The cut on the left represents one of the iron girders employed in building the London University. The whole length is 36 feet, and cast in one piece; it rises in the middle about 25 inches, and is provided with a wrought iron tie or circular bolt of about 3 inches diameter, which passes through apertures in the series of projecting pieces shown, and is strongly screwed up at the ends c c. On each side of the girder are bolted wooden scantlings, into which the joists are framed.
Fig. 1 represents a trussed girder, invented by Mr. J. Conder, on the principle of suspension; and Figs. 2, 3, 4,5, represent separate parts of the plan of trussing, and the same letters refer to similar parts in all the figures. The girder a a Fig. 1 is furnished with cast iron plates, turned down at right angles, to extend over its ends. These end plate3 have on their upper surfaces circular hooked projections, shown in elevation by Fig. 2, and in plan by Fig. 3. The use of these hooked projections is to receive round rods of wrought iron, bent in the middle to correspond and fit into the hooked projections, as represented by b Fig.3. The iron rods extend along each side of the girder one-third of its length, in a sloping direction from b to d. where their ends pass through holes in cross pieces of iron, and are secured by screwing thereon nuts, as shown at Fig. 4. Between the pieces d d and the lower side of the girder are placed prism-shaped blocks of oak c c, shown in section by Fig. 5, which vary in size according to the depth of the roof or floor which the girder is intended to support.
Below the middle of the girder, and parallel thereto, extends a single rod f, equal in strength to a double rod e e; this rod passes through the middle of the cross pieces d d, and is secured by nuts screwed en its ends, as represented by Fig. 4. All the parts of the truss may be brought to any required tension, and the girder made to camber simply by screwing up one of the nuts on the rod j. A somewhat simpler plan is represented in the following figure, whilst it possesses the sam advantages as to strength and durability. The girder d to he trussed, is divided longitudinally into two flitches, and between them is introduced a single rod of iron e, the ends of which pass through the kneed plates b b, and are then secured by screwed nuts; the ends of the flitch are bevelled off at right angles, to the direction of the trussed rod. Beneath the girder are placed two triangular blocks d d, proportionate to the strength required. The two flitches are kept apart the thickness of the truss rod by the introduction of slips of wood between them, and kept in their places by straps at e e e e.
Mr. Renton's arrangement of the suspension trussed girder is shown in the figures beneath. Fig. 1 is an elevation of the truss, with one of the flitches removed to show the iron work; and Fig. 2 is a section of the girder, a a the two suspension links, connected with the two tie links b b by bolts and keys, through the cast iron saddle pieces d d. The upper ends are united to the abutment pieces r. c by bolts passing through them; the beam is adjusted to its bearing, or cambered, if necessary, by the folding wedges (seen at e e Fig. 2) at the back of the saddle pieces, which it may be found necessary to steady sideways by blockings spiked to the beams. Figs. 3 and 4, elevation and plan of another mode of connecting the tie links and adjusting them by wedges. Fig. 5, another form of link, which may be used, instead of the double bar link. The subjoined figures represent one of the girders employed at Messrs. Nicholson's distillery, to support a liquor back containing 19000 gallons, which, when full, weighs nearly 100 tons.
Fig. 1 is the elevation of the girder, with one of the flitches removed.
Fig. 2 a plan of the truss, a a a Fig. 1 are three strong plates of cast iron, forming a sort of arch, of which the centre piece may be considered the key-stone, and b b cast iron plates, resting on the wall, as the abutments, c c cast iron blocks, in which the upper ends of the two side plates a a, and the ends of the middle plate are lodged; d d blocks of cast iron, which are screwed up against the under side of the girder, by nuts on the end of the screw-bolts passing through the blocks c c. e is one of two wrought-iron tie bars, passing through the blocks d d and b b, and secured by nuts at the ends e, and which ends, as a further security, are chained. The blocks b b have protuberances f f which are let into the bearing timbers g on the walls h. The ends f b of the blocks incline outwards about 10 degrees, on which account the flitches of the girder cannot slip down, but must press at the angle b, as must also the points between b f of the plates a a, when the weight presses down the queens by the part of the girder bearing on their shoulder or on the blocks d d, thus giving the whole weight to the bars e in the direction of their length, just as if the weight were suspended vertically from those bars, or nearly so, the girder being merely a rest for the base of the back.
Fig. 3 is the end, with the girder trussed on; 4 is the end view of the blocks d d, through which the tie bars pass; 5 a section of the inner part of the end block, when trussed; 6 is one of the iron braces which saddle over the flitches, to keep them to at top; and 7 is one of the pieces of oak which fit into the apertures between the flitches to preserve the bearing. The bars e are 21/8 inches in diameter, or upwards of 31/2 inches area.
We shall conclude this article with a description of a trussed girder proposed by Mr. Gutteridge, and which we insert rather for the novelty of the contrivance, than for any great merit which we can discover in it. a is a beam of wood or girder to be trussed, lodging on the walls h. b g b a wrought iron plate or bar lying on the beam, and attached to iron levers b c d by pivots at b. These levers are attached to the ends of the beam by iron plates t, which are fulcra, c being the centre. To the lower extremity or pivots of the arm c d is attached a bar of iron f at each end, and these are connected by pivots at e f to a similar bar m, and are kept below the beam by cast iron blocks k. The object of this construction is to cause any weight laid upon the beam at g to counteract its own tendency to bend the beam, by its increasing the tension of the suspension rods l ml, which would cause the blocks k k to rise; but the weight of any load is made to increase the tension of the tie-bar by much simpler means in some of the trusses previously described, as in Smart's bow and string rafter, or in the girders at Mr. Nicholson's distillery.