Lap Joints are formed by riveting together plates that overlap one another, as in Figs. 212-215.

The overlap should not be less than 3 1/4 to 3 1/2 times the diameter of the rivets in single riveting (Fig. 212), or 5 1/2 to 6 diameters in double riveting (Fig. 214).

1 Stoney.

There are formulael for finding the length of the overlaps, so that the joints may be of equal strength throughout; but the above rules will be a sufficient guide in ordinary cases.

Figs. 212, 213. Lap Joint single riveted.

Figs. 214, 215. Lap Joint double riveted.

Fish Joints are those in which the ends of the plates meet one another, the joint being "fished" either with a single "cover plate," as in Fig. 217, or with one on each side, as in Fig. 218.

When a single cover plate is used it should be of somewhat greater thickness than that of either of the main plates to be united, in order to allow for the extra stress caused by the cover plate being out of the direct line of stress (see Part IV.)

Fig. 216. Plan of Fish Joint.

Fig. 217. Section of Fish Joint, one Cover Plate.

Fig. 218. Section of Fish Joint, two Cover Plates.

"When two cover plates are used each of them should be of not less thickness than half the thickness of either of the plates to be united.

Butt Joints is the name given to fished joints that are in compression, so that the ends of the plates butt evenly against one another.

This seldom occurs in practice, for the very process of riveting draws the plates slightly apart, and the edges are sometimes caulked to conceal the gap.

Sometimes the gap is filled with cast zinc run into the interval.

If, however, the plates are carefully planed square at the edges, and brought very carefully into close contact throughout their width, the joint is called a "jump joint."

1 See Part IV.

Single Riveting consists of a single row of rivets uniting plates in any form of joint, as in Figs. 212, 213, 216, 217, 218.

Double Riveting is that in which the plates are united by a double row of rivets, as in Figs. 214, 215, 219.

Double riveting may be either "chain" as in Fig. 214, or "zigzag," as in Fig. 2 19.

Fig. 219. Zigzag Double Riveting.

Fig. 220. Chain Riveting.

Triple and Quadruple Riveting are formed by 3 or 4 rows of riveting respectively.

Chain Riveting is formed by lines of rivets in the direction of the stress, parallel to one another on each side of the joint, as in Fig. 220.

Zigzag Riveting consists of lines of rivets so placed that the rivets in each line divide the spaces between the rivets in the adjacent lines, as in Figs. 219, 221.

Fig. 221. Zigzag Riveting.

Comparative Strength of different kinds of Riveted Joints - The relative efficiency in tension of the different forms of joint, as compared with that of the solid plate, is stated by Mr Stoney to be as follows for wrought iron l: -

 Efficiency per cent. Original solid plate ... 100 Lap joint, single riveted, punched .. 45 „ ,, drilled .. 50 „ double riveted . . . . 60 Butt joint, single cover, single riveted . . . 45-50 ,, „ double riveted . . . 60 „ double cover, single riveted . . . 55 „ ,, double riveted . . . 66 Tension flanges of girders, triple or quadruple riveted 70-80

1 Provided the joint is so designed as to be on the point of yielding from the tearing of the plates or shearing of the rivets indifferently. - The Strength and Proportions of Riveted Joints, p. 41.