=39. Reinforced-Concrete Beams and Girders.=—The depth of the beams and girders in reinforced-concrete construction varies, of course, with the span and loads to be supported. Their width enters little into the strength, and they may be made as narrow as possible in order to cover the reinforcing steel. It is the best practice to make beams and girders of the same width, for then the process of forming the molds is greatly simplified and the cost reduced. In placing the reinforcement in the concrete, it should always be at least 2 inches from the outside surface, for a distance less than this is considered inadequate fireproofing. In order that the reinforcing metal _e_, Fig. 16, may enter over the top of the reinforcing metal at _f_, it is usual to make the secondary girders, or beams, 3 inches less in depth than the main girders. To stiffen the building, brackets are customarily introduced between the column and girders, as illustrated at _g_. These brackets tend to greatly increase the rigidity of the connection and shorten the span of the girder somewhat. [Illustration: FIG. 18] =40. Construction at Window Heads.=—Where it is necessary to have the window head near the top of the ceiling, reinforced-concrete construction lends itself readily to the requirements of this condition, for even where girders are supported over the window head, the construction may be followed out, as indicated at _h_, Fig. 16. Where it is desired to have the window head raised still higher, a construction similar to that shown in Fig. 18 may be used. In this case, however, care must be taken to have the girders bear on the piers between the windows, and to have no intermediate beams. [Illustration: (_a_)] [Illustration: (_b_) FIG. 19] =41. Column Footings.=—With factory buildings of more than five or six stories in height, great pressure is transmitted to the soil from the base of the bottom column, and as it is necessary with soils of even fairly good bearing capacity to have footings beneath the piers supporting columns of from 6 to 10 feet square, adequate means of providing these footings must be obtained. In Fig. 19 (_a_) and (_b_) are shown two types of footings for concrete columns. In (_a_) is indicated a reinforced-concrete column with a steel core. In such an instance, all the load is transmitted by the steel core through its angle plates and webbing at the foot to grillage beams. These grillage beams are, however, not made sufficiently large to transmit the load to the soil, but merely to distribute the load on the bed of concrete. The spread portion of the footing is reinforced with steel rods _a_, _a_ crossed each way, and longitudinal shear is taken up in the footing by means of stirrups _b b_. This is the usual type of footing construction under reinforced-concrete factory columns.