The novel method of bridge construction avoided traffic disruption on a major road upgrade project being carried out for South African National Roads Agency Limited (SANRAL).
Main contractor Lonerock Construction and subcontractor Tzandeboo Construction used the Megatruss system to build the 60m-long bridge over the N4 as part of a contract that also involves widening the R24. The two contractors worked with RMD Kwikform to devise a solution that would reduce the impact of construction activities on the live N4.
RMD Kwikform’s local branch manager and senior engineer Rossouw Fourie and technical manager and senior engineer Marius Els designed the final solution in collaboration with RMD Kwikform’s UK-based headquarters.
Fourie said: “Due to the location of the bridge, we had to create a solution that minimised the impact of construction on the surrounding areas, and didn’t affect the flow of traffic on the N4 Highway. Using RMD Kwikform’s Megashor high-duty modular propping system, we constructed a total of two towers and five Megatrusses, each weighing 34 tons.
“We were able to suspend the bridge deck 710mm above the initial design level by tie bars attached to the Megatrusses; once the concrete had been poured and struck, the Megatrusses were then removed and the bridge deck constructed in mid-air before being lowered into place.”
One of the key challenges was the casting sequence of the bridge deck. Tzandeboo Construction had to pour the first and second abutments from the ground up in order to support the towers; the towers and trusses were then situated on top in preparation for the bridge deck.
The site team also had to coordinate each concrete pump to sit between the trusses, to ensure the concrete could be poured from the middle outwards without hindrance. In total, construction of the bridge deck used 954m3 of concrete.
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