Specialist supplier of suspended access systems to the building and construction industry Riggers Steeplejacks has designed a glass replacement rig system to remove and replace glass window panes on large glass buildings.
The glass carrier frame was specifically designed for the curtain wall system of 15 Alice Lane Towers, in Sandton, which has its north and south facades wrapped in a patterned ‘skin’ of panes of clear, dark grey and translucent glass.
Owing to the curve of the building, replacing a glass pane is difficult and hiring cranes or erecting scaffolding is impractical. The building, which is the head office of law firm Deneys Reitz, needed a solution to allow the large, broken panes of glass to be replaced without damaging the other panes, while also ensuring the safety of workers.
The frame is made from tubular mildsteel and has a power grip window sucker with electronically controlled suction cups that run off battery packs. It also features an early warning alarm system, which notifies technicians if the window is about to to fall or if the battery pack starts to go flat. The pane of glass is also attached to the rig with soft webbing slings to prevent any unnecessary movement.
The frame is fitted with tubular wheels with ball bearings, with rubber tracks to allow it to ride on top of the glass and to ensure that it does not damage the other glass panes. The wheels can pivot and turn to allow them to always be in contact with the glass.
Rope access solutions provider Skyriders was contracted to provide the rope access technicians and to test the glass carrier frame. “It was a challenging project as the top of the building had a 3-m-high parapet over which we had to get the rig and the two technicians,” says Skyriders marketing manager Mike Zinn.
Multidisciplinary construction and engineer- ing group Grinaker-LTA built scaffolding at the top of the building to enable the technicians to abseil down the building with the frame. It is lifted and swung over the edge of the parapet with an electric winch and is then transferred onto static ropes and lowered using traditional rope access techniques.
“The process was quite labour intensive,” says Zinn. The technicians had to lower themselves, the 200 kg rig and a 146 kg double glass pane. The technicians had to lower the rig in line with the broken pane and put the power suction machine in place to stabilise the broken glass.
They then had to cut and remove all the seals, remove the window and the old sealant. The broken pane was taken down, the rig dismantled, taken back up to the roof by an inter- nal lift, reassembled and abseiled down with a new pane.
New sealant was applied on the inside of the window frame and the new pane was installed with locking lugs placed on the window. This had to be left for 72 hours, after which the technicians removed the lugs and put sealant on the outside.
“The rig and the technicians could not go back up the outside of the building because the rig was not designed to be raised externally as it would require an electric winch and steel wire ropes, which would damage the facade,” Zinn explains.
At the base of the building, the technicians hung away from the building, owing to the inward curve. This problem was solved by Riggers Steeplejacks designing a specialised clip to insert into the grooves between the panes of glass, which allowed the technicians to pull themselves and the rig closer to the building.
Skyriders replaced four window panes, and the company expects to be contracted in future should any other window panes need to be replaced, as it has the methodology set up.