. The strength of materials; a text-book for engineers and architects. r = C- Fig. 133.—Curves for various Column or Strut Formulae.(Mild Steel) Many of the leading constructional steelwork firms publishtables of safe loads on various struts. Having previouslychecked one or two to see that these firms work with similarformulae, we can choose a suitable section for our case, andthen apply our formula and see if such section is satisfactory. REINFORCED CONCRETE COLUMNSShort Columns Centrally Loaded.—We have shown onp. 38 that the safe load in a column in which buckling is COLUMNS, STANCHIONS AND
. The strength of materials; a text-book for engineers and architects. r = C- Fig. 133.—Curves for various Column or Strut Formulae.(Mild Steel) Many of the leading constructional steelwork firms publishtables of safe loads on various struts. Having previouslychecked one or two to see that these firms work with similarformulae, we can choose a suitable section for our case, andthen apply our formula and see if such section is satisfactory. REINFORCED CONCRETE COLUMNSShort Columns Centrally Loaded.—We have shown onp. 38 that the safe load in a column in which buckling is COLUMNS, STANCHIONS AND STRUTS 293 negligible (the length being less than 15 times the leastdiameter, and the notation being modified) is given by P = c (A, + m A,) Gross-binding of Reinforcement.—In addition to thelongitudinal reinforcementj some force of binding is necessaryto keep the bars at the requisite distance apart. This is dueto the following reason— Suppose that a reinforced column with bars a b, c d,.Fig. 133a, be compressed; then, quite apart from any buckling u R \ C. B I D ?^T Fig. 133a. of the whole column, the column will bulge out somewhatas shown, and the reinforcing bars will buckle because the value of ^ or the buckling factor for them will be large. If we bind the reinforcing bars together, as shown diagrammati-cally, so that they cannot buckle, the column will not bulgeto anything like the same extent, and so will be considerablystrengthened. From a large number of experiments found that the best results are obtained whenspiral coils are placed round the reinforcing bars at distancesapart equal to i to ~o of the diameter of the coil. 294 THE STRENGTH OF MATERIALS M. Considere suggested the following allowance for the coilsin the strength of the column— Let A/, be the equivalent area of longitudinal reinforce- volume of metal in coils \length of column Then safe load = c (A, + m A, + 2 4 m A) Long Columns Centrally Loaded.—Some authorities use Eulers form
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