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shearing, which would probably be analogous to that due to punching, the plates were all cut out in a slotting machine.
(17.) These experiments appear to be reliable, nevertheless there are some remarkable differences between them and the results obtained by other authorities. For example, Mr. Fairbairn's experiments in Table 1 give for Lowmoor iron 24.56 tons per square inch both lengthways and crossways, whereas Mr. Kirkaldy gives for plates not annealed 21.3 lengthways, and 20.3 tons crossways, and for annealed plates 20.1 and 19.2 tons respectively, these being the means for six kinds of Yorkshire iron, and they show a difference of 15, 22, 20, and 28 per cent. as compared with Fairbairn's results. Messrs. Napier and Son's experiments in Table 1 give 24.1 tons lengthways as the strength of Yorkshire plate iron; agreeing with Mr. Fairbairn. Another remarkable difference is that the loss due to punching, which as we have seen (16) was 13, and 17.26 per cent. by Kirkaldy, was as much as 24 per cent. in single riveted joints by Mr. Fairbairn, as shown by col. 4 of Table 5. Probably the fact that the strain is not central or symmetrical, as shown by the broken centre-line in A, Fig. 6, may account for the difference.
(18.) “Strength of Drilled Plates." — When the rivet-holes are drilled, the loss of strength in the metal between the rivet-holes is practically nothing, the mean result of eighteen experiments on six kinds of Yorkshire iron (16) was 1.13 per cent. lengthways, and 0.9 per cent. crossways. Notwithstanding the advantage which is thus shown to accrue from drilling rivet-holes, it is hardly likely ever to be adopted extensively in practice; the extra cost of drilling would not be compensated by the extra strength obtained.
(19.) “Shearing Strength of Rivets.”—It is shown in (123) that the resistance to shearing is equal to the tensile strength of the iron, and Mr. E. Clark's experiments gave 22:1 tons per square inch, Mr. Fairbairn's experiments gave 22:04 tons in a singleriveted joint, where the result might possibly be complicated by friction (20), but with such a joint friction would be eliminated at the point of rupture, the surfaces separating by the unsymmetrical strain (17). We may therefore take 22 tons, or 49,280 lbs. per square inch as the mean shearing strength of wrought-iron rivets.
(20.) “ Friction from Grip of Rivets.”—Mr. E. Clark made some experiments on the friction in riveted joints, and obtained some remarkable results, for he found that the friction increased considerably with the length of the rivet. With rivets & inch diameter, riveted hot in the usual manner, and 11, 13, and 25 inches long, the friction was 47, 5, and 8 tons respectively. The experiments were made in the following manner: three plates were riveted together with one rivet; the central plate, having an oblong hole, was then drawn between the other two, the frictional resistance to which was 5} tons. Two -inch washers were then added, making the length 25, when the strain due to friction became 8 tons. Two fplates and two washers gave a length of 14 inch, when friction became 4 tons. This last experiment approximates nearly to the conditions of ordinary riveted joints.
(21.) “ Principles of Riveting.”—We may now investigate the phenomena which occur with riveted joints, and to do that satisfactorily it will be well to take an experimental case, the reasoning can then be checked by practice. Fig. 7 is a joint of best Staffordshire plate, experimented upon by Mr. Brunel: the main plates were } inch thick, and the joint was formed with a front and back plate each inch thick, and twenty rivets 11 inch diameter. This joint failed with 164 tons, by the -inch plate tearing through the outer line of rivet-holes B, B: the rivets were not broken in this case, but evidently they must have been on the point of rupture, for in another and similar experiment the whole of the ten rivets in one half of the joint were sheared with a lower strain, namely 153 tons. We may therefore assume that 164 tons would or should rupture the plate and shear the rivets simultaneously. It was also found that a solid or unpunched plate of the same iron broke with a mean strain of 20.6 tons per square inch.
We have no experimental evidence of the damaging effect of punching on Staffordshire plates (16), but with Lowmoor iron, Table 4 shows a mean loss of 19.5 per cent. when strained crossways of the grain, and 17 per cent. lengthways; taking 18 per
cent. as a mean for Staffordshire plates, the metal left between rivet-holes will be reduced to 100 – 18 82 per cent of the strength of a solid plate; hence in our case, we have 20.6 x 82 = 16.9 tons per square inch. The area through the line B, B
Х = 140 tons, the breaking weight of the plate.
To this has to be added the friction due to the grip of the five rivets in that row; by Mr. E. Clark's experiments (20) this may be taken at 47 tons per rivet, or in our case 43 x 5 24 tons, making with that due to the plate 140 + 24 = 164 tons, which happens to be precisely as per experiment.
(22.) “ Real and Apparent Strength.”—The difference between real and apparent strength will now be manifest; the apparent strength or that of the whole combination is 164 tons, borne by 8.28 square inches,
inches, or 164 ; 8.28 = 19.8 tons per square inch, but the real strain on the metal between rivet-holes as we have seen (21) is 16.9 tons; the strain on the solid part of the plate at C, C is only 164 = 10 = 16.4 tons, whereas the breaking weight = 20.6 tons per square inch.
Thus the normal strength of the solid plate, or 20.6 tons, is reduced by punching to 16.9 tons per square inch, which again is increased by friction to 19.8 tons, being restored within 20.6 – 19.8 = 0.8 ton of the normal strength.
“ Rivets.”—The ten rivets were each 12-inch diameter = .3712 square inch area, and being subjected to a double shear give •3712 x 10 x 2 7.424 square inches shearing area; then, their apparent strength is 164 ; 7.424 = 22.09 tons per square inch, which is almost exactly the resistance given for double shear by Mr. E. Clark's experiments (123).
With certain proportions of double-riveted joints the apparent strength of the metal between rivet-holes per square inch may exceed that of the solid plate, a result that seems anomalous, but may be easily explained. Thus, let Fig. 8 be a joint with seven /-inch rivets in the outer row B, B; then the
x 6.94 square inches, giving 16.9 x 6.94 = 117.28 tons. Then, each rivet giving 44 tons of friction, we have 4.75 x 7 = 33.25 tons, and the total breaking weight of the joint = 117.28 + 33.25 150:53 tons, or 150:53 = 6.94 = 21.69 tons per square inch of metal between rivet-holes. But the solid plate yields 20.6 tons only, hence we have 21.69 ; 20:6 = 1.053, or 5•3 per cent. in excess of the solid plate, agreeing with Mr. Fairbairn's result in col. 4 of Table 5, which gives 1.0526, or 5•26 per cent. excess. Here the actual strength of metal between rivet-holes is 18 per cent. less than the normal strength or that of the solid plate, but the apparent strength is 5.3 per cent. in excess, the difference being due to friction.
(23.) These calculations are not given as absolutely correct, but as serving to illustrate the principles on which the strength of riveted joints depends, and to explain the differences in the apparent strength of various kinds of joints in Table 5. For instance, by col. 6 the mean strength of a solid plate of average British plate-iron = 48,454 lbs. per square inch ; by punching, the loss is 18 per cent. as in (21), and the strength of the metal left between rivet-holes is reduced to 48454 X •82 = 39723 lbs., and will be the same with all the different joints in that column. The oblique action of the strain in an ordinary single-riveted joint, as shown by the broken centre line 0, p at A, in Fig. 6, reduces the apparent strength to 36,898 lbs., and with one back plate as at B, to 39,248 lbs. per square inch, both being less than that of a punched but unriveted plate with a fair central strain, which, as we have seen, is 39,723 lbs. But with a front and back plate, friction becomes more influential and increases the apparent strength to 46,070 lbs.
(24.) “ Kinds of Riveted Joints.”—There are six principal kinds of riveted joint, which are shown by A, B, C, D, E, F in Fig. 6, and are described or specified in Table 5, which also gives the apparent strength of the metal between the rivetholes in each kind of joint, and with three different kinds or qualities of plate iron, namely, Yorkshire, Staffordshire, and the general average of British iron. Staffordshire is the weakest of the three, but is more extensively used than any other, and may be taken as a basis for calculation in ordinary cases. Taking it as a standard, British iron gives 48454 -- 44800 = 1.082, or TABLE 5.-Of the STRENGTH of RIVETED Joints in WROUGHT-IRON
Breaking-strain of Metal between Rivet-holes, in Lbs. per
Kind of Joint.
Mean of Stafford
Plates. Plates. ments.
Solid plate, not punched 61,588 49,852 56,264 1.0000 8 48,454 44,800 Single-riveted, simple lap, 49, 325 36,588 42,847 7615 10 36,89834, 110
Fig. 6 A Single-riveted, with backplate, Fig. 6 B
53,880 37,262 45,570 •8100 239,248 36,290 Single-riveted, with back and front plate, Fig.ck } 58,461 48,534 53,497-9508
2 46,070 42,600 Double-riveted, simple lap, Fig. D ..
58,286 45,590 52,503 9330 6 45,20841,800 Double-riveted, with backplate, Fig. E
54,64353,116 53,879 -9570 2 46,520 42,870 Double-riveted, with back and front plate, Fig. F )
62,27956,175 59,225 1.0526 3 151,000 47,160 (1) (2) (3)
(6) (6) (7)
8.2 per cent., and Yorkshire 56264 - 44800 = 1.256, or 25.6 per cent. greater tensile strength.
(25.) “ Proportions of Riveted Joints.”—In fixing the proportions of riveted joints, it is necessary to consider the subject under two different heads ; 1st for girder-work, where we have simply to secure equality between the shearing strength of the rivets and the tensile strength of the plate between rivet-holes, so that both may fail simultaneously; and 2nd, for steam-boiler work, where we have not only to consider the question of strength, but also the maximum pitch of rivets consistent with tightness of the steam-joints. This will vary with the pressure of the steam and the thickness of the plate; if with a given thickness and pressure the distance between rivet-holes exceeds a certain amount, it will be difficult, or perhaps impossible, to make the joint permanently steamtight (45). On the other hand, if the pitch is unduly reduced, the proportions of the metal left between the holes to the