Peter Parker and light structures
05-04-2018 | Posted by Alejandro Soler
Or on how finite element analysis saved Spiderman.
I can imagine what Peter Parker thought when he had to become Spiderman. Comics, though, do not tell the full story. How did he manage to design his famous webs to reach from one building to the next without mishap? As might be expected, being a good engineering student, he had to make use of simulation to find the answers.
The same problem faced by Parker is constantly encountered by architects, engineers and even artists, who want to design ever lighter structures that remain strong and safe. And spiders, after 400 million years of evolution, provide an example, producing one of the strongest biomaterials known, outperforming even Kevlar and high-strength steels.
And it’s not just the strength, but also the elegance and functionality of these structures make them a reference when trying to find structural solutions. Understanding the reasons for the success of spider webs would allow us to apply that knowledge to the design of light structures or the development of biomaterials with higher strengths than are currently available.
Spider webs owe their properties to two factors: the mechanical characteristics of the silk threads, which combine high strength and deformability, and the design of the web, which constitutes an optimised structure resistant to impact.
Leaving aside the chemical composition and concentrating on the structural aspects, the more common web design, used by the largest percentage of known species, is the spiral orb web. Comprising a combination of radial and spiral threads, this well-defined topology allows the use of simple models to study it and to analyse the effects on structural behaviour of the various intervening factors, such as thread diameter and length, spiral parameters, wind forces, etc.
For characterising the structure of a spider web, the quickest and simplest strategy is to conduct finite element simulations in a CAE modelling environment, which is ideal for analysing dynamic non-linear problems while minimising the computational cost and the risk of mistakes.
Studies of this type have determined how spiders modify web design to cope with wind, taking account of the aerodynamic forces. They have shed light on how changes in structural details, such as the secondary frame, alter the stress distribution in the web and optimise the performance of the silk threads. And other studies have examined how the mechanical properties of the silk combine with thread prestressing to tune the web and thus get better information from the waves propagating in it.
De hecho hay múltiples ejemplos de estructuras arquitectónicas que recuerdan a las telas de araña, fuente inagotable de inspiración a medida que avanzamos en la comprensión de su estructura y funcionamiento. No hay más que contemplar las estructuras de Frei Otto o la cúpula del Millenium Dome en Londres, que es el mayor domo de techo único del mundo.
Indeed, we can find quite a few examples of architectural structures reminiscent of spider webs which, as we get to understand their structure and performance better, are an inexhaustible source of inspiration. Suffice to look at any of Frei Otto’s structures or the London Millennium Dome, the largest single-roofed dome structure in the world.