It is required that this member shall have a net area of 21 500 16 000X 1} = 1.08 square inches in tension. The net area of theangle, one rivet-hole being taken out, is 1.92 square inches, which shows the angle to be safe in tension.
The number of rivets required is determined by single shear, since they tend to shear off between the member itself and the con necting plates. The number required is 2 X 21 500 6 field rivets.
6013X 1f Since the above angle is the smallest that can be used, and since the remaining angles of the panel of the lateral bracing have smaller stresses than the one just designed, it is evident that this size angle must be used in all panels of the lower lateral system other than the first.
92. The Shoes and Roller Nests. For bridges of short spans and for plate-girders whose spans require rocker bearings to be pro vided (80), several different classes of bearings are in use. Two such bearings are shown in Fig. 196 (a and b). The type illustrated by a is seldom used on any spans except plate-girders. That shown in b may be used on either plate-girders or small truss spans; it is the invention of Mr. F. E. Schall, Bridge Engineer of the Lehigh Valley Railroad, who uses it on plate-girders. It has given very great satis faction; and for simplicity of design and also for economy it is to be recommended. Some railroads have used a bearing which consisted of a lens-shaped disc of phosphor-bronze, the faces of which fitted into corresponding indentations in both the masonry and the bearing plates. One advantage of this bearing is that it allows movements due to the deflection of the girder, and also lateral deflection of the floor-beam. It is claimed to have given satisfaction.
A bearing which is used on both short-span and long-span bridges is shown in Fig. 197. This class of bearing will be used. The end reaction of the bridge proper is equal to the vertical component of the stress in the end-post, and is 3(1.1 X 410 500 = 336 500 pounds, 36-.7 ?36 500 which requires a hearing area (19) on the masonry, of 600 _- 561 square inches. According to the table on page 193, the masonry plate will be 28 inches long.
The total hearing area for one of the vertical plates is: 336 500 — 7.0 square inches; 2 X 24 000 and the total required thickness is: 7.0 = 1.12 inches,
6.2.2 5 a 6k-inch pin being used at Since the vertical plates will be made inch thick, this leaves a remainder of inch to be made up of pin plates.
The amount of stress which is carried by the Finch pin-plate is 0.375 336 500 X = 56 100 pounds. These plates will tend to shear 1.125 2 56 100 off the rivets at a plane between the plates, and therefore = 8 7220 shop rivets will be required to fasten them to the vertical plate.
Since the length of the masonry plate is 2S inches, and the total area required is 561 square inches, the required width is o61 28 = 20 inches. The actual width will be greater than this, since it must be sufficient to allow for the connecting angles and also for the bearings of the end floor-beam. The connecting angles should be } inch thick, and should not be less than 6 by 6 inches; and the plates to which they are connected should not be less than # inch in thickness, and likewise they should not be greater, on account of the punching. The bottom plate should extend outward about 3 inches, in order to allow suf ficient room for the anchor bolts, which should be a inch in diameter and should extend into the masonry at least 8 inches.
In addition to the reaction of the bridge proper, the masonry plate must be of sufficient area to give bearing for the end reaction of the end floor-beam. The maximum end reaction (see Article 83, p. 197) is 104 740 pounds. The bearing area required on the masonry is 10 0 = 175 square inches; and assuming that the base of the bearing will be 12 inches long (see Fig. 197), the required length will be 14.6 inches. Usually, however, the bearing is extended the entire length of the masonry plate, which is 28 inches in this case.
The distance from the center of the pip to the top of the masonry will be the same for both the fixed and the roller end. This distance should be such that the angles of the shoe will clear the bottom chord member and allow the floor-beam to rest upon the plate as shown. Since the first section of the bottom chord is 181 inches deep, the top of the angles of the two must be at least 9+ inches from the center line of pins. This requires that the distance from the center line of the pin to the base of the angle shall be at least (91 + 6) = 154 inches, or more.