In these it is only necessary that the pieces abut firmly, as long as there is no force tending to make them slide off laterally.
Fig. 190. Bridle Joints for foot of Principal Rafter.
This form of joint is frequently rendered more secure by a cast-iron shoe formed to receive the ends of the timbers at the angle. Tie and Brace Joints. - When two pieces of timber, meeting at an angle, are tied together, such as two rafters, united by a collar tie, or wall plates by an angle tie, it is very important that the joints between the ends of the tie and the other pieces should not draw out or yield in any way.
One method of forming such a joint is to cut out of the rafter or wall plate a notch of dovetail form, just sufficiently deep to afford a bearing for the tie to rest upon, a corresponding notch is made in the collar tie, and the joint is secured by a nail or pin driven through it.
The dovetail in this joint is objectionable, for the reasons already given (p. 64), and in order to avoid it, Tredgold recommended a joint similar in form to that shown in Fig. 170.
Suspending Pieces are used for supporting beams below them at one or more points. When adopted in a roof they hang from the point of junction of two rafters, and support the ends of the struts, as well as the tie beam.
The rafters generally abut against the head of the suspending piece, as shown in Figs. 183, 184, 185; but a better arrangement, in many cases, is to make the suspending piece in two thicknesses - the rafters being allowed to abut against one another, a thickness being placed on each side as shown in Figs. 194, 195. R R are the rafters butting against one another; ss the suspending pieces, notched upon the rafters, and bolted together through the blocks, b b.
Fig. 192. Strut and Beam Joints.
Fig. 193. Dovetail Tie and Brace Joint.
Fig. 194. King Post formed Fig. 195 with double Suspending Pieces.
1 The angular notch in the strut, into which b fits, is called a birdsmouth.
The lower end of the suspending piece, supporting a pair of abutting struts and the centre of a tie beam, is shown in the same figures.1