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246 Barry’s Advanced Construction of Buildings
Tensile steel cables
Anchor foundation
Cylindrical
steel masts
Figure 4.84 Main components of lightweight tensile fabric structure.
Lightweight, tensile membrane structures
Film and fabric roof coverings are used in many different ways to create large canopies over
open landscaped areas, sport facilities, and buildings. They can also be incorporated in a
multi-function fabric providing a watertight, thermally efficient and light emitting enclosure
(Figure 4.84).
The Olympic stadium in Munich is a well-known example of a tensile structure, designed
by Frei Otto. Because of the exposed structure the components can clearly be seen (Photograph
4.22). The stadium was a pioneering design in creativity and scale, designed and
built for the 1972 Olympics. The principles now form the basis of many lightweight tensile
membrane structures.
The stadium is a tensile steel structure primarily designed to cover a large area and allow
in natural light. The lightweight translucent skin is supported by masts anchors and cables,
making a precise steel net covered by rigid acrylic panels. Lightweight acrylic panels are
often used in construction, sometimes called acrylic glass, glass/plastic laminate or polymethyl
methacrylate (PMMA). PMMA is a transparent shatter-resistant thermoplastic used
as a lightweight alternative to glass, often used in profiled cladding and rooflights.
The structure relies on central masts (columns) and ties, with a network of cables that
are pinned together by connectors, which distribute the tensile forces to the ground anchors.
The cylindrical welded tube masts are up to 80 m in length. The connectors are made of
cast steel, which act as central nodes to resolve and distribute the tensile forces. Each cable
is connected to the node by an end bracket which is linked by a large pin to the connector.
The nodes and cables are literally pinned together and it is the pin that allows for rotation
and movement in the structure. Tensile forces are resolved through the network of pinned
cables, which are then distributed to the foundations and ground anchors.
The acrylic panels are 4 mm thick and measure 2.9 × 2.9 m square. They are bolted to
the intersection nodes laid on the cables. Neoprene gaskets are used to join, seal and accommodate
6° of movement. The net uses 750 mm aluminium clamps pressed on to all of the
strands at 750 mm centres. Connections use one bolt per joint, providing a node that can
freely rotate. The cable is made from 19 heavily galvanised, 2 and 3 mm diameter, steel
wires. The main cables are made from five strands formed by 37–109 wires each. The cables
are held under high tension to control the level deformation that could take place under
snow and wind loads and the ropes are coupled to accommodate higher loadings. A combination
of tension foundations are used to anchor the main cables including: