Iron Columns Or Pillars. Iron columns are always made of cast-iron, never or rarely of wrought-iron, this latter not being calculated to resist the strains of compression in which columns are chiefly subjected, like cast-iron. In section columns are generally circular, as a in fig. 389; but they may be varied in outline, as at b, or fluted, as at c, c', or c", or flat, as at d, or as across at e. They are usually made hollow, not solid, as at a!. The hollow column gives the greatest strength with the least metal, but it has to be of greater diameter to support a given weight than a solid one.
The strength of a cast-iron column depends upon the proportion of the length to the diameter - for buildings where heavy weights have to be sustained, the length should not exceed ten times the diameter; eight times will be safer; for buildings where lighter weights have to be sustained, or slight shocks from machinery given, the length may be increased to thirteen times the diameter; up to fifteen for public buildings, and for ordinary structures twenty times, which proportion should never be exceeded. Columns are generally tapered from base to cap, a good taper is one in ten. If the diameter of the column at base is one foot, and the length ten times the diameter, the thickness of metal should be one and a half inches, for a length of thirteen times the diameter, the thickness to be from three quarters to one inch; for fifteen times six-tenths to three-quarters of an inch; and for twenty times from half an inch to five-eighths of an inch. The section of cast-iron struts, or braces, may be as at e, fig. 390, or as in fig. 390 at a, this being a square and hollow set diagonally; b is another section.
The forms or outlines of columns are various, according to the taste or desire of the designer; examples of caps and bases are given in fig. 1, Plate LVI I; figs. 2 and 4, Plate LVIII; in figs. 1, 2, and 9, Plate LIX.; and in figs. 9, 10, and 11, Plate LX. In place of columns round in section, cast-iron pillars or " stancheons," as they are sometimes called, are used of the section, as in fig. 391 at a; the form here illustrated is used to carry a series of horizontal timber beams or bearers b b, the ends of which rest upon the cross part c, cast at intervals in the recess.
The methods adopted for securing the bases of iron columns to the ground, etc., are various; one method we show in fig. 391 at d, a projecting part being cast at base, which goes into a socket cut in the stone block d. In Plate LX., in figs. 9 and 10, two other methods are shown, the block or projecting part a a going into the hollow part b of the base of column.
47. Iron Beams, as substitutes for timber, are formed either of cast or wrought iron. The usual and most approved form of cast-iron beams is shown in fig. 392, in which the area of section of the upper flange c d is one-sixth of that of the lower flange ab. Beams of cast-iron are also made of the section as shown at a, fig. 393, although this is a section not to be recommended. Fig. 393 also illustrates the method of supporting brick arches for roofs or ceilings to fire-proof apartments; a the cast-iron beam; b the stan-cheon or pillar supporting it at intervals in its length, the ends of the beam a being let into the end walls, as shown at e; d d one of the side walls, against which one of the ends of the arch c c butts, the other butting against the beam. Wrought-iron beams are of various forms. In fig. 394 a shows a solid rolled beam, of which the sections in use are various. In the left-hand half of fig. 11, Plate LX., the form of beam known as a "plate" or a "built beam" is shown. This is made up of a central plate of wrought-iron i; a top plate e e, and bottom plate to correspond i i is called the "web" of the beam, the top and bottom plates are connected to the central plate or web by the angle-irons h h, one on each side, and two at top and at bottom; fig. 12 shows the appearance of a "built beam" at the side, ii "web," h h angle-irons, e e top plate.
A "box beam" is illustrated in fig. 2, Plate LX., this being made up of two side plates, as G, a bottom plate I, a top plate E, these being connected and secured together by means of the angle-irons F and H. This is a section on the line a b, in fig. 4, same Plate, which is a side elevation of the beam in fig. 2. The upper part of fig. 4 shows two box beams, forming a double box beam, or a "cellular beam" B B. In fig. 395 we illustrate "Phillip's flanged beam," in which the rolled beam a b b is provided with a plate c c, riveted to the upper flange of the beam. This simple arrangement adds greatly to the strength of the beam a b b. In fig. 396 we illustrate the form known as Zore's beam, from the name of the (French) inventor; it is now being largely introduced into practice. In fig. 397 we illustrate an "open beam," "lattice" or "trellis beam." These two latter names are, however, only applicable where there are two central stays or braces, as shown by the dotted lines a a, and the lines b b. The full lines represent a form of " open beams," in which only one brace or cross-piece, as 159 b b, is used. The top member c c is of iron, the lower e e of flat bar-iron, the vertical d of T-iron, the other vertical or end-piece of " L"-iron, and the brace or cross-piece b b, flat bar-iron.
Sections Of "Irons" Used In Frame Work - Rivets