Engineering of fabric
membranes requires expertise in two primary areas; in the
conceptual design and analysis of stressed skin structures and in the
use of advanced geometry manipulation in the manufacture of the built
form. In order to realise the complex three dimensional forms, it is
necessary to use predominantly computer modelling techniques. Complex
three dimensional shapes can be generated in special software suites
which simulate applied environmental loads such as wind and snow. The
software can compensate for different loads and component properties
such as fabric stiffness and cable forces. At each stage of the design
and analysis process the geometry can be checked for suitability for
manufacture. The software can output not only technical information such
as readouts of forces at node level to assist in specifying supports,
but design aides such as graphic output of deflections and contours, in
addition to membrane, cable, and vector forces. Cutting patterns are
output from the three dimensional form to ensure the design information
is optimised.
Compared to traditional buildings,
fabric structures present a unique set of design
challenges, as the shapes of tension membrane
structures cannot be chosen at random. The absence of
bending resistance requires designers to work within the constraints of
feasible membrane equilibrium shapes, which can only be easily arrived
at with the use of software. The structure can be considered in
equilibrium when all forces and reactions balance each other out so that
there is no net change. Membrane forms are usually complex, doubly
curved surfaces which must be pretensioned in such a way as to resist
applied environmental loading such as wind and snow. With a wealth of
information at hand, every performance characteristic can be assessed.
The post analysis form can be exported to visualisation packages to
create photo realistic visuals and animated fly-through's which provide
an unparalleled opportunity for a potential client to assess the
project.
This design loop of feasibility study, cost
analysis, structural analysis, design for code
provision, manufacturing detailing, and transport and erection
documentation forms a specialised branch of engineering which is
practiced by a select few engineers in the world. A simple example that
can be shown is that a typical membrane has single and multi layered
fabric, reinforcing belts, and steel wire rope cables all bound together
in a complex interaction of forces. These materials all exhibit
different stretch characteristics which have to be allowed for in the
manufacturing geometry. The materials have to be tested in the
laboratory and the compensations included in the production drawings so
that when the structure is installed all components in their loaded
state arrive at the correct point in three dimensional space. An
important part of the design process is final certification of the
project. Certification and insurance are required for the safe use and
operation of leading edge buildings and rely upon a high standard of
engineering. As all potential, performance parameters can be assessed,
most project information can be extracted.
Our design and
manufacturing staff have developed specialised techniques for shape
modelling, material testing procedures, structural
analysis, cutting pattern generation, membrane seaming
machinery and manufacturing techniques.
Most quality control
measures centre around checking that the workshop has interpreted the
manufacturing drawings correctly. This has been
resolved by eliminating a whole level of manufacturing which was
traditionally the 'black art' of tent making, i.e. the 'cut'. The three
dimensional shape is turned into digital two dimensional cutting
patterns and then exported into the cutter/plotter software, which
automates the process, reducing potential errors. For more information
on the membrane design process click here.