PARTIAL FAILURE of a massive thrust bearing has emerged as the most likely cause of the fault which closed Glasgow's 105m high 'Wing Tower' this week.
Designed by Millennium Dome structural engineer Buro Happold, the dramatic £8.5M structure is designed to rotate through 360¦ to continuously face the wind. It is the focal point of the Glasgow Science Centre (GSC) and was opened less than a year months ago.
A GSC spokesman confirmed that the entire 450t tower appeared to have settled 15mm into the 15m deep pit which houses the lower bearings.
'Last week, we discovered that the sprockets on the four drive motors no longer lined up with the drive chain welded around the base of the main tower, ' the spokesman explained. 'Instead, they were fouling the edges of the chain, causing high friction and excessive wear.'
This chain is at ground level, where the tower is supported by a turntable mounted on roller bearings made by Stockholmbased SKF. (NCE 21 September 2000). Below this, a steel 'root cone' extends down to the bottom of the pit, where a radial roller bearing taking overturning loads surmounts the suspect thrust bearing.
According to a spokesman for main contractor Carillion, the bearing housings show no sign of displacement. 'We are planning to jack up the tower and remove the bearings to see what has happened, ' he said.
Provision was made in the design to allow this jacking process so that the bearings could be replaced at the end of their 20 year design life.
The GSC spokesman confirmed that it has been concerned about water and oil leaking into the base pit for some time. Corrosion of the beams is an obvious possibility, he added.
Water in the basement pit could have caused corrosion.