_Answer._ The strength through the rivet holes is calculated by TAKING THE AREA IN SQUARE INCHES OF THE METAL WHICH IS LEFT BETWEEN THE RIVET HOLES, AND MULTIPLYING IT BY THE ULTIMATE STRENGTH OF THE METAL AFTER THE HOLES ARE MADE. Thus, in fig. 53, the area of each of the plates between the rivet holes is 1.78 square inches. As already stated, good boiler plate will break at a strain of about 50,000 pounds in the direction of its fibres,[30] but the strength of the metal left between punched holes is probably 20 per cent. and that between drilled holes 10 per cent. less than that of the solid plate. We must, therefore, in calculating the strength of a punched seam, take the ultimate strength of the metal between the holes at only 40,000 pounds per square inch. The calculation for the strength through the holes would therefore be: 1.78 × 40,000 = 71,200 pounds. [30] Boiler plates should always be so arranged that the greatest strain will come on them in the direction of their greatest strength, which is parallel with the fibres of the metal. It has also been found by experiment that the strength of rivets to resist shearing is about the same as that of good boiler plate to resist tearing apart, or 50,000 lbs. per square inch. The strength of the rivets, therefore, is calculated by MULTIPLYING THE AREA IN SQUARE INCHES OF ONE RIVET BY THE NUMBER OF RIVETS, AND THE PRODUCT BY THE STRENGTH OF THE METAL TO RESIST SHEARING. The calculation for fig. 53 would therefore be: Area of ¹¹⁄₁₆ rivet = .3712 × 4 × 50,000 = 74,240. or a little more than the strength of the plates through the holes. The resistance offered by a plate to the crushing strain of a rivet has been found also by experiment to be about 90,000 pounds per square inch. It can be proved that the area which resists the crushing strain of a rivet in a plate, fig. 53, IS MEASURED BY MULTIPLYING THE DIAMETER OF THE RIVET BY THE THICKNESS OF THE PLATE. The calculation for the strength of this part of the seam will therefore be: diameter of hole = .6875 × .375 × 4 × 90,000 = 92,812. The strength of the solid plate would be EQUAL TO ITS SECTIONAL AREA MULTIPLIED BY 50,000 POUNDS, or 7.5 × .375 × 50,000 = 140,625 pounds. The ultimate strength of our seam would then be as follows: Plates through rivet holes (tearing) = 71,200 lbs. Rivets (shearing) = 72,240 lbs. Plates in front of rivets (crushing) = 92,812 lbs. Solid plate (tearing) = 140,625 lbs. It will thus be seen that the strength of the weakest part of the above seam, fastened with a single row of rivets in punched holes, is very little more than half (50.6 per cent.) of that of the plates. It will be noticed that the weakest part of the seam is the plates between the holes. [Illustration: _Fig. 57._] [Illustration: _Fig. 58._] [Illustration: _Fig. 59._] [Illustration: _Fig. 60._] QUESTION 105. _How can the strength of such a single-riveted boiler seam be increased?_