Issue 11

Readers with long memories may recall that, in 1976, my father was President of the Institution. Those with unusually sharp memories will recall that, in his Presidential Address, he discussed the problems of attracting into our profession an adequate supply of engineers and technicians. He had spotted, at a very early stage, the downturn in birthrate which occurred in the early 1970s and was one of the first to draw attention to the problems faced by a society whose population declines in numbers. At the time, this caused but a brief flurry of press comment. However, as we all know, the effects of a falling birthrate are now about to be felt on the labour market and have been a matter affecting the direction of the Government’s social policies for some years past. R.C.A. Eastwood

A time-dependent analysis of a general, monosymmetric, steel-concrete, composite cross-section subjected to constant sustained loading is presented. Dischinger’s differential constitutive relationship is used to model the inelastic creep and shrinkage strains that develop with time in the concrete parts of the cross-section. The procedure involves a stiffness formulation of the coupled differential equations that describe cross-sectional behaviour and a simple tractable mathematical solution. Compatibility of strain is maintained at every point on the cross-section. The solution is most readily obtained using a programable calculator or small microcomputer, but manual solution is also possible. The method is illustrated by example, and the effects of both creep and shrinkage on the behaviour of the cross-section are determined and discussed. R. Lawther and R.I. Gilbert

There has been much said and written recently about the vexed question of Codes of Practice. Such is the intensity of emotion aroused that we have seen the setting up of the rival ‘permissible stress’ Code group who have written their own Code in place of the (apparently) much unloved ‘limit state’ Code. The fact that this is a concrete Code is of no particular significance, since similar reactions have been experienced with respect to all the new ‘limit state’ Codes which have been published so far (in the UK at 1east)- similar, that is, in terms of the level of anger at their increased complexity and the replacement of comprehended engineering parameters by non-dimensionalised mathematical criteria. J.E. Dibley

Brief reviews of the behaviour of masonry arch bridges and of popular methods of analysis highlight the need for a simple, practical analysis of arches under working loads. A three-hinge model is proposed and is shown to lead to the same solution as four-hinge mechanism analyses when the structure approaches ultimate load. The three-hinge method is extended to enable failures by local crushing of the masonry to be simulated. It is also shown to permit realistic allowances to be made for movements of abutments. F.W. Smith, W.J. Harvey and Professor A.E. Vardy