1、 外文原稿 2 The 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 London Abstract： It is rare nowadays for
2、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 reg
3、arded. 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 o
4、n 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
5、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； Pr
6、ogressive Collapse； Robustness； Steel structures； Structural design 1. Introduction Over time various different structural design philosophies have been proposed, their evolutionary nature reflecting： * Growing concern to ensure adequate performance. * Improved scientific knowledge of behaviour. * E
7、nhanced 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 inc
8、reasingly 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. There
9、fore 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 topi
10、cs 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 encasemen
11、t 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 betwe
12、en 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 int
13、elligently 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
14、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
15、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 ti
16、me - 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
17、 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
18、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
19、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 resistance
