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The Structural Engineer, Volume 53, Issue 12, 1975
The opening section of the clause on design in the Code of Practice for concrete reads: 'The purpose of design is the achievement of acceptable probabilities that the structure being designed will not become unfit for the use for which it is required.. . ' The clause goes on to refer to variations in loading and in the properties of materials used; it mentions the need for statistical data on these variations and introduces the partial safety factors necessary to achieve this design objective. It does not, however, define the acceptable probability of a structure becoming unfit for use which is basic to the design concept. At present this is not possible in quantitative terms and may never become so; it can however be stated qualitatively after appraisal whether individual structural failures or cases of unserviceability are acceptable or not. Experience shows that structural inadequacy is seldom due to a single cause; it is often the result of a combination of effects, which may include overloading, fire, impact or explosion, settlement, design errors and faults in construction. Of these, faults in construction have played a major contributory part in causing failure, as illustrated by a few examples drawn from the building field:
Mr. A. M. Muir Wood (Sir William Halcrow B Partners): I think I am possibly the only one here who has been concerned with each stage of this project from its rebirth, as it were, in 1959 until the date of its suspended animation in 1975. While I have been concerned with it on and off-mostly off-nevertheless, I have seen a number of changes and constant evolution.
Dr. Goode's paper gives some very interesting data on long-term torsional effects in reinforced concrete and particularly illustrates how 'torsion shedding' can occur in continuous structures. The comparison of strengths with those calculated from CP110 raises two points. Dr. R.A. Swann