Increasing The Thickness Of Beams. When beams are required to be of great thickness, in place of employing one very thick beam, two beams, a and b, fig. 332, are used, laid face to face, and strengthened either by inserting a flitch or plate of wrought-iron c between the two beams, and securing them together by screw bolts and nuts. The arrangement thus shown is sometimes called a "sandwich" beam, although generally a " flitch " beam. In fig. 332, A is a cross section, B elevation of the iron flitch, C plan of top. The two beams are secured together by screw bolts, which pass through the beams a, b, and the flitch c, as at d d. In figs. 3, 4, 5, 6, Plate XLIII, we give different forms of "trussed beams/' figs. 3 and 4 are trussed with flat cast-iron bars a ab, figs. 5 and 6 with wrought-iron rods a ab; in all these drawings A is an inside elevation of one beam, with the truss fixed in place, B is the plan of bottom edge looking upwards. The beam to be trussed is usually made out of two beams formed by cutting up a beam in the direction of its length, and reversing the sides, so that what formed the inside of the beam is turned to the outside. This plan of sawing up a single beam to form either a flitch beam or a trussed one is very good, as it exposes the central part of the wood to the action of the air, and shows defective parts. In fig. 4, Plate XLIII, b and c are the two beams, and A shows the arrangement of the truss between the two. This consists of a central stud of wrought-iron, d, the head of which is formed with a plate which lies on the upper edges of the beam, as shown in plan at B; the lower part is provided with a screwed part and a nut, c, for tightening up the stud; the nut presses upon a small washer plate as shown. The upper part of the stud, d, fig. 4, Plate XLIII, is made with two angular butting faces, against which the upper ends of the struts or braces, a a, of hard wood or of iron butt, the low end butting against the study! This stud is provided with a bolt, g, to resist the pressure and keep it in place; or the stud is made wider, and let in at both sides into grooves cut in the faces of the two beams. The whole parts are further secured by bolts, h. Fig. 3, Plate XLIII, is part elevation and part plan of a beam trussed on the queen post principle, a straining piece, b, being placed between the two studs, c; a the struts. In Plate XLIII., figs. 7 and 8, the elevation of a method of forming girder beams of greater depth than could be made out of a single beam or of two beams, is illustrated. This form, as the student will perceive, is an open beam, and is sometimes called a "trellis beam," although the more correct form of a trellis beam is illustrated in fig. 2, Plate XLIII. In fig. 7, Plate XLIII, the open beam is made up of a sill, or lower beam, a a, this may be according to the span or bearing of the beam - either in one length, or if made up of one or more lengths, these may be scarf jointed as already illustrated. The " head," or upper beam, b b, supported at intervals by studs, posts, or puncheons, or short beams, c c, placed vertically. Between the beams, braces or Struts, d d, are stretched; butting at the ends against the sills, heads, and studs, as shown. The heads and sills are further secured together either by screw bolts and nuts as shown at e, or by straps at f. Fig. 9 is a vertical section showing how the posts, c c, are mortised into the head 6, and sill &, and secured by the bolt e, or strap f. Pig. 11 is a section showing the parts, a a, in which the ends of the cast-iron struts, d d, fig. 8, are placed; the struts d d, fig. 7, are wholly of wood. In the "trellis beam," fig. 2, Plate XLIII, the space between the heads and sills is filled up by double strutting, forming a series of diagonal squares or openings. Fig. 10 shows a method of making the central stud of a king post trussed beam other than that shown in fig. 5.

26 Increasing The Thickness Of Beams 151

Fig. 332.

27. Brestsummers, or Bressumers, are beams of considerable thickness and depth thrown across wide openings, as that of a shop front, to support breast of front wall, built above the opening. They may be strengthened by one or other of the methods just described, and should have a bearing of at least nine inches in the wall at each end. " Templates" of stone, or timber, should be nsed, on which the ends of the brestsummer rests; a very usual size for the brestsummer is 14 in. by 12, or 14 in. by 9. A lintel is a beam or small brestsummer thrown across a narrow opening made in a wall, as that for a window or door opening of the usual width. It is the ordinary practice to allow one inch in depth for each foot of width of opening; a good proportion for a lintel is 7 in. by 5. The bearing on the wall should be nine inches. If the wall be thick, two or more lintels are used; and it is good practice to give the lintels a bearing upon oak templates, which should stretch across the full breadth of wall.