Book Description

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1914 edition. Excerpt: ... line and to insure its action as a unit. Previous to the collapse of the Quebec Bridge in 1907, very few designers attempted the calculation of stresses in lace bars, or their rational design. They were put in by empirical rule and roughly proportioned to the size of the member according to the judgment of the designer.3 The failure of the Quebec Bridge was due directly to the weakness of the latticing of the lower chord compression members, and since that time much has been written ff on the subject and now most specifications require the calculation of the stresses in the lace bars.4 A column under stress will deform into a curve with a point of contra-flexure near each end,5 the I / distance from the end depending upon the degree of kf fixity of the end. At these points of contra-flexure the bending moment is zero, and consequently the stress on the column cross section is uniform. t/ Midway between these points the maximum bendFig.57. ing moment occurs, and the maximum unit stress in compression occurs on the concave side, therefore in a distance equal to one half the length between the points of contra-flexure, the unit stress in the concave side of the column must change from the average to the maximum allowed. 1 See article by the author on "Fixed End Columns in Practice," in Engineering News, Nov. 2, 1911, Vol. 66, page 530. 2 See Heller's " Stresses in Structures," Chapter X. 3 See Cooper's "General Specifications for Steel Railway Bridges and Viaducts," 1906, Section 97. 4 See Report of the Royal Commission on the Failure of the Quebec Bridge, Appendix No. 16, and also the attached Report by Mr. C. C. Schneider. See also " General Specifications for Steel Railway Bridges," 1910, of the...