103. This was one of the four largest buildings of the Exposition, being 150 feet wide and 500 feet long. The framework is supported on columns arranged in four longitudinal rows, as shown in Fig. 246, thus giving a clear central hall 97 feet wide and side aisles each about 17 feet wide, between columns. Two of the four longitudinal rows of columns are 12 x 15 1/2 inches in cross section and the other two are 14 x 40 inches, enlarged sections of the columns being shown by Fig. 247.
The small columns are built up of Norway pine planks laid flat and breaking joint every 3 feet, each having two 5/8-inch staggered bolts 12 inches apart, one through the column on each side of each joint. The edges of the planks are protected by a plank on each side of the column spiked to every plank with sixty-penny spikes 18 inches apart. Each of the large columns has two. principal members each similar to the cross-section of the small column, and spaced 26 1/2 inches apart on centers on the plane of the roof trusses. The separate members of each column are united by solid diagonal sheathing of 2 x 12-inch boards, inclined in different directions on the opposite sides of the column and secured by six sixty-penny spikes in each end of each board.
Fig. 246. - Transverse Section.
Fig. 247. - Enlarged Sections of Posts.
The main roof trusses are supported by the intermediate rows of columns, a small column at one end of each truss and a large column at the other end. One member of the large column is cut off square to form a seat for the end of the lower chord, and the other member is continued up to form a seat for the top chord. At the other end of the truss the small column is continuous to the seat for the top chord, and a special seat is keyed and bolted to it on the inside to receive the bearing for the lower chord. The truss is extended at each end to connect with the outside column and the inner column is knee-braced to the lower chord and X-braced to the outside column, as shown in Fig. 248, thus forming a rigid transverse framing to stiffen the columns against flexure and to resist wind stresses.
The trusses are made with 10-foot panels and a depth of 13 feet on centers. All compression members are of long-leaf southern yellow pine, and tension members are medium steel round rods with screw ends, most of which are upset. The trusses are seated on framed brackets which project from the intermediate columns and are keyed and bolted to the whole length of the end lower chord panels so as to virtually form long corbels and stiffen the trusses or have some effect of reducing the span.
Excepting the counters in the middle panels, all top-chord and diagonal members are single timbers nearly square in cross-section. At the middle point of the top chord, there is a reinforcement piece keyed and bolted to the under side to receive the diagonal members; at the adjacent top chord panel points and at the middle bottom chord panel points there are cast-iron angle blocks for the diagonals; elsewhere the diagonal members are notched or tenoned into the chords. The bottom chord is lap-jointed in the middle, where it is spliced with two 8 x 5/16-inch steel splice plates 46 inches long with twenty-four 1 1/8-inch bolts. All the nuts on the lower ends of the vertical rods take bearing on standard cast-iron washers. The rods pass through holes bored through the chords and their upper ends are received in holes countersunk in the under sides of the purlins. The upper nuts take bearing on 1/2-inch steel plates which project on both sides of the chords and form seats and splices for the purlins, to which they are spiked. At the ends of the trusses the steel bearing plates are bent to receive the sway-braced diagonal rods. The purlins support 2 x 6-inch rafters, 18 inches apart on centers, which are sheathed with 1-inch boards covered with metal tile and rubberoid. The trusses are cambered 3 inches in the center, and, where reinforcement pieces are keyed to the chord, they have 2-inch oak pins driven tight in holes bored half in each piece and provided with a 3/4-inch through bolt at each key. In the middle of the roof there is a horizontal skylight 40 feet wide covered with a translucent material.
Where the roof trusses have very narrow seats on one side of the 10 x 10-inch column their yellow pine lower chords are reinforced with an oak angle block deeply notched to receive the square end of the inclined end post. A corresponding oak shoe is put opposite to it on the under side of the lower chord and supports it for a length of about 4 feet, thus reducing the unit pressure on the pine and giving a solid bearing on the end of the column member. Both shoe and angle block are keyed to the lower chord, and are secured to it with the same straps and through bolts, which are arranged so as to avoid unnecessary cutting of the cross-section.
Mr. George F. Shepley was the architect of this building, and the construction was detailed and supervised by the staff of the Exposition.