Greece’s capital and its surroundings are a huge buzzing mass of last minute rebuilding and construction as contractors battle to complete works in time for the mid- August 2004 Olympic events. Right in the middle of new roads, metro and railway lines, and accommodation and media centres, sits the Olympic Athletics Centre of Athens (OACA) with the highest profile of all – quite literally.
High over the main stadium – 80m in the air – two giant, double, cable-stayed steel arches are being assembled, which will be the main structure for a new roof. Across the multi-facility complex, past the indoor baseball courts and swimming pools, both indoor and outside, a smaller but equally spectacular arching assembly of steel tubes, called fins, and cable supports is being put together for a new roof on the cycling velodrome.
Both stadiums already exist, built in the late 1980s for European championships and in preparation for Greece’s emotional but unsuccessful bid for the 1996 centenary Olympics. But they were built as open air facilities, too hot and unsuitable for the demands of modern TV cameras, and anyway needing upgrading to modern standards.
For inspiration the Greek government hired Santiago Calatrava, the unconventional Spanish architect/engineer famous for radical designs throughout Europe on bridges, airports, stations and exhibition centres. His grand scheme for the Olympic centre is to add special steel structures. There will be an avenue covered by steel arches and glass, a spectacular tower for the flame, and the two new roofs.
The larger roof is built up from huge curving steel tubes, 3.25m in diameter and 303m long. They push against huge thrust blocks at either end. Using stay cables, these support even bigger 3.6m diameter lower tubes – called torsion tubes – with dozens of projecting steel fins. These torsion tubes in turn hold up cross beams with purlins and eventually thousands of square metres of special UV and infrared filtering glass sandwich panels.
‘But we are not building all this in place,’ explains Salvatore DeLuna, project manager for the specialist Italian steel maker and erector Cimolai, which is creating the steel tube structure for the main stadium. The firm is working for the Greek main contractor, Aktor, on the overall E 171m project.
‘Instead we are working in free space on either side of the stadium. Once the whole interlocking and balanced structure is assembled we shall jack it sideways over the top of the stadium.’ Both these 8,000t structures, one on either side, will form a coherent whole, after which the glazing will be fitted.
Cimolai has spent much of the past 18 months on fabrication in Italy. Tubes were made from high grade steel plate up to 95mm thick; a 6,000t pressure roller mill shaped each half tube which is welded to form one 5m long section. Two tubes were welded into a single 10m section then transported to site by boat and truck.
The factory also made 10m high, and 16m long, end pieces called shoes which are cut in half for delivery and rewelded on site.
Meanwhile a team of mobile cranes, mainly Liebherr all terrains but with a Demag among them, began working this summer on erecting 82m-high steel temporary works to seat the strand jacks that do much of the main lifting. A 500t capacity and 400t capacity crane do the biggest work, but there are also two 300t cranes, a 160 tonner and a couple of 80 tonners, mostly supplied out of Italy by hire firm Midolini. ‘The market is so busy in Greece at present we could not get the resources in the country’DeLuna says.
The same cranes also help move around the steel tubes as they arrived and position them for on site welding into longer sections.
‘We have five towers each side of the stadium for the strand jacks, which are operated by a subcontractor to us, PSC Fagioli.’
A complex lift sequence begins with short tube elements lifted and slid into the towers themselves first of all. Meanwhile intermediate sections are welded into 40m-long arches at ground level. They are lifted by strand jacks to the tower tops and then welded. The geometry of the arches alters as load is added so the sequence must be right.
‘We also have to be sure of the wind, although the 36-hour weather forecast by a British service is pretty good and most lifts take about one day,’ adds Cimolai’s site manager Frederico Siriani. Cables are fitted before main lifts and these then later connect the top to the lower tube, which is 42m high in the centre. Smaller cables support the end of each projecting fin.
Meanwhile concrete is being poured in long trenches at either end of the tubes. These will be the rails for the sliding operation at the end that will move the whole to its final location, where the shoes will take to load into heavily piles.
‘It is the part we will watch with bated breath,’ says Evangelis Lazaris, design project manager for supervising engineer Bung Hellas, a Greek/German company.
Cimolai is holding its breath too, says Salvatore DeLuna. ‘Everything must be done by April when we disappear – one way or the other.’
