Author: Farebrother, J E C
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Farebrother, J E C
Investigation of the behaviour of twisted steel reinforcement (TS) in axially loaded columns revealed several important advantages over the more usual type of reinforcement, namely mild steel (MS). TS to C.P. 1144 is more efficient than MS and will devclop a stress of 54,000 psi at ultimate load, whereas the useful strength of MS is limited to that at yielding and may only be about 36,000 psi. 'Toughness' is also a valuable feature in the behaviour of TS columns. The load at first cracking of the concrete was reached at strains of 0.0013, this corresponding to the development of maximum stress in the Concrete, but ultimate strength was not developed until strains of 0.002 - 0.0025 were reached at loads some 10 per cent higher. In columns with MS the steel yields before the concrete dcvclops its full strength and the column fails immediately without warning. Hajnal-Konyi and the Authors' also pointed out that the effect of crecp is to increase the factor of safety for columns with TS as compared with columns with MS. Creep occurs under sustained loads and over a long period of time large deformations may take place. Strains at failure are much higher than a short laboratory test shows and therefore the steel will develop a higher stress. This increased load on the steel will partly offsct the effect of a reduction in concrete strength due to fatigue. The samc is not true for columns with MS becausc the stress level in the steel is limited by yielding. R. H. Evans and and K. T. Lawson
A sense and a tacit belief in certain properties of symmetry is deeply rooted in almost all of us. It is intended to state here with little if any proof what is very widely known or felt about symmetry, and to apply this, initially at least, to structures which, by virtue of containing a great many similar elements symmetrically disposed, can be analysed with great facility by applying one's knowledge of symmetry. The work has a bearing on any symmetrical structure: however, a general treatment calls for an inconvenient generality of language and of demonstration, and for this reason it is for the most part confined to plain rigid framesuch as portals and multi-storey building frames. Simon Woolf
The three-dimensional stress-distribution in the end anchorages of the prestressed concrete beams used in the construction of a railway gantry was investigated by photoelastic methods and electrical resistance and mechanical strain gauges. S. P. Christodoulides