混凝土板柱子结构抗连续倒塌试验研究

节点脆性冲剪破坏易导致板柱结构体系的连续倒塌。对1个横、纵向均为2跨的混凝土板柱子结构进行连续倒塌静力加载试验,试件制作时移除底部中柱以模拟初始失效,试验中首先对中柱柱头施加向下的集中力使其节点发生初始冲剪破坏,其后对楼板施加均布荷载直至发生后继连续倒塌破坏,分析了试件不同变形阶段的受力机理并对承载力进行了评估。结果表明：子结构的中柱节点冲剪破坏具有一定延性,但板内张拉力导致冲剪承载力比中国规范计算值低50%;初始加载时边中柱和角柱分别承担82%和18%的荷载,随着变形增大,边中柱节点逐步损伤,边中柱承担荷载下降、角柱承担荷载上升,结构倒塌时边中柱和角柱分别承担51%和49%的荷载;小变形下试件通过楼板面外受弯能力和面内受压薄膜效应承载,在中柱节点发生冲剪破坏的时刻,受压薄膜效应提供的承载力贡献为12%;大变形下试件通过节点区的残余受弯能力和面内受拉薄膜效应承载,当节点发生严重损伤后,荷载由板底整体钢筋的受拉薄膜效应承担。     

基于纤维模型的单层球面网壳抗震倒塌反应分析

通过纤维模型对悬臂杆荷载-位移(P-δ)效应进行模拟,并与采用其他有限单元的模拟结果对比,验证时程纤维模型在模拟单层网壳结构杆件二阶效应变形以及塑性发展路径两方面的精确性。基于纤维模型和动力增量时程分析法,以倒塌边缘比(CMR)作为抗地震倒塌评估指标分析了单层球面网壳结构的初始几何缺陷、屋面荷载、结构矢跨比、结构跨度对抗地震倒塌能力的影响。     

对带几何缺陷的FGM圆板的非线性热力学后屈曲现象的分析

带有几何缺陷FGM圆板的非线性热力学后屈曲现象是由力学荷载及横向不均匀温度升高导致的。基于组成材料的体积分数导致的能量分布法则,FGM板的材料特性假定在板厚度方向呈梯度变化。根据VonK偄rm偄n平板理论,推导出FGM板在温度荷载作用下的轴对称大变形的计算公式。在此分析中同时考虑了板的几何缺陷。通过运用目标法,解决了那些带有固定边界条件的非线性方程。数值算例中考虑了是否带有几何缺陷、均质或非均质的钢板。带缺陷FGM圆板的后屈曲变形特征曲线根据温度荷载、缺陷参数和体积分数的变化绘制而成。文中同时讨论了荷载参数、材料构成及板的几何缺陷对变形的影响。     

十字加劲钢板剪力墙的变参分析

利用有限元软件ANSYS对十字加劲钢板墙进行变参分析,研究板的高厚比、高宽比、柱刚度、柱轴压比及肋板刚度比对其水平极限承载力和抗侧刚度等性能的影响,对比分析参数变化时钢板墙的面外变形和最终破坏状态的应力分布.参数分析表明:板的高厚比和高宽比变化明显改变了钢板墙的受力性能和破坏机制,对其抗侧性能影响显著;柱刚度主要影响内...     

钢筋混凝土框架结构底部相邻两柱失效的抗连续倒塌性能研究

为研究钢筋混凝土结构在角柱和相邻边柱同时失效情况下的抗连续倒塌性能,采用12点等效均布荷载加载系统,对移除角柱和相邻边柱后的钢筋混凝土梁-板-柱子结构进行PUSHDOWN加载,并对钢筋混凝土子结构的破坏模式、承载能力、变形能力、钢筋局部应变、支座水平位移及边梁扭转变形进行分析。试验结果表明：角柱和相邻边柱同时失效的钢筋混凝土梁-板-柱子结构反应与悬挑板相近,梁与板无法形成有效的压拱机制、悬链线机制或薄膜机制来抵抗连续倒塌的发生。采用有限元软件DIANA建模对试验结果进行了数值模拟分析,证明了数值模型的合理性。采用塑性铰线法对试验屈服荷载和第一极限荷载进行分析,理论分析结果表明,与试验结果相比,塑性铰线法的分析结果偏于保守。     

钢框架高等分析中初始几何缺陷的考虑方法

结构整体和构件的初始几何缺陷是结构产生非线性行为的影响因素之一,在目前的高等分析中常按最不利的缺陷分布来考虑它们的影响。采用蒙特卡罗法可以考虑初始几何缺陷的随机遇合问题,能更加合理地确定初始缺陷的分布规律。通过统计分析得到柱顶侧移和梁跨中挠度的概率密度函数,可由此确定框架可能的最大变形。某一六层单跨框架的计算结果表明:当按缺陷的最不利分布来施加不同的初始几何缺陷时,对框架的极限承载力影响不大,但对框架的侧向变形影响较大:初始几何缺陷越大,框架的最终变形也越大。但按蒙特卡罗法考虑不同的初始缺陷时,与无缺陷框架相比,结构变形增加有限。算例还表明,当框架按高等分析的极限承载力设计时,相应标准荷载作用下的变形不能满足正常使用要求,因此,设计常受正常使用极限状态控制。     

大跨度钢结构抗连续倒塌动力分析关键问题研究

对大跨度钢结构抗连续倒塌动力分析中的关键问题进行研究,运用等效荷载瞬时卸载法对结构进行抗连续倒塌的动力分析,并借鉴美国规范对等效荷载提出取值方法建议。分析表明,应用等效荷载瞬时卸载法分析结构抗连续倒塌的精度主要取决于加载的时程曲线。根据动力学知识推导出求解结构关键构件失效前等效荷载最小作用时间的计算式,并与实际工程算例进行比较,其结果吻合较好。同时通过有限元数值分析,提出等效荷载卸载的最长时间为构件失效后模型的第1阶竖向自振周期的1/10。通过实际工程算例介绍抗连续倒塌动力分析的承载力和变形判定准则,分析在关键构件失效瞬间结构的应力比和变形能否满足设计要求。结果表明,应用等效荷载瞬时卸载法模拟大跨度钢结构关键构件失效后的受力和变形情况可行,与静力法相互补充可对大跨度钢结构进行抗连续倒塌分析。     

单层柱面网壳抗连续倒塌性能

研究了不同荷载布置形式、支承方式条件下,单层柱面网壳的抗连续倒塌性能和倒塌破坏模式,采用基于构件承载能力的敏感性评价指标,分析了初始缺陷、压杆失稳等因素对杆件、节点敏感性指标的影响。结果表明,当采用四边支承时,满跨均布荷载起控制作用,跨中节点为敏感构件,与之相邻斜杆为关键构件;当采用纵向两边支承时,半跨均布荷载起控制作用,杆件和节点的敏感性指标在1/3跨处最大,支座处最小。当考虑初始缺陷时,杆件、节点重要性系数分别增大了41%和53%;当考虑压杆失稳时,杆件和节点重要性系数分别增大了45%和62%。通过对关键构件进行加强,可以优化该类结构的抗连续倒塌性能。     

板片结构稳定性分析的改进随机缺陷法

初始几何缺陷对板片结构体系稳定性的影响是板片结构计算和设计中的一个关键问题。提出一种考虑初始几何缺陷的改进随机缺陷法 ,它弥补了一般随机缺陷法人工计算量大的缺点 ,也回答了设计临界荷载和一致缺陷法得到的临界荷载的可靠性问题。实例为一试验模型 ,通过理想模型、一致缺陷法、改进随机缺陷法以及试验结果的对比 ,得出一些对板片结构体系设计和研究有益的结论。     

梅江会展中心张弦桁架抗连续倒塌分析

通过对天津梅江会展中心张弦桁架移除关键构件后的残余结构的承载力分析,得到张弦结构的支座、边索和边跨桁架支座处下弦杆等关键构件的破坏对结构承载力影响最大;为了模拟杆件失效前静力荷载产生的初始变形对结构连续倒塌的影响,采用考虑初始变形的全动力等效荷载瞬时卸载法模拟杆件失效。对支座、边索和边跨桁架支座处下弦杆失效进行连续倒塌动力分析,研究了纵向联系桁架对张弦结构抗连续倒塌的作用,得到平面张弦桁架通过纵向联系桁架组装成一整体,其整体性随着纵向联系构件抗弯刚度的增大而提高,共同作用效果明显。在此基础上,利用山墙的抗风柱,将边跨张弦桁架改变为多支点支承的普通桁架,设计时该抗风柱不仅承担水平风荷载,还承担竖向荷载,从而提高结构的抗连续倒塌能力。并根据该工程的特点提出集桁架支座、张拉端（锚固端）和桁架下弦管于一体的铸钢节点构造,不仅满足建筑要求,还使得该处节点承载力大大加强,可供相关工程参考。     

Analysis of plate deflections during ultimate strength experiments of corroded box girders

The objective of this work is to analyze the initial and post-collapse plate deflections based on measurement records of the experiments of three corroded box girders subjected to pure vertical bending loading inducing a compressive stress on deck. The effect of initial imperfections and corrosion degradation on the final post-collapse deformation shape has been investigated and a relationship between different loading responses, shape of initial imperfections and plate slenderness has been derived. Analyzing initial imperfections, plate slenderness and final post-collapse deformations, a slenderness criterion has been established to predict the post-collapse deformation shape.     

Imperfection sensitivity of plate girder webs subjected to patch loading

This paper is aimed at studying the influence of initial geometric imperfections on the postbuckling behavior of longitudinally stiffened plate girder webs subjected to patch loading. A sensitivity analysis is conducted herein using two approaches (deterministic and probabilistic) in order to investigate the effect of varying imperfection shape and amplitude on both, the postbuckling response and ultimate strength of plate girders under patch loading. This sensitivity analysis is performed by means of nonlinear finite element analysis. At first, the initial shape imperfections are modeled using the buckling mode shapes resulting from an eigenvalue buckling analysis. Thereafter, the amplitude of the buckling shapes for the various modes is varied, and then introduced in the nonlinear analysis. The results show the influence of these modes and amplitudes on the resistance to patch loading.     

负载下焊接加固钢结构压弯构件受力性能的影响因素分析

为研究负载下焊接加固钢结构压弯构件的受力性能,采用考虑焊接热影响的有限元分析方法,对不同初始负载、偏心距、长细比及焊接热输入等级等影响因素进行分析。完成了包括未加固压弯钢柱及加固压弯钢柱共72个构件的受力全过程模拟分析,获得了各因素影响规律,并验证了考虑二阶效应的新的名义应力比计算公式。结果表明:未加固构件的初始负载水平可通过二阶式反映;初始几何缺陷模式及大小影响失稳破坏方向及焊接残余变形大小;影响加固构件极限承载力的主要因素依次为偏心距、长细比、焊接热输入、初始应力比;影响焊接残余变形的主要因素依次为焊接热输入、初始应力比、长细比;为新编《钢结构加固设计规范》关于负载下焊接加固压弯构件设计计算方法提供了参考和依据。     

Strength assessment of steel plates subjected to compressive load and dent deformation

This work presents an assessment of the ultimate compressive strength of damaged steel plates with a local dent. Extensive non-linear finite element analyses are performed, where three groups of analyses are considered. In the first group, the effect of the dent orientation (longitudinal and transverse) is studied for three plate thicknesses. For the second group, the direction of the dent depth (upward and downward) with respect to the global initial imperfection is explored. In the third group, the variation of the dent size for several plate thicknesses and its influence on ultimate compressive strength is investigated. The post-collapse behaviours are discussed and the inflection plate slenderness with and without dent is observed, at which the behaviour of the plate changed. A certain dent breadth to the plate breadth ratio is established, revealing the different plate response. Based on the performed analyses, a generalised expression of the ultimate strength reduction factor due to dent is developed.     

Stiffened steel plates under uniaxial compression

The stability of steel plates stiffened with tee-shape sections under uniaxial compression and combined uniaxial compression and bending was investigated using a finite element model. The emphasis of the work presented in this paper was to find the parameters that uniquely describe the strength and behaviour of stiffened steel plates. A finite element model, validated using the results of tests on full-size stiffened plate panels, was used to investigate the scale effect for five dimensionless parameters. The parameters investigated were: the transverse slenderness of the plate, the slenderness of the web and flange of the stiffener, the ratio of torsional slenderness of the stiffener to the transverse slenderness of the plate, and the stiffener-to-plate area ratio. Average magnitude residual stresses and initial imperfections were assumed for this study.A parametric study covering a wide range of dimensionless parameters indicated that stiffened steel plates do not fail by stiffener tripping unless a bending moment is applied to create flexural compressive stresses in the stiffener. Although plate buckling and overall buckling were found to lead to a very stable post-buckling behaviour, the interaction between these two buckling modes was found to give rise to a sudden loss of capacity following initial plate buckling. The plate transverse slenderness, the stiffener slenderness-to-plate slenderness ratio, and the stiffener-to-plate area ratio were found to have a significant effect on this behaviour.A comparison of the numerical analysis results with API and DnV design guidelines indicates that the guidelines predict stiffened steel plate capacity with various degrees of success, depending on the governing mode of failure. Neither guidelines address the potential interaction-buckling phenomenon.     

On the size and shape of initial out-of-plane curvatures in structural glass components

For many structural glass components, buckling is known to be a major design issue, which is influenced significantly by several parameters. The latter include boundary conditions, slenderness and geometrical imperfections, in particular initial curvatures. However, in spite of their importance for building practice, experimental data for the latter are very poorly documented. Consequently, an extended experimental campaign is presented in which initial curvatures of 312 monolithic and laminated glass beams with a variable length, height, glass thickness, glass type and – wherever applicable – interlayer, have been accurately measured and analysed. Major conclusions have been drawn regarding the shape and the size of initial curvatures.     

Theoretical investigation on the behaviour of a plate strip undergoing local and global deformation

The behaviour of a plate strip with local as well as global imperfections is investigated in this paper. The function used to describe the deformation of the plate was based on a previously conducted experimental investigation. The behaviour of the plate well into the large-deflection post-buckling range has been considered. It is shown that various buckling modes are possible and the effects of the imperfections on the buckling and post-buckling behaviour are presented.     

Empirical formulations for estimation of ultimate strength of continuous stiffened aluminium plates under combined in-plane compression and lateral pressure

The present research was undertaken based on the results obtained by the same authors in a sensitivity study on the buckling and ultimate strength of continuous stiffened aluminium plates. Empirical expressions are developed for predicting ultimate compressive strength of welded stiffened aluminium plates used in marine applications under combined in-plane axial compression and different levels of lateral pressure. Existing data of the ultimate compressive strength for stiffened aluminium plates numerically obtained by the authors through the previously performed sensitivity analysis are used for deriving formulations that are expressed as functions of two parameters, namely the plate slenderness ratio and the column (stiffener) slenderness ratio. Regression analysis is used in order to derive the empirical formulations. The formulae implicitly include effects of the weld on initial imperfections, and the heat-affected zone.     

Flat bar steel ring stiffeners on cylinders subjected to external pressure

It is known that plates are not sensitive to initial imperfections, since, after buckling, their load deformation curve is upwards. Flat rings on circular cylinders are circular ring plates. Therefore, their postbuckling behavior is the same. This is proved theoretically in this paper. Hence, it follows that the slenderness of flat rings is not restricted by stability considerations, in contrast to the ECCS and BS 5500 recommendations.     

Torsional buckling of outstands in longitudinally stiffened panels

A non-linear finite element (FE) package has been used to investigate the torsional behaviour of flat-bar stiffeners in longitudinally stiffened panels subject to axial loading. The effects of plate slenderness, stiffener slenderness and boundary conditions have been studied including the modelling of the outstand both as part of a stiffened panel and in isolation. A simple analytical approach is proposed by using a theoretical mechanism model developed by Murray I combined with a simple elastic loading line to give an upper bound to the tripping failure load. The results are compared with existing design guidance.