The roof is held up by a total of 40 short pillars down to the top edge of the grandstand structure and is designed as a single large unit with no movement joints. Horizontally the roof is stabilized by four vertical joints in the centre of short sides. Temperature stresses in the roof are minimized by providing all pillars and vertical joints with angle deformation bearings at the top and bottom.
The main load-bearing system is made up of four triangular frameworks which extend 162m across the arena, but there is also a scale effect in the roof which causes pressure in the beams around the rectangular roof opening and drag in an external ring beam around the arena. The primary function of the scale effect is to help to bear the load on the short sides. Essentially, it may be stated that the scale effect provides vertical support to the roof at the corner points of the roof opening.
The structure is designed to be screwed together at the assembly location, with a few exceptions. The exceptions are the tie beam bars in the main frameworks and joints to treadways for the mobile roof.
Description of the mobile roof
The mobile roof consists of two halves, 108x34m in size, which moves on eight circular moving beams. Each half of the roof weighs a total of 420 tonnes. Each half of the roof has five bogies which run on each moving beam. At the second outermost moving beams, there is a winch which pulls up. The drive stations for these are located directly beneath the eaves on either long side; that is, there is a total of four drive stations. There are guide rollers at one of the inner moving beams for guiding the movement of the roof.
The mobile roof is equipped with a large number of walkways and suspension beams for event equipment. These structural elements are constructed as space frames and constitute a system for bearing vertical and radial loads on the roof. One major advantage of placing event equipment in the mobile roof is that the roof opening is as clean as possible during use as an outdoor arena.
The design challenge for the mobile roof has involved handling the relatively small, widespread loads which result in a ground system with very slim profiles, in combination with the concentrated, very high forces which occur when hauling ropes are attached, at end stops and when the roof is moved to the sides mechanically. At the same time, for financial reasons the aim has been to produce as lightweight a roof structure as possible in order to restrict the cost of mechanical components and drive stations. The plane element action in the roofing sheets have been utilized for the mobile roof.
COMPREHENSIVE CHECK
Task 1. Answer the questions.
1. Who commissioned the project?
2. How are the temperature stresses minimized?
3. What is the main function of the scale effect?
4. What does the main load-bearing system consist of?
5. What does the walkway system serve for?
6. How many drive stations are used to open the mobile roof?
7. What is the total capacity of the Friends Arena?
Task 2. Decide whether these sentences are true or false. Correct the false ones.
1. The mobile roof consists of four parts.
2. The mobile roof is equipped with a large number of installations, such as lighting, electricity, ventilation, monitoring and etc.
3. This project witnesses new ideas and innovative technologies.
4. The stadium was renamed after a nonprofit organization.
5. It takes people less than 10 minutes to open and close the retractable roof.
6. The roof is supported by a total of 60 short pillars.
7. The total weight of the retractable roof is more than 800 tonnes.
8. The attendance can follow what is happening at the stadium from a 240m2 big media cube placed between grandstands.
