St John’s College, one of 31 colleges at the University of Oxford, is a Grade I listed building dating back to the 16th and 17th centuries. The east and west façades of the Canterbury Quadrangle feature ornately decorated elements supported by a series of stone columns. During the original construction, these stone columns were installed with the layers of sedimentary rock oriented vertically rather than horizontally, leading to the development of fissures over time.
RDG was commissioned to design a temporary propping scheme to enable the safe removal and replacement of the columns while also accommodating the refurbishment of the permanent foundations. An initial site inspection revealed that the capital stone was not a monolithic piece, making it unsuitable for transferring loads.
The frontispiece features double columns flanking a central arch, supporting an ornate façade above. The stonework was securely supported by a T-shaped header beam arrangement, integrated into the temporary works for effective load transfer. To minimise congestion around the foundations, the temporary works were designed with inclined props positioned at three strategic points around each column.
The arches along the rest of the façade were supported using a compressive layer of shaped plywood fronted with Filcor, designed to distribute loads onto a propped scaffold system. Existing services close to the surface of the courtyard ground restricted the size and placement of the temporary works foundations. Raking members were used to transfer loads from the wide arch support frames to the narrow concrete foundations.
Steel lifting frames were designed to safely lift, manoeuvre, and position both the existing and replacement stone column pieces. All temporary works were engineered to limit deflections to 2mm, a precautionary measure to prevent settlement during the scheduled works.
