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

432 Chapter Sixteen
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FIGURE 16-1 Forms for a concrete bridge slab. (Source: Dayton Superior Corporation)
Design of Decking to Resist Concrete Pressure and Live Loads
The total vertical pressure on the decking will be the dead load of the
concrete plus the 75 lb per sq ft live load as follows:
Concrete dead load (150 lb per cu ft)(8/12 ft) = 100 lb per sq ft
Live load on forms = 75 lb per sq ft
Design pressure on decking, w = 175 lb per sq ft
The physical properties and allowable stresses for ¾-in.-thick
Class I Plyform decking are shown in Tables 4-11 and 4-12. From
Table 5-4, determine the spacing of the joists based on bending, shear,
and deflection of the decking as follows:
For bending, from Eq. (5-41),
l b
= [120F b
S e
/w b
] 1/2
= [120(1,930)(0.455)/175] 1/2
= 24.5 in.
For rolling shear, from Eq. (5-48),
l s
= 20F s
(Ib/Q)/w s
= 20(72)(7.187)/175
= 59.1 in.
Deflection criteria less than l/360, from Eq. (5-57a),
l d
= [1,743EI/360w d
] 1/3
= [1,743(1,650,000)(0.199)/360(175)] 1/3
= 20.9 in.
Following is a summary for the decking:
For bending, the maximum span = 24.5 in.
For rolling shear, the maximum span = 59.1 in.
For deflection, the maximum span = 20.9 in.
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