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solid part of the plate are reduced also, and a loss of strength will ensue.
With girder-work we have the choice of any of the six kinds of joint in Table 5, but for boilers we are practically confined to two, namely, single and double riveted; these alone being easily made steam-tight by caulking.
(26.) “ Diameter of Rivets.”—The proper size of rivets in proportion to the thickness of plate is to some extent arbitrary, and within certain limits may be varied considerably, so long as the great principle is observed, namely, so to adjust the pitch and thickness as to secure equality between the tensile strength of the plate and the shearing strength of the rivets.
Nevertheless, practice has dictated as expedient, certain proportions between the diameter of rivet and thickness of plate which should be followed in ordinary cases, and may be expressed by the rule :(27.)
d = (t x 11) + c
or d = (t x 1.25) + .1875. In which t = the thickness of plate, and d diameter of rivetholes, both in inches : col. 2 of Table 14 has been calculated by this rule. It should be observed that the diameter of the hole should be taken rather than that of the cold rivet: the rivet is always made smaller than the hole for facility in inserting it; but when riveted hot in the usual way it fills the hole completely, and the strength is therefore governed by the size of the hole itself.
(28.) It is a practical dictum that the diameter of the rivets shall be proportional to the thickness of the plate irrespective of the pressure of steam and other considerations. This leads to no difficulty with girder-work, because we can always adjust the pitch so as to obtain equality between the strain on the rivets to that on the plate (25). But for boiler-work the pitch is restricted by the pressure of steam (45), and we are conducted to the anomaly, that as the pressure is increased, the diameter of the rivets should be reduced, a result precisely contrary to that expected (53).
RIVETED JOINTS FOR GIRDER-WORK.
(29.) “ Pitch of Rivets in Single-riveted Joints.—The main principle in riveting, as we have stated, is so to proportion the space between rivet-holes to the area of the rivet as to obtain equality of strength, that is to say, that, theoretically at least, the rivets shall be sheared and the plate ruptured simultaneously. In a simple single-riveted joint, if the shearing strength of rivets per square inch and the tensile strength of boiler-plate were equal, the area of plate between two rivet-holes should be equal to the area of a rivet-hole, and it is commonly assumed that such is the proper proportion. But by col. 6 of Table 5 the mean strength of the metal between the rivet-holes in singleriveted joints is 36,898 lbs. per square inch, whereas the shearing strain of rivets by (19) is 49,280 lbs.: hence the area of the rivet in this kind of joint should be 36898 • 49280 = .75 of the area of metal between rivet-holes.
(30.) Thus, with X plate, and it rivets, as per Table 6, the area of id = .3712, hence the area of metal between two rivetholes should be .3712 = .75 = •495 square inch; the distance between rivet-holes
• 495 = 3
1.32 or 14 inch, and the pitch 11 + 1 = 2 inches. The ratio of the metal between holes to the solid plate is 1.32 : 2 = .66, hence the strain on the solid plate, when the joint is breaking through the line of rivet-holes, is 36898 x 66 = 24353 lbs. per square inch. This reduced strain on the solid plate as thus found, is useful for the purpose of calculation, as we shall find when we come to apply these results to girders, boilers, &c.
The general proportions of single-riveted lap-joints calculated on these principles are given by Table 6; with steam-boilers the pressure of the steam has to be considered in fixing the pitch of the rivets (44), but for girder-work the proportions given by the Table require no correction.
( 31.) “Single-riveted Joints with Back and Front Plate.”—The advantage of a single back-plate, as at B, Fig. 6, is inconsiderable, as shown by col. 4 of Table 5, but with a front and back plate, as in Fig. 8, it is very great, which is due not only to the greater apparent strength of the metal, but also because
TABLE 6.-Of the PROPORTIONS and STRENGTH of SINGLE-RIVETED
JOINTS in WROUGHT-IRON PLATES: for GIRDER-WORK ONLY.
11 11 11 21
9 $ 16
36,898 24,611 11:00
26,640 11.89 27,673 12:35 23,725 10:59 25,238 11:27 26,124 11.66 27,046 12:07 22,139 9.88 23,981 10.71 24,611 11.00 26,161 11.68 26,840 12:00 21,696 9.68 23,467 10.47 24,131 10.77 25,349 11:32 22,471 10.00 23,246 10:38 24,353 10.87 25,238 11.27 22,139 9.88 22,914 10:23 23,946 10.69 25,644 11:45 21,844 9.75 22,618 10:10 23,172 10:35 23,984 10.71
NOTE.—The rivet-holes marked * are the most suitable for the given thickness of plate, in ordinary cases.
the rivets are subjected to a double-shear, and their area in proportion to the plate may be reduced to half.
The apparent strength of metal between holes being by col. 6 = 46070 lbs. per square inch, the area of the rivets should be 46070 = 49280 •93 of the area of metal between two holes. Taking plate, and it rivets as before, the area of the rivet with double shear = .3712 x 2 = •7424 square inch ; the area of metal between two holes • 7424 ; .93 = .8 square inch; the distance between the holes = 8= 2 inches, and the pitch = 2} + 12 = 21%; the ratio of the metal between holes to the solid plate 2} = 21, or 34 - 45 = .756, and the strain on the solid plate = • 756 x 46070 = 34829 lbs. per square inch, which is 34829 = 24353
1.43, or 43 per cent. more than with a simple single-riveted joint (30). Table 7 gives the general proportions and strength of single-riveted joints, with front and back plate calculated in the manner we have illustrated.
(32.) “ Amount of Lap.”—A riveted joint may give way 1st, by the rivets shearing ; 2nd, by the plate breaking across through the line of the rivet-holes; and 3rd, by the rivetholes tearing out: we have considered the two former, and bave now to consider the latter. Theoretically, the metal a, b, c, d, in Fig. 10, should be torn out, but the rivet would be flattened and deformed by the plate, and we may assume a starting-point for the line of fracture at m, say midway between a and n: then the sum of the distances m, o and p, r should be equal to the space c, e between two rivets. Taking, therefore, half the distance c, e, and setting it from m to 0, we obtain the lap for single-riveted joints, as in col. 5 of Table 6.
(33.) With a double-riveted joint, Fig. 11, the plate F might break on the line of rivets A, B; in that case the plate E and all the rivets may remain intact; conversely, the plate E may break on the line C, D, the plate F and all the rivets remaining firm.
If, as in Fig. 12, we make the space T = half S, fracture might take place on the zig-zag line J, K as easily as on the line A, B, or C, D, in Fig. 11, because the breadth of plate strained is the same in both cases. This shows that T should be half S.
In another case all the rivets might be torn out, as in Fig. 13,
Table 7.-Of tho PROPORTIONS and COHESIVE STRENGTH of SINGLE and DOUBLE-RIVETED JOINTS in WROUGHT-IRON
PLATEs, with Front and Back PLATE as in Figs. 8, 9: for GIRDER-WORK ONLY.
STRENGTH, &c., OF SINGLE-RIVETED JOINTS.
Distance between the Back and Front Plates.
Rows of Rivets.
Strain on the Solid
sobre la orice the
4 43 5
110 14 25 216
218 215 315
2 2 2) 23 27
•772 • 757 • 756 • 745 • 735
35,567 34,876 34,829 34,323 33,862
15.88 15.57 15.55 15.32 15.12
STRENGTH, &c., OF DOUBLE-RIVETED JOINTS.