The Chicago Coliseum is about 160 feet wide and 302 feet long, and has a steel roof with eleven three-hinge arch trusses of the outline and dimensions shown by Fig. 233. The trusses are from 22 feet 10 inches to 25 feet apart, and are connected together by eight main lines of lattice-girder longitudinal struts, by the lateral diagonals, by the lantern framework, and by the beams supporting the side wall and galleries. The trusses are set entirely within the side walls, which rise several feet above the hips and support a line of dormer windows reaching back to the slope of the main roof. The end pins have semi-circular bearings in cast-iron pedestals on masonry piers, below the first floor level, and there is a lantern about 30 feet wide and 15 feet high which extends from end to end of the building on the center line of the crown pins. A gallery which extends around the four walls is 20 feet wide on the sides and about 30 feet wide at the ends, with octagonal inner sides 20 feet long at the corners.

Fig. 233   Elevation of Truss; Chicago Coliseum.

Fig. 233 - Elevation of Truss; Chicago Coliseum.

At the walls the gallery is 25 feet high, level with the hips of the trusses, and for a width of ten feet the floor is horizontal and supported directly from the truss members. Beyond this width the floor slopes inward and downward to a fascia girder about 18 feet above the main floor and suspended from the main trusses. Across the ends of the building, about 20 feet of the width of the gallery is horizontal and supported by the gable walls and by transverse rows of columns. The arch trusses are made with the bottom chords approximately conforming- to the chords of an arc of 72 ft. radius. The top chord corresponds to a larger radius, and is vertical to a height of about 23 feet above the end pins. Both chords are made throughout with two 12-inch channels, latticed, those in the top chord having a weight of 20 1/2 pounds per foot everywhere, and those in the bottom chord varying from 20 1/2 pounds at the crown to a maximum of 40 pounds in the second section above the bottom. In the end panels of the semi-trusses the chords converge to intersection on the hinge pins, Fig. 234, but their outline is contin-ued by pairs of curved angles and cover plates which make semicircular rounded ends. The web members are pairs and double pairs of angles, which are 5 x 3 inches up to the second panel above the hips and 3x3 inches above that point. All of them are shop riveted to double gusset plates on the webs of the chord channels. In each semi-truss there are thirteen vertical members about 5 1/4 feet apart, which vary in length from about 20 1/2 feet to 4 feet on centers of chords. On the west side of the building horizontal brackets are riveted to the vertical sections of the top chord to support the wall beams, and on all trusses there are pin connections at the fourth panel point of the lower chord for the 1 3/4-inch vertical suspenders for the gallery beams.

*From the Engineering Record of June 29, 1901.

Fig. 234.   End Hinge of Truss.

Fig. 234. - End Hinge of Truss.

Fig. 235.   Center Hinge of Truss.

Fig. 235. - Center Hinge of Truss.

The longitudinal struts between the trusses are lattice girders 2 feet deep, having pairs of 3 x 3 x 3/8-inch chord angles and single 2 1/4 x 2 1/4 x 5/16-inch zigzag web angles. They are web connected to the upper ends of the vertical members in the trusses, and have 3 x 3-inch knee-brace angles to the lower chords at both ends. There are longitudinal struts at the top and bottom of the middle vertical posts in the lantern, and there are sway-brace diagonal rods in their vertical planes. The main trusses are braced together from end to end of the building by a system of lateral diagonals in the middle panel of the top chords, and there are lateral rods in every panel between the last two trusses at each end of the building.

The building was erected in the summer of 1899.

After all the trusses had been swung, and before all their braces had been completed, while the traveler was being taken down, the whole of the steel framework of the building fell to the ground, killing and injuring a number of workmen, as described in the Engineering Record of September 16, 1899. The building was reconstructed according to the original designs as soon as possible after the accident. Messrs. E. C. & R. M. Shankland, Chicago, were the engineers of the steel construction and the Pittsburg Bridge Company was the contractor for its manufacture and erection.