Sliding a 2,100-tonne bridge into place: the Mara Rail Bridge launch

The N4 east of Mbombela is being widened, a critical tradecorridor linking Maputo to Mbombela and the rest of South Africa. Where arailway bridge crosses the N4, the structure had to be extended to span thewider road.

To minimise disruption to rail traffic, the new 29 m, 2,100t deck segment was built 35 m from its final position and then slid into place.This allowed Transnet to limit the rail shutdown to ten days, during which thedeck and piers were moved across and linked to the existing bridge.

Raubex Structures appointed PTS-S to carry out thehorizontal jacking. The system paired two 200 t launch jacks with two 200 trestraint jacks: the launch jacks pulled the bridge forward while the restraintjacks held it back, preventing uncontrolled movement down the 2% downhillgradient of the launch path.

The jacks connected to the deck via 40 mm steel bars castinto the bridge and threaded through each jack, so every 1 m launch strokeadvanced the bridge exactly one metre, with the restraint jacks holdingposition until the next stroke. Underneath, the bridge bearings slid on PTFE("Teflon") pads, chosen for their very low friction, set inside steelguide rails that kept the structure precisely on line.

The team established on site from 18 June for preparationand equipment installation, with the launch taking place on 22 June. EightPTS-S employees worked alongside a Raubex labour force, coordinating eachstroke by radio. From first stroke to final placement the launch took tenhours, concluding at 8 pm with the MC surveyor and PTS-S team landing thesegment with precision, allowing Raubex to continue with the rest of theirten-day programme.

Thanks to Raubex Structures for the team effort that madethis possible, to Struttura for their bridge design and launching expertise,and to Greenhouse for manufacturing the steel support system that held our OVMjacks in position.

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