Empirical formulations for estimation of ultimate strength of continuous stiffened aluminium plates under combined in-plane compression and lateral pressure

The present research was undertaken based on the results obtained by the same authors in a sensitivity study on the buckling and ultimate strength of continuous stiffened aluminium plates. Empirical expressions are developed for predicting ultimate compressive strength of welded stiffened aluminium plates used in marine applications under combined in-plane axial compression and different levels of lateral pressure. Existing data of the ultimate compressive strength for stiffened aluminium plates numerically obtained by the authors through the previously performed sensitivity analysis are used for deriving formulations that are expressed as functions of two parameters, namely the plate slenderness ratio and the column (stiffener) slenderness ratio. Regression analysis is used in order to derive the empirical formulations. The formulae implicitly include effects of the weld on initial imperfections, and the heat-affected zone.     

Influence of corrosion on the ultimate compressive strength of steel plates and stiffened panels

This study concentrates on a comparison between steel plate and stiffened panels subject to localised corrosion. A finite element analysis is used to investigate the effect of random corrosion on the compressive strength capacity of marine structural units. Variables include the extent of corrosion; slenderness ratio and aspect ratio. A corrosion prediction model is incorporated to determine the thickness reduction with time. Corrosion-induced volume loss results in a greater reduction of ultimate strength for slender plates compared to stiffened panels, up to 45%, showing the structural element selection can strongly influence the accuracy of the estimated corrosion damage effect.     

Ultimate shear strength of intact and cracked stiffened panels

The present paper focuses on the ultimate shear strength analysis of intact and cracked stiffened panels. Several potential parameters influencing the ultimate shear strength of intact panels are discussed, including the patterns and amplitudes of initial deflection, the slenderness and aspect ratios of the plates, and the boundary conditions defined by the torsional stiffness of support members. An empirical formula for the ultimate shear strength of intact stiffened panels is proposed based on parametric nonlinear finite element analyses in ANSYS. Furthermore, the ultimate shear strength characteristics of cracked stiffened panels are investigated in LS-DYNA with the implicit method. Three types of cracks are considered, namely vertical crack, horizontal crack and angular crack. A simplified method is put forward to calculate the equivalent crack length. And the formula for the ultimate shear strength of cracked stiffened panels is derived on the basis of the formula for intact stiffened panels.     

Stiffened steel plates under uniaxial compression

The stability of steel plates stiffened with tee-shape sections under uniaxial compression and combined uniaxial compression and bending was investigated using a finite element model. The emphasis of the work presented in this paper was to find the parameters that uniquely describe the strength and behaviour of stiffened steel plates. A finite element model, validated using the results of tests on full-size stiffened plate panels, was used to investigate the scale effect for five dimensionless parameters. The parameters investigated were: the transverse slenderness of the plate, the slenderness of the web and flange of the stiffener, the ratio of torsional slenderness of the stiffener to the transverse slenderness of the plate, and the stiffener-to-plate area ratio. Average magnitude residual stresses and initial imperfections were assumed for this study.A parametric study covering a wide range of dimensionless parameters indicated that stiffened steel plates do not fail by stiffener tripping unless a bending moment is applied to create flexural compressive stresses in the stiffener. Although plate buckling and overall buckling were found to lead to a very stable post-buckling behaviour, the interaction between these two buckling modes was found to give rise to a sudden loss of capacity following initial plate buckling. The plate transverse slenderness, the stiffener slenderness-to-plate slenderness ratio, and the stiffener-to-plate area ratio were found to have a significant effect on this behaviour.A comparison of the numerical analysis results with API and DnV design guidelines indicates that the guidelines predict stiffened steel plate capacity with various degrees of success, depending on the governing mode of failure. Neither guidelines address the potential interaction-buckling phenomenon.     

U型加劲肋加固的高强钢面板体系的面内极限抗压强度

通过非线性有限元分析(FEA)研究使用U型加固件纵向加劲的面板的极限抗压强度。对112个由各种细长参数的面板和柱以及加固件组成的模型进行分析。模型包括了普通钢材和高强钢的弹塑性应变硬化本构关系。有限元分析中也包括了初始几何缺陷和残余应力。将有限元分析得出的结果与欧洲规范3EN1993-1-5、FHWA-TS-80–205和其他可用公式计算出的强度进行比较。基于分析结果,可得出一个针对使用普通钢材或高强钢(HPS)加劲板系统的新的强度预测公式。结果表明:当柱的长细比较大时,使用欧盟规范3EN1993-1-5和FHWA-TS-80–205可能导致设计过于保守;而采用所提出简化形式的公式可更精确地预测强度,从而得出更经济的设计。     

平面内压力和侧向压力组合作用下预测连续加劲铝板极限强度的经验公式

在对连续加劲铝板屈曲和极限强度的敏感性研究基础之上,对压力作用下的铝板进行了深入研究。开发了一个经验公式,用于预测海洋工程中采用焊接加劲铝板在平面内轴压和各种侧向压力作用下的极限抗压强度。极限抗压强度的计算利用了一些的铝板敏感性分析的相关数据,推导出来的公式中含有两个参数,分别是板长细比和柱(加劲肋)长细比。推导过程中也用到了回归分析。公式考虑了焊接对初始缺陷和热影响区的影响。     

Residual ultimate strength assessment of stiffened panels with locked cracks

The residual ultimate strength of stiffened panels with locked cracks under axial compressive loading is analyzed. The influences of various geometrical characteristics of cracks and panels, such as the length and the orientation angle of cracks, are investigated by the nonlinear finite element analysis. The cracks are prevented from further propagation by holes with a diameter of 2 mm drilled at their tips. The finite element model has two bays in the longitudinal direction, employing periodical symmetrical boundary conditions at the ends of the loading edge. Beam tension test results are used to define the true stress–strain relationship of the material, which is used in the FE analyses to account for the nonlinear material property of steel.     

Structural behaviour of eccentrically loaded precast sandwich panels

Results of an experimental investigation to study the ultimate strength behaviour of precast concrete sandwich panels (PCSP) with steel truss shear connectors are reported. Six full-scale sandwich panels with variable slenderness ratio were cast and tested under eccentric loads. Deflection characteristics, variations of strains across the insulation layer, strains in shear connectors, crack appearance and propagation under increasing load were recorded and analysed. The role of the shear truss connectors in transferring load from the outer wythe (layer) to the inner and ensuring composite behaviour was also observed. Results obtained showed that all panels behaved in a fully composite manner under eccentric load till failure. The ultimate strength of the PCSPs was found to decrease non-linearly with the increase in the slenderness ratio. Because of the complex behaviour of PCSP due to its material non-linearity and the interaction between its various components, finite element analysis (FEA) was conducted. Comparison with test results indicated that the FEA closely estimate the wall strength and formulae based on reinforced concrete principles underestimate the wall strength.     

Validation of the equivalent plate thickness approach for ultimate strength analysis of stiffened panels with non-uniform plate thickness

The stiffened plate structures in ships and ship-shaped offshore installations often consist of non-uniform plate thicknesses. Nonlinear finite element methods are usually employed to predict structural strength for such panels. However, the introduction of non-uniform plate thicknesses renders such calculations difficult when analytical methods and design equations are used. The authors have suggested an equivalent plate thickness method that is based on the weighted average approach to analyse the strength of stiffened panels with non-uniform plate thicknesses. In the present paper, the validity of the equivalent plate thickness method to the ultimate strength analysis of stiffened panels with non-uniform plate thicknesses is checked through nonlinear finite element method computations. It is concluded that the equivalent plate thickness method is accurate for the panel ultimate strength analysis under combined biaxial compression and lateral pressure loads.     

圆端形椭圆钢管混凝土长柱偏压受力性能研究

为了获悉圆端形椭圆钢管混凝土偏压长柱的理论计算模型和受力性能,考虑了圆端形椭圆截面特征,提出了圆端形椭圆钢管混凝土本构关系等效方法;基于有限元法建立了圆端形椭圆钢管混凝土长柱在偏压作用下的理论分析模型。对钢材强度、混凝土强度、偏心距、径厚比、长短轴比和长细比等诸多参数进行了系统分析,评价了各参数对圆端形椭圆钢管混凝土长柱偏压承载力的影响,揭示了其破坏模式。研究结果表明:圆端形椭圆钢管混凝土偏压长柱的承载力随着混凝土强度和钢材强度的增大而增大;随着偏心率、径厚比、长短轴比和长细比的增大而减小。最后,基于统一理论提出了圆端形椭圆钢管混凝土长柱偏压作用下的承载力设计方法。研究结果将为建立圆端形椭圆钢管混凝土结构的设计和应用提供参考。     

Ultimate strength of stiffened plates with a square opening under axial and out-of-plane loads

The high strength to weight ratio and high stiffness to weight ratio of stiffened plates find wide application in aircraft structures, ship structures, offshore oil platforms and lock gates. The strength and stability of stiffened plates is highly influenced by openings and initial imperfections. The main objective is to study the behaviour of stiffened steel plates with openings up to collapse and to trace the post-peak behaviour under axial and out-of-plane loads. Four stiffened steel plates with a square opening were fabricated for testing. Angle sections were used as stiffeners. Imperfections in the plate, stiffener and overall imperfection of the whole panel were measured. All fabricated panels were tested to failure. A finite element (FE) model was developed for the analysis of stiffened plates with initial imperfections and validated with the test results. Parametric studies were conducted using the developed FE model, and interaction curves and equations were developed for the design of stiffened plates with initial imperfections and openings. The interactive effect for stiffened panels with a square opening was found to be linear, with proportional reduction of the ultimate axial load carrying capacity due to the constant out-of-plane load.     

Improved prediction of simultaneous local and overall buckling of stiffened panels

In this paper, improved expressions for elastic local plate buckling and overall panel buckling of uniaxially compressed T-stiffened panels are developed and validated with 55 ABAQUS eigenvalue buckling analyses of a wide range of typical panel geometries. These two expressions are equated to derive a new expression for the rigidity ratio (EI_x/Db)_CO that uniquely identifies “crossover” panels—those for which local and overall buckling stresses are the same. The new expression for (EI_x/Db)_CO is also validated using the 55 FE models. Earlier work by Chen (Ultimate strength analysis of stiffened panels using a beam-column method. PhD Dissertation, Department of Aerospace and Ocean Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA, 2003) had produced a new step-by-step beam-column method for predicting stiffener-induced compressive collapse of stiffened panels. An alternative approach is to use orthotropic plate theory. As part of the validation of the new beam-column method, ABAQUS elasto-plastic Riks ultimate strength analyses were made for 107 stiffened panels—the 55 crossover panels and 52 others. The beam-column and orthotropic approaches were also used. A surprising result was that the orthotropic approach has a large error for crossover panels whereas the beam-column method does not. Some possible reasons for this are suggested.     

轴向压缩荷载下双层中空钢管混凝土短柱的试验和数值研究

使用试验和数值方法研究轴向压缩荷载下双层中空钢管混凝土柱的性能。对一个外层为八边形钢管﹑内层为环形PVC-U管﹑且在两层间填充高强混凝土的双层中空钢管混凝土柱进行研究。测试混凝土强度﹑径厚比﹑空心率﹑长细比对双层钢管混凝土柱的极限轴压承载力的影响。经测试发现:双层中空钢管混凝土柱的极限轴压承载力随着混凝土强度的增加而增加,但随着径厚比或空心率的增加而减少。根据试验结果,提出一个能预测双层中空钢管混凝土柱极限轴压承载力的设计公式。     

Experimental studies on stiffened plates under in-plane load and lateral pressure

An experimental study on stiffened plates subjected to combined action of in-plane load and lateral pressure is described in the paper. Details of the experiments and finite element analyses of the specimens tested are presented along with the results. Measurements of initial imperfection in the specimens have been made and included in the analyses. Results show that lateral load carrying capacity of stiffened plate drops with increase in axial load and vice-versa. It is found that plate slenderness ratio has significant influence on the ultimate load capacity of stiffened plates subjected to both in-plane load and lateral pressure. Increase of plate slenderness ratio results in a decrease of ultimate load capacity of stiffened plate. The accuracy of the finite element modelling is established by comparing the results with the corresponding experimental values.     

Study on the influence of the initial deflection and load combination on the collapse behaviour of continuous stiffened panels

Using the finite element analysis, a series stiffened panels under combined normal loads and biaxial compressions are conducted to investigate the effect of several influential factors on the ultimate limit states. Two spans/bays FE model with periodical boundary condition is adopted to consider the interaction between adjacent structural members. The initial deflections assumed as Fourier components including symmetric and asymmetric modes are used to identify the half-wave number of collapse of the local plate, which is compared with half-wave number of buckling calculated by formula. Based on the numerical results, the influences of half-wave number assumed in the equivalent initial imperfection and loads combination on the collapse behaviours of stiffened panels are discussed. It is found that lateral pressure might increase the ultimate strength of stiffened panels for the stiffener-induced failure modes. The one half-wave region of local plate influences significantly the load carrying capacity of stiffened panels.     

Experimental and numerical studies of short concrete-filled double skin composite tube columns under axially compressive loads

This paper presents a study on the performance of concrete-filled double skin composite tube columns (CFDSCT) under axially compressive loads using both experimental and numerical methods. The CFDSCT column investigated consists of an octagonal steel tube as its outer skin layer, a circle PVC-U pipe as its inner skin layer, and high strength concrete filled in between the two layers. Influences of concrete strength, radius-to-thickness ratio, hollow section ratio, and slenderness ratio on the ultimate axial compressive capacity of the CFDSCT column are examined. It is found that the ultimate axial compressive capacity of the CFDSCT column increases with the strength of concrete, but decreases with either increased radius-to-thickness ratio or increased hollow section ratio. Based on the findings from the present experimental and numerical studies, a design formula for predicting the ultimate load of the CFDSCT column is proposed.     

非轴压下开裂的加劲钢板的极限状态和破坏状态的响应

开裂可能会导致加劲板极限强度的减小和破坏特点的改变。对此类问题,分析了不同形状及长度的裂缝对加劲板强度和破坏特点的影响。裂缝的位置为沿着轴向压力方向,而且不考虑裂缝的扩展。主要讨论了裂缝闭合对结构响应的影响。给出不同宽高比的加劲板的极限强度和破坏状态。最终,给出一个有限元建模方法,将有可能降低密肋板的分析成本。     

Ultimate strength formulations for stiffened panels under combined axial load, in-plane bending and lateral pressure: a benchmark study

This paper develops advanced, yet design-oriented ultimate strength expressions for stiffened panels subject to combined axial load, in-plane bending and lateral pressure. The collapse patterns of a stiffened panel are classified into six groups. It is considered that the collapse of the stiffened panel occurs at the lowest value among the various ultimate loads calculated for each of the collapse patterns. The panel ultimate strengths for all potential collapse modes are calculated separately, and are then compared to find the minimum value which is then taken to correspond to the real panel ultimate strength. The post-weld initial imperfections (initial deflection and residual stress) are included in the developed panel ultimate strength formulations as parameters of influence. The validity of the developed formula is confirmed by comparing with the mechanical collapse tests and nonlinear FEA. A comparison of the present method is also made with theoretical solutions from the Det Norske Veritas classification society design guideline. Important insights developed are summarized.     

十字加劲钢板剪力墙的抗剪极限承载力

我国《高层民用建筑钢结构技术规程》规定了钢板墙剪切弹性屈曲不先于剪切屈服,其明显的不足是没有利用板的屈曲后强度,同时弹性屈曲也不能作为结构在弹塑性阶段的设计指标。本文应用板的大挠度弹塑性有限元方法对十字加劲方形钢板剪力墙的屈曲后性能和极限承载力进行了系统的研究,并在大量数值分析的基础上,提出了以板的平均剪切应变相应的剪应力作为钢板剪力墙承载能力的极限状态,以达到利用薄板屈曲后强度的目的,进而提出了钢板剪力墙承载力的设计简化计算公式及钢板墙侧柱刚度阈值的计算公式,供设计参考。数值计算结果表明,影响钢板墙抗剪性能主要有三个参数:板高厚比、肋板刚度比和边柱刚度。     

混合钢U肋加劲板受压整体稳定承载力数值模拟与计算方法

建立受压混合钢U肋加劲板梁单元有限元模型并进行整体稳定分析,通过在梁单元模型中施加等效应力模拟U肋和被加劲板的不同强度,以5种不同强度组合的U肋加劲板试验试件的破坏模式和荷载-位移曲线对数值模拟方法进行验证。采用经试验验证的有限元模型,变化U肋高度、U肋与被加劲板强度与厚度、构件长度,得到混合钢U肋加劲板整体稳定系数,并与各国规范的柱曲线进行比较。结果表明:在压力荷载作用下,由于非等强钢U肋加劲板中钢材强度较低部分较早达到屈服,这将使得构件整体偏心受压,从而导致构件整体稳定系数均小于1; 等强钢M345-U345柱子曲线位于JTG D64—2015中的a,b类柱子曲线之间,并随着相对长细比的增大逐渐向b类柱子曲线靠近; 非等强钢柱子曲线在相对长细比较小时均低于等强钢M345-U345柱子曲线,而在相对长细比较大时的走势基本一致,其中M345-U420和M420-U345两条柱子曲线与JTG D64—2015中的b类柱子曲线接近; M345-U390和M390-U345两种柱子曲线随着相对长细比的增大逐步与等强钢M345-U345柱子曲线重合接近。