Stiffeners. All stiffeners except the second from the end should have the outstanding leg on the side of the gauge line away from the center of the girder. As a rule, the end stiffeners should have enough rivets to take up the end shear, and the intermediate stiffeners should have sufficient to take up the shear at that point. This would, if carried out, require a different number of rivets in each stiffener. Common practice requires that the spacing in all stiffeners should be the same and that this spacing should be the same as in the end stiffeners. In some cases, such as in heavy girders, it is not possible to do this on account of the large number required in the end stiffeners, and the rivet spacing is then made the same in all the intermediate stiffeners.
The rivet spacing should not exceed 4 or 5 inches at the most and should be so placed that it should he symmetrical about the center. When the web plates are of even inch width, the g inch may be put into one odd space at the center in order to avoid inch in the spacing. It may he necessary to put in a few more rivets than arc computed as necessary, but the advantage gained by thus making the punching of the plate on the multiple punch possible, makes this advisable. Fig. 72 shows this method of detailing. In order to make the shear plate at the web splice efficient to some degree in withstanding the moment—for although it is not computed to take moment yet it does in reality —the rivets near the flange are placed close together for a few spaces. If the space changes after that, it should increase towards the middle of the web, except in such a case as Fig. 72 where the center space may or may not be as great as those on either side of it.
In double-gauge flange angles the rivet in the stiffener should be in the inner guage line of the flange angle as shown, and no rivet should come closer than inches to the end of a filler.
Each like stiffener should be given a mark and in case others of the same kind both in size and punching occur, the mark may be used instead of the material notation and dimension. Those crimped will be given different mark even if size and punching are the same. It should be noted that some of the stiffener angles differ only from the fact that they have holes in their outer leg to which the cross-frames are con nected, hence a different mark.
The length of stiffeners listed on the drawing is the distance inside of flange angle legs. Without further instructions they will be ground by the shopmen so as to have a snug fit.
Fillers. Fillers arc placed under angles that are crimped since the angles are only crimped inch and not the entire :4- inch which is the thickness of the flange angles. The fillers are given marks for the same reasons and in accordance with the same rules that apply to stiffeners.
Flange Angles. In case of double gauge on the 6-inch flange angle it is better to put the 24,-inch gauge on the inside, no matter what the thickness may be, since by this operation the rivets in the horizontal flange, providing that is a double-gauge line, may be more advantageously spaced on account of the fact that the required stagger will be less.
The rivet spacing in the vertical leg of the flange angles should increase from the end towards the center and should remain the same, as far as possible, between any two stiffeners, any changes necessary being made near the stiffeners. Since a rivet must always be in the inner gauge line at a stiffener, an even number of spaces must be between any two stiffener gauge lines, since the rivets must stagger. This brings one rivet in the center of the girder, which can not occur in case there is a splice at the center of the girder. The stagger may then be broken as in Fig. 73, the stiffener angle being placed as shown and the rivet spacing being symmetrical on each side of the center of the girder.
Between the stiffeners at the end, the spacing should he the same as it is between the next two stiffeners.
The spacing at any point should never exceed the computed spacing unless constructive reasons require it. On account of rivet driving clearances, a -inch rivet can not be driven any closer than 1/ inches to another member.
Therefore, rivets can not be driven any closer to the stiffener than 11 inches, see Fig. 74. For this particular sized stiffener, the minimum spacings next to it will be 34 inches and 21 inches as seen in Fig. 74. The rivet-spac ing multiplication table, Table X, will be found very helpful in spacing the rivets here.
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/ inches to the out standing 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 he where n=the number required; s=the allowable unit flange stress; 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 =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 re quirement. ;l lost engineers, notwithstanding the specifications, re quire the majority of the spacing to be within 5 inches.