Where, however, the column is not reinforced with a steel core, but is merely a pier, footings may be designed as illustrated in Fig. 19 (_b_). Here the base of the column is enlarged in order to better distribute the load on the several steps of the footing, and where the bottom step has a considerable overhang, it is reinforced with steel rods and stirrups, as indicated. =42. Detail of Slab and Girder Reinforcement.=—In the previous article, the general construction of the floors and column supports of a factory building was explained. By referring to Fig. 20, it will be shown how the girders and beams are reinforced with the steel bars. In this figure, a plan is indicated at (_a_) and an elevation at (_b_). The rod reinforcement of the slab is shown in the plan at _a_, _a_. It will be noticed that over every other beam these rod reinforcements lap, or break joints, and that some additional tie or reinforcement is placed over the girders, as indicated by _b_, _b_. These latter rods tend to tie in the floor slabs still more rigidly than can be accomplished with their individual reinforcement. Referring to the elevation (_b_), it will be noticed that all the reinforcement of the beams is not usually carried along the lower portion of the girder for its entire distance, but that some of the reinforcement is bent up at a point about one-quarter of the span from the abutment, in the form of a camber rod. By arranging the reinforcing rods in this manner, an additional stirrup action, or tie, to the girder supports is provided, and the oblique section made by a horizontal line passing through these rods tends to provide additional resistance to the horizontal shear in the beams and also provide for negative bending moment produced in the beams near the support. To further provide for this, shear stirrups are placed closer together, toward the abutments, as indicated at _c_, _c_. These stirrups are ordinarily light pieces of bar iron bent in a =U=-shape, and sometimes bent around the rod reinforcement, a detail of this stirrup being shown in Fig. 20 (_c_). [Illustration: FIG. 20] STEEL-FRAME MILL BUILDINGS =43.= There is a type of building which, while not distinctly mill construction as usually understood, is frequently used for one-story buildings, such as rolling mills, cement works, machine shops, foundries, rail yards, and buildings of this class. The essential feature of these buildings is a steel-roof truss supported on steel columns, the columns being braced both to the truss and longitudinally of the building. It is usually the purpose in the design of such buildings to neglect everything but the necessary stability and the first cost. The steelwork, consequently, is of the lightest possible construction, usually designed for a unit fiber stress of from 18,000 to 20,000 pounds, and the covering of the sides of the building, together with window details, etc., is made only sufficiently good to keep out the weather.