椭圆抛物面双曲扁壳在均匀外压作用下的非线性弹性稳定性

本文研究了椭圆抛物面双曲扁壳在均匀外压作用下的非线性弹性稳定问题。文中指出不等曲率双曲扁壳的局部失稳周界可视为一椭圆(等曲率时为一个圆),其半轴长之比与壳面相应的曲率开平方成反比;文中用广义伽辽金变分方程求得了与能量法一致的结果,提出了临界荷载的实用公式,并得到了模型试验的证实。     

四类薄壳的临界荷载和失稳模态分析

本文应用非线性有限元法对球壳、扭壳、双曲扁壳和马鞍形壳在不同矢高情况下进行屈曲分析，获得了临界状态下的失稳模态和临界荷载。在此基础上找到了一些规律，供有关工程技术人员参考。     

组合型双曲抛物面扭壳仓库

双曲抛物面扭壳的两簇正交母线均为直线,其曲面是由直线移动构成的,在几何学上属于负高斯曲率壳体。扭壳施工时,模板制作和钢筋配置比较简便;单块扭壳可以结合成多种组合型扭壳,能较灵活地适应建筑功能和造型的需要;扭壳屋盖在建筑音响方面,比正高斯曲率壳体(如球壳、双曲扁壳等)优越,不必专作声学处理。由于具有上述特点,扭壳成为建筑中常用的壳型之一。我国近年     

单层双曲椭圆抛物面网壳弹塑性稳定性能

基于通用有限元软件ANSYS及自编的前后处理程序,有计划地针对400余例单层双曲椭圆抛物面网壳结构进行双重非线性全过程分析,系统地考察了屈曲模态、塑性发展分布等特征响应,总结初始缺陷和荷载不对称分布以及考虑材料非线性等因素对网壳弹塑性稳定承载力的影响规律,对现有网壳规程中安全系数取值进行重新核定。结果表明:双曲扁网壳屈曲模态通常表现为局部结点的跳跃失稳,并主要发生在网壳角部支座或边缘跨中位置;有缺陷双曲扁网壳的极限承载力可按完整结构的74%取值,并且此类结构对于荷载不对称分布不敏感;同时建议双曲扁网壳稳定性验算中安全系数的取值应根据不同结构形式和几何参数确定,取值范围为4.67~5.16。     

拟壳法分析双曲率网状扁壳的竖向地震响应

本文利用粗壳法研完了双曲率网状扁壳的动力问题，以两个双重级数为函数，求得了四边简支边界条件下双曲率网状扁壳固有频率的计算公式。在考虑阻尼力的情况下，求得了双曲丰网状扁壳竖向地震响应的解，并且计算公式中的系数可从《建筑抗震设计规范(GBJll-89)》规定的设计反应谱求得，本方法计算简便，电算手算均可。     

华南理工大学体育馆预应力钢筋混凝土双曲抛物面组合扭壳设计

广州大学城华南理工大学体育馆屋盖采用预应力钢筋混凝土双曲抛物面组合扭壳,壳体厚130 mm,屋盖的平面投影长轴99.8 m,短轴70.0 m,水平投影面积约6 568 m2。组合扭壳由四片扭壳组成,支承于周边边缘构件和两榀正交拱架上。两榀落地拱架跨度分别为149.33 m和108.95 m。分析表明：扭壳的控制荷载为竖...     

网格圆柱扁壳的稳定性

本文用将网格壳转化为连续壳的方法建立了网格圆柱扁亮屋盖的稳定平衡微分方程,所得的方程是属于异性圆柱扁壳的方程,并用方法求得简支边界条件的网格圆柱扁壳的临界荷载计算公式。     

四块组合型双曲抛物面扁扭壳的内力分析(上)

本文按弹性有矩理论对四块组合型双曲抛物面扁扭壳的内力分析进行了研究,其中将这种组合型扭壳视为一个整体来进行分析,对壳体顶部十字型非光滑连接问题,采用了脉冲函数。对于在系数中含有脉冲函数的偏微分方程,应用伽辽金变分法做出了解,并提出了改善级数收敛性的措施,得出壳体内力及位移的分布规律,文末还编制了在均布荷载作用下内力及位移的系数表,可供设计时应用。     

带孔简支薄壁梁弯扭屈曲的计算

本文用能量法和数值积分技术 ,提出了腹板开孔的简支薄壁梁在跨中集中荷载作用下的临界弯矩计算方法。利用ANSYSE通用有限元软件 ,采用板壳单元 ,对 1 5组共 30根工字梁进行了整体弯扭失稳分析。分析结果表明 ,本文方法是行之有效的。     

考虑初始缺陷的扭壳、扭网壳的整体稳定分析

本文应用非线性有限元法,对考虑初始缺陷的扭壳、扭网壳进行整体稳定分析,获得了临界状 态时的失稳模态和临界荷载。并在工程实例计算的基础上,找出了一些规律,供工程参考。     

Buckling of compound hyperbolic paraboloidal shells

This paper presents the first elastic buckling analysis of a compound hyperbolic paraboloidal (hypar) shell under a uniformly distributed load. The compound shell is composed of four hypar panels of rectangular ground plan. A special feature of this analysis is the use of the pulse function to deal with the curvature discontinuities at the ridges. The stability-governing equations are derived from the general equations of Reissner for the linear elastic buckling of hypobolic paraboloidal shells, taking into account the curvature discontinuities at the ridges. These equations are then solved in an approximate manner by assuming trigonometric variations of the buckling deformations. Numerical results are presented, which show that the buckling modes of the shell are either symmetrical or antisymmetrical about both axes of symmetry. For antisymmetric buckling, the critical load of the compound shell is the same as that for a single hypar panel.     

The effect of elastic foundations on the nonlinear buckling behavior of axially compressed heterogeneous orthotropic truncated conical shells

The buckling problem of a heterogeneous orthotropic truncated conical shell subjected to an axial load and surrounded by elastic media is analyzed based on the finite deformation theory. Using von-Karman nonlinearity, the governing equations of elastic buckling of heterogeneous orthotropic truncated conical shells surrounded by elastic media are derived. The governing equations are solved using superposition and Galerkin methods and obtained expressions for upper and lower critical axial loads. The influences of elastic foundations, heterogeneity, orthotropy and geometric characteristics on the upper and lower critical loads of conical shells with and without elastic foundations are studied in detail.     

Dynamic torsional buckling of cylindrical shells in Hamiltonian system

By considering the effect of stress waves in a Hamiltonian system, this paper treats dynamic buckling of an elastic cylindrical shell which is subjected to an impact torsional load. A symplectic analytical approach is employed to convert the fundamental equations to the Hamiltonian canonical equations in dual variables. In a symplectic space, the critical torsion and buckling mode are reduced to solving the symplectic eigenvalue and eigensolution, respectively. The primary influence factors, such as the impact time, boundary conditions and thickness, are discussed in detail through some numerical examples. It is found that boundary conditions have limited influence except free boundary condition in the context of the scope in this paper. The localization of dynamic buckling patterns can be observed at the free end of the shell. The new analytical and numerical results serve as guidelines for safer designs of shell structures.     

利用Hamilton函数分析圆柱壳动态扭转屈曲

在Hamilton函数中考虑应力波的影响,研究冲击扭转载荷作用下弹性圆柱壳的动态屈曲。采用辛方法将基本方程转化为对偶变量的Hamilton典型方程。在辛空间将临界扭转和屈曲模式分别简化为求解辛本征值和本征解问题。主要影响因素有冲击时间、边界条件和厚度等,通过数值算例对这些因素进行了详细讨论。研究结果表明,边界条件的影响有限(自由边界条件除外)。在壳体自由端能够观察到局部动态屈曲模式。新的分析和数值模拟结果可作为壳结构的安全设计准则。     

双参数弹性地基上的FGM壳体的热屈曲性能

分析双参数弹性地基上的FGM壳体的热屈曲性能。根据幂律分布,从厚度方向对各个构件的材料性能进行分级。周边的弹性介质被模拟为Pasternak弹性地基。在假定基本关系之后,对温度荷载下及位于双参数弹性地基上的FGM截顶圆锥壳体的稳定性和相容方程式进行分析。通过求解特征值,得到沿壳体厚度方向非线性分布的温度荷载下的基于或不基于弹性地基上的FGM截顶圆锥壳体临界温差。作为一个特殊案例,提出基于或不基于弹性地基上的FGM截顶圆锥壳体的方程。为了保证目前研究的正确性,详细地评价了临界温度的收敛性。     

Robust design of composite cylindrical shells under axial compression — Simulation and validation

Thin-walled shell structures like circular cylindrical shells are prone to buckling. Imperfections, which are defined as deviations from perfect shape and perfect loading distributions, can reduce the buckling load drastically compared to that of the perfect shell. Design criteria monographs like NASA-SP 8007 recommend that the buckling load of the perfect shell shall be reduced by using a knock-down factor. The existing knock-down factors are very conservative and do not account for the structural behaviour of composite shells. To determine an improved knock-down factor, several authors consider realistic shapes of shells in numerical simulations using probabilistic methods. Each manufacturing process causes a specific imperfection pattern; hence for this probabilistic approach a large number of test data is needed, which is often not available. Motivated by this lack of data, a new deterministic approach is presented for determining the lower bound of the buckling load of thin-walled cylindrical composite shells, which is derived from phenomenological test data. For the present test series, a single pre-buckle is induced by a radial perturbation load, before the axial displacement controlled loading starts. The deformations are measured using the prototype of a high-speed optical measurement system with a frequency up to 3680 Hz. The observed structural behaviour leads to a new reasonable lower bound of the buckling load. Based on test results, the numerical model is validated and the shell design is optimized by virtual testing. The results of test and numerical analysis indicate that this new approach has the potential to provide an improved and less conservative shell design in order to reduce weight and cost of thin-walled shell structures made from composite material.     

Lateral buckling analysis of thin-walled laminated composite beams with monosymmetric sections

Lateral buckling of thin-walled composite beams with monosymmetric sections is studied. A general geometrically nonlinear model for thin-walled laminated composites with arbitrary open cross-section and general laminate stacking sequences is given by using systematic variational formulation based on the classical lamination theory. All the stress resultants concerning bar and shell forces are defined, and nonlinear strain tensor is derived. General nonlinear governing equations are given, and the lateral buckling equations are derived by linearizing the nonlinear governing equations. Based on the analytical model, a displacement-based one-dimensional finite element model is developed to formulate the problem. Numerical examples are obtained for thin-walled composite beams with monosymmetric cross-sections and angle-ply laminates. The effects of fiber orientation, location of applied load, modulus ratio, and height-to-span ratio on the lateral buckling load are investigated. The torsion parameter and a newly-defined composite monosymmetry parameter are also investigated for various cases.     

Shear-flexible thin-walled element for composite I-beams

A shear-flexible finite element based on an orthogonal Cartesian coordinate system is developed for the flexural and buckling analyses of thin-walled composite I-beams with both doubly and mono-symmetrical cross-sections. Using the first-order shear deformable beam theory, the derived element includes both the transverse shear and the restrained warping induced shear deformations. Governing equations are derived from the principle of minimum total potential energy. Three different types of finite elements, namely, linear, quadratic and cubic elements are developed to solve the governing equations. The geometric stiffness for the buckling analysis of axially loaded, thin-walled composite beams is developed. The resulting linearized buckling problem is solved using a shifted inverse iteration algorithm. A parametric study of the effects of the aspect ratio and the fibre orientation on the tip displacement is presented. The convergence of the elements is also investigated. The elastic buckling loads for mono- and doubly-symmetric I-beam cross-sections are compared with other results available in the literature and with solutions using shell elements in a commercially available finite element program.     

Instability of cracked CFRP composite cylindrical shells under combined loading

Numerical analysis of cracked composite cylindrical shells under combined loading is carried out to study the effect of crack size and orientation on the buckling behavior of laminated composite cylindrical shells. The interaction buckling curves of cracked laminated composite cylinders subject to different combinations of axial compression, torsion, internal pressure and external pressure are obtained, using the finite element method. In general, the internal pressure increases the critical buckling load of the CFRP cylindrical shells while torsion and external pressure decrease it. Numerical analyses show that axial crack has the most detrimental effect on the buckling load of a cylindrical shell while for cylindrical shells under combined external pressure and axial load, the global buckling shape is insensitive to the crack length and crack orientation.     

Finite strip elastic buckling solutions for thin-walled metal columns with perforation patterns

Approximate finite strip eigen-buckling solutions are introduced for local, distortional, flexural, and flexural-torsional elastic buckling of a thin-walled metal column with perforation patterns. These methods are developed to support a calculation-based strength prediction approach for steel pallet rack columns employing the American Iron and Steel Institute׳s Direct Strength Method, however they are generally posed and could also be useful in structural studies of thin-walled thermal or acoustical members made of steel, aluminum, or other metals. The critical elastic global buckling load including perforations is calculated by reducing the finite strip buckling load of the cross-section without perforations using the weighted average of the net and gross cross-sectional moment of inertia along the length of the member for flexural (Euler) buckling, and for flexural-torsional buckling, using the weighted average of both the torsional warping and St. Venant torsional constants. For local buckling, a Rayleigh–Ritz energy solution leads to a reduced thickness stiffened element equation that simulates the influence of decreased longitudinal and transverse plate bending stiffness caused by perforation patterns. The cross-section with these reduced thicknesses is input into a finite strip analysis program to calculate the critical elastic local buckling load. Local buckling at a perforation is also treated with a net section finite strip analysis. For distortional buckling, a reduced thickness equation is derived for the web of an open cross-section to simulate the reduction in its transverse bending stiffness caused by perforation patterns. The approximate elastic buckling methods are validated with a database of 1282 thin shell finite element eigen-buckling models considering five common pallet rack cross-sections featuring web perforations that include 36 perforation dimension combinations and twelve perforation spacing combinations.