Issue 2

The paper attempts briefly to record and describe the construction of this unique combination of structure and machine, and the care and attention provided over the years to produce, in the opinion of the authors, a regeneration of the best known bridge in the world, now approaching its centenary. L.W. Groome, W.I. Halse, E.M. Longton and D.L. Stephens

During recent years, there have been numerous innovations in concrete technology which have resulted in the availability of materials with properties that are very different from those of conventional structural concretes. These materials include fibre-rein forced and polymer-modified concretes, high-strength concrete, macrodefect-free cements, self-levelling and high workability concretes, and many others. In addition, there has been greater interest in the use of waste materials such as ground granulated blas[furnace slag, pulverised .fuel ash or silica fume. Some of these materials have found no immediate application. J.L. Clarke and C.D. Pomeroy

Mr Robert Siggs (M): I wholeheartedly agree with Mr Tietz’s statement ‘good building is achieved when good design is well executed’, but let us examine this statement in greater detail. Good structural design is, hopefully, achieved by every member of our institution but, in practice, how good are we? Some of us make arithmetical errors, some of us omit details on drawings, and (dare I say) some of us make errors of judgment. Remember that very small box in the corner of our calculation sheets and drawings marked ‘checked by’? How often is it signed? Not often. Our good design is, hopefully, well executed on site by builders but, in practice, how good are they? Damp-proof courses are omitted, brickwork is not properly bonded, and reinforcement is misplaced. Who discovers these shortcomings, structural engineers, other professionals perhaps? I shall return to who later.

Box spine-beam bridges in prestressed concrete have become a widely used form of construction for spans in the range 20 m to 150 m. However, if inclined webs are adopted with prestressing tendon profiles parallel to those webs, the effects of longitudinal prestressing can give rise to significant transverse forces in the top and bottom slabs. R.M. Spiller, R.E. Kromolicki and M.I. Danglidis

The real behaviour of structures in contact with ground involves an interactive process beginning with the construction phase and ending with a state of balance after a period of adjustment of stresses and strains within the structure and within the ground influenced by the structure. S. Thorburn

Mostly micros The use of microcomputers in structural engineering, which was raised in this column several months ago, has attracted considerable interest among our readers; the correspondence this month has been concerned predominantly with their application and the resulting implications for many of us. Verulam