Concepts for retractable roof structures
Frank V. Jensen
Over the
last decade there has been a worldwide increase
in the use of retractable roofs for stadia. This increase has been
based on the
flexibility and better economic performance offered by venues featuring
retractable roofs compared to those with traditional fixed roofs. With
this
increased interest an evolution in retractable roof systems has
followed. This
dissertation is concerned with the development of concepts for
retractable roof
systems.
A review is
carried out to establish
the current state-of-the-art of retractable roof design. A second
review of
deployable structures is used to identify a suitable retractable
structure for
further development.
The structure chosen is formed
by a
two-dimensional ring of pantographic bar elements interconnected
through simple
revolute hinges. A concept for retractable roofs is then proposed by
covering
the bar elements with rigid cover plates. To prevent the cover plates
from
inhibiting the motion of the structure a theorem governing the shape of
these
plate elements is developed through a geometrical study of the
retractable
mechanism. Applying the theorem it is found that retractable structures
of any
plan shape can be formed from plate elements only. To prove the concept
a 1.3
meter diameter model is designed and built.
To increase the structural efficiency
of the proposed retractable roof concept it is investigated if the
original
plan shape can be adapted to a spherical surface. The investigation
reveals
that it is not possible to adapt the mechanism but the shape of the
rigid cover
plates can be adapted to a spherical surface. Three novel retractable
mechanisms are then developed to allow opening and closing of a
structure
formed by such spherical plate elements.
Two mechanisms are based on a spherical
motion for the plate elements. It is shown that the spherical structure
can be
opened and closed by simply rotating the individual plates about fixed
points.
Hence a simple structure is proposed where each plate is rotated
individually
in a synchronous motion. To eliminate the need for mechanical
synchronisation
of the motion, a mechanism based on a reciprocal arrangement of the
plates is
developed. The plate elements are interconnected through sliding
connections
allowing them mutually to support each other, hence forming a
self-supporting
structure in which the motion of all plates is synchronised.
To simplify the structure further, an
investigation into whether the plate elements can be interconnected
solely
through simple revolute joints is carried out. This is not found to be
possible
for a spherical motion. However, a spatial mechanism is developed in
which the
plate elements are interconnected through bars and spherical joints.
Geometrical optimisation of the motion path and connection points is
used to eliminate
the internal strains that occur in the initial design of this structure
so a
single degree-of-freedom mechanism is obtained.
The
research presented in this
dissertation has hence led to the development of a series of novel
concepts for
retractable roof systems.
[Cambridge University | CUED
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(last update 5 May 2005)