The project at 111 Old Broad Street incorporates prestressed stone trusses and mullion assemblies in its facade.
The
use of prestressing (or post-tensioning) in concrete structures is a relatively
common engineering technique. However, the application of this technology
to stone structures is a comparatively recent development and the small stone
section sizes required at Old Broad Street, presented a particular challenge
to the design team.
Working
in close collaboration with cladding contractor, Focchi and other specialist
subcontractors and suppliers, all aspects of the design had to be carefully
researched and analysed, from selection of the stone, including the required
quarrying and manufacturing techniques, to the assembly and installation
logistics and techniques.
Theoretical
assumptions were tested regularly throughout the design process using
technical mock-ups, culminating in a full size mock-up at the specialist
subcontractors works that demonstrated the assemblies ability to carry
the design loads of 2.5 tonnes with minimal deflection, and cope with
the typical loads and stresses that would be imposed on the prefabricated
units during transportations and installation.
