外文翻译通过建筑结构设计以改善建筑物的抗倒性.docx

1、外文翻译通过建筑结构设计以改善建筑物的抗倒性外文原稿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 r

2、are 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 d

3、esign-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 report

4、ed, 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

5、 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: Compos

6、ite structures; Progressive Collapse; Robustness; Steel structures; Structural design1. Introduction Over time various different structural design philosophies have been proposed, their evolutionary nature reflecting：* Growing concern to ensure adequate performance. * Improved scientific knowledge o

7、f behaviour. * 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

8、 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 unacceptabl

9、e” 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

10、 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

11、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

12、 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

13、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

14、 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

15、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 pr

16、oduced 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 phen

17、omenon 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 struct

18、ural 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 wil

19、l 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 m

20、ethod 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 resist

21、ance2.Design to resist progressive collapse The two most frequently used design approaches intended to address the issue of progressive collapse are:* Providing tying capacity * Checking alternate load pathsFigure 1: Tie Forces in a Frame Structure The first is essentially prescriptive and consists

22、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

23、 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

24、 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 radia

25、nce. 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 per

26、mit 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 brid

27、ge 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

28、 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 de

29、monstrated 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:* Events take pla

30、ce over a very short timescale and the actual failure is therefore dynamic.* It involves gross deformations, generating large strains, leading to inelastic behaviour as well as change of geometry effects.* Failure essentially corresponds to an inability of the structure in its damaged state to adopt

31、 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):* Process should cons

32、ist of a series of steps broadly similar in concept to those used for “conventional” structural design.* It should, preferably, be capable of implementation at a variety at levels of complexitywith the choice reflecting the importance of the structure.* Any required analysis should utilise familiar techniques; where these require computations beyond “hand methods”, these should be based on the use of available analysis software.* A realistic and recognisable criterion of failure should be used.* Approach should permit study of cause and effect and be suitable for the making