CONSULTANT ARUP last week blamed botched bolt installation for the failure of a timber strut in the roof of the Scottish Parliament debating chamber three weeks ago.
Preliminary investigations revealed that one of the two 10mm diameter bolts connecting the strut to its stainless steel node was missing and the other had no head.
The 4m long laminated oak strut came free from its lower node connection and swung down over the heads of MSPs on 2 March (NCE 9 March).
The strut and damaged bolt were shipped to Stanger Material Science in St Albans for investigation.
Original structural engineer Arup delivered its preliminary report to the Scottish Parliament Corporate Body (SPCB) last Friday.
The report says Stanger had concluded that the failed bolt had jammed during installation due to cross threading.
An attempt had apparently been made to remove it 'so twisting the head off, or coming close to it, ' says the report.
The report also says that one of the two upper connection bolts removed when the strut was lowered was found to be too short, fuelling suspicions about poor installation.
Arup and the SPCB refused to identify those responsible for inspecting the node connections after installation.
The project was procured under a construction management contract, with Bovis Lend Lease acting for the client. Laing O'Rourke was the trade contractor for the roof, although the struts were laminated and fittd by Cowley Structural Timber Work.
Arup's report also contradicted claims by some project sources that the bolts were for location purposes only.
It said that there were certain load cases where 'some timber struts are required and were specified to take tension loads'.
But when contacted by NCE it refused to answer detailed questions on the roof and connection design (see box), saying only that it would be reporting to the SPCB in two weeks.
Arup has ruled out inspecting every node connection and replacing any damaged or missing bolts.
Instead it proposes to modify the strut connections 'by adding some unobtrusive additional components.'