Issue 10

The purpose of this short paper is to describe in a simple way the operation of the finite element method and to indicate the principles involved. This has been approached by a description of the general processes of structural analysis by the stiffness method using simple matrices when their use is advantageous. The finite element method is presented as an approximation in which a continuum is replaced by a number of discrete elements and an indication is given as to bow the engineer can satisfy himself as to the accuracy of his results. It has not been possible to discuss the suitability of types of elements for particular purposes but details of some of the commonly used elements with appropriate references and comments have been given. Reference has also been made to the use of computers infinite element applications. O.C. Zienkiewicz, D.M. Brotton and L. Morgan

The paper provides the designer of precast concrete buildings with a valuable design aid. To enable general design rules to be established within the context of current design practice it would be of great assistance if the authors could offer some advice concerning the following: D.G.E. Smith

Early thermal and shrinkage cracking of reinforced concrete walls is a frequent cause for concern on construction sites, especially for water retaining structures. The revised edition of CP2007 (BS5337) includes specific limit state design recommendations to control the cracking in water containing structures by means of the distribution reinforcement. The paper therefore considers a service reservoir for the South Staffordshire Waterworks Company which was designed to the new recommendations, and which provided the opportunity of comparing theory with practice not only for this design but also with a typical design to the former Code, CP2007:1960, on which the amended design was based. Other equally satisfactory design solutions which would have been possible in accordance with the new recommendations are also indicated. B.P. Hughes

Introduction by Dr. Taylor: Four years ago, to this month, a paper of which I was a joint author (with Dr. Somerville) entitled 'The influence of detailing on the strength of reinforced concrete structures' was presented to this Institution. At the close of that paper, Mr. Geddes, then President, suggested that the Institution would like to hear more of our continuing research on detailing. Although this paper treats some more detailing problems in much the same way as before (and in one case presents more information on a subject discussed before) our approach to detailing problems has been extended. The basic message from our previous paper was that the normal Code rules for detailing (bond, bearing etc.) are not necessarily sufficient when considering the detailing of critical parts of concrete structures, in particular at intersections between elements. In the cases mentioned in the last paper it was suggested that, providing internal statically determinate truss systems could be envisaged and steel was provided to carry the tension, with concrete carrying the compression, the resulting details would have a good chance of working safely.

A definition of structuralstability is given in terms of the sensitivity of structures to variations of the design parameters. The problem of overall stability is then considered, as distinct from localmember stability, and two main modes of overall instability are identified, namely lateral and torsionalinstability. Each of these modes of overall instability are then examined in terms of some of the main factors involved, particularly the variability of live loads, stiffness and geometry, and the influence of geometrical changes during live loading and differential settlements. Statistical methods have been used where appropriate. David J. Dowrick

The paper describes how various factors peculiar to the site together with a desire to impose maximum design and construction standardization led to the use of precast MOT/C&CA prestressed concrete M beams for the decks of a large multi-viaduct interchange at the London end of the M11 motorway. B.P. Pritchard

It seems possible that BS449 is beginning to displace CP110 as a subject for comment to this column. Our old friend Mr. Hairsine writes : I should like to draw members' attention to a recent amendment to BS449 (Amendment No. 5: AMD 1787) which quietly introduces changes affecting the design of bolted connections and web buckling calculations. Verulam