Issue 7

Professional structural engineers will be grateful to Professor Kemp for his elegant generalization of Hillerborg’s strip-method to deal with concentrated loads. The moment-field throughout the slab is constructed by a meaningful distribution of shears. Design of slabs subjected to concentrated loads becomes thus possible by the strip-method. K. Rajagopalan

Author's reply: I am grateful to Mr. Rajagopalan for his comments which bring out a number of important points which for reasons of brevity were not made in my paper.

Mr. A. J. Harris (F): May I open the discussion by applauding this document and the labours of Mr. Creasy and his Committee. It is an important document, and it is a sound one.

Mr. T. S. Robson, OBE: As an electrical engineer I always admire structural activities and I have never been prouder to be associated with any project more than the Emley Moor tower. The whole concept and scale of it never ceases to amaze me. Although the timetable for the design and building programme is referred to in the paper, insufficient emphasis is given to the short time that was available for the preliminary thinking, for the decision-making and the design. Two weeks after the first hesitating thoughts, the designers were at work. Eight weeks later the contractors were digging the foundations. This short period had to accommodate not only the design and the flow of change in requirements from the client, but a concentration of both commercial and technical decision-making. We had to satisfy the local council of the unobtrusive nature of this 15 000 tonne (15 000 ton) structure. This involved the production of models, and our attendance at council meetings. It is interesting to note that it was at one of these meetings that it became apparent that without the turret room at the top we might not have received planning permission. In some ways, it adds a visual purpose to the structure and it relieves the stark tatement of the tower on its own.

The paper presents a linear programming formulation of the optimal design problem for reinforced concrete frames with compatibility, limited ductility, equilibrium, and serviceability constraints. It is required to determine the values of the design bending moment at all the critical sections such that the total volume of steel reinforcement is minimized. The program is solved by use of the simplex algorithm. The merits of the proposed optimal design are illustrated by practical design examples and comparisons are made with ultimate strength design based on elastic solutions for factored loads. It is shown that significant savings can be made using this optimization procedure. J. Munro, C.S. Krishnamoorthy and C.W. Yu

In this study single cell box girder bridges are examined in detail by means of finite element analysis. Realistic loading and support restraints are considered and the effects of shear lag, diaphragms, eccentric stiffeners and varying geometric properties are examined. The analysis uses triangular elements with eccentric stiffeners and can be used for stiffened plates as well as the three dimensional box-type structures considered.

A brief description is given of various methods of measuring the tensile strength of concrete and the advantages and limitations of these techniques are discussed. D.J. Hannant