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

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Forms for Beams and Floor Slabs 357
Bending in 4 ë 4 S4S Joists
Each joist will support a horizontal strip of decking 20-in.-wide,
which will produce a uniform load of 130 lb per sq ft × 20/12 ft = 217 lb
per lin ft along the entire length of the joist. The allowable span length
of the joists, that is, the distance between stringers, based on bending
can be determined as follows:
From Eq. (5-34), l b
= [120F b
S/w] 1/2
= [120(1,593)(7.15)/217] 1/2
= 79.3 in.
Shear in 4 ë 4 S4S Joists
The allowable span length based on shear in the joists can be
calculated.
From Eq. (5-36), l v
= 192F v
bd/15w + 2d
= 192(212)(3.5)(3.5)/15(217) + 2(3.5)
= 160.1 in.
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Deflection in 4 ë 4 S4S Joists
The permissible deflection is l/360, but not greater than ¹⁄16 in. Using
Eqs. (5-37a) and (5-37b), the allowable span lengths due to deflection
can be calculated as follows.
From Eq. (5-37a), l ∆
= [1,743EI/360w] 1/3 for ∆ = l/360
= [1,743(1,440,000)(12.51)/360(217)] 1/3
= 73.7 in.
From Eq. (5-37b), l ∆
= [1,743EI/16w] 1/4 for ∆ = ¹⁄16 in.
= [1,743(1,440,000)(12.51)/16(217)] 1/4
= 54.8 in.
Summary for 4 ë 4 S4S Joists
For bending, the maximum span length of joists = 79.3 in.
For shear, the maximum span length of joists = 160.1 in.
For deflection, the maximum span length of joists = 54.8 in.
For this design, deflection governs the maximum span length
of the joists. Because the stringers must support the joists, the
maximum spacing of the wales must be no greater than 54.8 in. For
constructability a spacing of 48.0 in. center to center will be used
for stringers.
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