厚度阶梯式改变圆柱壳体在均匀外部压力作用下的屈曲分析

厚度呈阶梯式改变圆柱壳体结构在工程实践中有着广泛的应用,例如垂直安放的各种容器和筒仓结构。这类结构在空置或部分空置时,在外部压力的作用下易发生屈曲破坏。由于壳体复杂的厚度变化形式,屈曲模态可能有多种形式,如何准确地判断壳体的屈曲模态是此类结构设计时的一个难题。提出一种新的方法——"加权平均厚度方法",这种方法可以对任何厚度阶梯式改变的短、中等长度圆柱壳体结构进行稳定性分析。用此方法得到的结果与利用有限元软件ABAQUS得到的精确结果以及用当前欧洲规范得到的结果进行对比,结果表明,"加权平均厚度方法"可以对厚度阶梯式改变的短、中等长度圆柱壳体在外部均匀压力作用下的屈曲强度及屈曲模态进行非常准确的评估。     

外压作用下偏心加劲功能梯度圆柱壳的非线性屈曲和后屈曲分析

通过解析法研究外压作用下功能梯度加劲薄圆柱壳的非线性屈曲和后屈曲性能。通过其在内部的偏心环和纵梁对壳体进行加固,假定壳体和加固件的材料性能在厚度方向为连续梯度。根据VonKarman理论中的刚度法和传统的壳理论推导出基本关系和平衡方程,可更准确地选择三种关于挠曲的近似公式,且使用盖勒金法得出的显式表达式可以推测出临界荷载和后屈曲压力-挠曲曲线。数值结果显示了加固件能有效地增强壳体稳定性。     

扭转作用下有缺陷柱形壳的屈曲和后屈曲性能

分析扭转作用下有缺陷柱形壳的屈曲和后屈曲性能。基于Karman-Donnell-Type非线性微分方程建立计算公式,采用壳屈曲的边界层理论进行分析,以获得能严格满足边界条件的解决方案。采用奇摄动技术,以确定屈曲载荷和后屈曲平衡路径。数值结果显示,目前的理论能对柱形壳的后屈曲性能进行较好评估。同时分析了几何参数对柱形壳的屈曲和后屈曲性能的影响。证实了扭转作用下柱形壳的后屈曲平衡路径并不稳定,并且相对更短的壳体具有更高的后屈曲平衡能力。最后,指出初始缺陷对柱形壳屈曲和后屈曲性能的影响。对具有初始横向挠曲的有缺陷壳体的分析结果显示：即便是非常小的缺陷,也确实会减少屈曲承载力,并使得后屈曲稳定性变差。扭转作用下柱形壳的屈曲和后屈曲性能显示出明显的缺陷敏感性。此外,如果缺陷更大,那么带来的影响也随之会变得更大。     

受损圆柱壳体压缩试验

压缩作用下壳体结构初始缺陷的敏感性已得到广泛研究。然而,由于受损的形状和程度范围很广,受损结构的实际性能有待进一步研究。对受损壳结构试件的屈曲和失效模式进行了试验。研究结果可用于径厚比类似的多种圆柱壳体。     

某复杂高层混合结构屈曲分析

对本工程从整体到局部进行了屈曲分析,采用SAP2000有限元分析程序对结构进行整体屈曲分析,综合考虑周围构件的边界约束条件,并用大型有限元软件ANSYS对单根柱进行屈曲分析,主要研究结构中的抗风水平桁架的弹性支承作用对所支承柱稳定性的提高作用.分析结果表明,抗风桁架改变了所支承柱的屈曲模态,提高柱子的屈曲荷载;荷载的分布形式对结构的屈曲荷载有一定的影响;在边界条件模拟合适的情况下,局部模型的屈曲分析也能取得可靠的结果.     

强冰雪灾害下大型薄壁圆柱钢壳结构稳定性研究

2008年我国南方地区发生强冰雪灾害,造成不少钢结构破坏。在化工、电力等工程中有很多作为整个系统关键设备的大型薄壁圆柱钢壳结构,柱壳内通常需设置一些横梁支承工艺设备,壳体既受到由上部壳体、顶盖和设备自重等荷载形成的沿环向均匀分布的整体轴向压力,又受到横梁支座传递来的局部轴向压力。在这些荷载作用下结构已经积累了一定的内力和变形,一旦再遭受强冰雪灾害,面积较大的顶盖和相连的其他管道上会快速积聚较大的雪荷载,导致结构发生失稳破坏。根据结构施工和使用过程,考虑加载路径的影响,先施加整体均布轴向压力,再施加局部轴向压力,然后施加模拟强积雪荷载的均布轴向压力,对112个带焊缝初始缺陷的薄壁圆柱壳结构进行了非线性稳定性数值分析。研究表明:随着初始整体荷载水平提高,柱壳承受积雪荷载的能力下降;随着缺陷幅值的增大,柱壳承受积雪荷载的稳定承载力与整体均布轴压下的稳定设计承载力的比值增大,其后屈曲承载能力也提高。柱壳下部储有浆液时;壳体承受积雪荷载的能力有小幅提高。根据大量计算结果,提出了考虑加载历史的遭受强冰雪荷载的圆柱壳稳定性设计建议。     

复合圆柱形壳在径向冲击荷载和轴压荷载作用下的瞬时动力响应

基于首次逼近理论,利用第一阶剪切变形理论对圆柱形壳的自由和强迫振动进行分析。边界条件（BCs）考虑为悬臂状态。分析复合壳体在横向冲击和轴向压力作用下的动力响应（轴压荷载小于临界屈曲荷载）,同时对复合柱形壳进行了建模分析。利用卷积积分对给定荷载状况下的壳体进行分析。揭示纤维方向、轴向荷载及一些几何参数对壳体时间响应的影响。结果表明：动力响应主要由结构的自振周期所控制。     

单层组合加肋拱支网壳的稳定性

介绍了某相贯单层组合加肋拱支网壳结构在竖向荷载及风荷载作用下的整体稳定性。采用有限元软件MIDAS,在两种荷载工况下分别进行了此网壳结构的特征值屈曲、几何非线性屈曲分析,初始缺陷对网壳结构的整体稳定性影响分析。结果表明:网壳结构对初始缺陷较为敏感,初始缺陷会明显降低结构稳定性;不同的荷载工况下,失稳的情况亦不同且网壳结构稳定临界系数随着荷载的增大而降低。     

风压下钢储罐屈曲荷载下限值计算的难点

介绍通用有限元代码编写的一种缺陷敏感壳单元,用于计算壳体屈曲荷载的下限值。风压下两种形状的钢储罐的稳定性较好,分别为:锥形顶式和顶部开口式。分析这两种钢储罐的一些几何关系,用于找出尺寸改变而引起的变化。折减能量法用于计算极限风压下钢储罐屈曲强度的下限值,而且将下限值与采用同一模型的静态非线性分析结果进行了比较。为优化原假设理论得到的结果,提出了实现折减能量法的另一个新思路。     

考虑竖向荷载影响的结构水平临界荷载分析

讨论了结构竖向荷载和水平向屈曲临界荷载的相互影响,分析了研究竖向荷载作用下结构水平临界荷载计算的必要性,并给出了其特征屈曲临界荷载计算的具体过程,通过算例分析,得到了某一结构竖向荷载和水平向临界荷载的相互关系,并提出了稳定区的概念及判断实际结构稳定性的具体方法。     

Non-standard stabilization of the post-buckling path for elastic–plastic cylindrical shells under combined state of loadings

The post-buckling behavior of elastic–plastic cylindrical shells under external pressure and twisting moment is unstable. The effect of stabilization of the post-buckling behavior is in most cases obtained by changing geometry of the structure. In this paper an alternative concept of modification of the post-buckling behavior is applied, namely modification of post-buckling path is achieved by application of additional loadings acting on the structure without changing the shape or sizes of the optimized element. Calculations are performed using ANSYS code for elastic–plastic shells of different length and thickness for the whole range of load from a pure external pressure to a pure twisting moment. It turned out that the active stabilizing force can always stabilize the post-buckling paths whereas the passive and ‘mixed’ variant of stabilizing loads are able to stabilize the post-buckling paths only for thicker elastic–plastic shells and for limited states of loading.     

A rigorous method for the analysis of localization of axisymmetric buckling patterns in thick cylindrical shells

This paper theoretically investigates the localization of axisymmetric buckling patterns in cylindrical shells because this phenomenon has a large influence on the strength degradation in the post-buckling range. The localization behavior is caused by a plastic bifurcation on the decreasing equilibrium path subsequent to the maximum load point. Thus, we first show a rigorous numerical method based on the finite-element method technique for analysis of plastic bifurcation under two-axial stresses. Then, using this method, we examine how the structural parameters, constitutive models and boundary conditions affect the deformation capacity of cylindrical shells.     

Post-buckling behaviour of prestressed steel stayed columns

A steel column that is reinforced by prestressed stays generally has an increased strength in axial compression. A geometrically nonlinear model accounting for the post-buckling behaviour of the stayed column is formulated using the Rayleigh–Ritz method and then validated using the finite element method. It is found that the post-buckling behaviour is strongly linked to the level of the initial prestress. As the prestress is increased, the following different levels of the responses can be observed in sequence: initial Euler buckling that subsequently restabilizes strongly, the critical load increasing with a post-buckling path that is either stable or unstable, an upper limit for the critical load where the post-buckling is unstable after an initially rather flat response. These findings are important for designers aiming to achieve safer and more efficient designs for this structural component.     

Finite element based coupled mode initial post-buckling analysis of a composite cylindrical shell

This paper presents a finite element formulation of Koiter's initial post-buckling theory using a multi-mode approach. Initial post-buckling theory provides direct information about the imperfection sensitivity of a structure under compressive loading, and is also the basis of a nonlinear reduced order model. The objective of the present work is to illustrate the capability of the implementation for buckling analysis of shell structures including modal interaction. A coupled mode initial post-buckling analysis for a composite cylindrical shell under axial compression, including the effect of a nonlinear pre-buckling state, has been carried out using a small number of representative modes. For small imperfection amplitudes the limit-point buckling loads obtained with the reduced order model compare reasonably well with full model nonlinear analysis, illustrating that a fast prediction of the coupled mode response of imperfect shells is possible using the approach proposed.     

Buckling and post-buckling behaviour of elastic seven-layered cylindrical shells – FEM study

The paper is devoted to buckling and post-buckling problems of an elastic seven-layered cylindrical shell under uniformly distributed pressure. The shell is an untypical sandwich structure composed of main corrugated core and two three-layer faces. Numerical FEM model for the shell has been elaborated. The calculations have been performed with the use of the ANSYS code for elastic shells of different dimensions. The linear and non-linear analyses of the shells have been performed with the use of the finite elements method. Critical pressure and equilibrium paths for the family of seven-layered shells subjected to uniformly distributed external pressure are calculated. The influence of corrugation pitch of main core and the length of the shell on the critical pressure has been determined. The results of these investigations are presented on the graphs.     

The effects of bend–twist coupling on the post-buckling characteristics of composite laminated plates using semi-energy finite strip approach

In composite laminated plates various mechanical properties may be attained by changing the lay-up arrangement. The bent–twist coupling is one of the significant properties which dominate the mechanical performance of a laminated plate structure in large out-of-plane deformations. The effects of bend–twist coupling on the post-buckling behavior of composite laminated plates have been studied in this paper by implementing a finite strip approach based on the concept of a rigorous post-buckling solution for composite plates and plate structures, namely the semi-energy approach. All the plates are assumed to be symmetrically balanced laminates having uniform in-plane stiffness properties. As far as the out-of-plane stiffness properties are concerned, all the properties, except for the bend–twist coupling terms which are assumed to change from one laminate to another, are the same among different laminates. The orthotropic solutions have also been determined by precluding the bend–twist coupling terms. A comprehensive set of parametric studies have been carried out to investigate the effects of bend–twist coupling terms on the post-buckling load–displacement path, post-buckling deformations and stress distribution. The comparison between the results revealed markedly different behaviors among different laminates due to the bend–twist coupling effects. The outcome of the paper can help structural designers to have a better understanding of the effects of bend–twist coupling terms on the post-buckling behavior of laminated composite plates at the design stage.     

Local–global mode interaction in stringer-stiffened plates

A recently developed nonlinear analytical model for axially loaded thin-walled stringer-stiffened plates based on variational principles is extended to include local buckling of the main plate. Interaction between the weakly stable global buckling mode and the strongly stable local buckling mode is highlighted. Highly unstable post-buckling behaviour and a progressively changing wavelength in the local buckling mode profile are observed under increasing compressive deformation. The analytical model is compared against both physical experiments from the literature and finite element analysis conducted in the commercial code Abaqus; excellent agreement is found both in terms of the mechanical response and the predicted deflections.     

Combined axial and pressure buckling of end supported shells of revolution

A reduced stiffness theoretical analysis of the imperfection sensitive elastic buckling for end supported shells of revolution is extended to the case of arbitrary combinations of axial and radial pressure loading. Depending upon the shell and loading parameters, the potential reductions in load capacity due to imperfections are shown to involve two distinct forms of post-buckling loss of stiffness. Lower bounds in each of these regimes are provided by appropriate reduced stiffness models, and shown by comparisons with available test data to be reliable even for relatively perfect test models. By attributing reductions in load carrying capacity to weakened end support conditions, it is suggested that past interpretations of these tests may have underestimated the deleterious effects of initial imperfections.