Figure 7-19. - Precast concrete block used for rebar support.

WALLS-2 inches for bars larger than No. 5, where concrete surfaces, after removal of forms, would be exposed to the weather or be in contact with the ground; 1 1/2 inches for No. 5 bars and smaller; 3/4 inch from the faces of all walls not exposed directly to the ground or the weather.

COLUMNS - 1 1/2 inches over spirals and ties.

BEAMS AND GIRDERS - 1 1/2 inches to the nearest bars on the top, bottom, and sides.

JOISTS AND SLABS - 3/4 inch on the top, bottom, and sides of joists and on the top and the bottom of slabs where concrete surfaces are not exposed directly to the ground or the weather.

NOTE: All measurements are from the outside of the bar to the face of the concrete, NOT from the main steel, unless otherwise specified.

Footings and other principal structural members that are against the ground should have at least 3

Figure 7-20. - Rebar hung in place.

inches (76.2 mm) of concrete between the 127.85 steel and the 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 (50.8 mm). It maybe reduced to 1 1/2inches (38.1 mm) for beams and columns and 3/4 inch (19.5 mm) for slabs and interior wall surfaces, but it should be 2 inches (50.8 mm) for all exterior wall surfaces. This measurement is taken from the main rebar, not the stirrups or the ties.

NOTE: Where splices in reinforcing steel are not dimensioned on the drawings, the bars should be lapped not less than 30 times the bar diameter nor less than 12 inches (table 7-7). The stress in a tension bar

Table 7-7. - Length of Lap Splices in Reinforcing Steel

INCHES OF LAP CORRESPONDING TO NUMBER OF BAR DIAMETERS*

Size of Bars

Minimum lap equals 12 inches! *Figured to the next larger whole inch