Institution of Civil Engineers Minutes of proceedings of the Institution of Civil Engineers Volume 86

Minutes of proceedings of the Institution of Civil Engineers Volume 86

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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1886 Excerpt: ...experimental fact in the case of the L bars tested by him. stress, it will follow that the apparent stress pl, which is capable of destroying the column by tension, will be given by--2(1 + ) W The tensile strength of cast-iron may bo taken at 14,000 lbs. j1 and the resulting values of the breaking load are represented by the lower curve in Figs. 8 and 9, marked "Failure by Tension." It appears, therefore, from the diagrams, that the column may be theoretically expected to give way by tension on the convex side if the ratio of length to radius of gyration is greater than 50 in round-ended columns, or than 83 in columns with fixed ends. The results of Mr. Hodgkinson's experiments with solid and with hollow cylindrical columns are given in the diagrams, and coincide practically with the theoretical limits at all proportions of length to diameter; so that there appears to be no necessity for separate formulas applicable to certain lengths. Steel Columns.--According to some experiments the modulus of elasticity in steel is no greater than in wrought-iron, but on the average it may probably be credited with a somewhat higher modulus, which will be taken at 29,000,000 lbs. The strength of r2 the ideal column, or p = 29,000,000 ir2, will therefore be only slightly greater than in wrought-iron. The ultimate strength of steel, whether in tension or compression, is known to vary within very wide limits; but, as before stated, this will not in any way affect the curve B C forming the upper limit of Figs. 10 and 11. It is necessary, however, to fix some value of / for the probable lower limit.2 Mr. Kirkaldy finds that the ratio of tensile to compressive strength in steel is the same as in wrought-iron; and therefore if / is taken at 70,000 lbs. for hard steel,...