6-31. The minimum clearance between parallel bars in columns is not less than 1 1/2 times the bar diameter. First, tie the column steel together and position it as a unit. Then erect the column form around the unit and tie the reinforcing steel to the form at 5-foot intervals. Minimum clear space between reinforcing steel and concrete forms must also be checked with the MSA in the concrete mix design. The aggregate must not become lodged between the form and reinforcing steel, preventing passage by any further concrete.
FLOOR SLABS
6-32. Figure 6-10 shows a typical arrangement of reinforcing steel in a floor slab. The required thickness of the concrete protective cover determines the height of the bolster. Instead of the bolster, you can use spacer blocks made from sand-cement mortar as described above. Hold the bars firmly in place by tying the intersections together at frequent intervals with one turn of wire.
　
Figure 6-10. Reinforcing steel arrangement for a floor slab
BEAMS
6-33. Figure 6-11 shows the position of bolsters and stirrups with the reinforcing bars in a reinforced-concrete beam. Note that the stirrups pass under the main reinforcing bars and are tied to them with one turn of wire.
　
Figure 6-11. Beam reinforcing steel
WALLS AND FOOTINGS
6-34. Unless you are using wire-mesh fabric, erect the reinforcing steel for concrete walls in place. Do not preassemble it as you do for columns. Use ties between the bars, from top to bottom, for high walls (see view 1 of Figure 6-12). You can remove the wood blocks after you fill the forms to block level. Place reinforcing steel for footings as shown in view 3 of Figure 6-12. Use spacer bars to support the steel above the subgrade to the proper distance. Welded-wire fabric (see view 2 of Figure 6-12) is also used as limited reinforcement for concrete footings, walls, and slabs, but its primary use is to control crack widths due to temperature changes.
　
Figure 6-12. Wall and footing reinforcement
 
cr.http://www.free-ed.net/free-ed/Resources/Trades/Construction/ConcreteMasonry/default.asp?uNum=1&iNum=0603