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Saturday, October 31, 2009 |
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The Umgeni-Inanda Inerchange upgrade
:: News
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Source: Grant Kruger
This project, undertaken by Stefanutti Stocks Civils KZN, comprises the upgrading of the Umgeni/Inanda Split Interchange on the N2 in KwaZulu Natal, for client SANRAL.
The upgrade includes:
• The construction of two new jackspan routes, retaining walls and soil anchor beams, as well as the construction of new infill decks between the existing decks of the bridges across the Umgeni River;
• the demolition of existing traffic barriers on the existing service road bridges and N2 bridges; and
• the construction of 690m of new F-type SANRAL traffic barriers.
Additional work on the contract requires the construction of 450m of structural steel walkway which will be installed on the outside of the service road bridges, thus allowing an additional traffic lane in each direction. The one kilometer long bridge site is situated on the N2 highway and forms part of a very busy intersection. The traffic volume is extremely high in this area, and lane closure was limited to off-peak periods only. Vehicular access is not always possible.
The original method of constructing the 44m long decks over the river would have been to span the piers with a
pre-stressed steel truss, and erect formwork on this truss. This would have necessitated the lowering of the truss
and the formwork units into the river and then moving them on to the next section as work progressed, however for
environmental reasons and ease of construction, the method was changed.
The adopted method therefore involves the precasting of the decks on one side of the river and then moving them into position using a gantry which runs along a rail. The major concern with this method was whether the cantilevers of the existing bridges could carry the weight of the new decks, which weighed 310 ton and 195 ton for the service road and median decks respectively.
Once it was established that the existing decks could carry the load, a concrete rail beam was cast on either side of the gap and a series of steel gantries were placed over the gap to carry the new deck. Seven gantries are being used in series to distribute the load sufficiently across existing cantilevers. The new decks were then cast in position on one side of the bridge and lifted using a computerised hydraulic system and then towed 180m across the river into their final position.
In order to lift the decks, a total of 28 jacks are used, each with a capacity of 30 ton. “The computerised hydraulic
system allows us to control all of the jacks to a 2mm tolerance between jacks” says Grant Kruger, contracts manager. “The system also enables us to tilt the beams in both the transverse and longitudinal directions if required”.
The project is 45% complete.
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