Strength Of Stiffened Panels Research Articles

Empirical formulae assessment of ultimate strength for perforated stiffened panels under longitudinal compression

The present paper studies the influence of cut-outs of local plates on the ultimate strength of stiffened panels based on the tests and numerical simulations. Four intact and perforated stiffened panels subjected to uniaxial compression loads were tested firstly. The initial imperfections of the specimens have been measured before testing, which were used in the FE (finite element) analysis. The tensile tests are used to determine the properties of material. The experimental results are used to verify the modelling technology of FE models. Based on the numerical simulations, the parametric studies with various configurations including the initial twisting distortion, boundary condition and the dimensions of opening are performed to investigate their influences on the collapse behaviours of the stiffened panels. It is found that the residual ultimate strength of perforated stiffened panel mainly depends on the transverse length of opening. Using numerical database, the empirical formulae of ultimate strength of perforated stiffened are developed.

Experimental and numerical analysis of ultimate compressive strength of long-span stiffened panels

Long-span stiffened panels, designed using girders with high webs and multi-web openings, are often used in the top of large spaces without inner columns, such as the theatre and the lounge in large passenger ships. This design, accompanied by in-tension pillars above the long-span stiffened panel, can decrease the deck deflection largely. In this paper, experimental and finite element analysis is performed of the ultimate compressive strength of two long-span stiffened panels subjected to combined uniaxial and lateral loads. The comparison of experimental results shows that the in-tension pillars only increase slightly the ultimate compressive strength of stiffened panel. The experimental results show agreement with the simulations performed by the ANSYS finite element solver. The validated numerical results illustrate the buckling and ultimate behaviour of long-span stiffened panels with their progressive collapse processes. The analysed ultimate loads are compared to the results calculated by seven existing empirical formulae. The finite element analysis also discusses the effect of girder openings on the ultimate compressive strength of the stiffened panel.

A study on the residual ultimate strength of continuous stiffened panels with a crack under the combined lateral pressure and in-panel compression

In this study, the effects of the crack on the residual ultimate strength of a continuous stiffened panel with a crack under the combined lateral pressure and in-panel compression are investigated numerically. Based on the fact that the extent of model should be sufficient to analyze the surrounding structure, a two-span (1/2 + 1+1/2) model is modeled. Periodic and symmetric boundary conditions are used to calculate the ultimate strength of stiffened panels with a crack, a Plug-in that can be executed in ABAQUS has been developed using Python language. The accuracy of the advanced model is verified, and the influences of various parameters on the ultimate strength reduction rate of a continuous stiffened panel with a crack are comprehensively investigated. The results of the investigation showed that crack location was very important in the evaluation of the residual ultimate strength of a stiffened panel with a crack, and in particular, the cracks under the stiffener have a great influence on the ultimate strength reduction rate of the stiffened panel. Finally, a prediction equation capable of predicting the ultimate strength reduction rate of continuous stiffened panels with a crack is proposed and verified for its accuracy.

Structural resistance of lightweight stiffened panels submitted to buckling

The primary goal of the study herein presented was to evaluate the remaining strength of a stiffened panel belonging to a ship’s deck that suffered some deformations during service.For this purpose, some representative panels of the ship were modelled, aiming to simulate a range of typical deformations, from the ones found on board, as is, through to some extreme cases of deformations that could lead to structural collapse. After shaping the stiffened panels, compressive in-plane loading was applied, simulating longitudinal bending of the hull in a sagging condition. Non-linear structural analyses were carried out using the Finite Element Method (FEM) and ANSYS software.It was found that the existence of large deformations between reinforcements led to the loss of strength of the original stiffened panel and the local deformations occurring near the reinforcements do not affect the strength of the panel significantly. The case with a higher loss of strength was the one relative to the collapse of a longitudinal reinforcement profile of the deck panel. In addition, the main types of buckling found in the panel were the local buckling of plating between stiffeners and the lateral-torsional buckling of the smaller stiffeners.Despite the moderate loss of strength found on some of the stiffened panel studied, it was possible to conclude that this loss of strength does not compromise the normal safe operation of the ship, even in extreme load.

Effect of a central dent on the ultimate strength of narrow stiffened panels under axial compression

This paper studies the effect of a central dented imperfection on the load carrying capacity of stiffened panels considering the residual stress caused by the indentation, and identifying the type of boundary conditions to adopt for a model to be used in an experimental programme for damaged panels. A quasi-static nonlinear finite element analysis is used to simulate the production of the local dent, followed by an ultimate strength analysis of the stiffened panels under uniaxial compressive load. The structural plastic strain causes the residual stress and the dent, which are included in the ultimate strength analysis of the stiffened panels under compressive load. To prescribe appropriately the boundary conditions for the central span of stiffened panels, two and three spans models are adopted in the FE analyses. The effects of residual stress, geometric range and dent depth on the ultimate strength of the stiffened panels with a central dented imperfection are investigated using nonlinear quasi-static finite-element analysis.

Ultimate strength performance of Northern sea going non-ice class commercial ships

In the early design stage of ships, the two most important structural analyses are performed to identify the structural capacity and safety. The first step is called global strength analysis (longitudinal strength analysis or hull girder strength analysis) and the second step is local buckling analysis (stiffened panel strength analysis). This paper deals with the ultimate strength performance of Arctic sea route-going commercial ships considering the effect of low temperature. In this study, two types of structural analyses are performed in Arctic sea conditions. Three types of ship namely oil tanker, bulk carrier and container ship with four different sizes (in total 12 vessels) are tested in four low temperatures (−20, −40, −60 and −80oC), which are based on the Arctic environment and room temperature (20oC). The ultimate strength performance is analysed with ALPS/HULL progressive hull collapse analysis code for ship hulls, then ALPS/ULSAP supersize finite element method for stiffened panels. The obtained results are summarised in terms of temperature, vessel type, vessel size, loading type and other effects. The important insights and outcomes are documented.

Influence of Model Geometry and Boundary Conditions on the Ultimate Strength of Stiffened Panels Under Uniaxial Compressive Loading

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.

Residual Strength of Stiffened LY12CZ Aluminum Alloy Panels with Widespread Fatigue Damage

Experimental and analytical investigations on the residual strength of the stiffened LY12CZ aluminum alloy panels with widespread fatigue damage (WFD) are conducted. Nine stiffened LY12CZ aluminum alloy panels with three different types of damage are tested for residual strength. Each specimen is pre-cracked at rivet holes by saw cuts and subjected to a monotonically increasing tensile load until failure is occurred and the failure load is recorded. The stress intensity factors at the tips of the lead crack and the adjacent WFD cracks of the stiffened aluminum alloy panels are calculated by compounding approach and finite element method (FEM) respectively. The residual strength of the stiffened panels with WFD is evaluated by the engineering method with plastic zone linkup criterion and the FEM with apparent fracture toughness criterion respectively. The predicted residual strength agrees well with the experiment results. It indicates that in engineering practice these methods can be used for residual strength evaluation with the acceptable accuracy. It can be seen from this research that WFD can significantly reduce the residual strength and the critical crack length of the stiffened panels with WFD. The effect of WFD crack length on residual strength is also studied.

An analytical method for the ultimate compressive strength and effective plating of stiffened panels

The aim of the present study is to develop a simple analytical method for calculating the ultimate strength of a stiffened panel subject to uniaxial compression. The behavior of the stiffened panel is analyzed by using a plate–stiffener combination model as representative of the stiffened panel. Three collapse modes, namely plate induced failure, stiffener induced failure and local buckling of stiffener web are considered. While several other approaches to the same problem exist, an analytical expression of ultimate strength is of value because it can explicitly show the influence of different parameters. The given formulations can be applied to stiffened plating employing all types of stiffener profiles. The Perry–Robertson approach is used to derive the criteria for plate induced and stiffener induced failures without rotation of stiffener web. The effect of possible stiffener web buckling is included through closed form expressions for predicting the elastic buckling strength of the stiffener web taking account of the influence of rotational restraints at the plate–stiffener and stiffener web–flange intersections. The web buckling strength expressions are used together with the Johnson–Ostenfeld formulation which provides a simple plasticity correction. The influence of initial imperfections (initial deflection and welding induced residual stresses) for both plating and stiffener are taken into account. As verification, the theoretical solutions from the study are compared with some existing experimental results for stiffened panel strength under uniaxial compression. As an interesting contribution, this study develops, presents, and uses a new refined procedure to reasonably accurately evaluate the effective cross sectional area of the representative plate stiffener combination in the stiffened panel. The effective width of plating between stiffeners is analytically formulated, accounting for applied compressive loads, initial deflections, and welding induced residual stresses.

Uncertainty Analysis of Structural Strength of Stiffened Panels

ABSTRACTA prototype computational methodology for reliability assessment of continuum structures using finite element analysis with instability failure modes is described in this paper. Examples were used to illustrate and test the methodology. Geometric and material uncertainties are considered in the finite element model. A Computer program was developed to implement this methodology by integrating uncertainty formulations to create a finite element input file, and to conduct the reliability assessment on a machine level. A commercial finite element package was used as a basis for the strength assessment in the presented procedure. A parametric study for a stiffened panel strength was also carried out.The finite element model for the stiffened panel is based on the 8‐node doubly curved shell element, which can provide the non‐linear behavior prediction of the stiffened panel. The mesh is designed to ensure the convergence of eigenvalue estimates. Failure modes are predicted on the basis of elastic non‐linear analysis using the finite element model.Reliability assessment is performed using Monte Carlo simulation with variance reduction techniques that consisted of the conditional expectation method. Conditional expectation estimates the failure probability in each simulation cycle, then the average failure probability and its statistical error are computed. The developed method is expected to have significant impact on the reliability assessment of structural components and systems. This impact can extend beyond structural reliability into the generalized field of engineering mechanics.

Ultimate strength of stiffened panels with cutouts under uniaxial compression

An approximate method based on strut approach to predict the ultimate strength of simply-supported stiffened panels with initial imperfections and square cutouts, subjected to uniaxial compression is presented. The reduction in stiffness of the plate between stiffeners is considered by using an ‘effective width concept’. Tests are reported on welded stiffened steel panels with varying plate slenderness ratio and column slenderness ratio. Based on the experimental investigations and the proposed method, the influence of square openings, extending the full width between stiffeners, on the ultimate strength of stiffened panels is evaluated.