Hello. I'm Ian Liddell. I'm a structural engineer from Britain and I have been engaged over the last 30 years on a number of projects which I find interesting. And I want to talk about some of the more interesting ones which have led to developments in one way or another. The first of these projects is the Riyadh Conference Centre and Hotel for which the architect was Trevor Dannatt. Trevor won this commission through a competition which was held by the International Architectural Union. Trevor entered this with Ted Happold. Prior to this I had been working in a construction company who did reinforced concrete work and I was building things like concrete cooling towers and chimneys. After Trevor and Ted had won this competition for Riyadh, I went and rejoined Ted at Ove Arup & Partners to work specifically on the project. It was very interesting to work with Trevor Dannatt who was an architecture, I would say, of the old school, although he was engaged essentially in Modern architecture. It had a lot of Classical values and proportions associated with it. Trevor's partner, Colin Dollimore, was looking after the hotel, Trevor was looking alter the Conference Centre which was a building that was made mainly in pre-cast concrete with wooden boarded finishes. The foyer had these 4-part columns on a regular grid with mushroom heads. It was divided into grids so that there was a unit sitting on top of a column and then, in between that, there was another unit, and then a central one in the middle of the square which was a gridded piece. Both buildings were a great success and they're still there and they're looking very well.

The next project, which I think was easily the most unusual project that I've ever worked on, was the Mannheim Multihalle for the Mannheim Bundesgarten show in 1974. This was designed by Frei Otto and he had developed the idea of building on a dome using a regular grid of timber laths spaced at 50 cm in both directions. And to develop the form of this he used a hanging chain model after the style of Gaudi; the idea being that when the building was completed and built the right way up, it had a moment free structure, so that the shell was theoretically in pure compression. Frei brought his friend Ted into the job. The engineer they had in Germany had to admit that he was unable to calculate the strength and stability of the timber shell. So we were asked to take over the role and it was quite a challenge. At the time that we took over, the contractor for the timber work had already been selected and they were all set to start work. The first thing we did was to make a model, a structural model out of Perspex lathes and put some loads on this, to try and ascertain by direct modelling what the buckling capacity of this shell was. For the construction that was intended, we discovered that the buckling capacity was the same as the self weight. So there followed an intense period of development to increase the stiffness of the shells, by doubling up the layers of the masts and the layers of the laths, adding the components, diagonal ties, onto it until it became satisfactorily stiff. The project was very interesting because of the use of models in the development of it.