Author: The Institution of Structural Engineers' Health and Safety Panel
27 November 2014
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The Institution of Structural Engineers' Health and Safety Panel
Director of Structural-Safety, Alastair Soane, explains why it's important to understand the reasons behind structural failures.
In the concluding part of this article, Sean Brady explores in more detail the technical cause of the Quebec Bridge collapse and the human factors that lay behind this.
A check on stability is required for all structures in both their permanent and temporary states. An unstable structure is one that can begin to displace significantly under a small disturbing force and where further gross displacement follows any initial displacement. Reported failures have usually arisen because the parties involved just failed to consider the possibility. Many failures have occurred during construction when elements of the structures are necessarily not interconnected, or in building refurbishment/demolition when stabilising elements have inadvertently been removed out of sequence. The forces that may cause instability are often unclear, but as a general principle, anything in its temporary or permanent condition should be considered to have an applied horizontal force acting. For external structures, an obvious force is wind. A clear danger for internal structures is the absence of wind, which leads to the possibility that a destabilising force will be overlooked.