One of the most intricate operations has begun at the National Stadium – the elevation of the roof line structure. Until January 4 the 70-meter spire will be elevated to the height of 34 meters above the pitch by means of 72 steel ropes.
The central point of construction – a huge spire with “garage” mounted on it for the movable part of the roof will be elevated by more than 40 meters. The whole “big lift” operation (described in such a way by the builders) will take several days. The deadline for the completion of the operation is scheduled for January 4. The structural designer, a German engineer Kurt Goeppert promises, however, that under favorable conditions the roof will be elevated until Christmas.
The whole structure, i.e. the spire and 15 kilometers of steel ropes weighs about 1800 tons. Elevation is being done by simultaneous tightening of 72 ropes connecting the spire with the structure mounted on the top level of the stadium. The ropes are connected to it using special castings prepared by an Italian factory. The largest connector weighs 14 tons, while the casting to which the ropes are connected on the lower part of the spire weights more than 18 tons. All connections, despite their enormous size and weight, are made with millimeter precision. After elevating the whole structure to the desired height the next stage of works will begin, this is the installation of a membrane for the parts over tribunes and then covering the movable roof over the pitch..
The ropes will be stretched by hydraulic actuators which are used in the construction of rope-ways. However, this will not be a spectacular show. Of course, actuators are able to tighten ropes even at the rate of several meters per hour, but in the situation when precision is required the roof will be elevated slowly. The ropes are of the same length and cannot be tighten in an irregular way. The tip of the spire must be set perpendicularly. The pace of works can be affected by atmospheric conditions such as strong wind – in this case the process of elevation will be postponed. This is a unique operation on a global scale because the roof of our stadium has a self-supporting roof. A similar roof in Frankfurt is based on a fixed structure – explains Raphael Kaper, President of the National Sports Centre.
On Wednesday the initial stage of the operation began. This operation involved elevating the spire which now rests in a 8-metre hollow in the middle of the pitch. Until Thursday the spire moved by less than a meter. The whole process requires great precision and constant monitoring so as to avoid even the slightest tilt. When the lower part of the spire is over the ground level, ropes will be attached to the spire and only then the whole construction will be elevated, doing more than 40 metres perpendicularly.
The National Stadium in Warsaw (55,000 seats and the costs of 1.915 billion zlotys) is to be ready in July 2011. It is one of the four facilities that are to host the matches of the EURO 2012 in Poland. The first completed facility is the City Stadium in Poznan (537 mln PLN and 42,000 seats). Other ones are constructed in Gdansk (864 million and 40,000 seats) and in Wroclaw (853 million and 40,000 seats).