设加劲肋防止畸变屈曲卷边Z型钢梁的性能研究

采用设置加劲肋的方法控制冷弯薄壁卷边Z型钢梁在均布荷载作用下的畸变屈曲,应用有限元软件ABAQUS分别对4种带有加劲肋不同卷边角度的冷弯薄壁卷边Z型钢梁进行分析。综合考虑屈曲荷载的提升程度和用钢量,给出最佳加劲肋形式。研究结果表明卷边角度越小,加劲肋加固效果越好。     

局部屈曲或局部和畸变屈曲综合作用下冷弯型钢梁的有限元模拟

有限元法可以解决冷弯钢梁复杂的相关联屈曲问题,其中包括很多重要的关键因素:几何缺陷、材料非线性和后屈曲等。也是该方法与其他分析方法的不同之处。根据特定的冷弯Z型钢梁的材料和几何非线性建立了两类研究屈曲性能的有限元模型。其中,一个模型用于分析局部和畸变屈曲综合作用,而另一个仅用于分析局部屈曲。通过先前的四点弯曲试验证实了有限元模型的有效性。利用ABAQUS软件,模拟了一个简化的试验装置。在局部屈曲有限元模型中,通过在梁翼缘角部设置弹簧以防止畸变屈曲。由于更多的模型与试验结果相吻合,证实了对承载力和变形的预测。未来的研究将优化有限元模型,以得到侧向受约束的冷弯型钢梁不同的屈曲形式,如:局部,畸变或局部与畸变综合作用。     

集中荷载作用下卷边Z型钢檩条防畸变屈曲研究

为预防冷弯薄壁Z型钢檩条畸变屈曲的发生,采用有限元软件ABAQUS分别对承受跨中和三分点处集中荷载的简支Z型钢檩条进行防畸变屈曲研究,对比分析了四种形式的隔板对四种卷边角度的Z型钢檩条的加固效果和经济性。结果表明,仅在檩条的受压部分布置隔板材料的隔板d最有效,在设计的四种隔板加固形式中,隔板形式d的单位用钢量对屈曲荷载提升最大,且防畸变屈曲加固效果不弱于其他三种隔板形式,从经济性上应优先考虑。     

卷边加强冷弯型钢梁局部和畸变屈曲

设计时,应重点考虑冷弯型钢构件的屈曲特性及其导致的有效性损失,以保证结构的经济性。数值模型改进后,能够反映考虑几何缺陷、材料非线性特性、后屈曲性能等因素的冷弯型钢梁的真实屈曲特性。针对侧向约束下冷成型Z型钢梁,采用已有的有限元模型,研究钢梁卷边及其与受压翼缘的相互作用对后屈曲特性的影响。利用卷边翼缘宽度比以及卷边倾角,观测局部屈曲、畸变屈曲和局部/畸变屈曲相互作用下截面抗弯刚度的变化。评估了EC3中适用于冷成型Z型钢梁局部和畸变屈曲的设计方法的有效性。总体而言,采用EC3计算的截面抗弯刚度并不保守。指出其中的不足并提出改进建议,改善卷边受压翼缘的失稳系数。     

复杂卷边冷弯薄壁槽型钢梁畸变屈曲承载力研究

为研究复杂卷边槽型截面钢梁的畸变屈曲承载力,对该截面梁的畸变屈曲性能进行试验研究和有限元分析,获得其变形性能和极限承载力,探讨了二次卷边宽度对复杂卷边槽钢梁畸变屈曲承载力的影响规律。结合试验和有限元分析结果,对北美规范的受弯构件畸变屈曲承载力的直接强度法公式应用于复杂卷边槽钢梁的适用性进行了分析评价。在此基础上,基于对现有直接强度法公式的修正,提出了冷弯薄壁复杂卷边槽钢梁畸变屈曲承载力的计算公式。     

蜂窝钢梁屈曲模型的相互影响

基于侧扭屈曲模型,采用三维非线性有限元法,考虑初始几何缺陷和材料非线性,研究普通和高强蜂窝钢梁的性能。通过不同跨度和横截面的蜂窝梁试验,对模型进行验证。研究了蜂窝钢梁的破坏荷载、屈曲模型间的相互影响、荷载-侧移曲线。采用有限元模型进行参数分析,研究横截面尺寸、梁长、型钢强度对蜂窝钢梁承载力和屈曲性能的影响。腹板的畸变屈曲较大地降低了细长蜂窝钢梁的承载力。将有限元分析得到的侧扭屈曲下钢梁破坏荷载与澳大利亚规范进行比较,结果表明:规范对侧扭屈曲下普通蜂窝钢梁的破坏分析偏保守,对腹板屈曲下蜂窝钢梁的破坏分析较合理,而对侧扭屈曲下高强蜂窝钢梁的破坏分析非常保守。     

腹板开孔冷弯薄壁槽钢梁屈曲性能试验及直接强度法研究

为了研究腹板开孔冷弯薄壁槽钢梁的屈曲性能和完善直接强度法,对开孔数量、卷边长度不同的冷弯薄壁槽钢梁进行了纯弯试验研究,其中长卷边和短卷边试件各8个,每种卷边的试件分别在腹板开设0、1、2、3个100 mm×40 mm的矩形孔洞。试验结果表明:腹板开孔使试件破坏模式从单一的畸变屈曲或局部屈曲变为以畸变屈曲为主的畸变-局部相关屈曲或以局部屈曲为主的局部-畸变相关屈曲;与未开孔钢梁相比,开孔钢梁的承载力有所降低,但开孔数量对钢梁承载力影响不大。采用ANSYS有限元程序对试验进行了模拟,模拟结果与试验结果吻合良好,验证了有限元分析此类开孔构件的可行性。进而开展了有限元参数分析,验证了基于折减腹板厚度法利用有限条程序CUFSM求解腹板开孔冷弯薄壁槽钢梁弹性畸变屈曲临界应力的准确性,并对此类构件的弹性局部屈曲临界应力计算公式进行了修正。基于腹板开孔冷弯薄壁槽钢梁的试验结果、有限元分析结果以及弹性屈曲临界应力求解方法,得到了此类构件在以畸变屈曲为主和以局部屈曲为主破坏模式下的直接强度法修正公式。     

国际期刊导读

<正>1轻钢梁的侧向屈曲数值模拟及设计摘要:轻钢梁是一种通过双电阻焊接和冷弯加工形成的新型空心翼缘槽钢,由刚性矩形受扭空心翼缘和细长腹板组成,通常作为受弯构件。然而,轻质钢梁受弯构件会发生新形式的侧向畸变屈曲,导致其抗弯承载力降低。与侧向扭转屈曲不同,轻钢梁的侧向畸变屈曲同时产生由腹板扭曲导致的侧向变形、扭曲和横截面变化。采用试验和有限元分析方法,分别对轻质钢梁的侧向屈曲性能进行研究。建     

碳纤维布加固受弯钢梁力学性能分析

首先对不同加载方式和不同加固模式下的碳纤维增强复合材料加固H型受弯钢梁进行了2组对比试验,并对试验结果进行了综合分析.在此基础上,应用扩展有限元法(extended finite element method,XFEM)建立了CFRP加固H型钢梁的有限元模型,应用该数值模型分别分析了CFRP布加固无损伤和有损伤H型钢梁的极限承载力、胶层界面应力和开裂损伤等力学特性.分析结果表明,扩展有限元法对CFRP加固受弯钢梁力学性能的研究具有较好的适用性.     

冲击荷载作用下热轧H型钢梁数值模拟研究

为了研究热轧H型钢梁在冲击荷载作用下的力学性能与破坏形式,对H型钢梁的冲击试验建立精细化有限元模型,再与试验结果进行对比,验证有限元模型的准确性。基于有限元模型分析冲击荷载作用下钢梁的荷载重分布和内力变化。之后开展拓展参数分析,研究钢材强度、锤头几何形状、有无局部加固、冲击位置、边界条件对钢梁抗冲击性能的影响。结果表明:冲击荷载作用下,钢梁出现局部屈曲,并在响应结束阶段承受不对称剪力,其主要破坏形式为局部屈曲和扭转变形; 提高钢材强度,相应钢梁整体抗冲击性能得到增强; 改变锤头几何形状,导致接触刚度改变,冲击力时程曲线出现变化; 在冲击区设有局部加固可以提高冲击区的刚度以及稳定性,钢梁抗冲击能力得到提升; 当冲击位置靠近支座时,冲击力出现至支座反力出现的时间间隔缩短,钢梁能更好地抵抗冲击荷载造成的破坏; 当钢梁边界条件由铰接改为刚接时,由于钢梁长度增加受惯性荷载影响增大,并且由于支座对梁体约束减弱,冲击力整体大幅降低,梁跨挠度增大。     

Distortional buckling of thin-web beam-columns

An approximate finite element method of analysis is developed for the distortional buckling of beam-columns. The member consists of a flexible web, to which is connected two rigid flange assemblies of arbitrary shape which remain undistorted during buckling. The method permits an economic computer analysis to be made of elastic distortional buckling of members under various conditions of loading, end support and restraint.Following studies of the convergence and accuracy of the buckling solutions, the method is used to demonstrate the effects of web distortion on the elastic buckling of lipped channel beams under moment gradient.     

Lateral-distortional buckling of tee-section beams

A fine element method that incorporates plate behaviour is developed for modelling the lateral-distortional buckling of tee-section beams. The method is shown to agree well with independent buckling results for tee-beams. Since relatively few elements are needed to obtain satisfactory convergence, the method is efficient computationally. The finite element analysis is used to study the elastic distortional buckling of tee-beams of practical geometry under moment gradient. The disparities found between the elastic flexural-torsional and distortional buckling moments are discussed.     

不同斜卷边檩条的局部屈曲和畸变屈曲

利用Hancock的简化模型分析了卷边槽形、卷边Z形檩条的畸变屈曲,用有限元方法计算了卷边槽形、卷边Z形檩条的畸变屈曲荷载以及翼缘局部屈曲系数,研究了卷边角度对畸变屈曲荷载的影响,提出斜卷边加劲板的屈曲系数取值以及屈曲系数关于卷边角度变化的公式。经对比验证,在卷边角度40°～90°的范围内,误差在2%以内。可供实际设计参考。     

工字钢-混凝土组合梁弹性约束畸变屈曲研究

约束畸变屈曲是不同于侧向屈曲和畸变屈曲的一类特殊的屈曲形式,通常发生在组合梁负弯矩区。基于弹性地基压杆方法对组合梁弹性约束畸变屈曲进行了研究。将Svensson压杆模型进行改进,考虑了腹板参与部分,并推导了两种基于改进压杆模型的变轴力稳定计算表达式。借助于有限元方法,分析了现有变轴力弹性地基压杆方法用于组合梁约束畸变屈曲的求解精度,研究结果表明：弹性地基压杆方法对组合梁作用纯弯矩及三角形负弯矩情况符合良好,但对非线性弯矩分布情况精度较差。对约束畸变屈曲引入等效弯矩假设,并对其适用性进行了分析,提出了约束畸变屈曲等效弯矩假设临界长度简化公式,进而通过三步简化实现了连续组合梁弹性约束畸变屈曲计算。图16表7参17     

Simulation of cold-formed steel beams in local and distortional buckling with applications to the direct strength method

A nonlinear finite element (FE) model is developed to simulate two series of flexural tests, previously conducted by the authors, on industry standard cold-formed steel C- and Z-section beams. The previous tests focused on laterally braced beams with compression flange details that lead predominately to local buckling failures, in the first test series, and distortional buckling failures, in the second test series. The objectives of this paper are to (i) validate the FE model developed for simulation of the testing, (ii) perform parametric studies outside the bounds of the original tests with a particular focus on variation in yield stress and influence of moment gradient on failures, and (iii) apply the study results to examine and extend the Direct Strength Method of design. The developed FE model shows good agreement with the test data in terms of ultimate bending strength. Extension of the tested sections to cover yield stresses from 228 to 506 MPa indicates that the Direct Strength Method is applicable over this full range of yield stresses. The FE model is also applied to analyze the effect of moment gradient on distortional buckling. It is found that the distortional buckling strength of beams is increased due to the presence of moment gradient. Further, it is proposed and verified that the moment gradient effect on distortional buckling failures can be conservatively accounted for in the Direct Strength Method by using an elastic buckling moment that accounts for the moment gradient. An empirical equation, appropriate for use in design, to predict the increase in the elastic distortional buckling moment due to moment gradient, is developed.     

Lateral, local and distortional buckling of I-beams

A theoretical study of the elastic buckling modes of I-section beams under various loading conditions is presented.

The analysis is based on energy considerations and the energy equations governing instability are derived using plate theory to allow for distortion of the cross-section. The resulting analysis is able to predict lateral, local and distortional buckling modes.

The results are compared with classical lateral buckling solutions based on beam theory.     

Buckling of elastically restrained beams with web distortions

An energy method is developed for studying the distortional buckling of monosymmetric I-section beams subjected to elastic restraints. The buckling solution is developed in terms of an eigenproblem for four by four symmetric matrices. The distortional buckling of monosymmetric I-beams with translational, minor axis rotational and twisting restraint applied to the smaller tension flange is considered, and the solutions are compared with predictions which assume non-distortion of the cross-section.     

卷边翼缘工形截面梁的稳定性能及设计方法

基于大挠度弹塑性板壳有限元分析方法,系统地研究了卷边工形梁在两端等弯矩作用下的失稳机理与稳定承载力,揭示了卷边工形截面构件的局部屈曲、畸变屈曲、整体侧向失稳以及它们之间的相互作用。系统地分析了截面宽高比、腹板高厚比、翼缘宽厚比、长细比等构件参数对侧向稳定承载力的影响,并基于大量的数值计算数据给出了卷边工形梁在两端等弯矩作用下的稳定承载力设计公式,可为规范修订以及工程设计提供依据。     

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.     

Design for distortional buckling of flexural members

For thin-walled flexural members composed of high-strength steel and/or slender elements in the section, a mode of buckling at half-wavelengths intermediate between local buckling and flexural—torsional or flexural buckling can occur. The mode is most common for edge-stiffened sections such as C- and Z-purlins, and involves rotation of the flange and lip about the flange—web junction. The mode is commonly called distortional buckling. This paper presents a design method for distortional buckling of flexural members recently drafted for use in the Australian/New Zealand Standard for Cold formed Steel Structures. Methods for computing the elastic buckling stress, and design curves for determining the distortional buckling strength are presented. Comparisons of different methods for computing the elastic distortional buckling stress are made with accurate solutions based on the finite strip method of structural analysis.