Bridge collapse mystery solved
REPORT: 18-TON COIL OF STEEL ON VEHICLE HIT PIER
‘Marks on the road led from the point of impact to where steel coil came to rest.’
The recent collapse of the Geldenhuys pedestrian bridge over the N3 was caused by a heavy coil of steel on a truck hitting a supporting pier, the SA National Roads Agency (Sanral) said yesterday.
This was revealed in an investigation by Superstructure Consulting Engineers.
“The collapse of the Geldenhuys pedestrian bridge, B1187, on the N3 in the early hours of August 9, 2017 was caused by an impact force on the pier in the median of the highway, our investigation has established,” the roads agency’s acting engineering executive, Louw Kannemeyer, said.
Five people were injured in the incident. Driver Robert Banda was with his wife and their seven-year-old daughter when the bridge fell on their truck. They were badly injured and had to be hospitalised.
Kannemeyer said evidence suggested the impact was caused by an 18.1-ton coil of steel found lying 1 00m north of the collapsed bridge on the N3 northbound road.
“Marks on the road led directly from the point of impact to the position where the steel coil came to rest.”
The road agency said the weight of the coil of steel moving at a speed could induce an impact force far in excess of the pier’s capacity. Debris scattered radially away from the pier to more than 40m away, confirming an external impact force of very large magnitude. The report indicated the force involved was far in excess of the design requirements of the bridge.
The Sanral report said statistically, it was “an extremely rare occurrence” for a bridge support to be subject to an impact 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 afterwards inspected at ArcelorMittal premises in Vanderbijlpark and the marks on it indicated substantial impact with concrete.
Sanral insurers are pursuing the matter with the third parties involved and the SA Police Service is performing its own investigation.
The bridge was constructed in 1978 to provide pedestrian access between mining operations on the Germiston side to the east and the Geldenhuys railway station to the west. The mining operation ceased some years ago and the bridge was closed for pedestrian traffic.
Although the structure was no longer in use, it remained on Sanral’s bridge management system and it was inspected as part of the agency’s general bridge inspection programme.
The last inspection in 2016 picked up no items of concern on the main structural elements. All defects were designated as minor and irrelevant by the bridge inspector, a professional engineer.
“Speculation about the cause of the collapse were proffered immediately after the incident and these included seismic effects, explosives and illegal underground mining.
The consulting engineers identified all possibilities and then ruled them out systematically until the actual cause was identified,” said Kannemeyer. – ANA
Statistically, it was an extremely rare occurrence.