If the bottom of the bay is of stone, and the projection is not more than 2 feet, the bay may be supported directly from the wall by corbeling out the stonework as shown in Fig. 213. The stone A should be the full size of the bay if possible, and should be bolted down by means of long rods built into the wall and secured to two channel bars (as in the figure) placed on top of the stone and with their ends built into the main wall.
If the bottom of the bay is of copper, and at a floor level, the simplest and strongest method of supporting the bay is that shown in Fig. 214.
Steel I-beams are extended across the wall of the story below and framed to a pair of channels, bent to the shape of the bay. The I-beams should be carried far enough inside of the walls to give them a sufficient anchorage to offset the leverage of the outer end, and should be secured to a girder or partition running parallel with the wall or to another steel beam at right angles with them, and forming part of the floor construction.
The channel bars forming the support for the walls of the bay should also be built into the wall on each side and anchored by iron rods built into the masonry below.
Fig. 215 shows a method of supporting a light bay by cast iron brackets bolted to the wall, which has been used where the bottom of the bay was above the floor line. The bottom of the bay in this construction may be either of copper or terra cotta, the latter, if used, being suspended from the bracket by hook anchors. If such construction is used a steel channel should be bolted to the top of the wall and extended well into the side walls, to prevent the brackets from pulling away the brickwork. Examples of bay supports in skeleton construction are also shown in Figs. 221 and 222.
In buildings built on the skeleton plan, now so generally used for high office buildings, all the weight of the walls, including the masonry surrounding the outer columns, is supported by the steel skeleton, at least above the third story. The outer walls of the lower stories, when of stonework, are sometimes supported directly from the foundations, as was the case in the New York Life Building, Chicago.*
When the walls are supported by the steel skeleton they are generally made very thin - about 12 inches, and sometimes only 9 inches thick - and in the more recent buildings the wall is supported at every story, so that the wall in any story could be removed without affecting the wall above or below.
The materials generally used for the outer walls are brick and terra cotta, these being preferred on account of the ease with which they maybe handled and the facility with which they maybe built about and between the beams and columns. Brick and terra cotta also appear to be about the only suitable materials for the walls of a fireproof building.
It has been found very difficult to attach stonework to the metal frame, and this, together with the low fire-resisting qualities of most building stones, has practically prohibited the use of this material except in the lower stories. In the Reliance Building, Chicago, thin slabs of highly polished granite enclosed in ornamental metal frames were used for casing the columns in the first story.
The general plan of the exterior walls in this class of buildings consists of vertical piers, from 3 to 4 feet wide, which inclose the exterior columns and extend from the bottom to the top of the build-ing. The space between these piers is generally nearly filled by the windows, either flat or in the form of bays, leaving only a small piece of wall, from 4 to 5 feet high, between the tops and bottoms of the windows to be supported by the frame. These portions of wall between the piers and the windows are called spandrels.
The mason work of the piers is generally supported by angle brackets attached to the columns, and the spandrels are supported by steel beams or girders of various shapes, called spandrel beams. The spandrel beams extend from column to column, and are riveted to them.
* Jenney & Mundie, architects.
The arrangement of the metal work for supporting the spandrel walls will depend largely upon the architectural effect sought by the designer and upon the materials used, so that the details vary somewhat in every building, and often in different portions of the same building. No general rule or form of construction can therefore be given for arranging such supports, but the architect must use such arrangements as seem best suited to the design of the building he has in hand. The following examples, however, will show how the walls have been supported in several buildings, and with slight variations one or another of these methods can be adapted to almost any building.
It is probably hardly necessary to say that the metal work in this class of buildings should be very carefully designed and studied to suit the conditions of the building, and to provide ample strength, as well as arranged so that it may be fully protected from heat. Consideration must also be given to the effects of expansion and contraction in the frame.