Fig. 211.—Column and Floor Slab Construction for Factory Building.
The circular interior columns, varying from 30 ins. to 12 ins., in diameter were molded in permanent shells of cinder concrete. The shells were made in sections about 30 ins. long, with walls 1½ ins. thick, which were set one on another with mortar joints to form the column mold. In fabricating the shells the first step was to wind a helix of steel wire on a collapsible mandrel about 4 ft. long; the mandrel was set with the axis horizontal and was revolved by hand, the wire being fed on also by hand and under a slight tension. After the wire helix was completed it was wrapped with a sheet of expanded metal, the longitudinal edges of which lapped a few inches and were tied by wire ties. The expanded metal covering was also wire tied to the helix. Each of these cylinders of expanded metal and wire was 30 ins. long and formed the inner mold for making the shell. The outer mold consisted of a sheet metal cylinder in two parts assembled and supported by wooden yokes and framework. The two molds were assembled on a plank platform, one inside the other, and about a common center. The annular space was then filled with a 1-5 cinder concrete mixed moderately dry so that while it would exude slightly through the expanded metal mesh it would not waste to any extent. After from 18 to 24 hours the outer mold was removed for reuse and the shell was left standing on the molding platform until safe to handle. The larger shells, 30×30×1½ ins., weighed about 150 lbs. each.
Fig. 212.—Device for Bending Reinforcing Rods.
Some 2,000,000 lbs. of plain round steel rods from ¼ in. to 1½ ins. in diameter were required for reinforcing the concrete. For the main girders these rods were cut, bent and assembled into frames or trusses which were placed as units. The main rods were ordered cut to length, but the stirrup rods were ordered in lengths of 20 ft. and cut to lengths as required. The rods were brought to the work in carload lots and were stored according to lengths and sizes in racks under sheds. Another shed was provided for the steelworkers, who cut and bent the rods and assembled the girder frames ready for the workmen on the building. There were about 50 different patterns of frames required. They were made entirely by hand. For bending large size rods, heavy compound levers were used; the lighter rods were bent by the device shown in Fig. 212. The assembling of the trusses was accomplished as shown by Fig. 213, using the steel framework of the erection shed as a staging. Across the horizontals of the framework were placed two false temporary top chord bars marked to the stirrup spacing of the truss being assembled. On these bars, at the spaces marked, were suspended stirrups with their lower ends hooked. The lower chord bars were then suspended in the stirrup hooks and the whole assemblage of bars and stirrups was then clamped rigid by the lever bars and intermediate clamps. The loop ends of the stirrups were then bent by special wrenches to the position shown at 2, then closed by hammering to the position shown at 3, and finally they were wire tied. The process was a simple one, and by adopting a regular routine the men became so expert that two of them could complete many trusses in a working day. The contract price for shaping the steel and assembling it into frames was 1 ct. per lb.; the cost of the work to the contractor has been stated by Mr. E. P. Goodrich, Engineer, Bush Terminal Co., to have been about ¾ ct. per lb. The cost of placing the steel in the building was ¼ ct. per lb.
Fig. 213.—Sketches Showing Methods of Fabricating Girder Reinforcing Frames.
PLACING.—With unit frame reinforcement the number, size and location of the bars have been made certain in the shops where the frames are fabricated so that the erector has nothing to do but to line and level up the frames in the forms, place such temporary braces as are needed to hold them true, and make the end connections with abutting frames. Such frames are usually provided with "chairs" to hold the bottom bars up from the form so that little bracing or none is required. With separate bar reinforcement the erector may either place the reinforcement complete in the form by wire-tying the bars to each other, to temporary braces or templates and to the forms, or he may insert the various pieces of reinforcement in the concrete as the pouring advances, depending on the surrounding concrete to retain them where inserted. Generally a combination of both methods is employed.