Issue 4

The end panel of a plate girder is analysed for plastic collapse under high shearing load by means of the upper bound theorem. Two possibilities are considered for the behaviour of the web: either (a) it remains unbuckled or (b) it develops a full plastic tension field. Curves are presented showing how the collapse load depends on the dimensions and on a parameter signifying the full plastic bending strength of the flanges in relation to the web strength. In general, the numerous experimental results available in the literature lie between the predictions based on (a) and (b) respectively. C.R. Calladine

Mr. C. B. Stone (F): I like the idea of making the external wall do its job. We can fall readily into the trap in high buildings-in assuming that the central core will take the wind load; undoubtedly it will resist it, but before it takes the load a lot of the stresses are likely to be forced into the external perimeter of our 10-storey, 15-storey and 20-storey buildings in London. I think we are suffering now from perimeter walls not being designed to take forces that come about from the comparatively small wind loads in London; and we all know about vertical shrinkage problems which are also affecting cladding, whether it be brickwork or a precast unit. The extreme conditions in Hong Kong have fortunately forced us to recognize this problem.

The lateral buckling of a beam having different support conditions at each end when loaded by either equal or unequal moments is dealt with in this paper. New theoretical solutions are presented which deal with any combination of the loading and end support conditions. For all these solutions simple expressions, suitable for use in a design office, have been derived which provide good estimates of the critical loads. Erratum in vol 51, no 4, April 1973, pp138-139 D.A. Nethercot and K.C. Rockey

Designs made according to the limit state of plastic collapse are not quite the same as designs made by simple plastic theory. It is however, possible to retain the simplicity of plastic methods within the framework of limit design concepts, and at the same time partially relieve the designer of unnecessary elastic calculations. J. Heyman