Joint Actions and the Design of Steel Frames

Suddenly applied loads In September, we published a letter from Mr N. W. Sutton of New Zealand, posing a question about dynamic loading. He sought the help of readers in resolving his uncertainty in proving that the stress due to the sudden application of a load is twice the stress due to its gradual application. The response was rapid and comprehensive from many parts of the world, and we were faced with the most unusual situation of having more letters than we could publish and also of having to select one letter as being broadly representative of the whole response. The letter that we now reproduce was one of thecfirst to be received and came from Mr N. M. Hallett of The City University. Mr Hallett offers the following explanation: Verulam

Dr. W. S. Baraiiski (Technical University, Lodi, Poland): I would like to comment on the problem of internal instability illustrated in Fig 11. It seems that any purely elastic model of soil is not appropriate for the phenomenon because-as it can be easily derived-elastic internal instability requires great values of stresses to be applied.

Dr. J. D. Ball (Simon Engineering Laboratories, University of Manchester): I congratulate the authors on unravelling data and providing design guidelines for wind forces on certain complex structures, and I would like to draw their attention to a similar problem in water flow.