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SIR,-In the issue of The Structural Engineer last August there appeared a discussion on Dr. Glanville’s paper “Strength Tests for Cement.”
Mr. LEEMING, in presenting the paper, said that with regard to fixed-ended and free-ended conditions he was expressing only his own personal opinion. He wished it to be clearly understood that he did not mean to make any actual comparison; he preferred fixed ends, as compared with free ends, where no proper hinge was provided. In the case of certain bridges built by Hayden, in America, it appeared very doubtful that complete freedom had been achieved; if freedom were not achieved there was liability to some unintended stresses occurring in the leg of the frame and also near the points of fixation, which stresses had not been allowed for. That did not appear to be very good practice.
WITH the growing use of the load factor method of design in place of the "Factor of Safety ” method, more especially in connection with struts, where applied load and stress caused, do not bear a linear relation to one another, and particularly in aeronautical structures, it becomes necessary to calculate stresses at "factored” loads nearer the Euler Critical Load than heretofore. (The principle of the load factor method is, of course, to calculate the stress caused by design load multiplied by the load factor, i.e., "the factored load," and to ensure such stress is not above the yield stress.) Hugh A. Warren