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

156 Chapter Five
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Bending in 4 ë 6 S4S Stringers
Based on bending, the span length of the stringers must not exceed
the value calculated.
From Eq. (5-34), l b
= [120F b
S/w] 1/2
= [120(1,243)(17.65)/572] 1/2
= 67.8 in.
Shear in 4 ë 6 S4S Stringers
Based on shear, the allowable span length of the stringers must not
exceed the value calculated.
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From Eq. (5-36), l v
= 192F v
bd/15w + 2d
= 192(218)(3.5)(5.5)/15(572) + 2(5.5)
= 104.9 in.
Deflection in 4 ë 6 S4S Stringers
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)(48.53)/360(572)] 1/3
= 83.9 in.
From Eq. (5-37b), l ∆
= [1,743EI/16w] 1/4 for ∆ = ¹⁄16 in.
= [1,743(1,440,000)(48.53)/16(572)] 1/4
= 60.4 in.
Summary for 4 ë 6 S4S Stringers
For bending, the maximum span length of stringers = 67.8 in.
For shear, the maximum span length of stringers = 104.9 in.
For deflection, the maximum span length of stringers = 60.4 in.
For this design, deflection governs the maximum span length of
the stringers. Because the shores must support the stringers, the maximum
spacing of shores must be no greater than 60.4 in. For simplicity
in layout and constructability, a spacing of 60.0 in. center to center will
be used.
Shores for Support of Stringers
Based on the strength of the stringers in bending, shear, and deflection,
the stringers must be supported every 60 in. by a shore. A shore
must resist the concrete pressure that acts over an area consisting of
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