This paper gives an overview of the factors that affect the strength and structural design of advanced thin-walled marine structures with reduced plate thickness or alternative topologies to those used today in the marine industry. Due to production-induced initial deformations and resulting geometrical non-linearity, the classical division between primary, secondary, and tertiary responses becomes strongly coupled. Volume-averaged, non-linear response of structural element can be used to define the structural stress–strain relation that enables analysis at the next, larger, length scale. This, today’s standard homogenization process, needs to be complemented with localization, where the stresses are assessed at the details, such as welds for fatigue analysis. Due to this, the production-induced initial distortions need to be considered with high accuracy. Another key question is the length-scale interaction in terms of continuum description. Non-classical continuum mechanics are needed when consecutive scales are close. Strain-gradients are used to increase the accuracy of the kinematical description of beams, plates, and shells. The paper presents examples of stiffened and sandwich panels covering limit states such as fatigue, non-linear buckling, and fracture.

The objective of the present work is to carry out the strength assessment of jacket offshore wind turbine support structures subjected to progressive rupture. A defect existing in a structure made during the fabrication may turn into a small-scale rupture and because of the high-stress concentration and low-cycle fatigue load. Therefore, the ultimate load-carrying capacity of the support structure is analyzed accounting for the progress of the rupture until the leg component experiences a full rupture along its circumference. The effect of imperfection severity is also investigated. The moment–curvature relationship of the structure concerning the studied cases is presented. Furthermore, the jacket support structures, at different water depths, are also analyzed and discussed. Finally, some of the leg components are removed one by one to study the redundancy of the jacket support structure at 80-m water depth.

The purpose of the present study is to investigate dynamic ultimate strength of global hull girder of container ships using large-scale nonlinear finite element analysis (FEA). A series of time domain nonlinear finite element (FE)-simulation is carried out using large-scale FE models of a 8000 twenty-foot equivalent unit (TEU) container ship where a hogging moment is applied to the midship section. Five types of finite element models (three full models, a half hold model, a one transverse model) are used. These models adopt elastoplastic material model, which includes strain rate effect. The hogging moment, which is modeled by sinusoidal impulse, is applied to these models, and collapse mechanism as well as dynamic hull girder ultimate strength is investigated by varying the load time duration. Moreover, effects of load time duration, mass inertia, strain rate, and analysis models are investigated in detail. It is found from the present study that ultimate strength as well as collapse mode is significantly dependent on load time duration of hogging moment.

The objective of this study is to investigate the variation of neutral axis of ship hull girder due to asymmetric geometry or asymmetric load, and its influence on the ultimate strength (ULS) of hull girder. In order to account for asymmetric geometries and loads of hull girders, the force equilibrium and force-vector equilibrium criteria together with a minimum convergence factors (error) method are employed to determine the translation and rotation of neutral axis plane (NAP) of symmetric or asymmetric hull cross section in the application of Smith's method at each step of curvature of the hull girder. The ULSs of Dow's 1/3 frigate model with three predefined structural integrity states, one intact and two damaged, respectively, is investigated by the improved Smith's method (ISM) for a range of variation of heeling angles. The influence of asymmetric geometry and load on the motion of NAP and on the ULS are analyzed and discussed. The results show that the improved iteration strategy together with the minimum convergence factors (error) method is efficient and more accurate in searching the translation and rotation of NAP. Finally, the envelope curves of the bending moments in the three predefined integrity states are obtained, which can be used for assessing ULS of hull girders under combined vertical and horizontal wave bending moments.

This paper presents a study of traditional netting materials subjected to disinfecting chemicals during fish farming and treatment of net cages. A series of tests were performed in order to study the effect of various concentrations of disinfecting chemicals on the tensile strength of Raschel knitted Nylon netting materials. Simulated spill of diluted hydrogen peroxide (HP) to the jump fence during de-lousing did not affect the strength of the applied new and used knotless nylon netting samples. Hydrogen peroxide reacted with biofouling forming gas bubbles, but this did not result in reduced netting strength. The performed tests did not indicate any effect on netting strength from a simulated single, traditional bath disinfection as performed at service stations applying the disinfectant Aqua Des (AD) containing peracetic acid (PAA). However, increasing the AD concentration from 1 to 10% resulted in a strength reduction of 3–6%. Simulated spill of concentrated AD on the jump fence of a net with copper coating residuals resulted in a severe reduction in strength of 45%. This strength loss was probably a consequence of chemical reaction between copper and Aqua Des, and uncoated netting did not experience any loss in strength subjected to the same chemical exposure. These findings from application of AD should also apply to other PAA disinfection chemicals with trade names as, for example, Perfectoxid and Addi Aqua.

The ultimate strength of metallic pipelines will be inevitably affected when they have suffered from structural damage after mechanical interference. The present experiments aim to investigate the residual ultimate bending strength of metallic pipes with structural damage based on large-scale pipe tests. Artificial damage, such as a dent, metal loss, a crack, and combinations thereof, is introduced to the pipe surface in advance. Four-point bending tests are performed to investigate the structural behavior of metallic pipes in terms of bending moment–curvature diagrams, failure modes, bending capacity, and critical bending curvatures. Test results show that the occurrence of structural damage on the pipe compression side reduces the bending capacity significantly. Only a slight effect has been observed for pipes with damage on the tensile side as long as no fracture failure appears. The possible causes that have introduced experimental errors are presented and discussed. The test data obtained in this paper can be used to further quantify damage effects on bending capacity of seamless pipes with similar D/t ratios. The comparison results in this paper can facilitate the structural integrity design as well as the maintenance of damaged pipes when mechanical interference happens during the service life of pipelines.

The girth weld tensile properties of API X80 grade high-frequency electric resistance welded (HFW) steel pipe for surface casing with the chemical composition of 0.05C–1.6Mn–0.06Nb (mass %) and the diameter of 558.8 mm and wall thickness of 25.4 mm were investigated by simulated postweld heat-treatment (PWHT). The tensile specimens taken from girth butt welded pipe were heat-treated under the conditions of 625 °C × 2 h and 675 °C × 2 h in an air furnace in order to simulate PWHT of casing products. The result of the girth weld tensile test of the heat-treated specimens showed that yield strength and tensile strength decreased very little and these properties sufficiently satisfied the API X80 specification. The change in strength due to heat treatment was discussed based on microscopic observation of the submicrostructures of the base metal by the electron back-scattered diffraction (EBSD) technique, transmission electron microscopy, X-ray diffraction (XRD), and the extraction residue precipitate classification method. The authors concluded that the fine NbC with a diameter of 12–18 nm, which precipitated during the heat treatment, prevented the decrease of strength due to the slight grain growth and dislocation recovery associated with PWHT. Additionally, the effect of PWHT conditions was evaluated by using small-scale laboratory specimens obtained from the base metal. Tensile properties were summarized as a function of the tempering parameter. As a result, strength remained almost constant at the tempering parameter equivalent to the PWHT conditions of 625 °C × 16 h.

The aim of this study was to analyze the ultimate strength of stiffened aluminum panels by the nonlinear finite element method. A new type of stiffened aluminum alloy panel has been designed, which has fixed longitudinal and alternating floating transverse frames. Based on material tensile tests, the material properties of the aluminum alloy were obtained. Then, the simulation method of welding residual stresses and the effect of heat-affected zone (HAZ) are investigated. The finite element analysis (FEA) software abaqus V6.11 is used to estimate the ultimate strength of these stiffened panels under axial compression. The results show that: (1) the mechanical imperfections have significant effect on the ultimate strength of stiffened panels; (2) residual stresses may have positive effect on the ultimate strength; and (3) the new stiffened panels also have good performance on ultimate bearing capacities.

This paper presents test results on temporary-creep properties, recovery of strain postcreep and postcreep tensile properties of a Raschel knitted netting material with a combination of ultrahigh molecular weight polyethylene (UHMWPE) and polyester fibers. Specimens of the material were subjected to uniaxial loading over a period of 30 mins, at a constant creep target load of 10–90% of average tensile strength. The specimens were wet and tested in room temperature. The netting structure experienced creep strain with mean values in the range of 1.3–4.5%, increasing with increased creep target load. In addition, the netting experienced 2% creep strain during on-loading. The creep strains were elastic, while large proportions of the elongation accumulated during on-loading (structural strain of 8.8–27.8%) were long lasting and possibly permanent. Tensile tests showed that for the highest creep target load, strength, and elongation at break increased by 17%.

Most common studies on the strength of plates under compressive longitudinal loading are related to plates having unrestrained edges which lead to a zero net load in the transverse direction. In ships, the framing system and the continuity of the plating in the transverse direction tend to induce rather different boundary conditions on the “unloaded” edges, which results in a completely different state of stresses when the external loads are applied. This is due to the surge of a significant level of induced membrane stresses in the direction perpendicular to loading. In this work, the behavior of long restrained plates under compressive axial loading is analyzed and compared with the one of plates having other boundary conditions. The finite element method is applied for the nonlinear analysis of the plates using a commercial package. Fifty-six cases are considered corresponding to different levels of plate slenderness which ranges between 0.35 and 3.46 covering the practical range of structural plates used in the shipbuilding industry. Various shapes of initial imperfections are considered in order to establish the minimum level of resistance. Also, the influence of the magnitude of the distortions associated to each mode is discussed. The study conducted to the establishment of the minimum compressive strength of restrained plates and it defines the expected range of strength's variation due to the magnitude level of distortions. The biaxial state of stresses resulting from these boundary conditions is characterized and its dependence from the plate's slenderness is quantified for the most common type of the hull plating.

Extreme waves have led to many accidents and losses of ships at sea. In this paper, a two-dimensional (2D) hydroelastoplasticity method is proposed as a means of studying the nonlinear dynamic response of a container ship when traversing extreme waves, while considering the ultimate strength of the ship. On one hand, traditional ultimate strength evaluations are undertaken by making a quasi-static assumption and the dynamic wave effect is not considered. On the other hand, the dynamic response of a ship as induced by a wave is studied on the basis of the hydroelasticity theory so that the nonlinear structural response of the ship cannot be obtained for large waves. Therefore, a 2D hydroelastoplasticity method, which takes the coupling between time-domain waves and the nonlinear ship beam into account, is proposed. This method is based on an hydroelasticity method and a simplified progressive collapse method that combines the wave load and the structural nonlinearity. A simplified progressive collapse method, which considers the plastic nonlinearity and buckling effect of stiffened, is used to calculate the ultimate strength and nonlinear relationship between the bending moment and curvature, so that the nonlinear relationship between the rigidity and curvature is also obtained. A dynamic reduction in rigidity related to deformation could influence the strength and curvature of a ship's beam; therefore, it is input into a dynamic hydrodynamic formula rather than being regarded as a constant structural rigidity in a hydroelastic equation. A number of numerical extreme wave models are selected for computing the hydroelastoplasticity, such that large deformations occur and nonlinear dynamic vertical bending moment (VBM) is generated when the ship traverses these extreme waves. As the height and Froude number of these extreme waves are increased, a number of hydroelastoplasticity results including VBM and deformational curvature are computed and compared with results obtained with the hydroelasticity method, and then, some differences are observed and conclusions are drawn.

The aim of this paper is to determine an appropriate configuration of the boundary conditions and geometric model to calculate the ultimate strength of a continuous stiffened panel under compressive loading in the finite element (FE) analysis. The 1 + 1 spans model with periodical symmetric boundary conditions is proposed to be used in the FE analysis, whose results are compared with the 1/2 + 1 + 1/2 span model with periodical symmetric and symmetric boundary condition, and the 1/2 + 1 + 1 + 1/2 span model with symmetric boundary conditions. The effects of the continuity of the stiffened panel with different geometric models and boundary conditions on its collapse mode are investigated. A beam tension test has been used to define the true stress-strain relationship in the FE analysis. The two-span model, either 1 + 1 or 1/2 + 1 + 1/2, with periodical symmetric conditions give a reasonable FE modeling, which can consider both odd and even number half waves and, thus, have the smallest model uncertainty.

The main target of this research is to identify the effects of camber parabolic curvature on the ultimate strength and behavior of stiffened plates under in-plane compression. A parametric model for the study of the problem is created. The model includes different parameters related to plate, stiffeners, and also parabolic camber curvature. Three distinct sensitivity cases are assumed. In each sensitivity case, many different models are analyzed and their ultimate strengths are obtained using an in-house finite element program. Ultimate strength and behavior of the models with different ratios of parabolic curvature are compared to each other and interpreted.

The primary objective of the present paper is to examine the effects of welding residual stresses on ultimate strength of high tensile steel plates under axial compression in terms of their magnitude and pattern. The ANSYS nonlinear finite element method is employed for the purpose. The secondary objective of the present paper is to study a nonlinear finite element method modeling technique for welded plate structures with residual stresses. Three levels of residual stresses, namely slight, average, and severe, are considered. As another important parameter of influence on the plate ultimate strength, the plate thickness is also varied in the numerical computations to examine their role and trend. Important insights and conclusions developed from the present study are documented.

The primary objective of the present paper is to experimentally examine the buckling collapse characteristics of fusion welded aluminum-stiffened plate structures under axial compression until and after the ultimate limit state is reached. The secondary objective of the paper is to study a nonlinear finite element method modeling technique for computing the ultimate strength behavior of welded aluminum structures. A set of aluminum-stiffened plate structures fabricated via gas metal arc welding is studied. The test structure is equivalent to a full scale deck structure of an 80 m long high speed vessel. The plate part of the structures is made of 5383-H116 aluminum alloy, and extruded stiffeners are made of 5083-H112 aluminum alloy. Welding induced initial imperfections such as plate initial deflection, column type global initial deflection of stiffeners, sideways initial distortion of stiffeners, welding residual stresses, and softenng in the heat-affected zone are measured. The ANSYS nonlinear finite element method is employed for the numerical computations of the test structure’s ultimate strength behavior by means of a comparison with experimental data. Insights and conclusions developed from the present study are documented.

Floating production, storage, and offloading systems (FPSOs) have been widely used for the development of offshore oil and gas fields because of their many attractive features. They are mostly ship-shaped and either converted from existing tankers or purpose-built. However, FPSOs have their own unique characteristics, including various operational requirements. In addition to that, the expectation of safety and economic aspects of FPSOs require an optimized structure to be designed. This calls for reliable structural assessment methodologies. One of the most important aspects of FPSO structural design and assessment is the hull girder ultimate strength. In this paper, different methodologies of hull girder ultimate strength assessment will be introduced and numerical calculations of hull girder ultimate strength will be presented based on six different FPSO designs. The results will then be analyzed in terms of their differences, and conclusions will be made based upon reliable methodologies for hull girder ultimate strength assessment of FPSOs.

The ultimate strength of a ship’s hull depends on its material and geometric properties, some or all of which may be random in nature. In addition, initial imperfections in the form of initial deflection and residual welding stresses in plating between stiffeners can significantly affect the hull ultimate strength. In this paper, the effect of randomness in yield strength and in the initial imperfections on ultimate hull girder strength is determined. Different levels of statistical dependence between yield strength and initial imperfection of stiffeners and plating between stiffeners have been considered. The methodology is applied on a bulk carrier and a VLCC tanker.

This paper presents the failure pattern, the ultimate strength, and the stress concentration factor of unstiffened T-joints obtained from experimental and numerical investigations conducted on them under axial brace compression loading. The numerical modeling was performed on the whole joint using ANSYS software package. This modeling has predicted the ultimate strength accurately when compared with that of the conventional modeling of only a portion of the joint. The nominal diameter and thickness of the chord of the unstiffened T-joints were 324 mm and 12 mm, respectively, and the corresponding values of the brace were 219 mm and 8 mm, respectively. The T-joint was approximately one-fourth the size of the largest joints in the platforms built in a shallow water depth of 80 m in the Bombay High field. The bending of the whole chord member combined with punching shear failure due to its ovalization was observed to be the predominant behavior of the unstiffened joint. The numerical analysis has simulated the behavior of the joint as was observed in the experiment and has also helped establish its correct failure pattern. It was also observed in these investigations that the unstiffened joint was stiffer in ovalization mode than in flexural deflection. The results obtained from the numerical modeling were observed, in general, to be in good agreement with that obtained from the testing. The stress concentration factor predicted by the numerical analysis is in close agreement with that measured in the experiment as well as that computed using well established parametric equations.

The hull girder ultimate strength of a typical bulk carrier is analyzed using a simplified method based on an incremental—iterative approach. First, vertical bending moment is examined by seven different methods. The moment versus curvature curves and the values of the ultimate longitudinal moments at collapse states are determined for both hogging and sagging cases. Second, the ultimate strength under coupled vertical and horizontal bending moment is accounted. An interaction curve is obtained, which corresponds to the results of series of calculation for the ship hull subject to bending conditions with different angles of curvature. It is found that the interaction curve is asymmetrical because the hull cross section is not symmetrical with respect to the horizontal axis and the structural response of the elements under compression is different from that under tension due to nonlinearity caused by buckling. The angles of the resultant bending moment vector and that of the curvature vector are different in investigated cases. The interaction design equations proposed by other researches are also addressed to discuss the results presented by this study.