Figure 7-22.-Devices used to support horizontal reinforcing.
The proper location for reinforcing bars is given on the drawings. To ensure that the structure can withstand the loads it must carry, place the steel in exactly the position shown. Secure the bars in position so that they will not move when the concrete is placed. This can be accomplished by using the reinforcing bar supports shown in figures 7-22, 7-23, and 7-24.
Footings and other principal structural members that are against the ground should have at least 3
Figure 7-23.-Precast concrete block used for reinforcing steel support.
Figure 7-24.-Beam-reinforcing steel hung in place.
inches of concrete between steel and ground. If the concrete surface is to be in contact with the ground or exposed to the weather after removal of the forms, the protective covering of concrete over the steel should be 2 inches for bars larger than No. 5 and 1 1/2 inches for No. 5 or smaller. The protective covering maybe reduced to 1 1/2 inches for beams and columns and 3/4 inch for slabs and interior wall surfaces, but it should be 2 inches for all exterior wall surfaces.
The clear distance between parallel bars in beams, footings, walls, and floor slabs should be a minimum of 1 inch, or one and one-third times the largest size aggregate particle in the concrete. In columns, the clear distance between parallel bars should be a minimum of one and one-half times the bar diameter, one and one-half times the maximum size of the coarse aggregate, or not less than 1 1/2 inches.
The support for reinforcing steel in floor slabs is shown in figure 7-25. The height of the slab bolster is determined by the concrete protective cover required. Concrete blocks made of sand-cement mortar can be used in place of the slab bolster. Wood blocks should never be used for this purpose if there is any possibility the concrete might become wet and if the construction is of a permanent type. Bar chairs, like those shown in figure 7-25, are available from commercial sources in heights up to 6 inches. If a height greater than 6 inches is required, make theContinue Reading