Structural Repair Welwyn Garden City
Newman’s were recommended for a prestigious contract to restore the structural integrity to Welwyn Garden City’s council owned central library which was suffering from extensive cracking. Along with the consultants at MACE group and the principal contractor ASHE construction, we carried out a structural survey and proposed a design scheme.
ASHE were carrying out the refurbishment of the library and whilst removal of the original windows and installing aluminium frames it was found that there was major cracking and rotation of the masonry panels leaving them unsecured posing a severe health and safety risk.
Newman’s were instructed to diagnose the cause of the cracking and the rotation to the masonry panels. Our surveyors discovered that the masonry had sagged and rotated outwards as the original construction was defective.
The brick panels were built on a concrete frame and usually up to one third of the brick work over hangs the concrete toe. In this case it was discovered the concrete had become defective and the brick work was sat just over halfway on the concrete toe allowing the masonry to lean outwards and sag. As well as the rotation the brick slips had become loose and some areas of brick work had actually collapsed. This defect was discovered above every opening and window span to the library.
Our scheme had to restore the structural integrity of the masonry and provide a permanent solution that would be insured by a genuine insurance backed guarantee in the event of a failure for peace of mind for the client. Being approved Twistfix contractors and members of IGL we were able to provide such a scheme that was guaranteed for 20 years.
With deep helical beams installed into the masonry panels at 450mm centres the structural loads and sagging across the 25m span was spread throughout the panel preventing any further sagging. 9mm stainless steel CD DriveFix ties were selected as the installation process is rapid with just a 7mm pilot hole required and the tie becoming load bearing as soon as they are installed so there wasn’t any setting times preventing the structural integrity being restored. Cracks were raked out to a depth of 45mm and injected with Twistfix high strength rapid setting resin providing a secure bond between the separated masonry.
The underside of the concrete toe, that bears the full load of the masonry panels, was found to be suffering from concrete failure which was caused by oxidisation of the reinforcing rods. This was due to the original build as well, with the reinforcing being too close to the concrete allowing moisture penetration. This was repaired by Newman’s using a zincrich primer sealing the exposed steal preventing further corrosion. We then applied a heavy duty repair mortar reinstating the strength of the concrete. Brick slips were fixed back to the concrete toe using Twistfix cementitious grout and a 9mm pinning tie ensuring they will not be able to come loose or drop in the future.