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

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Shores and Scaffolding 173
From Eq. (5-9), the section modulus S = bd 2 /6
= (15 in.)(1.5 in.) 2 /6
= 5.625 in. 3
From Eq. (5-8), the moment of inertia I = bh 3 /12
= (15 in.)(1.5 in.) 3 /12
= 4.218 in. 4
The allowable span length based on bending can be calculated as
follows.
For bending:
ww.EasyEngineering.n
For shear:
From Eq. (5-34), l b
= [120F b
S/w] 1/2
= [120(1,170)(5.625)/583] 1/2
= 36.8 in.
From Eq. (5-36), l v
= 192F s
bd/15w + 2d
For deflection:
= 192(175)(15)(1.5)/15(583) + 2(1.5)
= 89.4 in.
From Eq. (5-37a), l ∆
= [1,743EI/360w] 1/3 for ∆=l/360
= [1,743(1,600,000)(4.218)/360(583)] 1/3
= 38.2 in.
Bending governs and the maximum allowable span length for the
beam bottom is 36.8 in. Thus, a shore must be placed at a spacing that
does not exceed 37.4 in. For constructability, limit the spacing of the
shores to 36 in., locating the shores along the beam forms at 3 ft. 0 in.
(see Figure 6-5).
Consider the shores to support the slab between the concrete
beams. The weight of the 5-in.-thick concrete slab, including live loads,
will be:
Dead load, 5/12 ft × 150 lb per cu ft = 62.5 lb per sq ft
Assume dead load of form material = 8.0 lb per sq ft
Live load due to construction = 50.0 lb per sq ft
Total load = 120.5 lb per sq ft
For calculations, use 121 lb per sq ft
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