SIR,-In the issue of The Structural Engineer last August there appeared a discussion on Dr. Glanville’s paper “Strength Tests for Cement.”
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
THE CHAIRMAN (Dr. Oscar Faber, O.B.E., D.Sc., M.Inst.C.E., Past-President) drew attention to the fact that Mr. Mears was on the staff of Messrs. Rendel, Palmer & Tritton, who had been associated with the schemes relating to Waterloo Bridge. The bridge, he said, was probably of special interest by reason of the controversy with which it had been associated for so long a time, but which, happily, was at an end; thus, the matter was leaving the political and entering the engineering sphere, which meant that something would be done.
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.
T0 structural engineers, steel is perhaps the most fundamental material with which they have to deal: its strength, which term includes its remarkable properties of rigidity, and elasticity, makes it the building material best able to fulfil the many requirements of the profession. Not only is it the building material which will carry the greatest unit stresses, but its composition and capabilities are known definitely within narrow limits of accuracy. J. Gibson