reinforcing bars are needed to resist the bendingtension in the bottom over the central portion ofthe span. Fewer bars are necessary on the bottomnear the ends of the span where the bendingmoment is small. For this reason, some bars maybe bent so that the inclined portion can be usedto resist diagonal tension. The reinforcing barsof continuous beams are continued across thesupports to resist tension in the top in thatarea.SLAB AND SLAB REINFORCEMENT.—Concrete slabs come in a variety of formsdepending on their locations. Ground slabs takethe load directly to the ground. Plain slabs (similarin shape to ground slabs) take the load directlyfrom the floor and transmit it to the beams. Inother cases, joists, poured as part of plain slabs,carry the loads to the beams. Joists are used tostrengthen the middle portion of the slab.Figure 7-5.—Reinforcing steel for a floor slab.Concrete slab reinforcements (fig. 7-5) aresupported by reinforcing steel in configurationscalled slab bolster and high chair. Concreteblocks made of sand-cement mortar can be usedin place of the slab bolster. The height of theslab bolster is determined by the concreteprotective cover required. If the concrete surfaceis to be in contact with the ground or exposedto the weather after removal of the forms, theprotective covering of concrete over the steelshould be 2 in. Other devices used to supporthorizontal reinforcing bars are shown in figures7-6, 7-7, and 7-8. Wood blocks should beFigure 7-7.—Precast concrete block used for reinforcing steelsupport.Figure 7-6.—Devices used to support horizontal reinforcingbars.Figure 7-8.—Beam-reinforcing steel hung in place.7-5
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