Soon, bridges that last forever without repair

London: Imagine a bridge that can take any combination of permanent loading without generating complex stresses, offering long durability without the need for repair or restructuring. Such indestructible bridges could well be possible, thanks to new architectural design by a University of Warwick professor.

The new work is inspired by nature's design principles which allow natural objects to develop simple stress patterns, thereby helping them to withstand forces applied to them (such as wind hitting a tree) with ease.

Emeritus Professor Wanda Lewis took the design process called 'form-finding', inspired by the natural world, to another level.

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.

Lewis argues that "nature's design principles cannot be matched by conventional engineering design."

While classical architectural designs are appealing to the eye, they are not 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," Lewis said.

The question of how to build the optimal arch has been argued through history. In the seventeenth century, British architect Robert Hook demonstrated 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. 

Lewis' '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 was published in the Proceedings of the Royal Society part A.

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 would have enhanced safety, and long durability, without the need for repair or restructuring, said a University of Warwick statement.