Update: Sanral’s investigation into pedestrian bridge collapse concluded

Investigation into the pedestrian bridge collapse concluded.

A truck hitting the supporting pier of the pedestrian bridge over the N3 caused the collapse (GCN, August 18), the SA National Roads Agency SOC Ltd (Sanral) revealed on Wednesday.

“The collapse of the Geldenhuys pedestrian bridge, B1187, on the N3 highway, in the early hours of August 9, was caused by an impact force on the pier in the median of the highway, our investigation has established.

“Following the incident, Sanral commissioned Superstructure Consulting Engineers to perform an independent investigation into the cause of the collapse.

“The firm has completed the investigation and handed its report to Sanral,” said the roads agency’s acting engineering executive Louw Kannemeyer.

All 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. Marks on the road led directly from the point of impact to the position where the steel coil came to rest.

The weight (18.1 tons) of the coil of steel, and moving at speed, can induce an impact force far in excess of the pier’s capacity.

Debris which scattered radially away from the pier that was hit to a distance exceeding 40m confirms an external impact force was of very large magnitude.

The report indicated the force involved was far in excess of the design requirements of the bridge.

The report further stated that statistically, it is an extremely rare occurrence for a bridge support to be subjected 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 afterwards inspected at the ArcelorMittal premises in Vanderbijlpark and the marks on the coil indicated substantial impact with concrete.

Sanral’s insurers are pursuing the matter with the third parties involved while the SAPS are performing their own investigation into the coil and the transport vehicle involved.

 

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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 operations ceased some years ago and the bridge was closed to 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 roads agency’s general bridge inspection programme.

The last inspection was conducted in July, 2016 and no items of concern on the main structural elements were picked up.

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 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.

Kannemeyer thanked motorists who use the highway, the Gauteng Provincial Government, the SAPS, the Department of Labour and the Ekurhuleni metro for their co-operation in the aftermath of the incident, especially during the site clearing period.

 

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