The Natural Frequencies of Multi-Storey Frames

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.

With the growing importance of the light, metallic, reficulated dome as a structural form, the need for improved stability criteria is emphasized. For elastic, single-layer dome frameworks of the regular triangulated, reticular type an analysis is made of both local buckling and local snap-through instability. The critical constants are found to be functions of a single geometric characteristic parameter of the dome that corresponds to the effective slenderness ratio for columns. The buckling analysis can be generalized to cover the inelastic range by use of the tangent modulus, but it is shown that this bifurcation buckling load is of limited usefulness as an index for predicting structural behaviour. An improved criterion of local stability is given in a form suitable for design use, subject to experimental verification. N.C. Lind