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The paper presents a simple design aid for predicting long-term movements up to 50 years in buildings and bridges made of normal and lightweight aggregate concrete. The method is based on the principle of superposition and a creep factor chart which takes into account varying sizes of members, age at loading, exposure conditions, and percentage of reinforcement; it requires only a knowledge of the 28-day cube strength
and the loading history of the member. The method is developed from a study of in situ movements in two reinforced concrete structures subjected to incremental loading. The predicted load-induced and basic (i.e. elastic + shrinkage + creep) strains show excellent agreement with the measured strains in the two structures with an error coefficient within 11% at all ages. The method is shown to give good agreement with
measured strains on normal weight and lightweight aggregate concrete columns reported from America, and on the Medway Bridge.
R.N. Swamy and P. Arumugasaamy
Building Regulations fees
When money is involved, argument always ensues, so the question of these fees, of course, produces some argument.
A correspondent, who wishes to remain anonymous, suggests an equitable evaluation method: During the past year, since the Government instituted fees for Building Regulations approvals and inspections, the local authorities have necessarily had to set up administrative arrangements for their assessment and collection. The fees are related to the value of those parts of the work subject to the Regulations according to a scale. I uncierstand that considerable unproductive-and frequently abrasive-correspondence and negotiations are devoted to agreeing the value of the work. What a waste of effort! Why cannot the fees be related directly to the floor (and roof) area of the building and be updated yearly, or whenever, in accordance with the retail price index? I suppose they’d argue about the area then, though . . . .
Professor F. W. Williams (M) and Dr. J. R. Banerjee (Department of Civil Engineering and Building Technology, UWIST, Cardiff): It is vital that designers should be aware that the author’s method gives only some of the natural frequencies of structures, and that the second and other low natural frequencies are likely to be among those missed. This is illustrated by considering the rectangular grid of Fig 13, which consists of 1250 identical, rigidly jointed, inextensible members and is prevented from swaying.