Associate-Membership Review - The Structural Technician Engineer in the '80s

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

The importance of connection stiffness in influencing the behaviour of steel frames is discussed. Experimental data on connection performance are cited which show that all practical forms of beam-to-column connection operate as semi-rigid joints. Against this background the assumptions of the ‘simple design’ method for non-sway frames are reviewed and a more rigorous behavioural study is presented. Potential benefits and disbenefits of allowing for semi-rigid action in design are discussed. For sway frames the philosophy of the ‘wind connection method’ is explained and conditions under which its use should result in reasonable frames are identified. Some attention is also given to the assessment of effective length factors that properly reflect the restraint available to columns in non-sway frames. D.A. Nethercot

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.