The simplest case of spandrel supports is where the wall is perfectly plain and built of brick, with terra cotta caps and sills. In such cases a channel and angle bar may be used to support the outer face of the wall and an I-beam the backing, as shown in Fig. 216, which shows sections of the outer walls of the Champlain Building, Chicago.*
The channel and I-beam should be bolted together with cast separators made to fit.
For a plain wall, channels and angles seem to be the best shape for the outer portion of the spandrel support, as they are of an economical section, and, the flat face of the channel being outward, a 4-inch veneer of brick can be set in front of it without clipping the brick.
The face of the channel is generally set 5 or 6 inches from the face of the wall, and 3x3 angles are used for supporting the outer 4 inches of wall. The outer edge of the angle should come within 2¼ inches of the face of the wall.
Spandrel supports very similar to those shown in Fig. 216 have been used in several Chicago buildings.
Z-bars have also been used in several buildings in place of the channel and angle, but are not generally considered quite as satisfactory, as they do not give the same strength for the weight of metal used.
Fig. 217 shows a Z-bar support used for the attic wall of the Wyandotte Building, Columbus, Ohio.†
Fig. 218, from the New York Life Building, Chicago, shows the spandrel supported by a single I-beam, the 4-inch facing of the wall being supported by the terra cotta lintel which is hung from the beam.
* Holabird & Roche, architects. † D. H. Burnham & Co , architects.
In the Reliance Building* plate girders were used for the main spandrel supports, and two angles riveted together to make a T were bracketed from the outer face of the girder to support the wall, the girder being on the centre line of the columns.
Fig. 219 shows the method used for supporting the granite walls at the fourth floor level of the Masonic Temple, Chicago. It should be noticed that an open joint is left opposite the supporting angle to allow for expansion and contraction in the column.
When the wall is faced with ornamental terra cotta the latter can seldom be supported directly by the spandrel beams, and a system of anchors must be resorted to, to properly tie the individual blocks either to the brick backing or to the metal work. These anchors are usually made of ¼-inch square or round iron rods, which are hooked into the ribs provided in the terra cotta blocks, and then drawn tight to the brickwork or metal work by means of nuts and screw ends, as shown in Fig. 221. Hook bolts are largely used for tying terra cotta blocks to the metal work, the ends being bent around the bottom of the beams, channels or angles. Several examples of the use of hook bolts are shown in Figs. 218, 220, 221 and 222.
A great variety of methods for properly securing the terra cotta are possible. They should be carefully studied and the general scheme should always be indicated on the spandrel sections, in the manner shown in the illustrations, as the holes in the structural metal work necessary to receive the anchors should be shown on the detail drawings of the iron and steel work, so that the punching may be done at the shop. The inexperienced architect should also consult with the manufacturers of the terra cotta work as to the best manner of securing the blocks.
* D. H. Burnham & Co., architects.
The anchorage of the brick and terra cotta to the steel frame is a matter of vital importance, as very serious consequences are quite sure to follow any neglect in this matter. "An instance is known where a whole section of wall facing on the court side of a high building fell off because the workmen omitted the anchors." As all the anchors for every block cannot be exactly shown on the drawings, either the architect or some one in his employ should give this portion of the work the strictest superintendence.
328. Bay Windows.
These have become a very prominent feature in the modern office building and hotel. In skeleton buildings the mason work of the bays is made as light as possible, with slight terra cotta mullions and angles, and is supported in each story by brackets built out from the spandrel beams or girders, as shown in Figs. 221 and 222, which are sections from the Wyandotte Building.
As the leverage on these brackets is considerable, they should be securely riveted to the spandrel beam, and the latter well tied or framed to the floor construction to keep it from twisting.
Where mullions occur between windows, and at the angles of the bays, cast iron or steel angle or T-bars are bolted or riveted to the metal work above and below, to stay the frames and terra cotta mullions and angles, in the manner shown in Fig. 223.
The importance of thoroughly fireproofing the exterior columns has already been considered in Chapter IX (Fireproofing). Fig. 223, however, is given as an example of the pier construction in Chicago buildings.
Further illustrations of the manner of supporting the mason work in this class of buildings may be found in Architectural Engineering, by Joseph K. Freitag, C. E., and several numbers of the Engineering Record and the Brickbuilder.