Indestructible Bridges May
Become a Reality
University of Warwick -- A
new generation of indestructible bridges could be possible, thanks to research
from the University
of Warwick
Emeritus Professor Wanda Lewis in the School of Engineering
Form-finding enables the design of rigid structures that
follow a strong natural form – structures that are sustained by a force of pure
compression or tension, with no bending stresses, which are the main points of
weakness in other structures.
This could, for the first time, lead to the design of
bridges and buildings that can take any combination of permanent loading
without generating complex stresses.
Such structures will have enhanced safety, and long
durability, without the need for repair or restructuring.
For 25 years Professor Lewis has been studying forms and
shapes in nature: the outlines of a tree or a leaf, the curve of a shell, the
way a film of soap can suspend itself between chosen boundaries. In all of
these natural objects, Professor Lewis observed that they develop simple stress
patterns, which help them to withstand forces applied to them (such as wind
hitting a tree) with ease.
Professor Lewis has been developing mathematical models that
implement nature’s design principles and produce simple stress patterns in
structures. The principles behind her mathematical models are illustrated using
physical form-finding experiments involving pieces of fabric or chains, for
example.
A piece of fabric is suspended, and allowed to relax into
its natural, gravitational, minimum energy shape; then that shape is frozen
into a rigid object and inverted. She finds the coordinates of this shape
through computation by simulating the gravitational forces applied to the
structure. This produces a shape (a natural form) that can withstand the load
with ease.
Professor Lewis argues that “nature’s design principles
cannot be matched by conventional engineering design.”
While classical architectural designs are appealing to the
eye, they aren’t necessarily structurally sound: “aesthetics is an important
aspect of any design, and we have been programmed to view some shapes, such as
circular arches or spherical domes as aesthetic. We often build them regardless
of the fact that they generate complex stresses, and are, therefore,
structurally inefficient,” says Professor Lewis.
The question of how to build the optimal arch has been
argued through history. In the seventeenth century, Robert Hook demonstrated to
the Royal Society that the ideal shape of a bridge arch is that resembling the
line of an upside down chain line - the catenary form. The only other form
proposed by classical theory is the inverted parabola. Each of these shapes can
only take a specific type of load without developing complex stresses, which
are points of weakness. Professor Lewis’ pioneering ‘form-finding’ process
fills the gap in classical theory, offering a new mathematical solution in the
pursuit of the optimal arch subjected to general loading.
The work on discovering the optimal arch has been published
in the Proceedings of the Royal Society part A: http://rspa.royalsocietypublishing.org/cgi/content/abstract/rspa.2016.0019
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