Birkenhead-Mersey Tunnel Approach Viaducts. Discussion on the paper Part 1. Aspects of design by S.

Professor Wells (Queen's University, Belfast): 'I should like to ask two questions, one to each of the authors. As we utilise steels of higher strengths there are obviously two extreme problems: one of maintaining ductility, and the other of maintaining resistance to instability, and the problem with which the authors are concerned will require even closer attention in the future.'

'The detailing of reinforced concrete' was published by the Concrete Society in conjunction with the Institution in August 1968. The Joint Committee have considered any additional recommendations necessary mainly as a result of decisions taken since their original report was drafted. A revised version, in wholly metric terms will be published later this year. Copies of the 1968 version are still available, price S7 each, from the Concrete Society, Terminal House, London SW7.

Good approximations to engineering problems are, if anything, more important than lengthy rigorous solutions. This is particularly true in the dynamic analysis of structures since dynamic stability does not usually enter the design of a structure but will only be taken into consideration with regard to the safety of the established structure. I.D. Armstrong