Lord Baker of Windrush (F): The commentary on portal frame design by Dr. Morris is a most important and useful document.
Damage is rarely caused by the pressure of growing roots on structures and, in the rare cases when this does occur, the structure is usually very light, e.g. a garden wall. Indeed, it is a popular misconception that large roots cause damage. The damage is normally due to the very fine roots at the extreme tips of the root system. Russell G. Grahame
Mr C. Judd (Messrs Sandberg): The major welding requirement in the Peter Brett type steelwork is associated with site welding, and it has been our pleasure to be a member of the Peter Brett team on the steelwork projects to provide the inspection consultancy and testing services as required.
Mr A. C. G. Hayward (F) (Cass Hayward & Partners): The author is to be congratulated on his elegant bridge, which displays the attributes of steel in giving a slender structure, easy to construct. He states that a concrete design would not have been cheaper, and this reflects a current trend even for quite modest spans, in this case 34 m. As evidenced by recent winning contractor’s alternative designs, steel is again finding favour. This is often where official designs had been done in concrete quite correctly at a time when the relative economies had dictated against steel. This problem, of course, is often inevitable in larger projects where tenders are invited some years after the appraisal is first done and choice of design made. It can be alleviated if contract documents allow freedom for submission of viable alternative designs by contractors to defined rules of selection. An independent, design check is a vital part of such procedures.
On 24 March last, the Institution’s Informal Study Group ‘Model Analysis as a Design Tool’ organised a half-day colloquium on the subject ‘Offshore structural design using model analysis’. The following report on the proceedings has been prepared by Mr John Clarke of the Cement & Concrete Association. Details of the Institution’s Study Groups, with names and addresses of Conveners, were published in The Structural Engineer, June 1983, p197 The aim of the half-day colloquium was to illustrate the ways in which the use of models plays a significant role in the design of a major structure. The oil production platforms in the North Sea have required design expertise from many different disciplines. The colloquium covered the use of models in the design, fabrication and installation of a major steel jacket platform for the BP Magnus field, described by members of the John Brown - Earl & Wright design team. Mr John Clarke
Currently, two design philosophies are available for the design of reinforced soil walls. The first, known as the tie-back structure hypothesis, models lateral earth pressures using simple active pressure theories. This presupposes that the top of the wall rotates actively outwards about its toe. It is further assumed that failure in the soil occurs along a planar surface. The second and later approach, known as the coherent gravity structure hypothesis, assumes lateral earth pressures to vary from the ‘at rest’ condition at the top of the wall to the active condition further down the wall. This is coupled with the assumption of a logarithmic spiral failure surface. To achieve compatibility between these two assumptions there is the further assumption that the base of the wall rotates actively outwards aboul its top. This assumption is compared with field observations which clearly indicate wall rotation about the toe. Since neither of these theories quantifies the effects of compaction, a theory is introduced to relate compaction-induced earth pressures to basic compaction plant characteristics. Results from this compaction theory are then compared with those from several case histories. Finally, a comparison is drawn between the three design methods, and comments are made on the resulting design implications. Professor T.S. Ingold
Health and safety and the structural engineer From time to time, members of the Institution have found it necessary to draw attention to shortcomings, as they saw them, in developments in the form of structures and their design, which might endanger public safety then or in the future. In 1964, several members, who dealt with building controls in a major urban and industrial area of England, drew attention to the problems they could foresee arising in the increasing use of precast concrete systems in the construction of multistorey buildings. Their concern had been triggered by a report on the collapse of a precast building in Aldershot in 1963 and by their experience in checking design submissions. The response by the Institution was to hold a major symposium ‘Industrialised building and the structural engineer’, in 1966, which presented a comprehensive review of design and construction in a number of materials, with some reference to research and development; it dealt particularly with the function of the structural engineer. The response to this initiative was not, however, sufficient to stimulate the reappraisal of developments then taking place which might possibly have avoided some of the structural failures of the following decade. Verulam