Fort 4 Mortsel
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Mortsel / Antwerp
Year of construction
Function of building
Historical buildings & monuments
Degree of enclosure
Temperate - cold winters and mild summers
Primary function of the tensile structure
- Rain protection
Fort 4 in Mortsel was initially a military building. It has an internal court, which has a rectangular part and a wider round end. The rectangular part of the inner court is about 12m x 55m. The circular part has a radius of about 12m and an opening angle of 140°. The surrounding brick walls are about 12m high. The building is classified as a monument. The tensile roof covers about 675m².
The membrane roof was designed for the summer season to provide shelter for cultural open-air events. Since the roof will be set up and demounted regularly with a limited crew and without cranes, the setting up procedure and handling was studied to be simple and fast.
The tensile roof for Fort 4 unifies functional (weather protection) as well as artistic aspects. The shape reminds of vaults in gothic cathedrals. The light roof is interacting with the massive walls by means of convex and concave arches. The alternate change of the height of the anchoring points is forming the arches.
In the statical analysis only a medium upward wind load (since the surrounding walls protect the roof) and a minor wind pressure was verified. A PVC-coated polyester fabric of about 750gr/m² has been used, reinforced with stainless steel AISI316 cables. Up to now the structure did behave quite well, even under strong winds.
The cultural events at Fort 4 are very successful, acoustic performances are high, light quality (in combining transparent and translucent materials) as well as the out-door feeling are pleasing. The interplay of functional and artistic properties improves the architectural perception in this place.
Description of the environmental conditions
Material of the cover
Main dimensions and form
Covered surface (m2)
Total width (m)
Form single element
Duration of use
Temporary or permanent structure
Design lifespan in years