Vol. 13, No. 5, 2018

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The structural engineer's view of ancient buildings

Jacques Heyman

Vol. 13 (2018), No. 5, 609–615

Engineers, called on to advise on the repair of an old building — a cathedral, say — will usually have learned their skills in the design of modern buildings using modern materials — steel and reinforced concrete. Care must be taken in transferring those skills to ancient structures. In particular, the engineer is used to provide precise answers (for example, values of stresses) in order to satisfy criteria imposed by accepted practice.

Such an engineer will not have had occasion to consider the fact that a precise description cannot be given for the behaviour of any structure, modern or ancient. The states of all structures are critically dependent on unknown, and unknowable, defects in construction, and, above all, on unknowable movements of the environment. The footing of a column in a steel skyscraper, and the foundation of a pier carrying a tower in a cathedral, will in reality not be in the precise locations assumed by the engineer, and even small “defects” of this sort can have a very large influence on the structural state of the buildings being analysed.

Although unequivocal and unique answers cannot be given to questions that arise in the analysis and repair of old buildings, it is at least possible to calculate states of equilibrium with which a structure is “comfortable”. Although such states will not be observed in practice, their existence satisfies one of the basic theorems of plastic theory — if any one such state can be found, then this gives assurance that the structure is in fact safe. Further, it may be possible to calculate minimum and maximum values for important structural quantities.

ancient buildings, limit analysis, geometrical factor of safety, masonry equilibrium
Received: 18 April 2018
Revised: 3 December 2018
Accepted: 9 December 2018
Published: 6 April 2019
Jacques Heyman
Department of Engineering
University of Cambridge
United Kingdom