Author: Reed, James
First published: N/A
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The CHAIRMAN (Mr. Ewart S . Andrews, Vice- President) said that seldom had the work described in a paper been so well illustrated as in this case by lantern slides. He suggested that speakers in the discussion might with advantage express their views as to the manner in which one could calculate the resistance to an anchor block such as was shown in the type B construction referred to in the paper, to which anchor block the large tension rods were attached.
It is well known that the loading of certain -materials produces not only an initial
and immediate strain, but also a further deformation which continues to increase with
t'ime, although the applied load is unaltered. Just as a block of pitch flows continuously under the action of a load which may be merely its own weight, so, in varying degrees of magnitude, is the phenomenon noticeable in other materials such as cement, concrete, stone and wood, when they are maintained under constant load.
It is no exaggeration to say that the success of reinforced concrete as a structural material has depended very largely on the ability of concrete to adjust itself to stress conditions by means of creep. Scattered through the literature of reinforced concrete we find reference to this power of self -adjustment from the very early days of reinforced concrete construction, but it is only comparatively recently that the mechanism by which it operates has been investigated sufficiently to enable us to predict the progressive stress changes with some semblance of accuracy. It may well be suggested that this investigation, involving as it does all the factors producing progressive volume and length changes in concrete, has done more to extend our knowledge of the behaviour of reinforced concrete than anything else during the last decade. As a consequence, those who have studied these changes have learned to regard the assumptions we have to make in order to produce designs within a reasonable period from a new angle, and to realise that, although they serve reasonably well as a means to an end, they result in computed stresses that are, in general, very different from the actual stresses.