冷弯C型或Z型钢截面受弯时的畸变屈曲

对C型或Z型檩条受弯时的畸变屈曲进行分析,指出了目前澳大利亚和美国规范采用薄壁构件理论分析畸变屈曲的方法,过高估计了翼缘-卷边的刚度,因而采用降低腹板对翼缘约束的方式,使得结果符合有限条方法的结果。通过采用卷边等效抗弯刚度,对翼缘采用板件理论研究,推导了腹板对翼缘的约束刚度计算公式,并将其用于翼缘-卷边的畸变屈曲计算和局部屈曲计算,与有限元方法的计算结果对比表明,得到的屈曲系数精度良好且偏安全。     

暗扣屋面体系对檩条的扭转约束及影响

檩条在风吸力作用下会发生弯扭失稳,而当檩条上翼缘受到扭转约束时,对于风吸力作用下的整体稳定会有一定程度的提升。通过试验分析得到KLIP-LOK 406暗扣屋面板体系对冷弯Z形檩条的扭转约束刚度,然后利用得到的扭转约束刚度,采用能量法,为此种约束时风吸力作用下冷弯Z形檩条的临界弯矩提供理论解,并将理论解与ANSYS有限元模型的计算结果进行对比,两者吻合很好。     

压型钢板开孔受压翼缘的局部屈曲分析及设计对策

有效宽度法或直接强度法计算压型钢板承载力的关键之一是计算截面板件的局部屈曲应力,而针对压型钢板开孔受压翼缘,目前尚无成熟的对其局部屈曲应力的计算方法。基于折减厚度法和折减面积法,参照无孔受压翼缘局部屈曲应力的计算思路,通过引入折减系数Be,提出了压型钢板开孔受压翼缘局部屈曲应力的实用计算公式。通过数值模拟对受压翼缘单开孔、单排均匀开孔及多排均匀开孔的局部屈曲进行分析,并与公式计算结果进行对比,研究了实用计算公式在不同开孔情况下的适用性。结果表明,折减面积法简单易行,相比折减厚度法计算精度更高,且能考虑纵横向开孔间距不同的情况,满足实际工程设计需要,为《冷弯薄壁型钢结构技术规范》(GB50018—2002)的修订提供依据。     

压型钢板屋面对檩条的扭转约束

压型钢板屋面对檩条施加扭转约束,从而提高檩条的稳定性。针对杭萧钢构股份有限公司的HXY-478屋面压型钢板与檩条采用夹板连接的屋面体系,对檩条施加的扭转约束进行研究。通过ANSYS分析,对上下翼缘受压的扭转约束提出了计算公式。     

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。     

冷弯型钢檩条的有效截面

冷弯型钢檩条按(GB50018—2002)计算,截面大多达不到完全有效,需对其作屈曲后的强度计算。而翼缘非全部有效的卷边槽钢、Z形钢毫无对称性,使应力分析计算十分复杂。本文针对承受重力荷载檩条的特点,论证畸变屈曲对设计不起控制作用,从而得出翼缘和腹板全部有效比较宽松的条件,现有卷边槽钢和Z形钢规格大部分全部有效。提出的公式既可简化计算,又可节省钢材。     

设置两拉条的C形截面檩条绕上翼缘的扭转分析

对屋面板采用自攻螺钉与檩条上翼缘相连且设置两根拉条的简支檩条,在风吸力作用下的应力和变形进行分析,并与有限元分析结果进行对比。分析发现,绕上翼缘扭转的理论能够比较准确地预测下翼缘的侧向变形、拉条反力和非拉条附近的屋面板反力。拉条截面下翼缘卷边的压应力最大,采用EC3方法计算的压应力与ANSYS的结果符合;拉条截面上翼缘卷边的拉应力最大,必须考虑畸变的影响,且必须采用弯扭理论求解并计算出拉条反力,才能引入畸变正应力。     

压型钢板局部削弱后抗弯性能试验研究

为研究组合楼板作为承载构件时在压型钢板局部削弱后的受弯性能,对压型钢板的竖直与水平方向进行不同程度的弱化,并在弱化后对钢板进行无侧向约束的受弯试验,研究压型钢板削弱后的受弯性能及其破坏形式。试验结果表明：在均布荷载作用下,各组压型钢板的破坏均以跨中受弯屈曲破坏为主;水平方向洞口削弱了钢板上翼缘承载力,当水平洞口半径为20 mm时,试件抗弯承载力降低约15%;竖向洞口会阻碍钢板上、下翼缘应力的传递,当竖向洞口半径为25 mm时,试件抗弯承载力降低约10%。通过对比可知,水平方向的弱化对承载力的影响相较于竖直方向要更加明显。     

双侧闭口型压型钢板混凝土组合构件轴压力学性能研究

双侧闭口型压型钢板混凝土组合构件由两侧放置的闭口型压型钢板和内部填充混凝土组成,内嵌于混凝土中的闭口型板肋既可作为钢板与混凝土之间的连接件,保证两者的共同工作,又能有效降低钢板的宽厚比,提高闭口型压型钢板的屈曲承载力。相比传统的双钢板混凝土组合构件,双侧闭口型压型钢板混凝土组合构件无需额外的连接件即可实现钢板和混凝土的共同工作,增加了施工的便利性和高效性,同时保持了双钢板-混凝土组合构件的性能优势,在工程中具有广阔的应用前景。采用有限元方法分析了闭口型压型钢板混凝土组合构件在轴压荷载作用下的受力全过程,包括混凝土截面的应力分布、压型钢板板带的应力发展过程及屈曲性能;通过试验结果和理论分析明确了板肋在混凝土中的嵌固作用;研究了压型钢板布置形式、混凝土强度等级、钢材屈服强度、钢板厚度(板带宽厚比)和构件厚度等参数对双侧闭口型压型钢板混凝土组合构件轴压性能影响规律。通过对双侧闭口型压型钢板混凝土组合构件受力全过程的分析,可以得到以下结论:闭口型板肋将压型钢板分成若干个板带,各板带单独发生受压屈曲,改变了钢板整体受压屈曲的方式;混凝土能够对嵌入的闭口型板肋提供足够的嵌固作用,使得压型钢板与混凝土能够共同工作;嵌入混凝土中的闭口型板肋为压型钢板板带提供了可靠的边缘嵌固和支撑,使得闭口型压型钢板仅在板带上发生局部弹性屈曲,且能够发展屈曲后强度,压型钢板板带的屈曲后强度可以采用有效宽度法计算;闭口型板肋嵌于混凝土中使得板肋附近混凝土的应力分布不均匀,并对两侧板肋之间的混凝土产生一定的约束作用,但截面上并未形成明显的约束区和非约束区;双侧闭口型压型钢板混凝土组合构件轴压承载力可由混凝土抗压承载力和考虑屈曲后强度的压型钢板承载力叠加获得;压型钢板布置方式对构件的轴压承载力没有明显影响,构件各组成部分的材料强度、墙体厚度和压型钢板厚度对其轴压承载力和延性影响明显。     

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。     

Bending analysis of partially restrained channel-section purlins subjected to up-lift loadings

Cold-formed steel section beams are widely used as the secondary structural members in buildings to support roof and side cladding or sheeting. These members are thus commonly treated as the restrained beams either fully or partially in its lateral and rotational directions. In this paper an analytical model is presented to describe the bending and twisting behaviour of partially restrained channel-section purlins when subjected to uplift loading. Formulae used to calculate the bending stresses of the roof purlins are derived by using the classical bending theory of thin-walled beams. Detailed comparisons are made between the present model and the simplified model proposed in Eurocodes (EN1993-1-3). To validate the accuracy of the present model, both available experimental data and finite element analysis results are used, from which the bending stress distributions along the lip, flange and web lines are compared with those obtained from the present and EN1993-1-3 models.     

上举荷载作用下局部约束槽钢檩条的弯曲分析

建筑中,冷弯型钢梁作为次要结构构件广泛用于支撑屋顶和侧面的包覆层或挡板。因此,这些构件常被视为侧向或旋转方向受到全部或部分约束。给出描述上举荷载作用下局部约束槽钢檩条的弯曲和扭转性能的分析模型。基于薄壁梁的经典弯曲理论推导出屋顶檩条弯曲应力的计算公式。将该模型和欧洲规范(EN1993-1-3)给出的简易模型进行对比。采用该模型和EN1993-1-3分别计算沿卷边、翼缘和腹板的弯曲应力分布,并将计算结构与试验数据和有限元分析结果进行比较,验证了该模型的准确性。     

Theoretical analysis of partially restrained zed-purlin beams subjected to up-lift loads

Cold-formed steel section beams are usually used as the secondary structural members in buildings to support roof and side cladding or sheeting. Thus these members are commonly treated as the restrained beams either fully or partially in its lateral and rotational directions. In this paper an analytical model is presented to describe the bending and twisting behaviour of partially restrained cold-formed steel purlins when subjected to uplift loading. Formulae used to calculate the bending stresses of the roof purlins are derived by using the classical bending theory of thin-walled beams. Detailed comparisons are made between the present model and the simplified model proposed in Eurocodes (EN1993-1-3). To validate the accuracy of the present model, finite element analysis is also conducted and the bending stress distribution along the lip, flange and web lines obtained from the finite element analysis is compared with those obtained from the present and EN1993-1-3 models.     

Simplified models for cross-section stress demands on C-section purlins in uplift

The objective of this paper is to provide and verify simplified models that predict the longitudinal stresses that develop in C-section purlins in uplift. The paper begins with the simple case of flexural stress; where the force has to be applied at the shear center, or the section braced in both flanges. Restrictions on load application point and restraint of the flanges are removed until arriving at the more complex problem of bending when movement of the tension flange alone is restricted, as commonly found in purlin-sheeting systems. Winter's model for predicting the longitudinal stresses developed due to direct torsion is reviewed, verified, and then extended to cover the case of a bending member with tension flange restraint. The developed longitudinal stresses from flexure and restrained torsion are used to assess the elastic stability behavior of typical purlin-sheeting systems. Finally, strength predictions of typical C-section purlins are provided for existing AISI methods and a newly proposed extension to the direct strength method that employs the predicted longitudinal stress distributions within the strength prediction.     

设置拉条的连续檩条特征值屈曲数值分析

采用ANSYS弹性壳单元分析模块,基于刚周边及上翼缘仅受侧向约束的假定,针对设置拉条的两跨连续檩条进行屈曲分析,考察了广泛参数范围下檩条的屈曲模态,同时从受力上给予合理解释。     

Application of generalized beam theory to the design of thin-walled purlins

Cold-formed purlins have a high load carrying capacity because of their optimized cross-section and the stabilizing effect of the sheeting. The present contribution describes a simplified design method for these purlins suitable for use by practising engineers, which takes into account the lateral and torsional restraint of the purlin and the cross-section distortion. Using cross-section values determined for the whole section the stress resultants are evaluated using second-order theory, and the stresses are checked at the critical locations.     

轻钢结构中Z型连续檩条设计问题的探讨

针对我国现行钢结构规范中的不足 ,探讨Z型连续搭接檩条的结构性能 :荷载分布、搭接嵌套松动、内力计算、侧向稳定以及构件极限承载力等问题。此外 ,还讨论了带隅撑檩条的计算特点和双檩条的构造优点 ,提出了适合实际工程的算法 ,使冷弯薄壁型钢檩条设计更为经济合理。方法和结论可供设计人员参考     

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.     

Design of thin-walled purlins for distortional buckling

Roof purlins and sheeting rails are generally loaded through the cladding members that they support and this provides both rotational and translational restraint. This restraint reduces the tendency to lateral torsional buckling and thus increases the importance of distortional buckling in the design procedure. This paper shows that the fundamental behaviour of restrained purlins under both downward and uplift load can be best understood with the aid of ‘Generalized Beam Theory’ (GBT). GBT also provides a yardstick by which approximate design methods can be assessed. The existing approximate methods are evaluated and an improvement is proposed. The proposed design approach is then validated by comparison with test results.     

单箱双室箱梁对称弯曲时的局部扭转效应

为研究单箱双室箱梁在对称竖向荷载作用下的受力特征,基于横截面的荷载等效原理与荷载分解,分析了单箱双室箱梁对称弯曲时的局部扭转效应。基于截面的剪力流平衡和箱室受力分解,得到了局部扭转的等效荷载及应力计算式。通过与有机玻璃模型试验和有限元模拟结果的对比,验证了局部扭转效应计算式的正确性,并获得了单箱双室简支箱梁的局部扭转效应下的应力分布规律。研究表明,单箱双室箱梁在仅中腹板作用竖向荷载及两边腹板作用相等竖向荷载时,均存在纵向弯曲和局部扭转的组合变形模式。局部扭转由约束扭转、畸变和横向弯曲效应组成,在截面引起纵向应力和横向应力。局部扭转效应的理论计算结果与模型试验和板壳有限元分析结果吻合良好,表明基于截面剪力流等效的局部扭转荷载求解方法对双室箱梁是适用的;单箱双室箱梁的局部扭转效应在荷载作用点附近截面最为突出,截面上、下缘纵向应力和横向应力以中腹板为拐点呈折线分布,其应力分布和大小与荷载在横截面上作用的部位紧密关联;对算例箱梁,局部扭转效应产生的纵向应力可达初等梁弯曲应力的25%。