coils and fans for the heating and ventilation system, for plumbing and temporarily for heating plant. The remainder of the space under the steps will be suitable for storage. It is the intention of the architect to preserve in this space all of the models which are required for molding the exterior of the building. The remainder of the basement space will be subdivided for such uses as may be required.
There are a number of interesting structural features in connection with this building. The designer, in attacking a structure of this kind, usually begins at the top and works downward. The crowning feature of the building is, of course, the dome. The masonry of this dome is to be perforated for the purpose of admitting light from the outside during the daytime and for the purpose of throwing out light at night. The masonry is, therefore, only a screen or tracery and not a roof. The area of the perforations is about thirty per cent of the area of the surface. While this masonry could be made self-supporting, it was not considered expedient to do so, so it is supported by a steel framework. This framework consists of a series of ribs, spaced about nine feet apart at the base and coming together at the top with a suitable bracing between the ribs.
This metal skeleton then forms the base for the masonry screen above it. The roof will be made of glass inside of and entirely free from the masonry dome. This will be a difficult piece of work to construct on account of its shape. It will have to be a wire glass set in metal frames. Some of the frames need to be hinged so that they can be opened for ventilation and for cleaning, more particularly for the latter purpose. Lower down comes the inner dome or ceiling. This has an independent steel framework made of arched ribs with the bracing between, similar to the framework of the outer dome. This will support the inner envelope of glass. This inner glass may be in the form of mosaics or ornament. The weight of the dome is supported at nine points. At each of these points is a group of four columns extending from the base of the dome down to the foundations.
Following the structure downward, these columns gradually accumulate the weight of the dome and the floors until in the lowest section they carry a very considerable burden amounting to about one and one-half million pounds at each of the nine points.
In order to have a big central space in the basement, 72 feet in diameter, the ceiling and floor above had to be supported without the use of interior columns. To provide this support it was decided to use a reinforced concrete dome. As the dome is perfectly regular in its outline and uniformly loaded, it was not particularly difficult to design nor was it extremely difficult to construct although the construction offered some difficulties. The shell of the dome is 12 inches thick. It is reinforced with two layers of steel rods, one near the top and one near the bottom. Each of these layers is made up of rods in radial position and others in circumferential position. For its final support, this dome rests on the concrete encasements of the steel columns.
In general the framework of the structure is of reinforced concrete except the supports of the dome, which are structural steel. The structural steel consists principally of the nine groups of four columns each which extend from the basement level to the springing line of the dome and the structural steel dome framing. There are some odd members of structural steel in the first story and, of course, there is structural steel bracing between the columns. The framing of the first story outside of the dome section is of reinforced concrete as is all of the first floor framing and all of the columns other than the main columns just described.
The foundation problem is a somewhat intricate one. There are heavy loads at the nine points which support the main dome. At the other points the loads are comparatively light, carrying as they do
