The train shed for the new depot of the Pennsylvania Railroad at Pittsburg is about 555 feet long, 260 feet wide and no feet high over all. It is one of the largest in this country, and will have sixteen tracks with platforms between them, each track having a capacity for one twelve-car train or two five-car trains. The design of the shed is almost identical with that of the company's Jersey City terminal, and the dimensions are approximately the same, the two structures being practically alike except for some modifications of details.
The principal members of the framework are twenty-four three-hinge arch trusses, which are spaced alternately 9 feet and 40 1/2 feet apart on centers, and are braced together in pairs and connected by longitudinal girders and trussed purlins. The outline and general dimensions of the trusses are shown in the diagram elevations, Fig. 239, and the lateral bracing in the plane of the top chords is shown in the roof plan, Fig. 240. There are twenty-two lines of purlins which are lattice-girders in the planes of radial truss members. The short panels between the trusses of each pair have 3/4-inch square pin-connected diagonal rods in every panel of the top chords and purlins, and the long panels between the pairs of trusses are braced by diagonal rods 1 1/4 inches square, which extend across one or two intermediate purlins.
Each end of the building is braced against lateral and wind strains by a lattice-girder in a horizontal plane through the fourth panel point above the end pin of the arch truss, about 25 feet above the ground. Horizontal struts and X-braces at all the panel points up to the hip connect the trusses of each pair, and are made of angles with riveted connections. The vertical ends of the trusses up to the hips, about 35 feet above the end pins are braced on each side of the building by a continuous line of lattice-girders about 12 feet deep, which reach from the hip to the next panel point below. Besides this the wall panel between the end two pairs of trusses is braced by a horizontal longitudinal lattice-girder at the bottom and by diagonal rods, and the vertical posts in each pair of trusses from the end pin up to the hip are braced with horizontal struts at panel points and X-brace angles in each panel thus formed (see Fig. 240). Besides these braces, each pair of struts is additionally braced at the hips by longitudinal horizontal struts and diagonals in the three planes of the web members, which are indicated by heavy lines in the elevation of the arch truss, Fig. 239.
Fig. 239. - Outline of Trusses.
Pig. 240. - Roof Plan.
There is a monitor with clerestory windows on the center line of the roof, which extends to within about 10 feet of each gable, and there is a transverse lantern 8 feet high and 15 feet wide over each pair of trusses except the end pairs, and in the center of each panel between the pairs. Both monitor and lanterns have opaque roofs and glazed sash on horizontal pivots in the sides. The purlins support two intermediate jack-rafters parallel to the top chords of the arch trusses in each panel, and these carry longitudinal I-beams not shown in the roof diagram, on which are sheathing boards covered with copper. Both gable ends of the building are open for a height of about 25 feet, up to the horizontal wind truss, and above that are closed with flat plates and corrugated galvanized iron on angle iron framing; the latter is supported by vertical and horizontal struts attached to the suspenders which carry the wind truss from the lower chord of the end truss. These members divide the space into rectangular panels from 10 to 15 feet wide and high.
The arch trusses have a rise of 93 feet and span of 255 feet on centers of pin, and have a clear height of about 87 feet above the rail base. They are alike in the intermediate and end panels except that in the latter the weights of the angles are lighter and the connections vary. They are 7 feet deep at the crown and about 6 1/2 eet deep on a radial line at the hips. Each semi-truss was shipped in six sections of two or more panels each, varying according to the depth of the truss and the length of the panels. The adjacent sections have their chords spliced with field-riveted cover plates like ordinary lattice-girder bridge work, except at the crown. This joint is made in the center of a panel and the diagonals are made extra heavy to carry the chord stresses to the 5-in. center pin, which engages reinforced jaw plates locking the two sections together (see Fig. 242). The abutting vertical surfaces at the pin are milled to 1/4-inch clearance, and the top and bottom chords are spliced with bolts through slotted holes in the webs to allow for temperature distortions. The chords are straight and slightly divergent between panel points, and each chord is bent to a slight angle at every panel point.
From Uo to U22, eleven panels down from the crown to the hip, the truss is made similar to the panels shown next to the crown. From the hip to the end pin the four panels were shop riveted complete, the top chord is replaced by an intersecting vertical post in the plane of the exterior wall and the radial web members are replaced by vertical ones. The chord web plates also disappear in the two lowest panels and the members are lighter and proportioned chiefly for direct vertical loads. Connections not shown in the drawing are made to the horizontal truss members for the longitudinal and diagonal braces to the next trusses. In the gable trusses 11 x 1/2-inch plates are riveted between the pairs of angles in the web members and, projecting beyond both edges of them, make flanges to which and to the inner edges of the chord web plates, 5/16-inch solid web plates are field-riveted, as shown in the drawing of section U18, U22, Fig. 241 to form a wall surface, closing the whole area of the truss.
A double web shoe is field-riveted to the horizontal lower flange at the end of the truss (Fig. 244), and has a semi-cylindrical bearing and jaw plates engaging the lower hinge pin and locking it to the pedestal. The web plates of the shoe are heavily reinforced and are connected by two oblique transverse diaphragms, which converge from the feet of the truss chords to the pin centers. The pin receives the end of the horizontal lower chord or tie which takes the thrust from the foot of the arch truss. This chord is a single 12-inch 100-pound I-beam with the web reinforced to 5 1/2 inches in thickness for the pin bearing. It crosses the train shed in a closed trough under the floor level, and is composed of 30-foot sections spliced with sixty-two 7/8-inch field rivets through double web and single flange cover plates.
The shoes are alike at both ends of the trusses, but the pedestal at one end has a center rib riveted to the base plate to lock and guide it on a nest of six 3-inch rollers 2 feet long, which travel on 3 x7-inch bearing strips on a 7/8-inch bed plate 30 inches square. At the opposite end of the truss the fixed pedestal is like the roller one, except that it is about 5 inches higher to compensate for the absence of rollers, and is seated directly on the pier masonry, to which it is anchored by two 2-inch bolts upset to 2 3/4 inches. The foundations of the pedestals are shown by Fig. 245.
The train shed was designed in the engineering department of the Pennsyl-vania Railroad Company, Mr. W. H. Brown, chief engineer. The drawings were made and the work executed under the direction of W. A. Pratt, M. Am. Soc. C. E., now assistant to . the chief engineer. Mr. Geo. C. Clarke was the assistant engineer charge of construction. The steel work weighs about 2,350 tons, and was made by the Edgemoor branch of the American Bridge Company and erected by the employees of the Pennsylvania Railroad Company in charge of Mr. A. Braun.