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Air inflated dome in record time

For the city of Konstanz July 4th of 2015 was a tragic day. An accidental fire destroyed completely the municipal sports complex "Schwaketenbad". The largest swimming center of the city and the region had become ashes.

Cubierta presostática en tiempo récord

Therefore, before the new school year started in September, a quick reaction urged from the town hall in order to find an alternative indoor pool.

The decision of the council was to install a temporary air dome on top of the outdoor pool of the "Bodensee Thermal Bath”.  It has sufficient dimensions (50x30m) to meet the demand for swimming lessons during the winter. The structure should be removed each year with the beginning of the summer.

The cover was delivered on 24th of October. In less than three months it was achieved to design the structure, get the administrative permissions, manufacture and assemble it. As there was no standard solution only a concerted and well coordinated effort could lead to the desired success. It also should be noted that the operation took place in an award-winning building and that the intervention should take that same spirit.

The first requirement was that the air dome should be taken up in fall and taken down in spring over the next five years. It was also required that the intervention should be completely reversible to recover a free area around the pool. This coupled with the central position of the crane conditioned the design of each element according to its weight, dimension and ease of assembly.

The presence of installation tunnels and routing ducts precluded a conventional anchorage of the air dome on its perimeter. A ring of connected ballast elements has been the solution. It is made out of reinforced concrete and creates a continuous perimeter frame not be dismounted in summer. Its shape and weight were designed to counteract the forces resulting from internal pressure combined with wind suction that tend to raise or move the ballast. On the other hand the row of precast concrete elements was shaped as a functional bench with a screen print non-slip surface.

Despite the temporary character of the dome, not only economic viability has been demanded but also a maximum of thermal isolation. The roof is designed as a series of parallel unconnected cushions, covering the full width of the pool. The provision of three layers of PVC/ PES membrane provides a dual chamber thus increasing the isolation. At both ends of each cushion a control valve is placed easily accessible from the outside. In case of exceeding a snow load of 25 kg/m², these valves allow to evacuate air from the outer chamber so that the loaded membrane comes into contact with the inner one. The temperature of 10 °-12 °C helps to quickly melt down the snow.

For a better mobility and storage, the weight of the triple membrane made it advisable to divide into three parts the surface of the roof. Since during all maneuvers for mantling and dismantling the pool would remain full of water, two floating bridges had to be designed whose position coincided with element joints. An added challenge was the different water levels below the textile roof and in the open swimming channel connecting the pool with the thermal complex. Additional aluminum angles prevent water from overflowing.

The response of the users has generally been very positive. The membrane as a soft, luminous white envelope together with the light-grey concrete base avoids dead corners without height and provides a magical atmosphere in the inside. On the other hand, the ”armadillo-like design” adds greater acoustic comfort. The succession of parallel cushions attenuates the noise level inside because the sound-waves are broken. The concentration of the usual noise in a concave space partly disappears thanks to the convex surfaces of the cushions.