26 June 2011 - The Gauteng Freeway Improvement Project (GFIP), an initiative of the South African National Roads Agency Limited (SANRAL), will inject approximately R29 billion into the South African economy and approximately R13 billion into the provincial geographic product.
As part of this exciting initiative, Aurecon was appointed to complete the design and contract administration on the section of road from the Brakfontein to R21 interchanges on the N1 freeway between Tshwane and Centurion.
The structural work comprised the widening of six existing bridges and the construction of four new bridges, one of which was is a 240 m long incrementally launched bridge (Bridge B0041). Dubbed the “flying saucer” interchange, this bridge recently won a commendation in the Innovative Technologies category at the 2011 Fulton Awards. These awards, which are presented by the Concrete Society of Southern Africa (CSSA) every two years to honour excellence and innovation in concrete construction, are renowned for their recognition of cream of-the-crop engineering projects. “We are immensely proud of this commendation,” comments Aurecon engineer Craig Edwards. He goes on to say that “It’s gratifying to have played such a critical role in the success of this bridge.”
The new bridge, which spans eight existing carriageways, had to be constructed without any disruption to flow of traffic below it. “For this reason, we settled on an incrementally launched method of construction,” explains Edwards.
This decision, although practical, posed a number of significant challenges, including:
In addition, it was decided to use long constant section circular piers for aesthetic and clearance reasons. These provide a single support at each pier position. During launching operations, however, two additional temporary supports had to be constructed under the webs of the boxgirder at each pier position. These temporary piers were demolished after the bridge was placed onto its final bearings.
“Unlike conventional methods of bridge construction, this particular project required a more hands-on approach from Aurecon’s engineers, as well as the compilation of detailed monitoring, evaluation and progress reports,” says Edwards. “This attention to detail was a critical success factor in ensuring the bridge met both all of the necessary technical requirements, as well as
achieved outstanding aesthetic appeal.”
And it was exactly this approach that impressed the judges, who commented: “The innovative design and construction necessitated by the very narrow single, circular piers, demanded extreme accuracy in launching the deck.” They went on to conclude: “The final finish and quality of the concrete throughout was excellent, which makes this project worthy of a commendation.”