For the second day running, the head of the University of Pretoria’s Materials Science and Metallurgical Engineering Department, Roelf Mostert, gave evidence in the Department of Labour inquiry into the Grayston bridge collapse last year that killed two people and injured 19 others.
On Friday, Mostert, who is an expert witness for Murray & Roberts, reiterated his earlier testimony that "material failure" contributed to the collapse of the temporary bridge structure across the M1 near the Grayston Drive off-ramp on 14 October 2015.
On Thursday, Mostert had told the inquiry, sitting in Pretoria, that there was no noticeable movement on the structure until it collapsed and that it was his view that "material failure" contributed to the collapse.
However, on Friday, when Willem le Roux from the Johannesburg Development Agency quizzed Mostert about what the Murray & Roberts probe found as the reason for the collapse of the bridge, the professor declined to elaborate.
"I can’t comment on the actual cause of the collapse, only that material failure," Mosert said.
Murray & Roberts erected the support structure‚ including scaffolding and super beams. It has previously told the inquiry that it sub-contracted Form-Scaff to design the structure. The sub-contractor has denied doing so.
Mostert told the inquiry that he tested 20 samples of couplers, similar to the ones used on the structure, and was of the opinion they were not strong enough.
William le Grange from Formscaff, however, said that the couplers used on the bridge that collapsed were of good quality.
"The couplers are good quality, but not tightened enough," he insisted.
Le Grange cast doubt on Mostert’s evidence because the couplers he tested were not the actual ones used on the bridge.
The inquiry will resume on Monday.