工字形截面楔形梁的弹性稳定分析

采用摄动法研究了钢结构中常见的工字形截面楔形梁的弹性稳定,并求得工字形截面楔形梁发生弹性失稳时的屈曲模态,利用此屈曲模态函数,即可得到确定工字形截面楔形梁屈曲载荷的特征方程.     

基于板-梁理论的集中荷载下带侧向弹性支撑矩形钢管混凝土翼缘工字形梁的弯扭屈曲分析

基于板-梁理论和能量变分原理,建立集中荷载下跨中布置侧向弹性支撑的矩形钢管混凝土翼缘工字形简支梁的弯扭屈曲总势能方程,其中位移和转角模态试函数选用6项三角级数形式.引入无量纲参数并依据势能驻值原理,获得弯扭屈曲无量纲临界弯矩解析解.采用1stOpt数学优化分析软件,拟合矩形钢管混凝土翼缘工字形简支梁无量纲临界弯矩计算公...     

轴向及弯曲荷载作用下薄壁梁柱构件的侧向屈曲

基于非线性稳定模型,推导出弯曲和轴向荷载作用下具有双向对称I型截面的简支梁柱构件的分析方案。设计中对一些具有代表性的荷载工况提供了一种独特紧凑的截面形式。分析中考虑了一阶弯曲分布,装载高度,预屈曲挠度效应和轴向荷载。通过采用壳单元的非线性有限元分析对建议的解决方案进行验证。所提议方法与非线性平衡方程计算结果能很好地吻合,证明古典线性稳定性的解决方案低估了这种构件在侧向屈曲稳定中的抵抗能力,尤其是大翼缘的I型截面。对轴力在超静定梁的抗侧向屈曲中所起作用进行数值研究,发现：当梁的轴向变形受到限制时会在梁中产生轴拉力作用,这导致了一些梁截面变形减小,梁呈现出无分叉的非线性性能。     

楔形悬臂梁的侧扭屈曲分析

根据总势能公式引入无量纲参数,利用能量变分法推导出楔形悬臂梁侧扭屈曲临界荷载的近似求解公式。采用有限元软件Abaqus对理论计算结果进行了验证,理论计算与数值计算结果吻合良好,验证了理论公式的正确性。最后,分析了小截面高度与大截面高度的比值和跨度对误差产生的影响,可为完善钢结构设计规范提供有利依据。     

双轴对称楔形工字钢梁的弹性弯扭屈曲

本文利用基于板壳屈曲理论的有限元方法对楔形薄壁构件的弯扭屈曲进行了分析,对两种基于薄壁杆件理论的楔形工字钢梁弯扭屈曲分析方法进行了对比。基于较精确的楔形薄壁构件屈曲理论,对承受线性变化端弯矩作用的楔形梁的弯扭屈曲进行了大量分析,并提出了新的楔形工字钢梁临界弯矩计算公式。该公式形式与等截面梁的相同,便于工程应用。     

波浪腹板门式刚架侧向变形计算研究

为补充完善波浪腹板门式刚架侧向变形的空白,基于波浪腹板工形构件的受力特性,提出了适用于计算波浪腹板工形构件变形的两种梁单元有限元简化模型,通过与壳单元对比及模型参数敏感性分析,验证了梁单元简化模型的准确性和可靠性。此外,通过理论推导和有限元计算,提出了适用于单跨等截面、单跨变截面及多跨波浪腹板门式刚架侧向变形的计算方法;其中考虑了柱脚边界条件、斜梁坡度、侧向荷载作用点和分布形式等诸多因素的影响。     

考虑轴力和剪切变形影响的楔形梁自由振动分析

通过建立楔形梁包含轴力和剪切变形影响的平衡微分方程,以及寻求该方程的级数解得到楔形梁的 单元刚度矩阵,并运用所得的矩阵对腹板高度线性变化的工字形截面楔形简支梁的自由振动进行数值计算,分 析了多种因素对这种梁自由振动的影响．     

交叉梁系结构中变截面杆件(矩形截面抛物线楔形梁)的计算问题

矩形截面抛物线楔形梁作为一种变截面杆件在平面楼盖等交叉梁系结构中经常使用.本文通过求矩形截面抛物线楔形梁的单元柔度系数和刚度系数,提出了交叉梁系结构中矩形截面抛物线楔形梁的单元刚度矩阵,通过求矩形截面抛物线楔形梁的载常数,提出了交叉梁系结构中矩形截面抛物线楔形梁上几种作用荷载的等效节点荷载.     

基于等效刚度的蜂窝梁弯扭屈曲临界荷载计算方法

蜂窝梁是在梁腹板上开有连续规则孔洞的一种钢梁,腹板开孔后对其抗侧刚度有较大的削弱,因此整体稳定性能是蜂窝梁的重要问题。基于能量法推导出实腹梁弯扭屈曲临界荷载的计算式,采用等效刚度的方法,通过等效侧向抗弯刚度、等效翘曲刚度和等效扭转刚度推导了蜂窝梁的弯扭屈曲临界荷载的计算式。其次,考虑蜂窝梁截面尺寸、跨度、开孔率和距高比的影响,采用有限元方法对圆形孔和六边形孔蜂窝梁的弯扭屈曲进行了分析,得到了蜂窝梁弯扭屈曲临界荷载的变化规律,并验证了蜂窝梁弯扭屈曲临界荷载计算式的正确性,可为蜂窝梁的整体稳定设计提供参考。     

考虑荷载偏心的梯形波纹腹板工字梁弯矩修正因子

对不同荷载偏心和端部约束条件下梯形波纹腹板工字梁的弯矩修正因子进行研究。通过有限元屈曲分析获取弯曲修正因子。采用梁单元、新横截面属性公式及新梯形波纹腹板工字梁翘曲常数,建立有限元程序。将弯矩修正因子的理论结果与软件ABAQUS的壳单元模拟结果进行对比。以波纹形式和长度为参数,进行了大量有限元分析。通过数值研究,对理论结果进行验证,并将SSRC规范中的弯矩修正因子与有限元结果对比。将SSRC规范中弯矩修正因子Cb改进为Cb,c,提高了侧向畸变屈曲强度的准确性。     

Lateral buckling of web-tapered I-beams: A new theory

This paper presents a new theory for the lateral buckling of web-tapered I-beams. Linear analysis is first conducted by taking account into the tapering effects of web-tapered I-beams, where the deformation compatibilities of the two flanges and web are considered in terms of the basic assumptions of thin-walled members. Subsequently, the total potential for the lateral buckling analysis of web-tapered I-beams is developed, based on the classical variational principle for buckling analysis. The lateral buckling loads of web-tapered cantilevers and simply supported beams of I-sections from the proposed theory are compared with those from the finite element (FE) analyses using two shell element models and two widely used beam element models. The two beam element models respectively represent the equivalent method using prismatic beam elements and the typical tapered beam theory in existing literature. These comparisons show that the results based on the total potential proposed in this paper are more accurate in predicting the lateral buckling loads of web-tapered I-beams than those in existing theories, indicating that the theory proposed in this paper is superior to existing theories. It is also found that the equivalent method using prismatic beam elements may yield unreliable buckling loads of tapered beams.     

残余应力分布对焊接不锈钢工字形截面梁整体稳定性能的影响

焊接残余应力导致不锈钢梁截面纤维过早达到屈服,并严重降低不锈钢梁的抗弯刚度。为了研究残余应力对焊接工字形不锈钢梁侧扭屈曲的影响,根据目前被广泛采纳的不锈钢工字形截面残余应力分布模型,采用有限元方法,对残余应力分布模型的主要因素进行参数化分析,研究这些因素对不锈钢梁侧扭屈曲的影响,使对焊接工字形不锈钢梁的整体稳定性能的研究更加完善。结果表明:翼缘残余压应力峰值对不锈钢梁侧扭屈曲的影响最为显著。     

A numerical and analytical study on distortional buckling of doubly-symmetric steel I-beams

This study investigates the effect of web distortions in a lateral distortional buckling mode on the buckling moments of doubly-symmetric steel I-beams. Analytical buckling moment expressions applicable to both elastic and inelastic lateral distortional buckling were developed. These expressions account for the reductions in the torsional and warping rigidities of I-beams due to web distortions. Numerical results obtained from the finite element analysis showed that the buckling moments of steel I-beams with stocky flanges and slender webs are overestimated by the lateral torsional buckling solutions while the proposed distortional buckling solutions provide estimates in closer agreement with the numerical results. Finally, the lateral torsional buckling solutions in the structural steel standards were found to generally provide conservative buckling moment estimates for doubly-symmetric steel I-beams prone to web distortions.     

Lateral-torsional buckling capacity assessment of web opening steel girders by artificial neural networks — elastic investigation

Bridge girders exposed to aggressive environmental conditions are subject to time-variant changes in resistance. There is therefore a need for evaluation procedures that produce accurate predictions of the load-carrying capacity and reliability of bridge structures to allow rational decisions to be made about repair, rehabilitation and expected life-cycle costs. This study deals with the stability of damaged steel I-beams with web opening subjected to bending loads. A three-dimensional (3D) finite element (FE) model using ABAQUS for the elastic flexural torsional analysis of I-beams has been used to assess the effect of web opening on the lateral buckling moment capacity. Artificial neural network (ANN) approach has been also employed to derive empirical formulae for predicting the lateral-torsional buckling moment capacity of deteriorated steel I-beams with different sizes of rectangular web opening using obtained FE results. It is found out that the proposed formulae can accurately predict residual lateral buckling capacities of doubly-symmetric steel I-beams with rectangular web opening. Hence, the results of this study can be used for better prediction of buckling life of web opening of steel beams by practice engineers.     

Cyclic testing of a metal building moment frame system with web-tapered members

Cyclic testing of a full-scale metal building with built-up, web-tapered members was carried out as part of an effort to develop a seismic design procedure for this type of moment frame system. The test building was designed as an Ordinary Moment Frame (OMF) with bolted end-plate moment connection. Test results showed that the system had a very high deformability; the elastic behavior was observed up to more than 2% story drift. But the ductility of the test frame was limited; the system failed at 2.6% story drift due to lateral–torsional buckling of the web-tapered members with a significant strength degradation. The testing also revealed that improper flange bracing with slotted bolt holes could jeopardize the resistance of the framing system with premature lateral–torsional buckling. The experimentally derived member forces and the associated failure mode correlated well with the code provisions for strength evaluation of web-tapered members. The lateral bracing force of the rafter reached 2.6% of the nominal yield strength of the flange.     

On the application of the extrapolation techniques in elastic buckling

The critical buckling load of a structure undergoing lateral buckling can be determined experimentally by using the extrapolation or plotting techniques, without having to subject the structure to loading in the vicinity of critical. To achieve this, it is only necessary to have data relating load to a deformation characteristic. A search of the literature reveals that only certain and just a few deformation characteristics such as lateral displacement and/or twist have mostly been used by researchers in this regard. In this paper, the feasibility of application of various deformation variables for experimental determination of the critical buckling load is investigated in case of I-beams with different initial geometrical imperfections undergoing the elastic lateral-distortional mode of buckling. It is demonstrated that lateral displacement of the I-beams is directly coupled with different deformation variables such as web transverse and longitudinal strains, vertical deflection, and angles of twist of top and bottom flanges. Based on these key findings, the Southwell, Massey, Modified, and Meck Plot methods are applied on these various deformation variables, and consequently satisfactory and reliable estimates are obtained for the critical buckling loads. Finally, it may be concluded that the application of the extrapolation techniques does not actually need to be limited to some certain deformation variables.     

I型组合梁截面的局部与整体相关屈曲

在弯扭失稳(LTB)和受压翼缘局部失稳(FLB)2种极限状态下,根据钢结构规范(AISCLRFD360-10)得到的具有紧密腹板且没有紧密翼缘或细长翼缘的I型梁截面的名义受弯承载力可能偏低。该方法的主要假设是LTB和FLB是2个独立的状态,之间无相互作用。本文采用ABAQUS建立三维有限元模型对没有紧密翼缘或细长翼缘的I型梁进行非线性分析。通过估算具有不同翼缘长细比的局部屈曲的I型组合钢梁的抗弯承载力,以验证AISC-LRFD方法的适用性。研究发现整体和局部屈曲能力相差加大,故应考虑FLB和LTB之间的相关屈曲作用;对本文给出的梁还应考虑其局部屈曲后性能。     

焊接不锈钢工字形截面梁整体稳定性试验研究

不锈钢材料在建筑结构中已得到广泛应用。为研究焊接不锈钢梁的整体稳定性能,进行了纯弯状态下的静力试验研究。试验包括10个试件,材料类型为奥氏体型316。截面类型采用了双轴对称和单轴对称工字形截面,试件的端部约束采用夹支,试验过程持续加载,直至达到试件的承载力峰值。基于试验结果,研究了焊接不锈钢梁的失稳破坏形态和极限承载力;对比了试验极限弯矩与理论弹性弯矩、塑性弯矩的差异,并将试验结果与有限元分析结果进行了对比。结果表明：试件的承载能力随着跨度的增大而减小,有限元分析能够准确预测试件的承载力,与试验结果吻合良好。     

Interaction of buckling modes in castellated steel beams

This paper investigates the behaviour of normal and high strength castellated steel beams under combined lateral torsional and distortional buckling modes. An efficient nonlinear 3D finite element model has been developed for the analysis of the beams. The initial geometric imperfection and material nonlinearities were carefully considered in the analysis. The nonlinear finite element model was verified against tests on castellated beams having different lengths and different cross-sections. Failure loads and interaction of buckling modes as well as load-lateral deflection curves of castellated steel beams were investigated in this study. An extensive parametric study was carried out using the finite element model to study the effects of the change in cross-section geometries, beam length and steel strength on the strength and buckling behaviour of castellated steel beams. The parametric study has shown that the presence of web distortional buckling causes a considerable decrease in the failure load of slender castellated steel beams. It is also shown that the use of high strength steel offers a considerable increase in the failure loads of less slender castellated steel beams. The failure loads predicted from the finite element model were compared with that predicted from Australian Standards for steel beams under lateral torsional buckling. It is shown that the Specification predictions are generally conservative for normal strength castellated steel beams failing by lateral torsional buckling, unconservative for castellated steel beams failing by web distortional buckling and quite conservative for high strength castellated steel beams failing by lateral torsional buckling.     

Nonlinear viscoelastic analysis of thin-walled beams in composite material

Laminated composites of polymeric matrix show anisotropic viscoelastic behaviour, enhanced by temperature and humidity effects. The consideration of anisotropy and viscoelasticity are important for the determination of deformations and, as a consequence, of deformation-related phenomena, as elastic and creep buckling. This paper studies the behaviour of thin-walled beams of composite material under flexure and buckling, taking account of creep effects. The analysis uses a nonlinear viscoelastic finite element code with shell elements, whose basic formulation is given. The use of shell elements allows a better representation of constitutive properties and boundary conditions. Comparison with available analytical results is made for several cases like flexure of an I beam, buckling of beam columns and lateral buckling of this beams. The results show good correlation.