|Short description of the project
||In the centre of Athens in Piraeus Street (Municipality of Tavros) a multi storey shopping mall “Athens Heart” has been built. In Greece temporary covered areas are seen as open space, and allow so a higher usage of the land. This is the reason why many shopping malls in Greece are covered with a retractable roof.
The atrium of the shopping mall Athens Heart is covered with a membrane roof. The membrane panels can be reefed parallel to open the atrium. The goal during the design was, to find a light roof with direct view to the blue sky. The solution is a northlight roof, with highly translucent membrane panels giving shadow from the south, and with a transparent cladding on the north side of the parallel steel girders to allow the direct view, and the entrance of the cool northern light.
The main structure consists of 13 crescent-shaped tri chord trusses with a length between 13m and 60m. These trusses span freely over a length of up to 50m, with one top chord and two bottom chords. The trusses are sitting on a perimeter beam, which distributes the load to the building columns of the concrete structure. The front truss in the south towards Piraeus Street has two top chords and one bottom chord. With the bottom chord it is supported vertically by the steel canopy sitting in front of the glass façade. On the east side the trusses are fixed in all directions on the perimeter beam, and on the west side it has a slotted hole, allowing deformation perpendicular to the perimeter beam.
Where the concrete structure is divided with expansion joints, also the perimeter beam is divided, to allow movement in case of earthquake. The movement of the concrete building due to earthquake can be more than 20cm in any direction.
The diagonally orientated trusses are covered on their north side with 2 ETFE cushions each. The cushions are double layer, and are clamped to top and bottom chord, to close the atrium. The inner side of the cushions is formed by the diagonals of the trusses on which the cushion is sitting directly.
Between the topchord of one truss, and the bottom chord of the neighbour truss one layer of silicone coated glass fibre membrane is spanned. The membrane is attached with travellers to an aluminium rail, and can be opened and closed with a motor driven cable pull system. Spindle driven breaks anchor the roof on the western end. The membrane is attached with 1.2m distance to the rail. This leads to a reasonable size of the folds, and keeps the attachment forces low. To minimize the sag of the loose membrane, especially in the parking position, adjustable web belts have been introduced between the travellers.
To allow the movement of the membrane in between the trusses, the distance of the rails has to be kept constant over the complete length. Therefore the northern bottom chord follows a splined curve with equal distance to the neighbour top chord. The chosen silicone coated glass fibres are highly translucent. Together with the ETFE the shopping mall has a very convenient ambient light, even on cloudy day, and the atrium is an area where the people like to stay.