Designers of the Mbombela Stadium, which stages its first World Cup match next week, took their inspiration from African animals in the nearby game reserve.
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The Honduras versus Chile match on 16 June may not be a glamour tie but it will be the first competitive match at the iconic Mbombela Stadium in Nelspruit.
Mbombela Stadium is the most intimate and compact of all the World Cup venues with 43,500 seats arranged in a three-tiered bowl. At £66M it is also the most cost effective of all the 2010 stadiums in terms of per-seat cost.
Working with South African architect R&L and lead engineer Goba, Mott MacDonald was responsible for the stadium’s super-efficient roof and for the dynamic analysis of the stadium bowl. The lightweight roof structure is composed of steel trusses with primary trusses cantilevering 40m from concrete piers surrounding the stadium.
When the project kicked off, world steel prices were soaring and the structural engineers set out to control costs by minimising the quantity of steel used in the roof’s construction.
“We went through a number of design iterations with R&L, each time refining the design to increase efficiency,” says Mott MacDonald project manager Paul Officer.
The result is a roof weighing less than half as much as the average trussed stadium roof - just 55kg/m2 - setting new standards for structural efficiency.
Costs were controlled further by using local products. “That meant we didn’t get hammered by import tax. For example, the roof is 100% fabricated in South Africa,” explains Officer.
The roof was designed so that relatively large modules could be assembled on the ground. These were then lifted into position and supported on temporary scaffolding towers while bolted connections were made. “We wanted a structure that was easy, safe and quick to put up,” says Officer.
Structural requirements were given an African twist to give the stadium an iconic local identity. “We took inspiration from the nearby Kruger Park game reserve, which is a stone’s throw from the stadium,” he says.
“The 18 roof supports have been sculpted to resemble giraffes - structural requirements gave the supports four legs and tall slender form, so it was screaming out to be done.”
Meanwhile, the black and white seats have been arranged in zebra-like stripes. Mott MacDonald also advise Goba, which designed the bowl structure, on dynamic performance under crowd loading.
“What you don’t want is terracing that starts bouncing when the crowd jumps up and down - if there’s too much movement people can think the stadium’s going to collapse and they panic,” says Officer.
“All structures vibrate a bit, so what you’re aiming to create is terracing where the natural frequency won’t synchronise with a crowd leaping around, and that damps movement quickly.”
Construction started in February 2007 and the stadium was completed in November 2009. The building phase alone took a massive 5.5M man-hours, with up to 1,400 workers on site at any one time.
It is a measure of the expert management that the most serious injury was a broken ankle. This was despite a violent electrical storm which sent a crane crashing into the stadium roof.
Fortunately the site was closed at the time. Although the crane took out an entire section between supports, adjacent sections were unscathed, proving the design’s robustness.
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