Nature’s stress-resisting mechanisms can provide a manual for building bridges that resist tension and pressure without sustaining any damage.
The new nature-inspired bridge design method, described in the latest issue of the journal Proceedings of the Royal Society part A, has been developed by the University of Warwick professor Wanda Lewis.
Lewis spent a quarter of a century studying forms and shapes in nature such as outlines of tree leaves, curves of shells or the way a film of soap can suspend itself between chosen boundaries. She found that all of these structures follow certain patterns that help them resist gravitational and other forces.
She then developed an algorithm that allowed her to mathematically model optimal shapes of bridges that resist pressure using mostly the natural ability to spread load, compression and tension.
Lewis argues that bridges designed following her algorithm wouldn’t suffer from bending stresses and would therefore last much longer and require much less maintenance than those designed conventionally, mostly with aesthetics in mind.
“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,” said Lewis. “We often build them regardless of the fact that they generate complex stresses, and are, therefore, structurally inefficient."
The question of the optimal arch has been argued through history. In the seventeenth century, Robert Hooke demonstrated to the Royal Society that the ideal shape of a bridge arch is that resembling the line of a suspended chain - 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. Lewis’s method can address this weakness.
Lewis has verified her hypothesis in experiments with pieces of fabric or chains. She would suspend the material and allow it to relax into its natural minimum energy shape. She would then freeze the shape into a rigid structure and invert it. Subsequently, she finds coordinates of this shape through computation by simulating the gravitational forces applied to the structure.