Professor A. Bolton (F) I was interested to read the paper by Ji and Ellis. The static and dynamic stiffness of temporary structures is very important, as the authors’ results and recent accidents have shown, and when the structure is intended to carry a large number of excited people the effects can be very serious. It is therefore essential for all designers of such structures to take into account both static and dynamic loading and the authors have done well in bringing this matter into clear focus.
Dr J. R. Eyre (University College London) I am always interested in finding out more about the learning processes in young engineers. And let me say that I applaud anyone who makes contributions to this field as is being done tonight - not only because we all need to learn from it but because the valiant put themselves at great risk where so many others think that they know all the answers. You may think from this that I fit into this latter category.
This paper reviews various aspects of dynamic excitation of stadium structures by spectator activity. A historical review of relevant research and testing relating to the magnitude of forces generated by people involved in coordinated activity is outlined, together with data relating to the requirements of various Codes of Practice. The theory relating to the prediction of structural response to spectator jumping is presented, and a method for carrying out analyses is detailed. The paper considers a number of common stadium structures and discusses features which are potentially vulnerable to dynamic excitation. Finally, the paper gives examples where natural frequency predictions have been compared with the results obtained from monitoring of completed structures. W.M. Reid, J.F. Dickie and Professor J. Wright
Since March this year, BRE has been operating in the private sector - a major change after 76 years as a Government or Government-funded organisation. R.M.C. Driscoll
Circles and triangles Various members continue to write in with solutions to the problem posed originally by Owen Hope and developed by Graham Orr. Charles Banks has written from Beckenhum in Kent: You published a contribution from Graeme Orr in the 17 June issue which gave a relationship that must be satisfied for the in-circle to have an integral radius, but left the question of which right-angle triangles fulfil this condition open. Some time ago I investigated right-angled triangles with integral sides, and found a way of categorising them which can be used to show that all right-angled triangles with integral sides have integral radii for their in-circles. I doubt that I am the first to do this, but not being a follower of mathematics or number theory, I have not seen it previously.