Author: Andrews, Walter C
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Andrews, Walter C
The AUTHOR, introducing the paper, apologised for inflicting on a long-suffering profession yet another method of dealing with prestressed concrete, but explained that he had been horrified at the tendency to overwhelm the subject with formulae and notations, to say nothing of fundamentally unsound assumptions, such as that of using the standard moment of inertia for a beam for calculations outside the non-linear stress strain range. As his job was to teach students, with whom he had already taken some pains to train to think for themselves, he just dared not try to teach them the
current unsound theories, and evolved the present technique as a theoretically sounder method.
In introducing his paper, Dr. Eastwood said that there were two principal conclusions to be drawn from the tests described in the paper. The first was that the bearing power of foundations on denx inundated sand was higher than would be expected from the usually accepted theories, and the second was that the mechanism of failure was very different from that assumed in any of these theories. Hecause of this second conclusion
it would appear that any agreement between these theories and the results of experiment was quite fortuitous, and was unlikely to hold except over a narrow range of conditions.
Pull out tests have shown that the distribution of bond stress along the column is an exponential function, and that the maximum value of bond stress occurs at the loaded end of the steel before any slip takes place, the order of the maximum value being 700 lb./in.2. After initial slip, the position of maximum bond stress moves along the steel, its value remaining sensibly constant.
J.M. Hawkes and Professor R.H. Evans