薄壁复合箱型梁的弯曲—扭转屈曲分析

对一轴心受压薄壁复合构件的屈曲进行研究。提出一个广义的分析模型，可用于分析轴心受压薄壁复合箱型梁的弯曲、扭转以及弯扭屈曲作用。此模型基于经典层压理论，考虑了任意层压堆积规律，结构的弯曲和扭转模式的耦合问题，如非对称以及对称和各种边界条件。采用一个基于位移的一维有限元模型来预测薄壁复合钢筋的临界荷载和随后的屈曲模式。从总势能的平稳值原则中推导出屈曲控制方程。轴心受压薄壁复合件的数值计算结果可用于估测纤维角、各向异性和边界条件对临界屈曲荷载和复合件模态的影响。     

轴心受压开口薄壁构件弹塑性屈曲荷载的统一计算方法

通过分析构件截面上应变与轴向力间的关系，以构件轴向应变为基本参数，提出了轴心受压开口薄壁构件的弹塑性屈曲荷载统一计算方法，给出了轴压构件的弯曲屈曲、扭转屈曲、弯扭屈曲等屈曲荷载的弦截法迭代格式，可应用于H形、T形、L形、十形截面等不同开口形式的轴压构件屈曲荷载计算，并可考虑具有残余应力的弹塑性本构关系。该方法以无残余应力的弹性屈曲荷载对应的轴向应变作为初始值，根据不同屈曲形式对应的非线性方程计算弦截区间点的函数值，进行弦截法迭代计算，得到弹塑性构件的临界轴向应变，进而获得屈曲荷载等信息。该方法采用的弦截法收敛速度快、计算量小、无需嵌套循环，可有效解决两端铰接轴心受压开口薄壁构件的弹塑性屈曲快速计算问题，便于工程应用。     

冷弯薄壁卷边槽钢畸变屈曲的数值分析

利用大型有限元软件ABAQUS分析冷弯薄壁卷边槽钢受压时的弹性畸变屈曲荷载。首先,分析了ABAQUS建模时各主要参数对分析结果的影响,在此基础上建立了分析模型,然后分别对轴心受压和偏心受压两种荷载情况下冷弯薄壁卷边槽钢的弹性畸变屈曲荷载进行了特征值分析,分析时改变截面组成板件的尺寸,求出对应的畸变屈曲荷载和畸变屈曲半波长;最后,对计算结果进行分析,得出了截面尺寸、偏心荷载与畸变屈曲荷载/半波长的关系。     

基于广义梁理论的非线性材料薄壁受压构件屈曲荷载计算方法

提出适用于非线性材料的广义梁理论屈曲荷载计算方法,并对不锈钢薄壁受压构件屈曲荷载进行计算验证。通过定义材料非线性应力应变关系和瞬时弹性模量,对传统线弹性广义梁理论进行修正,建立非线性材料薄壁构件受压屈曲荷载计算方法,推导不锈钢薄板受压局部屈曲、冷弯薄壁不锈钢卷边槽形柱畸变屈曲及箱形不锈钢长柱弯曲屈曲荷载计算公式,并与既有试验数据对比。经验证,线弹性分析方法不适用于不锈钢材料;提出的修正GBT法具有较高精度,且本构关系采用变形法则结果偏于安全,可用于不锈钢等非线性金属材料薄壁构件受压屈曲荷载的确定,为研究和设计提供理论指导。     

预应力薄壁钢约束圆木柱轴心受压性能分析

为探索出性能更为优越的钢木组合柱,对薄壁圆钢筒施加预应力以形成主动围压,并设定预留量制作了预应力薄壁钢约束圆木柱试件,进行了其轴心受压性能试验,明确了其破坏过程和失效模式;整理获得了荷载-位移关系曲线和荷载-应变关系曲线,以及初始刚度、残余承载比和耗能等轴心受压性能指标,进行了轴心受压性能分析。同时,采用ABAQUS有限元软件开展了预应力薄壁钢约束圆木柱轴心受压试验的数值模拟分析,并提出了其轴心受压极限承载力计算公式。结果表明,预应力薄壁钢约束圆木柱受预留量、螺栓间距、薄壁钢厚度和长细比的影响,表现出四种不同破坏模式;考虑木材和钢材弹性模量差异大而设定一定的预留量,并采用合适薄壁钢厚度、螺栓间距和长细比,预应力薄壁钢约束圆木柱具有较好的轴心受压承载力、初始刚度、残余承载力和耗能等优越轴心受压性能。所建立的预应力薄壁钢约束圆木柱轴心受压有限元模型与轴心受压极限承载力计算公式计算结果与试验结果吻合良好,可用于相应的受力计算分析。     

夹芯板弯曲屈曲分析的有限条-棱方法

用有限条 -棱方法对冷弯薄壁型钢压型表面泡沫夹芯板进行了弯曲屈曲分析 ,得到了夹芯板受压面层屈曲时的临界应力、屈曲荷载及屈曲半波长 ,并与试验结果进行对比 ,理论值与试验值吻合较好     

冷弯开口薄壁帽型截面受压钢构件压弯承载力的研究

对冷弯开口薄壁帽型截面受压构件的压弯极限承载力进行了分析研究,主要考虑构件长细比、荷载偏心距和构件初弯曲对压弯极限承载力的影响。利用MATLAB7.0.1和ANSYS10.0计算得到受压构件基于截面边缘纤维屈服准则的临界荷载和弹性弯扭屈曲荷载,进而利用ANSYS10.0对受压构件的弹塑性极限荷载进行了计算。通过对三种不同的计算方法得到的极限荷载进行比较,分析了冷弯开口薄壁帽型截面受压构件压弯极限承载力的计算方法。结论中评价了单轴对称截面压弯构件的设计公式。研究表明,该设计公式具有一定的安全储备,满足设计要求。     

恒定压力作用下工字型和箱型截面压杆的局部屈曲效应、材料轴向刚度屈服和失效

局部屈曲显著影响薄壁受压构件的性能。局部屈曲将会引起薄壁构件失去轴向受压刚度,并导致受压承载力显著降低。用有限元模拟薄壁工字型和箱型截面压杆的屈曲后效应,并考虑了构件几何初始缺陷和材料非线性影响,给出了局部屈曲后应力发展和应力重分布、荷载作用下开始屈服和屈服发展的详细计算。详细介绍了构件截面平面内板件交点的平面内位移边界条件的影响和基于屈曲后刚度的屈服和破坏。结果显示,几何初始缺陷在屈曲和屈服几乎同时发生的杆件和设计最终破坏和卸载的杆件中的影响非常突出。一般地,几何初始缺陷影响与截面板件交点沿压杆长度的屈服发展和沿截面板件的中部发展有同等重要的地位。     

薄壁渡槽结构的整体稳定性分析

根据矩形薄壁渡槽整体扭转屈曲的变形特点,提出了矩形薄壁渡槽整体扭转屈曲的计算方法。考虑了屈曲前预应力和竖向变形的影响,采用伽辽金法推导了矩形薄壁渡槽的扭转屈曲临界荷载。对于矩形薄壁渡槽,在传统渡槽断面尺寸和跨径下,其侧向扭转屈曲临界应力大于混凝土抗压强度设计值cf,因此,在一般渡槽中不会发生侧向扭转屈曲。如果采用高屈服极限钢材,必须进行稳定性验算,所得结果和结论可为薄壁渡槽整体稳定性设计提供参考。     

局部封闭和开口薄壁压弯构件的弯扭屈曲

单轴对称开口薄壁压弯构件在荷载作用于对称平面内时有可能发生弯扭屈曲。在这种情况下,其临界荷载总是低于平面内弯曲失稳破坏荷载,如果在构件的开口边加上缀板,使之形成若干断续的封闭截面,则弯扭屈曲临界荷载将显著提高,并有可能使破坏模式由弯扭屈曲转化为平面内弯曲失稳。本文提出了一种计算薄壁压弯构件弯扭屈曲荷载的方法,这种方法对局部封闭和开口截面都能适用。曾经做了213根具有不同长细比、偏心距、缀板间距(或无缀板)的冷弯薄壁型钢压杆试验,其结果与理论符合较好。     

Flexural–torsional buckling of thin-walled composite box beams

Buckling of an axially loaded thin-walled laminated composite is studied. A general analytical model applicable to the flexural, torsional and flexural–torsional buckling of a thin-walled composite box beam subjected to axial load is developed. This model is based on the classical lamination theory, and accounts for the coupling of flexural and torsional modes for arbitrary laminate stacking sequence configuration, i.e. unsymmetric as well as symmetric, and various boundary conditions. A displacement-based one-dimensional finite element model is developed to predict critical loads and corresponding buckling modes for a thin-walled composite bar. Governing buckling equations are derived from the principle of the stationary value of total potential energy. Numerical results are obtained for axially loaded thin-walled composites addressing the effects of fiber angle, anisotropy and boundary conditions on the critical buckling loads and mode shapes of the composites.     

薄壁组合箱梁的自由振动

研究薄壁叠加组合梁的自由振动。建立了适用于薄壁组合箱梁截面动力性能的一般分析模型。该模型基于古典叠加理论，考虑任意层压板叠合次序情况下弯曲和扭转的耦合，也就是非对称和对称以及各种边界条件。对薄壁组合梁，建立基于位移的一维有限元模型以预测自振频率和相应的振型，并由Hamilton原理派生出运动方程；考虑薄壁组合梁纤维角度、模数比、振动频率的边界条件以及组合形式的影响，得出计算结果。     

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.     

Analytical and parametric investigations on lateral torsional buckling of European IPE and IPN beams

Lateral torsional buckling is one of the main failure modes controlling the strength of the slender thin-walled members. A transversely or transversely and axially combined loaded member that is bent with respect to its axis of greatest flexural rigidity may buckle laterally and twist as applied load reaches its critical value unless the beam is provided with a sufficient lateral support. This study intends to present a unique convenient equation that it can be used for calculating critical lateral-torsional buckling load of simply supported European IPE and IPN beams. First, an analytical model is introduced to describe lateraltorsional buckling behavior of beams with monosymmetric cross-section. The analytical model includes first order bending distribution, load height level and monosymmetry property of the section. Then, parametric study is carried out using the analytical solutions in order to establish a simplified equation with dimensionless coefficients. The effect of slenderness and loading positions on lateral-torsional buckling behavior of IPE and IPN beams are studied. The proposed solutions are compared to finite element simulations where thin-walled shell elements and beam elements including warping are used. Good agreement between the analytical, parametric and numerical solutions is demonstrated. It is found out that the lateral-torsional buckling load of European IPE and IPE beams can be determined by presented equation and can be safely used in design procedures.

     

Dynamic response of axially loaded monosymmetrical thin-walled Bernoulli–Euler beams

The dynamic bending–torsion coupled vibrations of elastic axially loaded slender thin-walled beams with monosymmetrical cross-sections are investigated by using normal mode method. The Bernoulli–Euler beam theory is employed and the effects of warping stiffness and axial force are included in the present formulations. The theoretical expressions for the displacement response of axially loaded slender thin-walled beams subjected to concentrated or distributed loads are presented. The method is illustrated by its application to two test examples to describe the effects of warping stiffness and axial force on the dynamic behavior of thin-walled beams. The numerical results for the dynamic bending displacements and torsional displacements are given. The proposed theory is fairly general and can be used for thin-walled beam assemblage of arbitrary boundary conditions subjected to various kinds of loads.     

Flexural–torsional behavior of thin-walled composite beams

This paper presents a flexural–torsional analysis of I-shaped laminated composite beams. A general analytical model applicable to thin-walled I-section composite beams subjected to vertical and torsional load is developed. This model is based on the classical lamination theory, and accounts for the coupling of flexural and torsional responses for arbitrary laminate stacking sequence configuration, i.e. unsymmetric as well as symmetric. Governing equations are derived from the principle of the stationary value of total potential energy. Numerical results are obtained for thin-walled composites under vertical and torsional loading, addressing the effects of fiber angle, and laminate stacking sequence.     

Buckling of shear deformable thin-walled members—I. Variational principle and analyticalsolutions

A variational formulation for the buckling analysis of thin-walled members is developed based on the principle of stationary potential energy. The formulation is based on non-orthogonal coordinates and captures shear deformation effects due to bending and warping. It is applicable to members of doubly symmetric cross-sections subject to general axial and transverse forces and naturally incorporates the effect of load position relative to the shear centre. Applying the conditions of neutral stability to the variational expression, the governing differential equations of neutral stability and associated boundary conditions are formulated. The resulting field equations are exactly solved for benchmark cases involving column flexural buckling, column torsional buckling, and lateral-torsional buckling for beams, and the results are compared to closed form solutions based on classical and other modern theories.     

Behavior of biaxially-loaded rectangular concrete-filled steel tubular slender beam-columns with preload effects

In composite construction, rectangular hollow steel tubular slender beam-columns are subjected to preloads arising from construction loads and permanent loads of the upper floors before infilling of the wet concrete. The behavior of biaxially loaded thin-walled rectangular concrete-filled steel tubular (CFST) slender beam-columns with preloads on the steel tubes has not been studied experimentally and numerically. In this paper, a fiber element model developed for CFST slender beam-columns with preload effects is briefly described and verified by existing experimental results of uniaxially loaded CFST columns with preload effects. The fiber element model is used to investigate the behavior of biaxially loaded rectangular CFST slender beam-columns accounting for the effects of preloads and local buckling. Parameters examined include local buckling, preload ratio, loading angle, depth-to-thickness ratio, column slenderness, loading eccentricity and steel yield strength. The results obtained indicate that the preloads on the steel tubes significantly reduce the stiffness and strength of CFST slender beam-columns with a maximum strength reduction of more than 15.8%. Based on the parametric studies, a design model is proposed for axially loaded rectangular CFST columns with preload effects. The fiber element and design models proposed allow for the structural designer to efficiently analyze and design CFST slender beam-columns subjected to preloads from the upper floors of a high-rise composite building during construction.     

Mode interaction in thin-walled equal-leg angle columns

This paper presents and discusses numerical results, obtained through Ansys shell finite element analyses, dealing with the post-buckling behaviour (mostly elastic, but also elastic–plastic), ultimate strength and failure mode nature of fixed-ended and pin-ended thin-walled equal-leg angle steel columns with coincident critical flexural-torsional and minor-axis flexural buckling loads (i.e., experiencing very strong coupling effects between these two global instability phenomena) – for comparative purposes, columns that are buckling in pure flexural-torsional and flexural modes are also analysed. Since the main aim of the work is to investigate the column imperfection-sensitivity, the analyses concern otherwise identical columns containing initial geometrical imperfections with different shapes and amplitudes, combining the competing critical buckling modes – particular attention is paid to the sign of the minor-axis flexural component. The results reported consist of column (i) elastic equilibrium paths and the corresponding peak loads and deformed configurations and (ii) elastic–plastic collapse loads and mechanisms, making it possible to assess how they are influenced by the initial geometrical imperfections.     

A theoretical analysis of the local buckling in thin-walled bars with open cross-section subjected to warping torsion

Results of a theoretical analysis of the local buckling in thin-walled bars with open cross-section subjected to warping torsion are presented. The local critical bimoment, which generates local buckling of a thin-walled bar and constitutes the limit of the applicability of the classical Vlasov theory, is defined. A method of determining local critical bimoment on the basis of critical warping stress is developed. It is shown that there are two different local critical bimoments with regard to absolute value for bars with an unsymmetrical cross-section depending on the sense of torsion load (sign of bimoment). However, for bars with bisymmetrical and monosymmetrical sections, the determined absolute values of local critical bimoments are equal to each other, irrespective of the sense of torsional load. Critical warping stresses, local critical bimoments and local buckling modes for selected cases of thin-walled bars with open cross-section are determined.