The building comprises a concrete frame structure and cavity brick infill panels. Weathering and building movement have contributed to the development of a number of problems requiring remediation including masonry cracking and corrosion of the original wall tie system.
In 2000, two Helifix repair schemes were called upon to help with works conducted to repair the building’s southern elevation. DryFix ties were used to reconnect the external and internal brickwork leaves of each infill panel while RetroTies were used to connect the edges of each panel to the surrounding concrete superstructure. To install the DryFix, small undersize holes were first drilled through the external leaf and into the internal leaf. DryFix ties were then driven in to finish just below the surface of the near leaf using a Power Driver Attachment.
To install the RetroTies, pilot holes were drilled through the brick and into the concrete behind before the holes in the near leaf were enlarged to 10mm. RetroTies, 8mm diameter, were then power driven into the pilot hole in the concrete to create a mechanical connection. Finally, resin was injected into the clearance hole to chemically bond the exposed end of the tie to the near leaf masonry. RetroTies were used in preference to DryFix in this instance to accommodate differences in the densities and structural performance of the materials involved.
Tests conducted recently to assess the performance of these remedial wall tie systems confirm that both continue to provide structural security after nearly 10 years of continuous service. The results indicate the strong, on-going performance of the resin bond into the near leaf of the RetroTies and the strong, continuing mechanical performance of the DryFix and RetroTie connections into the internal brickwork and concrete columns respectively. A new round of work organised to repair the remaining three elevations is now under way, and following the successful demonstration of the long term performance of the original Helifix repair programme, DryFix and RetroTies are again part of the remedial schedule. By completion, several thousand DryFix and RetroTies will have been installed by teams of experienced installers working off swinging stages.