CONSTRUCTION IN IRON.
Wrought iron and cast iron are coming- more and more into use in building construction, not only as accessory materials for making, nails, bolts, etc., but also for the construction of independent parts of building-s and of entire edifices. At present attention will be confined to the con sideration of buildings in which iron plays the principal part. Ent before proceeding to this branch of the subject it will perhaps be better to devote a few words to the manner in which the several portions of the iron-work are united. This union is effected by two distinct methods, to one of which belong riveting, soldering-, and welding-, while in the other are comprised the joining-s made by the use of screws and wedges.
llIelhoo's of Uniting is preferred for wrought iron, for which material it is used exclusively, while wedging- and soldering- are used for both wrought and cast iron, and screws especially for cast iron. In riveting, the joining, particularly of plates—for example, boiler plates— is effected by rivets, which are short wrought-iron pins with a conical head ou one end; these are passed through the rivet holes in the pieces to be joined, an additional head being formed on the plain end of the pin by hammering- after it has been set in place. Soldering consists in introdu cing- another metallic substance, in a melted state, between the surfaces to be joined, which must be quite clean. Pure copper affords the best solder for iron. Welding consists in heating red-hot the portions to be joined and uniting them intimately together in this condition by hammering. When pieces—for instance, two plates—are to be connected by screws, use is made of a screw-bolt with a nnt and head, the mit being set on and tightened up with the wrench. As in riveting, the pieces to be joined must have suit able holes pierced through them before they are screwed together. Wedg ing, where the pieces which have been slit are held toYetlier by wrought iron wedges driven in, is more used in machinery than in building. Fin ally, it may, be added that in these iron joints, just as in woodwork, the ends of the pieces may be fashioned in such special ways as will best in sure a firm and solid connection. In iron- as well as in woodwork, scarf ing, forks, dovetail, tenons, etc., are employed.
Bawls anti in the case of free-lying wooden beams the oblong cross-section stands in relation to the sides as 5 : 6, so in the case of iron girders the I-shaped cross-section is the best, so far as regards the least relative consumption of material. Other forms of cross-section—as,
for example, the simple T or the U—are 'used only in exceptional cases for free-lying beams and girders. Beams and girders of this description may be cast, or, if they are to be of wrought iron, may be rolled, or may be made of vertical and horizontal plates riveted together with the aid of angle-plates, or, finally, by riveting together sing,le rods crossing- each other and having horizontal top and bottom plates (lattice girder), also with the aid of angle-irons. The dimensions of the cross-section of all such girders will depend not only upon the material and the method of manu facture, but chiefly also upon the special purpose to which they are to be applied, and upon the stress to which they are subjected.
the construction of flat ceilings, iron beams are more employed as girders for wooden beams, though they also may serve the purpose of the ceiling-joist proper; but in vaulted ceilings they supply the place of the separating and supporting ribs of the transverse arches. Fig ures to 3 GO/. 4) show cross-sections of a number of ceilings, as con structed in Paris, with iron joists. The joists, made of rolled iron, here receive a camber of -2-&6- and a depth which must not be less than -alz- of the span. In the construction shown in Figure 1, first between the joists, that lie about 2X feet from one another, and upon their lower flanges, are laid square iron rods about X inch in thickness and at distances of from 2X to 3 feet; upon these are then set flat iron rails parallel with the joists and fastened to the square rods by wire, and upon these rails collies a course of hollow bricks, as is shown in the Figure. Finally, a layer of mortar or plaster is poured over the brickwork, which then receives either a stone flagging or a wooden floor. The ornamental plaster-work of the ceiling, of plaster of Paris, is poured upon a planking before the setting of the bricks, this planking being removed after the mortar has dried. • F. igure.3 2) exhibits various forms of hollow blocks of hard-burnt fireclay and terra-cotta, which are much in vogue at present in the United States in the building of important structures designed to be fireproof. According to their form, these are designed for the construction of flat and segmented arches between iron girders and wooden beams. They serve a useful purpose also for partitions, furring for walls, linings for flues, col umns, etc.