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

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Pressure of Concrete on Formwork 37
this value after the design is completed and all member sizes and
weights are known. The combined weight of the concrete, reinforcing
steel, and form material is often referred to as the dead load on the
forms.
Superimposed on the dead loads are the live loads that may be
imposed on the forms. Live loads consist of the weights of workers,
tools, equipment, and any storage material. ACI Committee 347 recommends
a minimum live load of 50 lb per sq ft to provide for workers,
tools, and equipment. For conditions where motorized buggies
are used, the minimum live load is increased to 75 lb per sq ft, reference
Table 3-6. A minimum combined dead and live load of 100 lb
per sq ft is recommended, up to 125 lb per sq ft if motorized buggies
are used.
Thus, forms for concrete slabs must support workers and equipment
(live loads) in addition to the weight of freshly placed concrete
and form materials (dead load). For normal weight concrete, 150 lb
per cu ft, the weight of the freshly placed concrete will place a load
on the forms of (150 × 1/12) = 12.5 lb per sq ft for each inch of slab
thickness.
The weight of the concrete on forms may be considered as a
concentrated vertical load (lb), a vertical uniform load (lb per ft),
or vertical pressure (lb per sq ft), as illustrated in the Examples 3-7
to 3-9.
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Thickness of
Slab, in.
Nonmotorized Buggies
Design Load, lb per sq ft
4 100 125
5 113 138
6 125 150
7 138 163
8 150 175
9 163 188
10 175 200
12 200 225
Motorized Buggies
Notes:
1. All values are based on 150 lb per cu ft concrete.
2. Weight of form materials and reinforcing steel are not included.
3. Values for nonmotorized buggies include 50 lb per sq ft live load.
4. Values for motorized buggies include 75 lb per sq ft live load.
TABLE 3-6 Design Vertical Pressures for Slab Forms
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