Progressive collapse of cold-formed steel framed structures

This study investigated the possibility of progressive collapse of a cold-formed steel framed structure. Five different analysis cases were considered, exterior wall column removal specified in General Services Administration (GSA) guidelines and Department of Defense (DoD) guidelines, corner wall column removal specified in GSA and DoD guidelines, and analysis by Successive Removal. The results showed that the removal of corner wall columns appeared to cause progressive collapse of a portion of the second and third floor of the end bay directly associated with the column removal, and not the entire building.     

Assessment of the Progressive Collapse Resistance of Double-Layer Grid Space Structures Using Implicit and Explicit Methods

A double-layer grid space structure is a conventional long span structure used where large column-free areas are required. Due to its’ large indeterminacy and the redundancy of its structural configuration, it is normally considered in design practice, that progressive collapse will not be triggered when the loss of an individual member occurs. However, research and several prior accidents have shown that progressive collapse could occur following the loss of some critical members when the structures are subject to abnormal loading such as heavy snow. To investigate the structural behavior of this type of structure, a 3D finite element model of a double-layer space structure grid was built by the authors, several collapse scenarios have been investigated using an implicit method which follows the alternative path method defined in GSA. In addition, case studies have been made using the explicit method which is to simulate the whole process of the structural collapse. In the analysis, different members failure or support collapses were studied. The response of the structure was investigated and the correspondent potential of progressive collapse was discussed in detail. Methods to mitigate the progressive collapse of this type of space structure have also been recommended.     

基于多尺度建模的高铁站雨棚结构抗连续倒塌分析

高速通过的失控列车是高铁站雨棚结构的倒塌风险源,对雨棚结构进行抗连续倒塌分析具有重要意义。为兼顾有限元分析的精度和效率,引入一致多尺度有限元结构建模方法,通过算例验证其应用于结构倒塌动力分析的合理性与准确性。以某高铁站的2个雨棚结构为背景,选取易受失控列车影响的区域建模,利用LS-DYNA建立多尺度模型。采用拆除构件法分析拆除柱后剩余结构的非线性动力行为,以考察雨棚结构的抗连续倒塌性能。结果表明:对于钢结构屋盖雨棚而言,拆除边柱、次边柱和中柱后,拆柱点竖向位移分别为17.6、13.1、12.4 mm,对应的梁端转角依次为0.001 5、0.001 1、0.001 1 rad,均小于规范限值0.009 6 rad,即钢结构屋盖雨棚在3种拆柱情形下均未发生倒塌; 对于钢筋混凝土屋盖雨棚而言,拆除边柱和次边柱后,结构均发生了局部坍塌,但坍塌未延续,即不会发生连续倒塌; 拆除中柱后,拆柱点竖向位移为88.6 mm,对应的梁端转角为0.007 7 rad,小于规范限值0.04 rad,即钢筋混凝土屋盖雨棚结构变形较小,未发生倒塌。     

Toward an economic design of reinforced concrete structures against progressive collapse

A three-dimensional discrete crack model based on the Applied Element Method is used to perform economic design for reinforced concrete structures against progressive collapse. The model adopts fully nonlinear path-dependent constitutive models for concrete and reinforcing bars. The model applies a dynamic solver in which post-failure behavior, element separation, falling and collision are predicted. First, the model is used to study the behavior of multi-story reinforced concrete buildings designed in a traditional manner according to the ACI 318-08 and subjected to accidental removal of one or two central columns at the ground level. In an iterative way, the model is then used to investigate a safe design against progressive collapse for such extreme loading case. Based on the analytical results of the AEM, it can be concluded that the collapse of only one column would not lead to any progressive collapse of the studied reinforced concrete structure. However, the collapse of more than one column may lead to a progressive collapse of a considerable part of it. It is concluded also that the AEM could be successfully used as an analytical tool to suggest economical designs that are safe against progressive collapse of reinforced concrete structures.     

柱贯通梁柱节点非对称钢筋混凝土柱-钢梁框架结构抗连续倒塌性能研究

建筑结构竖向连续倒塌破坏大多数由侧中柱破坏引起,而侧中柱两侧结构的抗侧刚度不同,易导致结构沿侧中柱发生非对称破坏.已有文献中对非对称连续倒塌研究相对较少,鉴于此,以非对称双半跨单柱子结构为研究对象,设计了1种钢筋混凝土柱-钢梁(RCS)结构全螺栓连接的柱贯通节点子结构,采用静力加载试验模拟结构在侧中柱失效工况下的非对称...     

Progressive collapse performance analysis of precast reinforced concrete structures

In this paper, the progressive collapse performance analysis of precast reinforced concrete (RC) structures is performed. A numerical simulation framework for precast RC structures is developed on the basis of the OpenSEES software, where the fiber frame element is used for beam and column type members and Joint2D element is used for the beam‐to‐column connections. The conjugated material models are then introduced, and a min–max failure criterion is imposed on the original models to reflect the steel fracture and concrete crushing when the structure is undergoing progressive collapse. In addition, to overcome the computational difficulties arisen from progressive collapse behavior, two enhanced nonlinear solutions , that is, the consistent quasi‐Newton algorithm and the explicit KR‐α algorithm, are employed, respectively, for static and dynamic analysis. A 10‐storey prototype precast RC structures is designed to verify the developed numerical framework, and the progressive collapse resisting mechanism of the structures is investigated through both static pushdown analysis and dynamic column‐removal analysis. Finally, influences of some typical parameters in precast RC structures on their progressive collapse performance are studied.     

超长复杂隔震结构抗连续倒塌性能分析

以某医院的超长复杂隔震结构为工程背景,对超长复杂隔震结构进行了抗连续倒塌研究。运用非线性有限元软件建立考虑楼板作用的精细三维模型和未考虑楼板作用的简化三维模型,通过非线性动力拆除构件法对两种模型进行了分析,对比两种模型的抗倒塌能力。结果表明：该超长复杂隔震结构仅拆除1根柱时,结构未发生连续倒塌,且角柱对该隔震结构的连续倒塌影响较大|拆除2根柱时,未考虑楼板作用的简化三维模型发生了连续倒塌,而考虑楼板作用的精细三维模型未发生连续倒塌。因此,不考虑楼板作用的简化三维模型计算结果会偏于保守,进行结构抗连续倒塌时需考虑楼板的影响。     

基于随机Pushdown方法的钢筋混凝土框架结构抗连续倒塌能力概率评估

为了评估钢筋混凝土框架结构的不确定性参数对其抗连续倒塌能力的影响,将确定性Pushdown分析与可以控制相关性的拉丁超立方体抽样方法（LHS）相结合,提出一种随机Pushdown方法。为说明方法的建立和应用,选择一栋8层4跨的钢筋混凝土框架结构,考虑结构的荷载、材料强度以及几何尺寸等17个不确定性参数,采用Pushdown方法分析获得的结构所能承受的最大竖向荷载作为其抗连续倒塌能力,统计得到结构连续倒塌易损性函数,并采用“龙卷风图”方法对不确定性参数的灵敏度进行了分析。结果表明,结构不确定性参数对抗连续倒塌能力影响显著,结构的抗连续倒塌能力的变异系数达到20%,其中,活荷载、楼层恒荷载、钢筋极限应力以及梁截面钢筋面积等参数对结构抗连续倒塌能力的影响最为显著。     

建筑物抗连续倒塌研究现状和亟待解决的问题

主要介绍了目前国外对结构进行连续倒塌评估和设计的方法,比较了各国规范相关条文的异同,概述了目前的连续倒塌试验研究方法,提出了结构连续倒塌研究中亟待解决的问题,为进一步研究提供参考。     

虹桥综合交通枢纽结构连续倒塌分析研究

为减少局部构件破坏引起结构连续倒塌的可能性,对虹桥综合交通枢纽东交通广场B3结构单元进行了3个单柱失效和1个双柱失效情况下的结构连续倒塌分析。采用有限元程序LS-DYNA对结构进行非线性动力分析,构件破坏判断标准参考美国国防部规范UFC4-023-03的要求。研究结果表明：在不同位置单柱失效情况下,该框架结构发生了局部破坏,但破坏限制在去除构件周围的一定范围内;支撑的存在可改变破坏路径;在双柱失效情况下,结构破坏范围明显加大,但最终破坏仍限制在局部范围,不会造成整体结构的连续坍塌。     

建筑结构抗连续性倒塌研究进展与发展趋势

偶然荷载作用下结构可能会发生局部破坏而引起大范围或整体结构的连续性倒塌,建筑结构的连续性倒塌已经成为严重威胁公共安全的重要问题和土木工程学科的前沿课题.2001年美国"9·11"世贸大楼倒塌事件后,国内外学者聚焦结构抗连续性倒塌研究,对不同类型结构的倒塌机理、鲁棒性评价及设计方法等进行了深入研究,取得了诸多代表性的成果...     

基于GSA指南的RC框架抗连续倒塌的线性静力分析

结构连续倒塌分析是结构抗连续倒塌能力评定和抗连续倒塌设计的基础,已成为当前土木工程界国内外的热点研究领域.结构连续倒塌的分析方法有线性静力分析、非线性静力分析、线性动力分析和非线性动力分析4种.基于设计效率和实用性,本文采用GSA指南的静力线性分析方法,对按我国规范设计的5层钢筋混凝土结构进行连续倒塌分析,选取不同位置拆除承重构件并计算剩余结构破坏情况的性能指标DCR值,最后,根据DCR值考察其抗连续倒塌能力.     

恐怖爆炸下建筑物连续性倒塌研究进展

爆炸袭击是当前恐怖活动中最经常也是危害最大的一种方式,是造成建筑物连续性倒塌的最主要原因。近年来,随着恐怖活动的日益猖獗,建筑物连续性倒塌越来越受到工程界的关注,并已成为一个研究热点。回顾了建筑物连续性倒塌研究的历史,明确了建筑物连续性倒塌的定义、原因及其分析目的与流程。归纳分析了目前连续倒塌分析的几种方法:备用荷载路径法、局部抵抗特殊荷载法、构造设计法以及连续性倒塌仿真,详细阐述了备用荷载路径法。提出了对今后研究方向和难点的思考。     

地震作用下钢筋混凝土框架结构倒塌全过程振动台试验研究

以玉树7.1级地震中某底层遭到严重破坏的钢筋混凝土（RC）框架结构为原型,设计了1个1∶5缩尺的三维模型,通过模型的倒塌全过程振动台试验,研究了汶川、玉树地震中高烈度地区RC框架结构出现的典型侧向逐层呈多米诺骨牌式连续倒塌现象的全过程和倒塌破坏机制。试验中该模型结构的倒塌过程共分为两个阶段,即侧向增量倒塌和竖向连续倒塌。当底层层间位移角达到1/19时,试验模型处于临近倒塌状态。在倒塌过程中,底层角柱C3最先丧失竖向承载力,此时竖向倒塌开始发展,结构在重力荷载及输入地震动的共同作用下,底层柱的水平侧移持续增加,造成其相邻的柱B2、B3、C2相继失效,丧失竖向承载力,模型结构的冗余度不足使结构产生更大范围的竖向倒塌,最终模型结构呈侧向逐层连续倒塌。通过对倒塌后废墟的研究,发现模型结构呈“强梁弱柱”型破坏,其破坏模式与震害调查结果一致。最后,讨论了此种废墟下人员生存空间的问题,给出了防RC框架结构倒塌的相关建议。     

建筑结构连续倒塌概念设计

建筑结构的连续性倒塌已三成为国内外的一个研究热点.在对现有连续倒塌概念分析比较的基础上,给出结构发生连续性倒塌的主要特征及其本质,并分析抗震设计和抗连续倒塌设计的异同点,讨论基础设计在结构连续倒塌控制设计中的作用.     

The influence of joints and composite floor slabs on effective tying of steel structures in preventing progressive collapse

The event of the terrorist attack on 11th September 2001 in the USA has attracted increasing attention of researchers and engineers on progressive collapse of structures. It has gradually become a general practice for engineers to consider progressive collapse resistance in their design. In this paper, progressive collapse of steel frames with composite floor slabs is simulated by the finite element method. The numerical results are compared with test results. The influence of the joints and the concrete slabs on the effective tying of steel beams is investigated through parametric studies. From the analysis, methods of preventing progressive collapse that can be considered in design and when retrofitting existing structures are proposed. The results show that retrofitting a structure with pre-stressed steel cables and an increase of crack resistance in the concrete near joints can effectively improve effective tying of a structure, which results in an enhanced structural capacity in preventing progressive collapse.     

RC框架结构连续倒塌影响因素与破坏机制的研究现状

鉴于近年来国内外连续倒塌事件时有发生,并带来大量的人员伤亡和巨大的经济损失,针对当前影响结构倒塌性能的主要因素及其倒塌破坏机制研究进展进行了综述。结果表明:楼板对结构抗连续倒塌的作用不可忽略;柱失效位置和柱距对结构抗连续倒塌性能具有重要影响;与不考虑节点影响时相比,考虑节点影响时结构的抗连续倒塌承载力降低;填充墙和抗震设计对结构抗连续倒塌能力有益;框架梁上先后作用梁机制（压拱机制）和悬链线机制,板上先后作用压膜机制和拉膜机制,但不同构件作用机制之间的耦合作用和度量指标等研究不足;今后的研究中要加强试验测试工作和倒塌影响的定量化研究,并体现到设计方法中,同时要加强偶然荷载的碰撞冲击对结构倒塌性能的影响研究。     

偶然荷载结构抗连续倒塌的设计方法

对于结构抗连续倒塌的设计研究,国外的设计规范中相继作了相关的抗倒塌要求规定,但是这些规范给出的只是概念性的要求,没有可操作可实施的设计方法,国内的设计规范此方面的研究还是空白。因此目前结构设计难以实现抗连续倒塌的性能设计。本文采用静力非线性有限元倒塌分析法,进行连续倒塌计算分析,提出与中国设计规范背景相适宜的、具有可操作性的抗连续倒塌设计方法。     

复杂高层钢结构抗连续倒塌能力分析关键技术研究

基于拆除构件法,通过显式动力有限元分析,对复杂高层钢结构待拆构件的选择、构件失效的模拟方法以及构件损伤评价标准的制定等关键技术进行了研究。结果表明：对于高层钢结构,竖向构件的敏感性可基本反映待拆构件的重要性,水平构件的敏感性可反映剩余结构发挥抗倒塌机制的储备大小。此外,还建立了基于美国性能化设计评估方法FEMA 356纤维模型的构件失效模拟方法,可使构件在动力响应过程中的失效破坏既满足FEMA 356构件变形极限又满足材料应变极限,同时还可依据FEMA 356中的构件性能水准与微观应变的对应关系评价剩余结构构件的损伤程度。运用该方法对案例工程钢结构的抗连续倒塌能力进行分析,结果表明：关键构件拆除后,结构未发生连续性倒塌,剩余结构能够形成有效的承载替代路径;大部分构件的塑性转角未达到IO水准,发生较大塑性变形的构件主要集中在替代路径的承载构件上。     

Influence of seismicity level and height of the building on progressive collapse resistance of steel frames

Influences of building height and seismicity level on progressive collapse resistance of buildings are investigated in this paper. For the height, 4‐story, 8‐story and 12‐story steel special moment resisting frames are focused. The obtained results indicate that taller buildings are safer against progressive collapse. To study the influence of seismicity level, different four‐story structures having special moment resisting frame systems are designed for different levels of seismicity, namely, very high, high, moderate and low. The structures are evaluated, using nonlinear dynamic method and two main scenarios of the codes, including sudden removal of a corner and a middle column in the first floor. Some graphs are presented for progressive collapse resistance of the structures, depending on their seismic base shears. It is shown that the structures designed for greater seismic base shears are more resistant against progressive collapse. Copyright © 2016 John Wiley & Sons, Ltd.