic finite element method were applied to predict the biaxial residual stress distributions. A comparison between full-scale measurements, numerical predictions and simple formula estimations was made. Details of the full-scale measurements are documented as they can be useful to validate the computational models formulated by other researchers.

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

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.

Full-scale collapse testing of a steel stiffened plate structure under cyclic axial-compressive loading

Plate panels of ships and floating offshore structures are likely subjected to cyclic loads arising from waves at sea. Depending on sea states, e.g., whipping in harsh sea states, the maximum amplitude of the cyclic loads may reach over 70% of ultimate loads. Of concerns is how the cyclic loads will affect the ultimate strength compared to a case of monotonically increasing loads. The aim of this paper is to experimentally investigate the ultimate strength characteristics of a steel stiffened plate structure under cyclic axial-compressive loading. A full-scale collapse testing in association with bottom structures of an as-built 1,900 TEU containership was conducted. It is concluded that the effects of cyclic loading on the ultimate compressive strength of steel stiffened plate structures are small as far as fatigue damages are not suffered due to the small number of load cycles and/or local structural members do not reach the ultimate strength during cyclic axial-compressive loading. Details of the test database are documented, which will be useful to validate computational models for the ultimate strength analysis.

Full-scale fire testing to collapse of steel stiffened plate structures under lateral patch loading (part 1) – without passive fire protection

ABSTRACT The aim of this paper is to present a fire test database on the collapse of a full-scale steel stiffened plate structure without passive fire protection under lateral patch loading. Steel plate panels of an as-built 1900 TEU containership in compliance with test facility in a maximum size and capacity were considered as a reference structure, with principal dimensions of 7 m long and 4.8 m wide fitted with two transverse frames and seven longitudinal stiffeners. Lateral patch loading was applied using two loading actuators at the centre of each transverse frame. A fire test was conducted in a furnace fuelled by liquefied petroleum gas, where the maximum gas cloud temperature inside the furnace was increased up to 800°C during testing. Time history of the lateral deformations of the test structure was measured with the focus on a critical period of time until the structure reached the ultimate limit state (or collapse) after the fires started. Details of the test database are documented, which will be useful for validating computational models for structural failure analysis in fires.

Full-scale fire testing to collapse of steel stiffened plate structures under lateral patch loading (part 2) – with passive fire protection

ABSTRACT This paper is a sequel to the authors’ article on a full-scale fire testing to collapse of a steel stiffened plate structure without passive fire protection (PFP) under lateral patch loading (Paik JK, Ryu MG, He KH, Lee DH, Lee SY, Park DK, Thomase G. 2020. Full-scale fire testing to collapse of steel stiffened plate structures under lateral patch loading (Part 1) – without passive fire protection. Ships Offshore Struc. doi:10.1080/17445302.2020.1764705). The test structure represents steel plate panels of a 1900 TEU containership in compliance with test facility in a maximum size and capacity. The aim of this paper is to experimentally examine the effects of PFP application on the fire collapse of steel stiffened plate structures. For this purpose, two transverse frames (primary strength members) of the test structure were insulated by cerawool which is a fire protection material. A fire test was conducted in a furnace burnt by liquefied petroleum gases. Structural collapse was monitored at discrete time intervals from when the fire started until the test structure entirely collapsed. The effect of fire-protected transverse frames on the structural collapse was investigated by comparison with test results on the structure that was unprotected from the fires.

Full-Scale Measurements of Welding-Induced Initial Deflections and Residual Stresses in Steel-Stiffened Plate Structures

Plated structures such as ships and offshore structures are constructed using welding techniques that attach support members (or stiffeners) to the plating. During this process, initial imperfections develop in the form of initial deformations (deflections or distortions) and residual stresses. These initial imperfections significantly affect the buckling and ultimate strength of these structures. Therefore, to assess the strength of welded plate structures, it is very important to predict the magnitude and pattern of welding-induced initial imperfections and their effects on buckling and ultimate strength. To determine the reliability of the prediction methods, it is desirable to validate the theoretical or numerical predictions of welding-induced initial imperfections through comparison with full-scale actual measurements. However, full-scale measurement databases are lacking, as they are costly to obtain. This study contributes to the development of a full-scale measurement database of welding-induced initial imperfections in steel-stiffened plate structures. The target structures are parts of real (full-scale) deckhouses in very large crude oil carrier class floating, production, storage and offloading unit structures. For parametric study purposes, four test structures by varying plate thickness are measured while the stiffener types and weld bead length are fixed. Modern technologies for measuring initial deformations and residual stresses are applied. The details of the measurement methods are documented for the use of other researchers and practicing engineers who want to validate their computational models for predicting welding-induced initial imperfections.

An empirical formulation for predicting welding-induced biaxial compressive residual stresses on steel stiffened plate structures and its application to thermal plate buckling prevention

ABSTRACTThe aim of this paper is to derive an empirical formulation for predicting welding-induced biaxial compressive residual stresses in welded steel plate panels. A test database for full-scale models of welded steel plate structures is developed. Elastic-plastic finite element method solutions, associated with thermal stresses in welded steel plate panels, are also developed. The proposed formula is derived by a curve fitting of the databases obtained from both full-scale measurements and numerical computations as a function of plate thickness and weld leg length. The paper demonstrates an applied example of the derived formulations to prevent the thermal buckling of thin steel plate panels that occurs during the welding process.

Three-Dimensional Thermo-Elastic-Plastic Finite Element Method Modeling for Predicting Weld-Induced Residual Stresses and Distortions in Steel Stiffened-Plate Structures

The objective of the present paper is to develop nonlinear finite element method models for predicting the weld-induced initial deflection and residual stress of plating in steel stiffened-plate structures. For this purpose, three-dimensional thermo-elastic-plastic finite element method computations are performed with varying plate thickness and weld bead length (leg length) in welded plate panels, the latter being associated with weld heat input. The finite element models are verified by a comparison with experimental database which was obtained by the authors in separate studies with full scale measurements. It is concluded that the nonlinear finite element method models developed in the present paper are very accurate in terms of predicting the weld-induced initial imperfections of steel stiffened plate structures. Details of the numerical computations together with test database are documented.

Ultimate strength assessment of steel stiffened plate structures with grooving corrosion damage

An approach to simulate the behaviour of steel stiffened plates subjected to weld-induced grooving corrosion using nonlinear finite element modelling is proposed. The model includes the effects of different initial geometric imperfections and weld-induced residual stresses. The influence of corrosion damage on the load shortening curves and ultimate strength is investigated. It is shown that grooving corrosion depth has a greater influence on structural performance as compared with corrosion width for the same volume loss. Such corrosion damage could cause a significant reduction in the ultimate strength of a plate panel. Considerations of weld-induced deflection and residual stresses further enhance the corrosion influence on the strength capacity.

Nonlinear finite element method models for ultimate strength analysis of steel stiffened-plate structures under combined biaxial compression and lateral pressure actions—Part I: Plate elements

For design and strength assessment of various types of structures such as ships, offshore platforms, land-based structures, and aerospace structures, it has been realized that ultimate limit states (or ultimate strength) are much better basis than the allowable working stresses. Within the framework of ultimate limit state design and strength assessment, the primary task is to determine the level of imposed actions which causes the ultimate limit states. The aim of the present study is to develop some useful insights on nonlinear finite element method application for ultimate limit state assessment of steel stiffened-plate structures subject to combined biaxial compression and lateral pressure actions. As an illustrative example, outer bottom stiffened-plate structures of 100,000 ton class double-hull oil tankers are considered. The present study consists of two parts; Part I deals with plate elements surrounded by stiffeners or support members, and Part II treats stiffened panels, where some important factors of influence such as structural dimensions, initial imperfections, loading types and computational techniques in association with ultimate limit states are studied. For ultimate limit state computations, ANSYS nonlinear finite element method together with ALPS/ULSAP semi-analytical method is employed. Important insights developed from the present study are documented.

Nonlinear finite element method models for ultimate strength analysis of steel stiffened-plate structures under combined biaxial compression and lateral pressure actions—Part II: Stiffened panels

The present paper (Part II) is a sequel to the previous paper (Part I) [Paik JK, Seo JK. Nonlinear finite element method models for ultimate strength analysis of steel stiffened-plate structures under combined biaxial compression and lateral pressure actions—Part I: Plate elements. Thin-Walled Struct 2008, this issue, doi:10.1016/j.tws.2008.08.005.] on the application of nonlinear finite element methods for ultimate strength analysis of steel stiffened-plate structures under combined biaxial compression and lateral pressure actions. In contrast to Part I dealing with plate elements, the present paper (Part II) treats stiffened panels surrounded by strong support members such as longitudinal girders and transverse frames. In similar to Part I, some important factors of influence such as structural dimensions, initial imperfections, loading types and computational techniques in association with ultimate limit states are studied. Some useful insights in terms of nonlinear finite element method modeling are developed using ANSYS code together with the ALPS/ULSAP semi-analytical method, the latter being for the purpose of a comparison.