Warwick Castle Trebuchet

Last weekend almost looked like the start of Spring so decided to head off to Warwick Castle. Not being local it was my first visit there and while its no edinburgh Castle it wasn't too bad. Of particular interest was the trebuchet.

This is a large medievel siege weapon designed to hurl rocks, fireballs or disease ridden animals over castle walls and into the poor besieged population. The Warwick Castle trebuchet is supposed to be the largest of its type in the world and was certainly impressive to see in action. Its construction is of particular interest being built with an oak superstructure and an ash throwing arm. The designers of the time carefully selected the best material for the job. The oak is dense and strong ensuring the base will be stable, strong and will last many a campaign, the ash arm is much more elastic, helping generate a whip action in the throwing arm. A nice bit of structural design. By contrast, a modern equivalent of the trebuchet was created a few years ago as part of Channel 4's Scrapheap Challenge. It's task was to throw a mini bodyshell - didn't quite manage it !!! (esp. 5:30 on)

B of the Bang

Manchester council have announced plans to dismantle the art work "B of the Bang". This statue takes the form of an exploding star some 56m high and designed to appear tilted over at 30 degrees. Unfortunately some of the spikes from the star have fallen off which has resulted in safety concerns. Though this is a work of art, it is highly structural and needed to be designed carefully in order to withstand static loads together with the direct and cumulative impact of wind loading.

The design failures which caused the spikes to fall off have resulted in the designer, Thomas Heatherwick, having to pay £1.7 million back to the council (ie. the cost of the artwork), in an out of court settlement. Lesson - if things aren't designed well don't expect to absolve yourself of responsibility once you've sold your product.

In some ways this is a shame. The B of the Bang is an interesting structure and Heatherwick is a very creative designer - see his design for a retractable canal bridge.

Let it snow, let it snow, let it snow...

The news has been full of chaos caused by snow. It must however be said that the snow we had in Birmingham and further South, in the whole scheme of things is fairly modest. Even back up in Scotland I would see these sort of snow falls two to three times per year and there would be little fuss.

In many areas however snowfall can be quite extreme and needs to be dealt with. Snow sitting on roofs can exert considerable forces and have in recent years caused failures. Typically these have been in large, flat roofed structures such as sports centres. An infamous case was in Katowice Poland in which 65 people died in 2006. The cause of this was a poorly designed and maintained roof, coupled to a build up of snow exerting large forces on the roof structure. http://en.wikipedia.org/wiki/Katowice_Trade_Hall_roof_collapse

In many countries building regulations specify snow loading allowance which designers must adhere to. Eg. Wisconsin in the US, an area used to large amounts of snow.

Heroic Landing

Heroic Landing
Originally uploaded by cecilgene

I think everyone was amazed to see how well the Airbus 320 which crashed into the Hudson River stood up to the impact with the water. The pilot certainly demonstrated high levels of skill in bringing the plane onto the river with little or no power available to him. That the wings withstood the unusual and very high forces exerted on them by the water is testament to there careful structural design, clever use of materials and also a good dose of luck.

The aircraft was however brought down by a flock of geese. Whether these physically damaged the engines directly or simply swamped the jets with debris preventing operation will come out in the accident report. Whatever the cause, birds and aircraft will always try to share the same piece of sky - is there a solution to preventing future accidents of this type ?

A picture study on early racing car wings.

The following images show a variety of products or devices encountered in everyday life and what sort of loading they experience.

Lotus 49, Graham Hill, 1968 : Autosport International, 12th January 2009, G Thomson

This car shows an early version of the now common racing car rear wing. The wing is supported by two struts and as the wing operates a downward pressure is exerted on the wing and struts. The struts will therefore experience compressive loading. As long slender members they will also be vulnerable to buckling. In addition to simple compressive failure, drag on the wing will also exert a backward force putting an additional bending load on the struts.

The designers of these aerodynamic devices often struggled to make these wing supports strong enough and this resulted in sudden and dangerous failure. As a result the very real danger of such failings, high wings were banned.

What is good design ?

Can we learn how products interact with users, society, the environment and other devices to ensure fitness for purpose ?

How do we design things so they will be strong enough and rigid enough to do the task asked of them ?

How can we use tools to help us design more efficient aircraft, better structures, more effective medical implants ?