Fig. 208* shows a semi-section of the dome over the Buffalo (N. Y.) Savings Bank Building, Messrs. Green and Wicks, architects. 'The framework of this dome is composed of 32 latticed radial segmental ribs, one of which is shown in elevation in Fig. 208 which also gives a section of the circular wall enclosing the foot of the dome, and shows the details of the granite blocks in its cornice, and their support on brackets attached to the ribs.
The foot of each rib is provided with horizontal angle flanges which are seated on and riveted to the tops of the main girders, and are made to offset from them and support the rib be-yond the centre where necessary. The ribs are vertical up to the springing line, about 4 ft. above the base, and are there encircled by a circular 12-inch channel having its vertical web riveted to their outside flanges. The tops of the ribs are connected by short vertical web angles to a drum, 14 ft. in diameter, made of a 15-inch channel and stiffened by two diametrical 12-inch beams at right angles to each other.
*This illustration and accompanying description is taken by permission from the "Engineering Record" of Nov. 25, 1899.
The roof was laid with 3x12x24-inch hollow book tile weighing 16 pounds per foot. This is covered with a bitumen damp course, lapped 3 ins. on which are bedded in slaters' cement semi-glazed terra-cotta tile, grooved. lipped and fastened with copper wire."
88. Figs. 209 and 210* show a partial section and plan of the steel frame of the dome over the New York Clearing House, Mr. R. W. Gibson, architect.
Fig. 209. - Section Through Dome, New York Clearing House.
The dome has a nearly hemispherical exterior surface and is supported by an octagonal arrangement of web-connected plate girders. It rests on each of these girders and intermediately on 20-inch rolled beams across their angles, which form with them a sixteen-sided polygon.
*These cuts and the accompanying description are taken by permission from the "Engineering Record" of Sept. 20, 1900. Several other details of the steel work in this building are given in the same issue.
There are sixteen radial dome trusses seated on top of this polygonal framing and having their top and bottom chords riveted at the centre (top) to a pair of horizontal circular steel plates 6 ft. 4 ins. in diameter. Each truss is made in two sections, field riveted together through the flanges of web members which are perpendicular to the dome surface. Trussed purlins 6 ft. deep are connected to the trusses in the planes of these members and support at their centre points, intermediate curved rafters extending to the foot of the dome. The trusses are also connected by horizontal circular T and angle bars riveted to their top and bottom, to support the roof and ceiling respectively. The horizontal reactions at the lower ends of the radial trusses are provided for by a 14x15/16-inch circular vertical steel plate, like a hoop around their feet. The dome is surmounted by a cupola or circular platform 11 1/2 feet in diameter and 20 ins. high. In the centre of this platform is a lantern 4 ft. in diameter and 6 ft. high with a hemispherical top. All the members of the cupola and lantern are made of pairs of 2 1/2 x2 1/2 angles riveted together back to back, and connected by 1/4-inch gusset plates and 5/8-inch rivets.
89.- Figs. 211 and 212 show a semi-section and plans of the steel dome above the administration building of the New Jersey State Reformatory at Rahway, built in 1897. This dome is 120 feet in diameter or 8 feet greater than the dome of St. Paul's, London, and only 4 3/4 feet less than the dome of the capitol at Washington. It is 130 feet high from the ground level to the top, and contains about 400 tons of open-hearth steel. The roof and ceiling are supported by 24 semi-arches, A, and 24 shorter ribs, B, interpolated between the main arches to carry the purlins of the lower part of the roof. Part of the arches rest directly on the top of the wall and part upon steel girders set across the corners of the hexagon. From the arches of the dome, a ceiling is suspended as shown in Fig. 209; this suspension work is in the nature of furring and does not form a part of the dome ribs.
The dimensions of the members of the main ribs of the dome are given in Fig. 211. The intermediate ribs B are of the same shape, but are built of lighter angles, the top and bottom chords being formed of pairs of 3 1/2" x 3"-7.9 angles with 2 1/4"x2 1/4"x1/2" web diagonals. The main ribs abutt at the top against a circular plate girder, and are riveted to it by means of connection angles.
In erecting the dome, a central tower was first built, on the top of which the circular girder was set in its exact position, and carefully levelled. On top of the tower and circular girder a revolving derrick was set, by means of which, and one six-spool hoisting engine, the ribs were raised into position. Each truss was received from the shop in three sections. The first, or lower section and the middle section were bolted together on the floor, then raised and held in place by tackle, while the third or top section was being raised and connected to the lower portion. After this connection was made the whole rib was dropped into place and became self-sustaining, being guyed to prevent turning over. These operations were simultaneously executed on diametrically opposite trusses and then the traveller was swung into the plane of another pair of trusses which were similarly erected.
Fig. 211. - Semi-Section Dome at Rahway, N. J.
Details of the erection plant and a complete description of the same may be found in the Engineering Record of May 14, 1898.
Fig. 213. - Plan of One Pavilion, South Park Conservatory.
Fig. 214. - Truss F of Fig. 213.