This section is from the book "A Practical Treatise On The Joints Made And Used By Builders", by Wyvill J. Christy. Also available from Amazon: Practical treatise on the joints made and used by builders.
More correctly, perhaps, Anchor and Collar Joint, which is the name given to a device forming the top hinge of a lock, dock, or other heavy gate. A strong piece called the anchor is firmly let into the stone work, and the collar of wrought iron is fixed to it, constituting a socket for the top of the heel post of the gate to work in. The joint occurring between any anchoring plate and its seat or bed is likewise an anchor joint, and may be as simple as that between a common plate or disc attached to a tie and the bulging wall it helps to sustain; or as grand as the junction between the anchorage plates of suspension bridges and the rock or immovable masonry on which they are seated. Iron skewbacks carrying spandril arches, and retaining walls steadied by anchoring plates, are kept in position by the reaction at the anchor joints at the further ends of their respective tie rods.
This occurs when two lengths of angle iron are united by a fishing piece, also of angle iron, as in Fig. 71, the whole being either bolted or riveted together. Similar joints are made in various ways with bolts and nuts; thus Fig. 72 shows an angle iron purlin joined to an angle iron rafter by means of an L cleat or short length of angle iron. Purlins in this or the reversed position, or rafters of angle iron, are often filled in with wood, unless the covering is to be of corrugated iron, or packings of wood are screwed or fastened to the iron work to fix boarding thereto. Slates, however, only require lead pegs or zinc or copper clips to unite them to iron laths, and boarding, therefore, in their case is not absolutely essential.
This is formed between plates when united by angle iron with rivets or screw bolts, according as the elements connected are wrought or cast. Square piers are thus formed by bolting together flat iron castings and building up the interior with brickwork in cement.
The cast iron segments of arched ribs in bridges form arch joints at their planes of junction, since the great additional strength gained by the curved conformation and radiating joints of the ribs is due to horizontal thrust, or in other words to their being de facto arches with long iron voussoirs, the necessity for an exact jointing of which has been already glanced at under Abutting Joint.
Bayonet Joint"is useful for joining pipes or rods requiring occasional disconnection where longitudinal stress only has to be met. It consists of a socket or sleeve, Fig. 73, in which an L-shaped slot is cut at the end of one of the pieces to take a stud attached to the other, which is slipped into it and turned round as far as the slot will permit. Circular gratings to drain traps are sometimes secured with this form of joint.