. An encyclopaedia of architecture, historical, theoretical, & practical. New ed., rev., portions rewritten, and with additions by Wyatt Papworth. e beam, as fig. 613/, having little or nothing to do withthe pressure directly, has been replaced in some cases by simple upright struts or diagonalbraces between the flanges, which in cast iron girders are in one casting, but experience hasproved this not altogether politic, particularly in cast iron. Hodgkinson remarked thatsuch beams were weaker than those with a solid rib. Rankine observes that transverserib« or feathers on cast iron beams are t
. An encyclopaedia of architecture, historical, theoretical, & practical. New ed., rev., portions rewritten, and with additions by Wyatt Papworth. e beam, as fig. 613/, having little or nothing to do withthe pressure directly, has been replaced in some cases by simple upright struts or diagonalbraces between the flanges, which in cast iron girders are in one casting, but experience hasproved this not altogether politic, particularly in cast iron. Hodgkinson remarked thatsuch beams were weaker than those with a solid rib. Rankine observes that transverserib« or feathers on cast iron beams are to be avoided, as forming lodgments for air bubbles,and as tending to cause cracks in cooling. Open work in the vertical web is also to beavoided, partly for the same reasons, and partly because it too much diminishes the resist-ance to distortion by the shearing action of the load. 16i!9e. Where the span renders it impracticable to roll a beam in one piece, Fairbairn,page 91, notices that convenient weights might be rolKd into sections of the proper form— and being united by properly proportioned covering plates at top and bottom, and tC. CUAP. I. BEAMS AND PILLAIIS. 427 B the joints (par. 1630y.), and all the riveting be well executed, the beam will be equal insirength to one of an entire length. Ihis construction may be carried to a pan of lO to50 feet. In practice it is found necessary to confine the use of cells to spans exceeding100 or 150 feet: within these limits the same olijeits are most etonomically obtained l>ythe use of thicker plates (l)age -215). The more nearly the bottom ajjproximates to asolid liomogeneous mass, ihe better it is calculated to resist a tensile strain (see pages 248to 256 for full instructions as to riveting plates; and Kirkaldy, Experiments, ^Sc. page196, for comparison of strength). Asthe bendin? moment of the load on agirder diminishesfrom tie middle towards the ends, and the shearing force from the ends towards themiddle, it follows tha
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