SCOTTISH PARLIAMENT structural engineer Arup this week confirmed that the strut which swung loose in the building's debating chamber almost certainly failed in tension.
It said that the strut should have been in compression under normal conditions.
No-one was hurt when the lower end of a 3.7m long, 100kg laminated oak strut swung free from its stainless steel connection (News last week).
But the chamber was evacuated and remains closed indefinitely.
Initial investigations revealed that one of the two 10mm diameter locating bolts in the connection had disappeared and the other had fractured (see diagram).
In a statement to NCE, Arup claimed that the bolts were designed to take load, 'although in most load arrangements at the connection in question the bolts would be unloaded'. This would be the case when the strut was subject to compressive forces only.
Arup said it was basing its investigation on three scenarios, including failure due to incorrect installation of the bolt and an under strength bolt. But its main line of enquiry centres on the reanalysis of the roof design.