Medieval builders did not have a scientific structural theory, however gothic cathedrals were not built without a theory. Gothic masters had a ‘scientia’ and this scientia was firmly based on geometry. It is the form which guarantees a safe state of equilibrium. In many gothic sources we find rules to design the structural elements, with special emphasis in buttress design. These rules lead in most cases to a proportional design, independent of scale (the depth of a buttress as a fraction of the span). The late-gothic Spanish architect Rodrigo Gil formulated arithmetical rules which lead to non-proportional designs (the buttresses become more slender as the general size grows). Gothic structural rules were a means to register stable forms. Proportional rules are essentially correct and apply to most cases. Rodrigo Gil’s rules express a finer adjustment to some non-proportional problems: buttress design for thin late-gothic vaults or wall design for towers. Prof. Santiago Huerta, PhD Departamento de Estructuras. ETS de Arquitectura. Universidad Politécnica de Madrid, Avda. Juan de Herrera, 4. 28040-Madrid. Spain
This paper seeks to determine the horizontal support movements necessary to cause collapse for a rigid-block arch. For masonry arches in historical buildings, small movements of the supports can destabilise the arch and can lead to collapse over time. As the supports move apart, the geometry of the arch adapts, causing the crown of the arch to descend, which increases the value of horizontal thrust. A rigorous application of thrust line analysis illustrates that various hinge locations are possible for extreme geometry changes. New computer programs are used to track the changing equilibrium conditions as the supports move and the results are verified experimentally. The analysis is extended to consider an arch supported on leaning buttresses and is illustrated by a case study. John A. Ochsendorf, BSc, MSc, PhD Assistant Professor of Building Technology, Massachusetts Institute of Technology, Cambridge, MA 02139 USA