ICE - Institution of Civil Engineers - Virtual Library

The Paper presents a new method for the determination of the collapse load for structures of any degree of complexity by a simple routine analysis. The method is limited only by the time which would be taken in the analysis for a large frame. It is shown, however, that a skilled analyst may be able to reduce the labour involved to a considerable extent. The method is contrasted with the method which is used at present, in which the designer guesses the locations of the plastic hinges which form when the structure collapses, and then adjusts his guesses in a systematic manner.

The Paper extends the plastic theory for plane frames of mild steel to cover the cases in which the detailed loading programmes of a set of independently variable loads are either wholly or partially unspecified and there is no restriction on the number of times each load may be applied.

A general method for analysing framed structures of mild steel, under arbitrary loading programmes, is presented. A two-bay portal frame with rigid joints, subjected to three independent forces, is taken as the basis for discussion, and a complete numerical analysis of the shake-down problem for this frame is given to illustrate the general method. Once the elastic analysis has been made, the time required for the shake-down analysis will, in many cases, be not much longer than that which would be needed to make the analysis for plastic collapse. Limitations of the present theory are discussed, and some suggestions as to its probable applications to design problems are offered.