The design for the bearing of the girder under consideration will now be made. The total reaction of one girder must now he computed. This will be due to the weight of the steel in the girder, to the weight of the track, and to the reaction pro duced by the E 40 loading when wheel 2 is directly over the end support. This reaction is: (123.5 + 10 61 .75) 61 .75 Weight of Steel, -- ---- — 11 430 pounds Weight of Track, -˘r (61.75 1.75) 1 = B 350 " Reaction Due to Engine Loading = 99 700 " Total = 117 480 pounds.
The square inches of bearing surface required is 117 480— 4i0; 250 and, as the length is 1 foot 9 inches, or 21 inches, the total width of the cast-steel pedestal will be 2 0 = 22.4, say 23 inches, or 1 foot 11 inches. .
A bearing plate must be riveted to the lower flange where it rests upon the pedestal. The pedestal must be so constructed as to allow this bearing plate to set in it. Hand-holes should be in the casting in order to allow the bolts which connect the casting to the girder to be inserted. These bolts should be at least i inch in diameter. Anchor bolts inch thick and at least 8 inches long should be provided and fox-bolted to the masonry. The thickness of the metal in all parts of the casting should be at least 14 inches. The details of the pedestal are given in Fig. 164, the length of the bearing being made 12 inches so as to allow one rivet to be driven in the flange angle in the space between the end stiffeners.
Allowance should be made for a variation of 150 degrees in tem perature. The coefficient of expansion for steel per unit of length is 0.0000065, and the amount of expansion for 150 degrees of tempera ture will be: 0.0000065 X (61 ft. 9 in.) X 150 0.06 foot.
This is about 4 inch, and therefore the holes in the flanges at one end of the girder should be made oblong and long enough to allow the girder to move n inch, or n inch either backward or forward from a central position. In determining the length of this slotted hole (see
Fig. 165), it must be noted that the 1,-inch bolt takes up part of this hole, and therefore its length should be -F i = say 14 inches. The width of the hole should be sufficient to allow for any over-run in the diameter of the bolt. It should be at least 11 inches wide.
1. Determine the distance center to center of bearings, and the size of the masonry plate, for a plate girder of 40-foot span under coping, the loading being E 40.
Ails. 41 ft. 4 in.; 350 square inches.
(Nora—Interpolate values in Ta ble f, Cooper, p. 80.) 2. If the girder span is 78 feet under coping, and the loading E 40, determine the maximum end reaction and the width of the masonry plate. Axs. 147 130 pounds; 241 inches.
78. The Stress Sheet. Plate II (p. 172) shows the stress sheet for the girder which has just been designed. It represents the best modern practice in that it gives, in addition to the sizes of all the sections, the curves for the maximum shears and moments, the rivet-spacing curve, and the number of rivets required in the different parts of the structure. This general form has been adopted by one of the largest bridge corporations in this country, and is to be recommended since it gives the draftsman all necessary data and thus prevents the loss of time by an inexperienced man in recomputing certain results. The results just referred to are the shears, the moments, the rivet spacing, and the number of rivets required in the various parts. Formerly it was not customary to give this information on the stress sheet, and the draftsman was therefore required to (10 all this computation which had previously been worked out by the designer but had not been placed on the stress sheet in available form, and thus unnecessary loss of time resulted.