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Inexperience and errors led to fatal Injaka bridge collapse

INCORRECT POSITIONING of temporary bearings during incremental launching have been identified as the primary cause of the fatal 1998 Injaka Bridge collapse in South Africa.

But the official investigation report into the collapse, which killed 14 people and injured 19, concludes that bearing problems were made worse by a catalogue of design, monitoring, construction and organisational errors.

Inexperienced design and construction staff, poor construction quality control and a failure to react to a 'clear warning that all was not well' with the structure, led to the disaster.

The conclusions are contained in a report to South Africa's director of public prosecution by presiding inspector Larry Kloppenborg and made public last month.

The report recommends that criminal charges under the Occupational Health & Safety Act be brought against the bosses of designer VKE Consulting Engineers' Pretoria office, contractor Concor Holdings and client the Department of Water Affairs & Forestry.

Kloppenborg also recommends that similar criminal charges be brought against Johan Bisschoff, who directly supervised VKE's permanent design and against Rolf Heese of Concor who was in charge of the temporary works design.

The report recommends that any charges brought should also consider the fact that 'the extent of the catastrophic failure of the bridge equally could have caused the deaths of any of the 19 injured persons.'

The collapse of the bridge on 6 July 1998 was one of the worst construction accidents ever seen in South Africa.

At 300m long, 14m wide and up to 37m above the river bed, Injaka Bridge was a major structure and the consultant and contractor had extensive experience with such incrementally launched post-tensioned structures.

The collapse occurred after the contractor had slid out five of the 20, 15m long sections of the 3m deep box section deck.

The sixth segment was being jacked as the structure collapsed. At that point the concrete deck extended 24.4m beyond pier 2 with the leading edge of the 27m long launching nose projecting 7.1m beyond pier 3.

Among those killed was Maria Gouws, the VKE engineer responsible for designing the structure. She was on the deck with several guests celebrating progress on the structure.

The primary cause of the collapse was found to have been the positioning of temporary bearings on which the deck structure slid out during construction.

These were located inside the permanent bearing positions which were to be under the box section webs. As a result the temporary bearings punched through the structure and caused the collapse.

Kloppenborg concludes that Gouws and Heese lacked sufficient experience to have been left in charge of the permanent and temporary work for such a complex, incrementally launched structure. Gouws had only around two years' bridge design experience.

The report highlights the lack of calculation checks carried out on the permanent and temporary works designs, as well as lack of construction and production monitoring. It criticises the designer and contractor for allowing inexperienced staff to have such operational freedom.

INFOPLUS For the full report go to www. nceplus. co. uk/magazine

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