ATTEMPTS TO fast track roofing work on an Australian aircraft hangar could have caused its collapse last year, investigators said this week.
Roofing work began during erection of the structure instead of before the operation.
The accident at RAAF Fairbairn in Canberra occurred last May as the structure was stress erected by Australian structural engineering company Strarch (NCE 5 June). No one was hurt.
The hangar was assembled at ground level, then partially raised using a method known as stress erection before roofing work began.
But staged erection may have overloaded temporary sliding plates used as longitudinal restraint during the lifting operation, said Kourosh Kayvani, a structural engineer at Connell Wagner, and principal investigator for ACT Work Cover. This caused them to fail, he added.
The patented steel portal frame structure is erected by stressing tendons running through the bottom chord of a roof truss to lift it off props into its final arched position.
Sliding plates called 'gap locks' allow the sections of the bottom chord to close together and shorten as the structure is raised into an arch.
Kayvani said that partially stress erecting the structure and removing supports beneath it would have created a 'complex stress state'. This exerted unforeseen loads on to the gap locks causing the bolts holding them together to shear.
Kayvani said the decision to partially erect the structure was taken to introduce curvature into the roof to make cladding easier.
But a source from Work Cover said that the project was running behind programme and that the cladding was applied while in the partially erected state to save time.