Reflecting the resurgent prosperity of western Europe in the middle of the twelfth century, a cadre of professional builders began to push the construction of Gothic churches to unprecedented heights. And in this quest, the builders encountered a new environmental realm. Lofty clerestory walls, in addition to having to resist the outward thrust of vaulting, were now subject to great wind forces, as were the high wooden roofs resting upon them. As the buildings grew larger, too, the design problems were exacerbated by what must have appeared to be the almost insuperable costs of obtaining and transporting stone, often from distant quarries, and of shaping and setting it into place. 1 Still another design restraint was imposed by the need to reduce the weight of the superstructure to relieve foundation loadings and hence reduce building settlements. It was the combination of all of these factors that led to the invention of the flying buttress and the consequent redefining of the style of Gothic churches.
Surviving records tell us almost nothing of the design techniques that were employed for so marked a technological achievement. We stand on firm ground, however, in ruling out the use of any kind of scientific methodology; more than four centuries would pass before the appearance of Galileo's seminal work in mechanics. The absence of structural theory eliminates also the possibility of quantitative modelling at small scale. Hence, the builders could not have predicted with any certainty whether or not structural elements perfectly valid in smaller buildings would perform reliably at the large scale of new construction. An important exception which is independent of scale, however, is gross stability against overturning under dead weight loadings. Indeed, a bench-top-size model could have served to indicate the gross stability of a full-scale building. And although the principles of this fact of structural behaviour would not have been known, its existence helped to offset some of the problems of new, large-scale design.
In view of the builders' inability to predict structural behaviour scientifically, the elegance of many Gothic structural solutions demanded some explanation. We suggested, on the basis of our structural studies, that the details of design could have been worked out with a crude type of experimental stress analysis performed during construction: tensile cracking observed in the weak lime mortar between building stones during the relatively long periods of construction could have led to refinements in design (Mark 1982:56). Building programmes in fact often called for the erection of one high bay at a time. In these instances, the first bays could have acted as experimental, full-scale models to fix the form of new building elements.
A case in point is the cathedral of Notre-Dame de Paris. The 33 m. (108 ft.) interior height of Notre-Dame's nave (c. 1180) exceeded that of all earlier Gothic churches by some 8m. (26 ft.). No doubt it was this singular increment in height that led its designers to employ flying buttresses for the first time to support the high clerestory walls. Unfortunately, we have only indirect evidence for the original configuration of this seminal structural device. Massive rebuilding of the cathedral, which altered the entire buttressing system, was begun in 1225, and extensive rebuilding was carried out again in the fourteenth and nineteenth centuries.
An archaeological reconstruction of the original, twelfth-century configuration of the Notre-Dame nave which included also structural modelling was recently developed by W.W. Clark and myself (Figure 1). The
Figure 1Analytical drawing of the reconstructed twelfth-century nave of Notre-Dame de Paris. (Source: after Clark and Mark 1984)
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Publication information: Book title: Companion to Contemporary Architectural Thought. Contributors: Ben Farmer - Editor, Hentie Louw - Editor. Publisher: Routledge. Place of publication: London. Publication year: 1993. Page number: 244.
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