A semisuspended floating bridge has been installed over the Umkomaas river, in KwaZulu-Natal, for the 2011 Subaru sani2c mountain bike race, being held from May 19 to 21.
After initial consultations with engineers dubbed the concept unfeasible, the route builders and organisers took up the challenge, with organiser Glen Haw explaining that they opted to conceive a temporary, portable bridging solution.
“Engineers considered statistics like the 100-year flood levels and took unseasonable rain and flooding into account. We are taking a calculated risk based on what we know of the seasonal factors,” he says.
The bridge extends 86 m and has a built-in safety mechanism that prevents it from washing away in strong currents, and, instead, swings out onto one of the river banks.
It is supported at either end by anchors and posts and is suspended on top of two cables and has pontoon supports on both sides.
“The basic structure is a galvanised steel framework, consisting of thirty 3-m-long floated steel sections that are bolted together. Wooden planks are then bolted to the steel sections to form the walkway,” explains Haw.
Each section weighs about 200 kg and the total weight of the bridge is 6 t.
The bridge can hold the weight of at least 30 adults at any given time.
The support structures take about four days to put in place and one day to erect the bridge itself. The entire structure can be dismantled in a single day.
The sections can be reused and added to, or subtracted from, to create a scalable solution.
The introduction of the bridge strengthens the Subaru sani2c tradition of coming up with innovations.
“The Subaru sani2c was the first mountain bike race to include a floating bridge. Originally designed to be used on still water, the proven structure has since been modified with cables to counter strong river currents. The Umkomaas is a powerful river with water flowing at a rate of 200 m3 a second.