Seminar - David Nethercot - Design Against Progressive Collapse: Understanding the Mechanics and Developing a Procedure

Tuesday 20 July 2010, 2.00 pm - 3.00 pm
Civil Engineering Lecture Theatre 1

Professor David Nethercot
Department of Civil and Environmental Engineering
Imperial College London

Abstract:
Collapse of the World Trade Centre placed progressive collapse on the TV screens of the world. Questions were asked about why this happened, could it have been prevented, was our understanding sufficient and, most importantly, what might be learnt and used to ensure a better future. In structural engineering terms, whilst this was the most spectacular illustration of progressive collapse, it was by no means the first, Oklahoma City and Ronan Point had previously shown what might happen to structures subject to locally severe effects. But comparatively little of the underlying physics of the problem, nor how it should best be tackled in structural design, was known. Available treatments tended to be prescriptive i.e. “Doing this should lead to better performance than not doing it”, and quantitative approaches permitting objective comparisons of alternative solutions were lacking.

Work at Imperial College London during the past 5 years has seen the development of a method for assessing susceptibility to progressive collapse. Essentially, it tests the ability of the damaged structure to attain a new equilibrium position in its grossly deformed state without triggering a progressive collapse. The method recognises the dynamic nature of the event, allows for inelastic material behaviour and gross changes of geometry, incorporates analysis to varying degrees of sophistication and can be applied to substructures ranging from a single beam to a complete 3 dimensional frame. Its basis will be explained, its implementation in a variety of forms illustrated and some results presented to show how it is now possible to assess the contribution of different components in resisting progressive collapse and thus in developing effective structural arrangements that eliminate potentially weak elements but do not require wholesale upgrading.