Building Design and Construction Handbook - Merritt - Ventech!

9.80 SECTION NINE
TABLE 9.19 Temperature and Shrinkage Reinforcement for One-Way Joist Construction
Top-slab
thickness,
in
Required area
of temperature
and shrinkage
reinforcement,
in 2 Reinforcement
Reinforcement
weight, psf
2 0.043 WWF 4 � 12, W1.5/W1 0.19
2 1 ⁄2 0.054 WWF 4 � 12, W2/W1 0.24
3 0.065 WWF 4 � 12, W2.5/W1 0.29
3 1 ⁄2 0.076 No. 3 bars @ 17 1 ⁄2 in 0.26
4 0.086 No. 3 bars @ 15 in 0.30
4 1 ⁄2 0.097 No. 3 bars @ 13 1 ⁄2 in 0.33
5 0.108 No. 3 bars @ 12 in 0.38
5 1 ⁄2 0.119 No. 3 bars @ 11 in 0.41
Fire Resistance. Table 9.17 gives minimum top-slab thickness for fire resistance
when a fire-resistant ceiling is not used.
Temperature and Shrinkage Reinforcement. This reinforcement must be provided
perpendicular to the ribs and spaced not farther apart than 5 times the slab
thickness, or 18 in. The required area of Grade 60 reinforcement for temperature
and shrinkage is 0.0018 times the concrete area (Table 9.19). For flexural reinforcement,
see Art. 9.56. For shear reinforcement, see Art. 9.57.
Embedded Pipes. Top slabs containing horizontal conduit or pipes that are allowed
by the ACI 318 Building Code (Art. 9.53) must have a thickness of at least
1 in plus the depth of the conduit or pipe.
Bridging. Distribution ribs are constructed normal to the main ribs to distribute
concentrated loads to more than one joist and to equalize deflections. These ribs
are usually made 4 to 5 in wide and reinforced top and bottom with one No. 4 or
one No. 5 continuous rebar. One distribution rib is usually used at the center of
spans of up to 30 ft, and two distribution ribs are usually placed at the third points
of spans longer than 30 ft.
Openings. These can be provided in the top slab of one-way concrete joist construction
between ribs without significant loss in flexural strength. Header joists
must be provided along openings that interrupt one or more joists.
9.56 REINFORCEMENT OF JOISTS
FOR FLEXURE
Reinforcement required for strength can be determined as indicated in Art. 9.46,
by treating as a beam a section symmetrical about a rib and as wide as the spacing
of ribs on centers.