The collapse of the Geldenhuys pedestrian bridge on the N3 last month was caused by an impact force on the pier in the median of the highway, an investigation commissioned by the South African National Roads Agency Limited (Sanral) has established.
An independent investigation into the incident by Superstructure Consulting Engineers has found that the impact was caused by an 18.1 t coil of steel that was found lying 100 m north of the collapsed bridge on the N3 northbound.
The weight of the coil of steel, and moving at speed, can induce an impact force far more than the pier’s capacity, Sanral said on Wednesday.
The report stated that, statistically, it is an extremely rare occurrence for a bridge support to be subject to an impact force of such an extreme magnitude at a height.
The pier was protected by the median concrete barrier, but the impact was higher up.
The coil was inspected at ArcelorMittal at its premises in Vanderbijlpark and the marks on the coil indicated substantial impact with concrete.
Sanral insurers are pursuing the matter with the third parties involved, while the South African Police Service is performing its own investigation into the coil and the transport vehicle involved.
Although the pedestrian bridge was no longer in use, it remained on Sanral’s bridge management system and was inspected as part of the roads agency’s general bridge inspection programme.
The last inspection was conducted in July 2016 and picked up no items of concern on the main structural elements, the roads agency said.