Shear buckling in foam-filled web core sandwich panels using a Pasternak foundation model

Web core panels, foam-filled sandwich panels with interior webs, are a structurally efficient option for transverse load bearing applications. In web core panels, the interaction between the webs and core material can have a substantial impact on web shear buckling strength and is a key element of lightweight structural design. The present work is an investigation of web buckling behavior in web core panels under a distributed load. To solve this problem, web shear buckling was analyzed for the case of pure shear loading with foam support, and this analytic model was extended to the case of panels with a transverse distributed load. The webs are modeled as simply supported plates resting on a Pasternak elastic foundation. To that end, a buckling model for plates on a Pasternak foundation is presented, along with closed-form approximations of the solution for square and infinitely long plates. An accurate model for the foundation constants is developed using energy methods. Applicability of the plate buckling model to web core panels with transverse loads is presented via a finite element study. In panels, the slenderness and spacing of the webs have a slight effect on the boundary conditions between the webs and face sheets. The effect is relatively small, however, and the model presented in this work underpredicts buckling strength by less than 25%. The model in this work is thus a reasonable approach to the practical design of web core panels.     

带有开口增强的复合板在剪切荷载作用下的应力集中和屈曲性能研究

数值和试验研究是了解碳／环氧复合板在面内剪力载荷作用下开口周边补强后应力集中和屈曲性能的两种重要方法。研究了采用四种不同开口型式及材料排列模式下的补强效果。采用有限元分析方法和基于平板理论的研究方法，分析了不同补强设计中的参变量。完成了4个试验板的制造和试验，并验证了分析结果。分析结果和试验结果吻合很好。基于有效分析模型，确定了最佳的开口补强方法。     

Residual ultimate compressive strength of dented square plates

Thin steel plates are widely used in many structural applications because of its high load carrying capacity with less weight. The load carrying capacity of thin plates mainly depends on its buckling behavior which in turn is affected by the imperfections present in it. Dent is one of the common geometrical imperfections present in thin shell structures which may be formed due to mechanical damage caused by accidental loading or impact. In this work, influence of various dent parameters (dent length, dent width, dent depth and angle of orientation of the dent) on the static ultimate strength of thin square plates of different thicknesses under uniaxial compressive loading is studied. The dent is modeled on the FE surface of perfect thin square plate of size 1000 mm (of different thickness) for different sizes and angles of orientation of the dent at the center of the plate. These dented plates are analyzed using non-linear static buckling analysis of general purpose FE software ANSYS V12. From the results obtained, it is found that both shorter and longer dents reduce the ultimate strength drastically. But in case of shorter dents, variation of ultimate strength of dented plates due to variation of size and angle of orientation of dents is insignificant, whereas in the case of longer dents, size and angle of orientation of dents have significant effect. It is also found that the reduction in ultimate strength of thin plates with a dent of same size and orientation increases with increase in shell thickness.     

Performance evaluation of intermittently CFRP wrapped square and circularised square reinforced concrete columns under different loading conditions

This paper presents the results of an experimental investigation on square and circularised square reinforced concrete (RC) columns intermittently wrapped with carbon fibre reinforced polymer (CFRP) under different loading conditions. Twelve RC specimens consisting of eight square RC specimens with 150?mm × 150?mm cross-section and 800?mm height and four circularised square RC specimens with 212?mm diameter and 800?mm height were tested under concentric axial load, eccentric axial load and four-point flexural load. The test results showed that intermittent wrapping increased the strength and ductility of square RC specimens. The test results also showed that circularisation combined with intermittent wrapping significantly improved the strength and ductility of square RC specimens. The experimental axial load-bending moment interaction diagram showed that the best performance was achieved by intermittently CFRP wrapped circularised square RC specimens.     

热处理方钢管短柱超低周疲劳性能试验研究

强震下钢结构构件会发生局部或整体屈曲,造成构件局部塑性应变集中,导致构件在反复荷载作用下最终发生断裂,因此有必要开展大塑性应变循环加载下局部屈曲和后续延性断裂的耦合破坏机理研究。通过热处理冷弯方钢管短柱的超低周疲劳试验,对上述破坏机理进行了研究。试验考察了宽厚比和加载历史对于方钢管短柱屈曲后断裂模式及抗震性能的影响,并给出了累积延性评估方法。试验结果显示:所有试件受压时承载力的下降皆由局部屈曲导致,而受拉侧承载力的退化则由延性断裂造成;构件的累积塑性耗能可分解为各向同性强化耗能和随动强化耗能,且两者受拉时对应值呈线性关系。     

中巴喀喇昆仑公路顺层岩质边坡受力分析

为了深入研究中巴喀喇昆仑公路洪扎河以北地段的顺层岩质边坡弯曲失稳机制,采用材料力学压杆稳定及刚性体平衡原理,在D.S.Cavers的基础上考虑地震力作用,分析得到岩质边坡的三种弯曲模型(平面边坡的柔性弯曲、平面边坡的三铰梁模型、曲线边坡的三绞铰模型)的失稳公式,将地震与非地震作用下平面边坡的柔性弯曲进行对比分析。研究结果表明:当内摩擦角φ_j处于0°~15°范围时,若水平地震加速度方向与岩体弯曲方向相反,平面边坡柔性弯曲模型在地震作用下不易发生弯曲变形;若水平地震加速度方向与岩体弯曲方向一致,地震作用下平面边坡柔性弯曲模型的临界状态总长度l总比非地震作用下的l小,平面边坡在此方向的地震作用下更易发生柔性弯曲变形。     

Buckling analysis of trapezoidally corrugated panels using spline finite strip method

Buckling of trapezoidally corrugated panels under in-plane loading is analyzed by a spline finite strip method. The influence on the elastic buckling load of various parameters, such as geometry. loading forms and boundary conditions, etc., is studied. It is found that: (1) for longitudinal compression the buckling load increases with the corrugation angle α, and for a given α the highest buckling load is achieved when the ‘proportion parameter’ γ = 1; (2) for shear loading the buckling load increases as α increases, and for a given α the highest buckling load is obtained when γ = 2; and (3) for a combined loading of compression and shear, interactive curves can be approximated by unit circles when α = 15°, 30°, 45°, 60° and 90°. However, when α = 75° a parabola seems to be a better approximation. Based on the numerical experiments, simplified formulae and interactive curves are suggested for practical design.     

Natural frequencies of square plates with reinforced central holes subjected to inplane loads

The natural frequencies and the elastic buckling loads of square plates, containing reinforced square holes and subjected to inplane loads, are determined using the finite element method. The reinforcing beams which are located at the four edges of the hole are either square or rectangular in cross section.

To determine the appropriate out-of-plane stiffness and mass matrices, a rectangular non-conforming bending element is employed. This element has three degrees of freedom at each of its four corner nodes. The finite element method is also used to calculate the inplane stress distribution prior to buckling. This inplane element is rectangular and is based on strain assumptions. The element also includes the inplane rotation as well as the two translational displacements as the three degrees of freedom at each of its four corner nodes. To model the behaviour of the reinforcement, a three-dimensional exact beam element is used. For this element, the degrees of freedom for out-of-plane displacement are consistent with the non-conforming bending element, and the inplane degrees of freedom are consistent with the inplane strain-based element.

In the present paper the natural frequencies and the corresponding modes of vibration are investigated when the reinforced plates are subjected to uniform uniaxial, biaxial and shear loads. The variation of the natural frequencies with various sizes of reinforcement is obtained for plates subjected to a range of magnitude of inplane loading.     

Tension buckling and parametric instability characteristics of doubly curved panels with circular cutout subjected to nonuniform tensile edge loading

This paper deals with the study of tensile buckling, vibration, and parametric instability behaviour of doubly curved panels with central circular cutout subjected to uniaxial in-plane partially distributed tensile edge loadings using finite element method. First order shear deformation theory is used to model the curved panels, to consider the effects of the transverse shear deformation and rotary inertia. The vibration analysis for this problem shows that for certain parameters of the tensile loading, the frequencies of the panel initially rise with the load, but begin to decrease with increasing tension, showing the onset of tension buckling. The parametric instability behaviour under tensile periodic edge loading with different load parameters shows that instability regions are influenced by the cutout size, load width and its location.     

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。     

薄壁方钢管再生混合柱抗震性能试验研究

通过15根薄壁方钢管再生混合柱在定常轴力和水平往复荷载作用下的拟静力试验,研究了废弃混凝土取代率、钢管壁厚、轴压比等参数对试件抗震性能的影响。基于新、旧混凝土的组合强度,根据国内外钢管混凝土结构的设计标准以及基于ABAQUS的纤维梁单元模型,对试件的水平承载力进行了计算分析。研究表明：废弃混凝土取代率在0~40%之间变化对试件的初始抗侧刚度、钢管局部屈曲、破坏位移、负刚度段行为、等效黏滞阻尼系数、滞回曲线形状影响有限,但再生混合柱的水平承载力总体上比全现浇柱有所降低;当钢管壁厚在1.78~5.50mm之间变化时,随钢管壁厚增加试件并未表现出更好的变形能力;在钢管壁厚仅1.78 mm（宽厚比168.5）的情况下,轴压比0.4的再生混合柱的破坏位移角可达1/35,满足我国现行抗震规范的层间位移角限值要求;采用5部现行标准计算薄壁方钢管再生混合柱的水平承载力可获得与同条件全现浇柱相当的安全性;横截面积和用钢量相同时,薄壁方钢管再生混合柱的抗震性能优于钢筋混凝土柱。研究发现,薄壁方钢管再生混合柱应用于中、低轴压比（实际轴压比小于0.4）的情况是可行的。     

反复荷载作用下方钢管混凝土柱与钢梁连接节点非线性有限元分析

本文首先选择合适的本构模型作为约束混凝土循环本构模型的骨架曲线,提出了考虑局部屈曲和开裂的钢材循环本构关系;进而建立两类方钢管混凝土柱与钢梁连接节点———缀板焊接连接节点和穿芯螺栓-端板连接节点的空间非线性分析模型,对其在低周反复荷载作用下的滞回性能进行了非线性分析计算。结果表明:由有限元模型所得的单调荷载-位移曲线与试验所得的低周反复荷载作用下的骨架曲线极为相似,但在峰值荷载后差异较大;由有限元模型所得的在低周反复荷载作用下滞回曲线也与在反复荷载作用下试验所得的相一致。有限元模型能准确地预测上述两类节点的弹塑性行为和整体抗震性能,可用于节点滞回性能的非线性参数分析研究。     

对轴压力作用下带有椭圆形开孔的圆柱形壳体屈曲的数值和试验研究

在圆柱形壳体的设计中,开孔对于其承载能力及屈曲性能的影响非常大。采用有限元方法对具有不同尺寸开孔的薄壁钢圆柱形壳进行模拟和分析,分析了开孔的位置、长度与直径比值（L／D）和直径与厚度比值（D／t）对圆柱形壳届曲和后屈曲性能的影响。采用INSTRON 8802液压系统对一些构件进行屈曲试验,并将试验结果与数值计算结果进行对比发现,两者具有非常好的一致性。最后,基于试验和数值分析结果,提出计算这类结构屈曲荷载的公式。     

方钢管螺旋筋复合约束混凝土柱偏压性能试验及承载力计算

为研究方钢管螺旋筋复合约束混凝土柱的偏心受压性能,完成了18个试件(其中17个方钢管螺旋筋复合约束混凝土试件和1个普通方钢管混凝土对比试件)的偏心受压加载试验。考虑了螺旋筋间距、径宽比、长细比、偏心率、纵筋配筋率以及钢管壁厚6个变化参数,通过试验,观察了试件的受力破坏过程及形态,获取了荷载-挠度曲线和荷载-应变曲线,分析了各变化参数对其偏压性能的影响规律。结果表明:方钢管螺旋筋复合约束混凝土的承载性能和破坏形态与普通方钢管混凝土的相似;螺旋筋主要在弹塑性和下降段发挥作用,并可提高试件的承载力和延性,延缓钢管壁的局部鼓曲,且材料强度能够充分发挥,其间距越密试件的变形性能越好;偏心率和钢管壁厚对承载力影响显著,其他参数的影响相对较小。最后提出了基于偏心率折减系数和内力相关关系的偏压承载力计算式,计算值与试验值均吻合较好。     

方钢管混凝土中钢管和混凝土抗压强度研究

对于方钢管混凝土柱在轴压作用下的受力性能,国内外学者已经进行了大量的试验研究和理论分析,但常规轴压试验无法得到钢管和混凝土各自承担的轴压力。为此,提出了一种在方钢管混凝土柱试件上部设置轴力测量段的试验方法,用于直接测量轴压下方钢管混凝土柱中钢管和混凝土所承担的轴压力。通过对5个不同宽厚比的方钢管混凝土柱试件开展轴压试验,发现方钢管混凝土柱中混凝土的抗压强度与其对应的轴心抗压强度相近。将试验得到的钢管抗压强度与已有经验公式结果进行对比,发现已有经验公式可合理预测钢管的抗压强度,针对钢管的屈曲后行为和其他因素的影响需要展开更深入的研究。在试验结果的基础上,提出了方钢管混凝土柱的轴压承载力计算式,其计算结果与文献试验结果吻合良好。     

钢-聚氨酯夹层板稳定分析

分别建立了钢-聚氨酯夹层板和普通钢板的有限元模型,在边界条件、加载情况均相同的条件下进行有限元稳定分析,夹层板采用板-实体-板结构模拟,结果表明在相同条件下,夹层板比普通钢板的屈曲强度均有较大程度的提高。同时进行了保持一定条件不变,分别改变夹芯层厚度、面层钢板厚度模拟分析,结果表明在一定范围内,夹芯层厚度与钢面板厚度增大,夹层板的屈曲临界荷载值也随之增大。夹芯层的抗弯刚度和横向剪切变形对板的影响不可忽略。     

方钢管混凝土柱与钢梁连接节点的拟静力试验研究

本文进行了6个方形钢管混凝土柱与钢梁连接节点足尺模型的拟静力试验,包括穿芯螺栓-加劲端板连接(SEP)节点、缀板焊接连接(SPW)节点与常规栓焊(NBW)节点三种。比较了这三种连接节点在不同轴压比下的滞回性能、强度与刚度退化、延性性能、耗能能力以及破坏特征。结果显示:破坏大多发生在节点连接部位或钢梁局部屈曲或开裂,SEP节点与SPW节点的整体抗震性能要优于常规栓焊节点。     

Behavior of beam web panel under opposite patch loading

Elastic buckling is studied for a panel with various boundary conditions including simple supports, fixed supports and elastic restraints. The panel is subjected to opposite patch loading. Following a review of existing work on the effects of localized compression, also known as patch loading, a study is conducted to take into account the restraints provided by the flanges of the I beam in a realistic manner. This study is based on a finite element model implemented in the CAST3M software. A new equation is proposed to calculate the buckling critical coefficient for a beam web panel considering the rotational stiffness provided by the flanges. The model is then applied to longitudinally stiffened web panels which are subjected to opposite patch loading.A parametric analysis is performed to determine the transition from a global buckling mode to a local buckling mode where the sub-panels on each side of the stiffener behave separately. The numerical results show that the flexural rigidity of the stiffener is the appropriate parameter that governs the buckling mode. From these results, a formula is proposed to calculate the buckling critical coefficient of stiffened web panels.     

Sandwich panels

In recent years, there has been increasing interest in the use of structural sandwich panels as the cladding of buildings and a good deal of research and development has been carried out. This paper reviews the state of the art with regard to the structural design of elements consisting of two thin metal faces separated by a lightweight core. Various aspects are discussed but two are given particular attention, namely methods of global analysis and the local buckling of compressed face elements. The analysis of sandwich panels under all possible loading and boundary conditions no longer poses any problem. Classical solutions, approximate solutions and numerical methods such as finite elements all have their place and are reviewed in detail. Local buckling phenomena in sandwich elements are similar to those in other thin-walled metal elements with the added consideration that buckling is resisted by the core material. This leads to some quite complex analysis which requires simplification for practical design. The paper includes a useful bibliography of recent references.     

复合约束方钢管混凝土短柱轴压性能有限元分析

为延缓轴压作用下方钢管的局部屈曲,提高方钢管对核心混凝土的约束能力,提出了一种内置方形箍筋的复合约束方钢管混凝土柱。采用有限元软件ABAQUS对该柱进行模拟,研究其在轴向压力作用下的破坏模式、承载能力、延性、箍筋应力分布和复合约束特性,并分析了混凝土强度、方钢管壁厚对其轴压力学性能的影响。研究结果表明：提高混凝土强度、增加方钢管厚度和增设方形钢筋笼均能显著提高短柱的承载能力;方形箍筋在弹性阶段约束作用较小,其主要在弹塑性阶段和流塑性阶段发挥约束作用,设置方形箍筋可以有效提高短柱承载能力和延性,且其对延性的提高更为显著;方钢管对混凝土的约束作用整体表现为“角部大”的特点,方形箍筋可以有效增强对方钢管边长中部区域混凝土的约束作用,进而使混凝土在各方向受到的约束作用趋于均匀。