Author: Dean, Arthur Creswell
First published: N/A
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Dean, Arthur Creswell
WATER ratio rules appear to afford a simple method of controlling the strength of concrete. It is true that the application of such rules in practice is complicated by
the necessity for allowances for the absorptions of the aggregates or for the free water which may be present in them, but this may be regarded as a legitimate problem for the engineer in charge. The real difficulty lies in the fact that strength is also affected by other factors relating to the composition of the concrete, and, in the brief introductory account which follows, methods of making allowance for the effects of these factors are mentioned.
Mr. M. N. RIDLEY, M.Inst.C.E. (Member of Council), proposing a vote of thanks to the author, welcomed the paper, particularly because it indicated the extent to which continuity in reinforced concrete work was being adopted. He had noticed that engineers were inclined to make pin joints in their bridges. They would put a pin joint in the centre of the arch and pin joints in the abutments, and he believed that in one or two cases there were as many as five. He had always maintained, however, that. a bridge of ordinary span was far safer and better, and sometimes more economically designed, if all pin joints were excluded. It was true that calculation was then more difficult, but he held that when that had been done one had the best type of work. Where there were very big spans, of course, one must consider pin joints or the equivalent, especially for expansion and contraction; but for shorter spans, at any rate up to 100 ft. and sometimes more, in reinforced concrete and steel work pin joints were quite unnecessary.
On some bridge sites it may be advisable to adopt two or even more different types of piles. Conditions may demand the adoption of a combination of two forms of piling to obtain the best results.