火灾下有支撑和无支撑钢框架的屈曲分析

考虑温度影响对钢框架进行屈曲分析,以评估火灾下柱的屈曲长度。将得到的屈曲长度与EC3中消防部分(第1.2节)所给出的值进行比较,该部分用于火灾情况下有支撑框架柱的设计。EC3第1.2节并没有给出无支撑框架屈曲长度的消防设计准则,因此,该研究给出了无支撑钢结构中柱的屈曲长度。将火灾情况下若干不同框架的力学抗力计算结果(利用简单模型计算)和估算的屈曲长度与高级模型的计算结果进行了对比。     

侧向扭转屈曲时冷成型钢梁的特性及设计

建筑物中越来越多地使用冷成型钢梁作为楼板的辅助及受力构件,其在没有足够侧向约束时的性能和瞬时承载力将受到侧向扭转屈曲的影响。以往对侧向扭转屈曲的研究主要针对热成型卷边钢梁,因此需要对简单支撑下相同弯曲度冷成型卷边槽钢梁的特性进行数值模拟。采用业内广泛认可的有限元分析软件ABAQUS进行建模,对不同条件下冷成型钢梁微单元的侧向扭转屈曲性能和承载力进行分析和模拟。将瞬时承载力结果与冷成型钢结构规范中当前设计准则的预测结果进行比较并对其进行适当的修正。欧洲的设计规范较为保守,而澳大利亚、新西兰和北美的设计规范则较为宽泛。基于有限元分析结果,对规范中的瞬时承载力设计公式进行修正。阐述了参数分析的细节问题,修正了当前设计规范,提出了侧向扭转屈曲时冷成型卷边槽钢梁的新设计准则。     

火灾中Ⅰ型不锈钢柱的力学性能研究

英国研究人员开展了火灾中I型不锈钢柱的弯曲屈曲行为研究。建立并验证了能够准确反应不锈钢柱火灾响应的有限元模型。参数分析考虑了不锈钢等级、截面几何形状、细长度和高温水平。建立了Ⅰ型不锈钢柱在火灾下的新的设计方法。研究结果表明,现有的不锈钢柱在高温下设计方法较为分散和不准确。提出了一种新的设计方法,该方法可以更为准确、实用的对火灾不锈钢柱进行设计,并且符合EN1993-1-2中现有的设计规则。提出的不锈钢柱火灾设计方法将写入新版的EN1993-1-2标准。     

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。     

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     

圆孔蜂窝梁的弯扭屈曲分析

为了对纯弯状态下圆孔蜂窝梁的弯扭屈曲进行研究,将蜂窝梁翼缘和腹板分离,采用有限元软件ANSYS对蜂窝梁开圆孔腹板进行侧向纯弯分析,由挠度-刚度关系反算侧向刚度,得出开孔腹板相对于实心腹板的刚度折减系数ky。考虑开孔腹板的径高比和距高比,经拟合给出了刚度折减系数ky的计算公式,用该系数对蜂窝梁的自由扭转刚度进行修正,代入实腹工字截面梁弯扭屈曲临界弯矩计算公式,得到蜂窝梁的相应计算公式。最后利用该公式分别对不同跨度、不同孔况的简支蜂窝梁在纯弯状态下的弯扭屈曲临界弯矩进行计算,并与有限元分析结果进行对比。分析结果表明,修正后的临界弯矩计算公式具有较高精度。     

非弹性侧向屈曲的悬臂钢梁强度

两端支承钢梁的设计方法不适用于抗侧向屈曲的悬臂梁。悬臂梁与两端支承梁的约束不同,其最大位移和转角发生在自由端,而不是在跨中附近。因此,它们的屈曲模态不一样。这些方法考虑了弯矩分配法对两端支承梁弹性及非弹性屈曲的影响,但不适用于悬臂梁。悬臂梁的侧向屈曲设计法是对端支承梁设计法的修正,但其精度不高,有时过于保守,某些情况下,不能用于设计。使用弯矩分配法进行结构的屈曲分析,总结了该方法对悬臂梁弹性屈曲的影响。改进两端支撑梁的非弹性屈曲设计方法,使其能考虑弯矩分配法对悬臂梁非弹性屈曲的影响。改进的方法与简支梁的设计法是一致的。以某工程为实例,演示了此方法的应用。     

应力梯度下不锈钢梁腹板局部屈曲强度

研究应力梯度下不锈钢梁腹板的局部屈曲强度。由于比例极限相对较低,应力作用下不锈钢的承载能力超出了比例极限。因此,设计时应考虑这类钢材的非弹性屈曲强度。为确定这一强度,在进行局部屈曲计算时,通常采用塑性折减系数来考虑其非弹性后屈曲性能。研究选用的钢材有AISI304型、410型和3CR12不锈钢。选择合适的截面尺寸以促进局部屈曲,并抑制其他形式的屈曲(如畸变和侧向扭转屈曲)。为研究不同长细比的槽钢,采用不同的腹板高度。研究结果表明,可采用有效宽度法来预测不锈钢梁腹板的局部屈曲强度,而无需使用塑性折减系数。     

对预装体外钢筋的钢-混凝土组合梁弹塑性屈曲的数值分析

连续组合梁的极限承载力由侧向畸变屈曲、局部屈曲,或者由两者的相互作用决定,这一点与纯钢梁的扭转屈曲破坏模式完全不同。利用有限元模型对负弯矩区的组合梁进行了弹塑性有限元分析,其中考虑了初始几何缺陷和残余应力,最终发现有限元分析结果与试验结果吻合良好。另外,对负弯矩区的预装体外钢筋的组合梁进行了参数研究。分析了影响组合梁承载能力和屈曲弯矩抗力的因子,如初始几何缺陷、钢梁的残余应力、力比值、预应力范围、负力矩钢筋、板、翼缘和梁的宽厚比。利用有限元法对负弯矩作用下的25组共200根具有不同截面参数、初始几何缺陷、残余应力和不同力比值的组合梁进行了分析。将计算出的屈曲弯矩率与改进宽厚比的曲线与中国规范中钢柱设计曲线进行了对比。结果证实:对于改进了的宽厚比值,本文依据中国规范的设计曲线推导出来的设计方法可以用于对组合梁屈曲强度的评估。     

火灾中不锈钢柱和梁的屈曲

材料特性和它们对高温的反应构成结构防火设计的关键部分。当遇到高温时,与碳钢相比,不锈钢表现出更好的材料强度和刚度。尽管独立而言,强度和刚度都很重要,但是在高温作用下,它们之间的关系同样也会对结构构件的屈曲反应产生显著影响。检查了现有的试验结果,并且介绍了数值参数研究的结果,即利用ABAQUS对火灾中的不锈钢柱进行分析。由于对局部和整体初始几何缺陷的敏感,通过冷作和对柱端的局部保护可以提高焊脚强度。为探究局部横截面长细比、整体构件长细比和荷载变化的影响,还进行了参数研究。试验结果与现有设计规范欧洲规范3(part1.2),欧洲Inox/SCI设计手册中对结构不锈钢的规定及CTICM/CSM中提到的规定相对比。分析了在全部23个柱屈曲抗火试验中,6个短柱和6个梁的抗火试验结果。文中标出过度保守和互相矛盾的结果以及变形极值。通过修订,可以使得今后不锈钢梁和柱能在火灾中更有效的使用。改进后,柱的抗屈曲能力提高了6%,短柱的抵抗能力提高28%,平面内抵抗弯矩提高14%,高于现有欧洲规范的要求。     

Lateral-torsional buckling of stainless steel I-beams in case of fire

This work presents a numerical study of the behaviour of stainless steel I-beams subjected to lateral-torsional buckling in case of fire and compares the obtained results with the beam design curves of Eurocode 3.New formulae for lateral-torsional buckling, that approximate better the real behaviour of stainless steel structural elements in case of fire are proposed. These new formulae were based on numerical simulations using the program SAFIR, which was modified to take into account the material properties of the stainless steel.     

Interaction of bending and axial compression of stainless steel members

The paper deals with the buckling behaviour of stainless steel members with the main focus on developing design formulae for use in the latest version of the European Standard EN 1993-1-4: Eurocode 3-Design of steel structures-Part 1-4: General rules — Supplementary rules for stainless steel. Brussels; 2005.It is based on numerical simulations of single span members of various section type, which are subjected to axial compression and bending. Both flexural buckling and lateral-torsional buckling are dealt with so that the buckling behaviour of both I-sections and hollow sections can be covered.On the basis of these numerical results interaction factors have been derived in context with the design model for member design in Eurocode 3-1-1. For statistical evaluation the test results available from other authors have been used.The outcome of this investigation has been incorporated in the present EN 1993-1-4 as a recommendation in restricted form.     

Class 4 stainless steel I beams subjected to fire

Structural elements composed of Class 4 sections are common in stainless steel buildings structures. These thin walled profiles are more susceptible to the occurrence of local buckling. Additionally, in beams the lateral-torsional buckling is also a common failure mode. These instability phenomena are intensified at high temperatures. This work has the main objective of presenting a numerical study on the fire behavior of beams with Class 4 stainless steel sections when subjected to pure bending and high temperatures. The influence of several parameters, as geometrical imperfections and residual stresses, on the ultimate load will be evaluated and comparisons between the numerical results and the Eurocode 3 rules will also be made.     

Numerical validation of the general method in EC3-1-1 for prismatic members

Part 1-1 of Eurocode 3 includes a general method for lateral and lateral-torsional buckling of structural components that uses a Merchant-Rankine type of empirical interaction expression to uncouple the in-plane effects and the out-of-plane effects. In this paper, the safety of this approach is assessed for prismatic members subjected to compression, bending and bending and axial force by comparison of both with advanced nonlinear numerical simulations (GMNIA) using beam and shell elements and the other Eurocode 3 approaches based on the European buckling curves. Analytical expressions are derived for columns, beams and beam-columns that show the variation of resistance with varying slenderness. A parametric study is carried out whereby cross-sectional shape, type of loading, slenderness and steel grade are varied. It is concluded that the method gives similar levels of safety as the methods prescribed in clauses 6.3.1 to 6.3.3 of Eurocode 3, part 1-1.     

焊接H型钢局部纵弯失稳下抗弯强度计算

对由厚度为6.0mm、名义屈服强度为315.0MPa的钢板制成的H型钢进行了一系列弯曲试验,研究焊接H型钢的抗弯强度。截面几何形状和侧向边界条件决定了薄壁受弯构件的屈曲形式(局部屈曲、侧向扭转屈曲或交互屈曲)。翼缘或腹板宽厚比较大的受弯构件最先出现局部屈曲,继而发生侧向扭转屈曲,在交互屈曲作用下材料最终破坏。侧向扭转屈曲下局部屈曲对抗弯强度有负面影响。计算薄壁抗弯构件名义屈服应力时应将该现象考虑在内。对翼缘和腹板宽厚比不同的焊接H型钢梁进行了试验。进行有限元分析时将局部和侧向扭转屈曲模态的初始缺陷及残余应力考虑在内。基于考虑焊接型材局部和侧向扭转屈曲相互作用的试验和有限元分析结果,给出直接强度法(DSM)计算抗弯强度的简化公式。计算强度曲线与AISC规范(2005),EC3(2003)及试验结果进行比较,验证了DSM方法所计算的强度曲线的准确性。通过试验得出薄壁焊接H型钢的抗弯强度和结构性能的有关结论。     

Effective width method to account for the local buckling of steel thin plates at elevated temperatures

The local buckling of thin steel plates exposed to fire is investigated using a finite element model. The reduction of strength and stiffness that occurs at elevated temperatures needs to be taken into account in the design, as it increases the susceptibility to local buckling of the plates thus affecting their load carrying capacity. The obtained results show that the current existing design method of Eurocode 3 to take into consideration the local buckling in the calculation of the ultimate strength of steel thin plates at elevated temperatures needs to be improved. These methods are based on the same principles as for normal temperature but using for the design yield strength of steel, at elevated temperatures, the 0.2% proof strength of the steel instead of its strength at 2% total strain as for the cases where the local buckling is not limiting the ultimate strength of the plates. This consideration, however, leads to an inconsistency if cross-sections are composed simultaneous of plates susceptible and not to local buckling. To address this issue, new expressions for calculating the effective width of internal compressed elements (webs) and outstand elements (flanges) are proposed, which have been derived from the actual expressions of the Part 1.5 of the Eurocode 3 and validated against numerical results. It is also demonstrated that it is not necessary to use for the yield stress at elevated temperatures the 0.2% proof strength of the steel instead of the yield stress at 2% total strain, given that the necessary allowances are considered in these new expressions, thus leading to a more economic design.     

钢压弯构件弯扭屈曲的研究

本文简要介绍了近年来在西安冶金建筑学院完成的有关钢压弯构件弯扭屈曲研究的成果,包括以下几个方面;(1)确定钢压弯构件设计承载力的典型截面选择;(2)考虑钢材屈服非连续性或焊接残余应力影响时构件的非弹性弯扭屈曲;(3)单轴对称截面压弯构件的弯扭屈曲分析和试验研究;(4)双轴和单轴对称截面构件弯扭屈曲的实用相关公式;(5)绕截面弱轴弯曲的压弯构件的弯扭屈曲分析和试验;(6)冷弯薄壁型钢构件的非弹性弯扭屈曲的分析和试验。     

Local buckling of steel plates in concrete-filled thin-walled steel tubular beam-columns

The availability of high strength steels and concrete leads to the use of thin steel plates in concrete-filled steel tubular beam-columns. However, the use of thin steel plates in composite beam-columns gives a rise to local buckling that would appreciably reduce the strength and ductility performance of the members. This paper studies the critical local and post-local buckling behavior of steel plates in concrete-filled thin-walled steel tubular beam-columns by using the finite element analysis method. Geometric and material nonlinear analyses are performed to investigate the critical local and post-local buckling strengths of steel plates under compression and in-plane bending. Initial geometric imperfections and residual stresses presented in steel plates, material yielding and strain hardening are taken into account in the nonlinear analysis. Based on the results obtained from the nonlinear finite element analyses, a set of design formulas are proposed for determining the critical local buckling and ultimate strengths of steel plates in concrete-filled steel tubular beam-columns. In addition, effective width formulas are developed for the ultimate strength design of clamped steel plates under non-uniform compression. The accuracy of the proposed design formulas is established by comparisons with available solutions. The proposed design formulas can be used directly in the design of composite beam-columns and adopted in the advanced analysis of concrete-filled thin-walled steel tubular beam-columns to account for local buckling effects.