The collapse of the N3 Geldenhuys pedestrian bridge, on August 9, was caused by an impact force on the pier in the median of the highway.
This was according to findings from an investigation commissioned by Sanral. Superstructure Consulting Engineers conducted an investigation into the cause of the collapse.
“Evidence suggests that the impact was caused by an 18.1 ton coil of steel that was found lying some 100m north of the collapsed bridge on the N3 northbound road,” stated Sanral’s acting engineering executive, Louw Kannemeyer.
“Marks on the road led directly from the point of impact to the position where the steel coil came to rest.
“The weight of the coil of steel, and the coil moving at speed, can induce an impact force far in excess of the pier’s capacity. Debris that scattered radially away from the pier that was hit, to a distance exceeding 40 metres, confirms that the external impact force was of large magnitude. The report indicated the force involved was in excess of the design requirements of the bridge,” said Kannemeyer.
Also read: WARNING: Full road closure on N3 highway following bridge collapse
He said the investigation report further stated that statistically, it is a rare occurrence for a bridge support to be subject to an impact force of such an extreme magnitude at a height.
“It must be noted that the pier was protected by the median concrete barrier but that the impact was higher up. The coil was later inspected at Arcelor Mittal and the marks on the coil indicated substantial impact with concrete. Sanral insurers are pursuing the matter with the third parties involved while the SAPS is performing its own investigation regarding the coil and the transport vehicle involved.”
The bridge was constructed in 1978 to provide pedestrian access between the 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 since.
Although the structure was no longer in use, it remained on Sanral’s bridge management system and it was inspected as part of the roads agency’s general bridge inspection programme.
Also read: UPDATE: Removal of N3 bridge could take up to TWO days
“The last inspection was conducted in July 2016 and picked up no items of concern on the main structural elements. All defects were designated as minor and irrelevant (minimal relevancy) by the bridge inspector who is a professional engineer with several years of bridge design experience.
“The handrails were missing but as the bridge was no longer in use and cordoned off, this was of no concern.
“Several speculations about the cause of the collapse were proffered immediately after the incident had occurred and these included seismic effects, explosives and illegal underground mining in the area.
“The consulting engineers identified all possibilities and then ruled them out systematically until the actual cause was identified,” said Kannemeyer.
Also read: EXCLUSIVE VIDEO: Update on N3 Bridge Collapse
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