PLACING THE REINFORCEMENT. There is always more or less difficulty and uncertainty in properly placing the reinforcement for beams and slabs when it consists of separate rods. Sometimes the steel is supported by chairs resting on the bottom of the forms and sometimes it is suspended by wires attached to rods resting upon the top of the forms. The chairs are sometimes blocks of cement mortar with a groove in the top, or sometimes a thin square steel plate about 4 inches on a side with a hole in its center, the two halves of which are bent to an angle of 60 to 90 degrees with each other to form feet for the chair, the hole forming a seat for the reinforcing rod.
Sometimes the steel is kept at the right distance above the bottom of the beam by first depositing say 2 inches of concrete in the forms and then laying the steel upon the concrete; but this procedure is objectionable since (1) the placing of the steel is likely to interfere with the placing of the concrete, (2) there is liability that the concrete in the bottom of the forms will set before the succeeding layer is added, and (3) a comparatively dry concrete is required which is more expensive to lay and does not give as good adhesion to the steel as a wet mixture.
It is sometimes necessary to splice the reinforcing rods. There are in common use four methods of doing this. 1. Simply lap the rods, and trust that the grip of the concrete will bind them firmly together. This is not very satisfactory. 2. The rods are lapped and wrapped with soft steel wire. With plain rods this is only a slight improvement upon lapping. 3. A better method is to lap the rods and fasten them together with a screw clamp. With deformed bars and a good clamp this is quite satisfactory. 4. For plain bars the best method is to thread the ends of the rods and use a screw coupling.
In anchoring rods by bending the end, short bends should be avoided, as otherwise there is a concentration of pressure on the concrete at the angle of the bend which will crush the concrete and prevent the effect sought.