The Collapse of Holyrood Abbey
Sexpartite vaults were used initially in the nave of Holyrood Abbey, probably so their lateral thrusts could be distributed to more supports along the lateral wall (as discussed in the ribbed vault section). This vaulting system, coupled with narrow clerestory windows, was adopted as a conservative solution because of the uncertainties surrounding containment of lateral thrusts in the upper structure. The replacement of the sexpartite vaults in the nave with quadripartite vaults in the early 16th century subsequently resulted in signs of geometrical instability. Consequently, a system of flying buttresses were installed to contain the lateral thrusts from the nave vaults, and thus reduce the lateral deformations in the upper structure. The weight of the upper structure would have been transferred through the classic elevation of clerestory, triforium, and arcade. As for the aisle vaults, their transverse thrusts were sufficiently contained by the outer church wall and nave piers which were already highly stabilised by the weight of the upper structure. This flow of forces, which is typical of most Gothic structures, is illustrated in the figure adjacent to this text. As a consequence of periods of warfare, riots and neglect, the roof of the Abbey was extensively decayed and this ultimately prompted its replacement in 1758. A somewhat questionable decision was taken by the architect of the time to replace the timber roof trusses with stone diaphragm arches. These 40cm thick arches rested on the extrados of the vault at 61cm centres, and coupled with the stone flag roof they supported, would have placed a tremendous load on the already delicate upper structure. Despite noticeable deformations in the lateral wall, which were sufficient to cause a voussoir of one the arches to fall down, no mitigating action was taken and a progressive collapse began on 2nd December 1768. This collapse took out the entire nave vaults, north arcade and aisle vaults, however the south aisle vaults are still standing. The clerestory of the south aisle has gone, with only the triforium and arcade remaining. Today, with much more appreciation of critical load paths and the importance of containment of lateral thrusts, it is unlikely such an ill-informed restoration would ever be repeated. Anything that compromises the delicate transfer of loads through these structures could place the structure in a perilous state, as was the case in Holyrood. This forms the motivation for our thesis, as there are still many aspects of vault collapse which are not fully understood. We will therefore be building upon Dr. Theodossopoulos' extensive research into the vaults of Holyrood Abbey to determine the effect of the instability of the upper structure on the side aisle vaults, i.e. when the side vault abutments are spread. |
All photos are the property of Michael Scott or James Sanderson unless otherwise stated.
© 2013 James Sanderson and Michael Scott | All rights reserved.
School of Engineering, College of Science and Engineering, University of Edinburgh
© 2013 James Sanderson and Michael Scott | All rights reserved.
School of Engineering, College of Science and Engineering, University of Edinburgh