外文翻译---通过建筑结构设计以改善建筑物的抗倒性.docx

外文原稿2The Twelfth East Asia-Pacific Conference on Structural Engineering and Construction Design of Building Structures to Improve their Resistance to Progressive Collapse D A Nethercota a Department of Civil and Environmental Engineering, Imperial College LondonAbstract：It is rare nowadays for a “new topic” to emerge within the relatively mature field of Structural Engineering. Progressive collapse-or, more particularly, understanding the mechanics of the phenomenon and developing suitable ways to accommodate its consideration within our normal frameworks for structural design-can be so regarded. Beginning with illustrations drawn from around the world over several decades and culminating in the highly public WTC collapses, those features essential for a representative treatment are identified and early design approaches are reviewed. More recent work is then reported, concentrating on developments of the past seven years at Imperial College London, where a comprehensive approach capable of being implemented on a variety of levels and suitable for direct use by designers has been under development. Illustrative results are used to assist in identifying some of the key governing features, to show how quantitative comparisons between different arrangements may now be made and to illustrate the inappropriateness of some previous design concepts as a way of directly improving resistance to progressive collapse.2011 Published by Elsevier Ltd. Keywords: Composite structures; Progressive Collapse; Robustness; Steel structures; Structural design1. Introduction Over time various different structural design philosophies have been proposed, their evolutionary nature reflecting：*cGrowing concern to ensure adequate performance. *cImproved scientific knowledge of behaviour. *c Enhanced ability to move from craft based to science based and thus from prescriptive to quantitatively justified approaches This can be traced through concepts such as: permissible stress, ultimate strength, limit states and performance based. As clients, users and the general public have become increasingly sophisticated and thus more demanding in their expectations, so it became necessary for designers to cover an ever increasing number and range of structural issuesmostly through consideration of the “reaching this condition would be to a greater or lesser extent unacceptable” approach. Therefore issues not previously considered (or only allowed for in an implicit, essentially copying past satisfactory performance, way) started to require explicit attention in the form of: an assessment of demand, modelling behaviour and identification of suitable failure criteria. The treatment of topics such as fatigue, fire resistance, durability and serviceability can all be seen to have followed this pattern. To take a specific example: designing adequate fire resistance into steel framed buildings began (once the need had been recognised) with simple prescriptive rules for concrete encasement of vulnerable members but it has, in recent years, evolved into a sophisticated discipline of fire engineering, concerned with fire loading, the provision of protective systems such as sprinklers, calculation of response in the event of a fire and the ability to make quantitative comparisons between alternative structural arrangements. Not only has this led to obvious economic benefits in the sense of not providing fire protection where it gave only negligible benefit, it has also led to increased fire safety through better understanding of the governing principles and the ability to act intelligently in designing suitable arrangements based on a proper assessment of need. Prior to the Ronan Point collapse in London in 1968 the terms robustness, progressive collapse,disproportionate collapse etc., were not part of Structural Engineering vocabulary. The consequences of the damage done to that 22 storey block of pre-cast concrete apartments by a very modest gas explosion on the 18th floor led to new provisions in the UK Building Regulations, outlawing for many years of so called system built schemes, demolition of several completed buildings, temporary removal of gas in high rise construction and the formation of the Standing Committee on Structural Safety. Eventually, the benefits of properly engineered pre-fabrication were recognised, safe methods for the installation of gas were devised and the industry moved on. However, the structural design guidance produced at that time - that still underpins much present day provision - was essentially prescriptive in nature with no real link to actual performance. Subsequent incidences of progressive collapse such as the Murragh Building and the World Trade Centre brought increased attention to the actual phenomenon and issues of how it might reasonably be taken into account for those structural designs where it was considered appropriate. In doing this it is, of course, essential to include both the risk of a triggering incident and the consequences of a failure so that the resulting more onerous structural demands are used appropriately. Arguably, a disproportionate response in terms of requiring costly additional provisions in cases where the risks/consequences are very low/very minor may be as harmful as failing to address those cases where the risks/consequences are high/severe. This paper will review current approaches to design to resist progressive collapse and contrast these with work undertaken over the past seven years at Imperial College London, where the goal has been the provision of a realistically based method suitable for use in routine design. The essential features of the method will be presented, its use on several examples described and results presented to illustrate how it is leading to a better understanding of both the mechanics of progressive collapse and the ways in which structural engineers can best configure their structures so as to provide enhanced resistance2.Design to resist progressive collapse The two most frequently used design approaches intended to address the issue of progressive collapse are:*cProviding tying capacity *cChecking alternate load pathsFigure 1: Tie Forces in a Frame Structure The first is essentially prescriptive and consists of ensuring that beams, columns, connections and floor (or roof) can act together to provide a specified minimum level of horizontal tying resistance; the actual values required are normally related to the vertical loading. Figure 1, which is taken from recent US Guidance (SEI 2010), illustrates the principle. The approach is simple to appreciate, requires minimal structural calculation and, in situations where the original provisions are found to be inadequate, can be made to work by providing more substantial connections and/or additional reinforcement in floor slabs In an interesting recent development, that recognizes the link to the generation of catenary action, US Guidance has restricted the use of tying between the structural members to situations in which it can be demonstrated that the associated connections can carry the required forces whilst undergoing rotations of 0.2 radiance. Where this is not possible, tying should act through the floors and the roof. However, recent studies (Nethercot et al 2010a; Nethercot et al 2010b) have suggested that tying capacity correlates poorly with actual resistance to progressive collapse. Moreover, being prescriptive, it does not permit the meaningful comparison of alternative arrangements - a fundamental feature of structural design. In its most frequently used form the alternative load path approach presumes the instantaneous loss of a single column and then requires that the ability of the resulting damaged structure to bridge the loss be demonstrated by suitable calculation (Gudmundsson and Izzuddin 2010). The approach may be implemented at varying levels of sophistication in terms of the analysis; for example, recent thinking in the United States (SEI 2010) makes provision for any of: linear static, non-linear static or non-linear dynamic analysis and provides some guidance on the use of each. It may also be used as the basis for more sophisticated numerical studies of particular structures and particular incidents e.g. forensic work; the best of thesewhich are likely to be computationally very demandinghave demonstrated their ability to closely replicate actual observed behaviour.3. Essential features of progressive collapse Three features have previously (Nethercot 2010) being identified as essential components of any reasonably realistic approach to design against progressive collapse:*cEvents take place over a very short timescale and the actual failure is therefore dynamic.*cIt involves gross deformations, generating large strains, leading to inelastic behaviour as well as change of geometry effects.*cFailure essentially corresponds to an inability of the structure in its damaged state to adopt a new position of equilibrium without separation of key elements.Figure 2: Simplified multi-level approach for progressive collapse assessment Additional features, designed to make the approach attractive for use by practicing Engineers have also been proposed (Nethercot 2010):*cProcess should consist of a series of steps broadly similar in concept to those used for “conventional” structural design.*cIt should, preferably, be capable of implementation at a variety at levels of complexitywith the choice reflecting the importance of the structure.*cAny required analysis should utilise familiar techniques; where these require computations beyond “hand methods”, these should be based on the use of available analysis software.*cA realistic and recognisable criterion of failure should be used.*cApproach should permit study of cause and effect and be suitable for the making of quantitative comparisons. It was against this background that the studies at Imperial College London have been undertaken. An approach incorporating the three essential features but observing the five desirable features was originally developed (Vlassis 2007); it has subsequently been refined (Stylianidis 2010). Although the starting point was column removal, the approach contains a number of distinctive features:*cAlthough dynamic response is allowed for, only static analysis is required (Izzuddin et al 2007).*cThe approach may be implemented at structure, sub-structure, floor grillage or individual beam level, see Figure 2.*cA realistic criterion of failure is employed, corresponding to reaching the ductility limits in connections.*cQuantitative comparisons between alternative structural arrangements may readily be made.*cThe approach may be implemented using only explicit formulae, thereby permitting simple and rapid calculation.Full details of the method, both in its original form which utilises ADAPTIC to perform the calculations and in its simplified form, may be found in the series of Imperial papers (2-12).*a)First yielding of the tensile components (top bolt row of the support connection)*b)Ultimate capacity of the beam flange at one of the connections (support)*c)Ultimate capacity of the system (failure of the bottom bolt row of the mid-span connection)*d)The axial load becomes zero (the deflection of the beam where the axial load changes from compressive to tensile)*e)The deflection of the beam where the axial load becomes equal to the flange capacity of one of the connections (mid-span connection)Figure 3: Non-linear static response for a single beam 中文翻译2通过建筑结构设计以改善建筑物的抗倒性D A Nethercota 土木与环境工程学院伦敦帝国学院摘 要：如今的“新话题”出现在相对成熟的结构工程领域这是一件罕见的事。抗连续倒塌，或者，更特别的是，了解力学的现象和发展适当的方式，以适应我们正常的框架内审议的结构设计，可以这么认为。在过去的几十年，从来自世界各地的插图画开始，到高高的世贸中心倒塌为止，这些功能必不可少的为具有代表性的治疗和早期的设计方法进行了综述。最近的工作是当时的报道，集中精力在过去7年在伦敦大学帝国学院的发展，在一个能使用各种水平和由设计师一直在发展适合直接使用的综合方法。说明性的结果是用来帮助发现一些关键的管理功能，去展示如何定量比较安排现在可能使和说明赫尔墨斯的一些以前的设计概念之间的不同来直接改善抗倒性。关键词：复合结构，渐进式折叠，鲁棒性，钢铁结构，结构设计1.引言随着时间的推移各种不同的结构设计原理被提出,他们发展的自然回想：*c越来越关注确保足够的性能。*c改进过的性能的科学知识。*c加强能力从工艺为基础的移动科学依据从而从规范的定量合理的方法。这可以通过追踪的概念,如:容许应力，强度极限，极限状态和基础性能。作为客户：用户和公众已经变得越来越复杂,因此要求更高的期望，因此，它成为必要的设计师代替一个永久的越来越多的结构性问题的范围的主要是通过考虑达到这个条件将或多或少受到不可接受的方法。所以问题不是以前认为（或只允许在一个隐式的,基本上复制过去的令人满意的性能,方式）开始需要显式的形式的关注：需求评估，模型行为和识别合适的失效准则。论题的处理比如疲劳，耐火性，耐久性和适用性都可以被看作是这个模式。举一个具体的例子：设计充分耐火钢框架建筑开始(已经被认可的)和简单的法定规则对混凝土外层脆弱的构件。但是,近年来,发展成为一个复杂的消防工程学科，关心火灾荷载，提供防护系统,如洒水装置，在发生火灾情况下的反应的计算,能够使定量对比结构安排之间选择。不仅导致了在某种意义上不提供防火时明显的经济效益,在它给了只有微不足道的好处的时候；它也导致了消防安全通道更好的调节原则的理解和明智的行事能力在设计适合安排一个合适的评估基础上的需要。在罗南点于1968年在伦敦坍塌之前，鲁棒性原则，抗连续性倒塌，非比例破坏等是不属于工程词汇里的。这栋在18层发生瓦斯爆炸被破坏的22层预制混凝土公寓建筑导致了新的英国建筑法规诞生。取缔了多年来所谓的系统构建方案，拆除了几个完整的建筑物，排除高层建筑物里的临时瓦斯和建立建构安全方面的常务委员会。最终，合理设计的预处理的好处是公认的，安全的方法来安装燃气设计然后开始进入工业。然后，结构设计指导在当时产生仍然决定了很多现在的条款是自然本质上的处方式,没有真正的链接到实际的性能。后来，连续倒塌的发生率如同Murragh Building和世贸中心带来增加如何合理地考虑那些结构的设计实际现象和问题的关注，它被认为是合适的。在这样做,当然,至关重要的风险,包括一个触发事件和失败的结果,所以更繁重的结构要求被适当地使用。可以说，一个不成比例的反应在风险/后果是很低/很轻的地方要求昂贵的附加条款的情况下，也许如同未能解决那些情况在风险/后果是高/严重的地方一样有害。本文将回顾当前用来设计抵制连续倒塌的方法和对比过去七年在伦敦大学帝国理工学院进行的这些工作，那里的目标是提供一个依据于实际方法适合用在常规设计。方法的基本特征将被提交，它被使用在几个例子的描述和结果来说明它是如何导致更好的连续倒塌的机制的原理和结构工程师的方式能最好的配置结构,以提供增强的抗性。2.设计抵抗连续倒塌两种最常用设计方法旨在解决连续倒塌这一问题：*c提供绑扎能力*c检查交替的荷载通道图1:领带部队在一个框架结构首先，本质上的规范和包括确保梁，柱，楼梯和楼板（或者屋盖）可以联合起来提供一个规定的低级的水平联系抗力等级；垂直荷载的实际值要求是通常有相关的。图1，这个来自最近的US Guidance，演示了原理。这个方法对于观察是简单的，只需要很少的结构计算和在最初的规定被发现是不充分的的情况下，能通过提供更多的实质性的连接或在一个有趣的近代发展中水泥楼板中施加额外加固，认识到链式反应的连接的生成，US Guidance已经限制可以展示相关的连接可以携带所需的弹性元件同时进行0.2光辉的旋转的情况的结构构件之间的绑扎的使用。这是不可能的，连系材料应该通过楼板和屋盖。无论如何，近代研究（Nethercot et al 2010a; Nethercot et al 2010b）都建议绑扎力相关较弱和实际抗力去抗连续倒塌。此外，它被规范不允许有意义的替代安排的比较结构设计的一个基本特征。在其最频繁使用的形式替代负载路径方法假定一个单柱的瞬时损耗，然后需要这作为结果的被损伤的构件的能力去渡过这个损失已经被合适的计算证明（Gudmundsson and Izzuddin 2010）。该方法可以在分析方面的高度化的不同程度被实现；比如，在美国最近的研究为线性静力分析，非线性静态或非线性动态分析制定规定和为各自的使用提供一些指导。它也可以被使用作为基点为特定结构或特定工作（如法医）的更精致的数字的研究；最好的这些可能是计算非常苛刻的已经证明了他们的能力去紧密地复制的真实的可观察的特性。3.抗连续倒塌的基本特性三个特征已经预先被鉴证出作为任何合理的现实的方法去设计对抗连续倒塌的必要部分：*c事件发生在非常短的时间段内和正在的失败是因此动态。*c它包括总变形，发生大应变，导致非弹性行为和几何效果的改变一样。*c失败基本上对应于在受损状态下构件的无能通过一个新的没有关键元素的分离的平衡位置图2:简化的多层次评估方法抗连续倒塌附加装置也有人提出，为了让这种方法被工程师使用。*c程序应该由一序列的在概念中广泛相似于那些用于“传统”的结构设计的步骤构成*c从实际出发，合理的，能够实现在一个复杂水平上的一个品种伴随选择反映结构的重要性。*c任何必需的验定都应该利用熟悉的技术；这里需要的计算多于“手工”，是基于可用的分析软件的使用的计算。*c一个现实的知名的破坏的准则应该被使用。*c方法应该允许原因和结果研究和适用于定量判断的制定。 正是在这样的背景之下,伦敦帝国学院的研究正在进行。一个结合了三个基本特征但是观察五个理想功能的方法最初被开发（Vlassis 2007）；它后来被开发的跟精确（Stylianidis 2010）。尽管出发点是柱移动，但该方法包含一些独特的特性：*c虽然动态反应是被允许的，但是只有静态分析是必需的（Izzuddin et al 2007）。*c该方法可以实现在结构，亚结构，地板格栅或单梁的标准（见图2）.*c一个现实的破坏标准被采用，对应于在连接中到达延性限制。*c定量对比替代结构安排可能容易就能做出。*c该方法可以实现只使用显式公式，从而允许简单和快速计算。该方法的完整细节，无论是原来利用ADAPTIC执行计算的形式还是在它的简化形式，应该都能在帝国文件中被找到（2-12）。 图3：单梁的非线性静力反应*a)首先拉力组件的产生（支撑连接的顶级螺栓排）*b)其中的一个连接（支撑）的光束翼缘的总功率*c)系统的总功率（底部中跨连接的螺栓行的破坏）*d)轴向载荷变成零（在轴向载荷从抗压到抗拉变化的地方的梁的挠度）*e)一个连接的翼缘力在轴向荷载变相等的地方的梁的挠度参考文献1 Gudmundsson GV and Izzuddin BA. The Sudden Column Loss Idealisation for Disproportionate Collapse Assessment. The Structural Engineer; 2010. 88 pp. 22-26. 2 Izzuddin BA, Vlassis AG, Elghazouli AY, and Nethercot DA. Assessment of Progressi ve Collapse of Multi-Storey Buildings. Proceedings ICE Structures and Buildings; 2007, Vol. 160. No. SB4 pp. 197-206. 3 Izzuddin BA, Vlassis AG, Elgha