Formwork for Concrete Structures by R.L.Peurifoy and G.D- By EasyEngineering.net

338 Chapter Eleven
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A stringer must be wide enough to transmit the loads in bearing
from the joists without exceeding the allowable unit stress. Also, it
must be large enough in transverse section to resist the bending
moment and horizontal shearing stress without exceeding the safe
limits. The deflection will usually be small and often will not govern
the design.
Ledgers
As illustrated in Figures 11-2 and 11-3, the ends of joists may be supported
by ledgers, which are nailed to cleats, usually 2 × 4 members,
nailed to the side forms for beams. The ledgers must be able to support
the joists.
If the ledger supports this entire load between the joist and the
ledger, it must have an adequate bearing capacity. It is common
practice to nail the ends of the joists to the cleats attached to the
forms for the sides of the beams. If this method is used to construct
the forms, the spacing of the cleats on the beam form should be the
same as for the joists.
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Forms for Flat-Slab Concrete Floors
Figure 11-4 illustrates a method of using prefabricated panels for the
decking for flat-slab concrete floors, where the concrete columns are
spaced at 12 ft in one direction and at 16 ft in the other direction.
The same method may be used, with modified form panels, for other
spacings of columns.
4'0"
16'0"
12'0"
4'0"
Drop panel
4'0" × 12'0" panel
Column
4'0"
4'0" × 12'0" panel
4'0" × 12'0" panel
8'0"
12'0"
End joint
Side joint
4'0"
FIGURE 11-4 Form panels for flat-slab concrete fl oor.
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