This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
Since the single gauge is used in the top flange and, according to the stress sheet, two rivet holes are taken out of each angle, it is possible to space the rivets in the outstanding leg and cover plates without reference to those in the other leg of the angle, due care being taken that they do not come closer than 1 1/4 inches to the outstanding stiffener leg. No special rule governs the spacing in the cover plates, the only requirement being those of the specifications, and that the number of rivets from the center of the span to the end of the cover plate or the number of rivets from the end of one cover plate to the end of another shall be and v= the value of a rivet in single shear or bearing in the cover plate, whichever is the smaller. For the first cover plate on top of the flange angles this equation gives
(net area of cover plate) s /v n= where n=the number required; s=the allowable unit flange stress;
Fig. 74. Minimum Rivet Spacing for Stiffener Angles.
_ [(16 X 9/16) - 2 (7/8 + 1/8) 9/16] X 10000 / 6013
= 13 which shows the number 78 to be amply sufficient in this respect. A clause in most specifications requiring the maximum spacing to be not greater than 16 times the thinnest plate and not greater than 6 inches, further governs the number, which would be 50 by this requirement. Most engineers, notwithstanding the specifications, require the majority of the spacing to be within 5 inches.
Fig. 75. Typical Stiffener and Rivet Spacing Diagram.
In case the spacing in the top flange is on a double-gauge line, care must be taken to see that the minimum stagger, Table IX, is not violated. In such cases it is customary to place a rivet in the inner gauge line of one leg opposite a rivet in the outer gauge line of the other leg, and to do this until a stiffener interrupts, when spacings are made with the observance of Table IX, until the rivets can be placed opposite again.
In order to Illustrate the above principles in regard to spacing when double-gauge lines are used on both legs and the maximum spacing for any particular distance is shown by the rivet curve, an example will be given. Let the stiffeners and the rivet-spacing diagram be as in Fig. 75. This shows the allowable rivet spacing to be 2 1/2 inches at the second, 3 1/4 inches at the third, and 3£ inches at the fourth stiffener, the distance between stiffeners being 6'-7 1/4". Let it be required to determine the rivet spacing between the second and fourth stiffeners
Fig. 76. Detail Drawing Showing Determination of Rivet Spacing between Second and Fourth Stiffeners.
Since the stiffener angles have a 3-inch leg on the web, the gauge of which is 1 3/4 inches, and no rivet can be driven closer to the edge of the leg on the web or to the outstanding leg than l 1/4 inches, no rivets can be driven closer to the gauge than 3 inches and 2 1/2 inches on the sides of the outstanding leg and the edge of the other leg, respectively, see Fig. 76. Since 3 inches is the minimum distance it must be used at stiffener (2) notwithstanding the fact that the spacing diagram requires not less than 2 1/2 inches. This leaves (6'-7 1/4") -3"=6'-4 1/4" from that rivet to the one in the gauge at the top of stiffener (3), no attention being paid to 3 inches, the minimum distance here, since it is less than the 3 1/4 inches required by the diagram.
An odd number of spaces must be used since the last rivet is on the other gauge line; and from the rivet-spacing diagram it is seen that the spacing can not exceed 2f inches until half way between the two stiffeners, and that a space or two of 3 1/4 inches would be allowed at stiffener (3).
By consulting Table X it is seen that 29 spaces at 2 1/2 inches are equal to 6'-0 1/2". Now (6'-4 1/4")- (6'-0 1/2") = 3 3/4" or 15 fourths (15/4), from which it is seen that if \ 'inch was added to 15 of the 29
@ 2 1/2", the result would be all that is desired; but this would leave the last space 2f inches and by Fig. 76 it is seen that it must be at least 3 inches. By making the last space 3 inches, which is \ inch, or 2/4 greater than 2 1/2 inches, there remain 28 spaces between rivet a and rivet b, Fig. 76, and only15/4-2/4 = 13/4 left. If, therefore, 1/4 inch be added to 13 of the 2 1/2-inch spaces, making 13 of
2 1/2"+1/4"=3 3/4" each, the spacing will be correct. It is:
In a similar manner the second space between stiffeners has its rivet spacing determined. Here it is seen that the rivet spacing may start at 3 1/4 inches, can not exceed 3 1/2 inches until past the middle, and can have a few spaces at 3f inches at the stiffener. By Table X it is seen that 24 spaces at 3 1/4 inches equal 6'-6". Now (6'7 1/4") - (6'-6//) = l 1/4" or 5/4 and if one of the 24 spaces be increased \ inch and two of them are increased 1/2 inch the entire 5/4 inch will be used up and the spacing will have been completed. It is.
In a similar manner almost any combination can be made to fill out any dimension.
The rivets in the horizontal flange of the angle and the cover plate are, when the spacing is greater than 2 5/8 inches, placed opposite those in the vertical flanges as is shown in Fig. 76, since according to Table IX, Y being (2 1/2" - 5/8") = 1 7/8" no stagger is required, and where the spacing is less than 2f inches it is changed so as to be 3 inches or more. In such cases as this it is not necessary to give spacing in the cover plates, a note, "Spacing same as in vertical legs" or "Spacing same as in web" being all that is required.