Formwork - Design of Reinforced Concrete - page 614

the face of the concrete. After the forms are removed, the small holes resulting can
easily be repaired with cement mortar.
Column clamps: These devices, which are placed around column forms, withstand
the outward pressure of the fresh concrete.
Studs: The vertical members that support sheathing for wall forms are called studs.
(See Figure 20.2.)
Wales: The long horizontal members that support the studs are called wales. (See
Figure 20.2.) Notice that each wale usually consists of two timbers with the ties
passing between so that holes do not have to be drilled.

20.8 FORCES APPLIED TO CONCRETE FORMS

Formwork must be designed to resist all vertical and lateral loads applied to it until the
concrete gains sufficient strength to do the job itself. The vertical loads applied to the
forms include the weights of the concrete, the reinforcing steel, and the forms themselves,
as well as the construction live loads. The lateral loads include the liquid pressure of
freshly placed concrete, wind forces, and the lateral forces caused by the movement of the
construction equipment. These forces are discussed in the paragraphs to follow.

Vertical Loads

The vertical dead loads that must be supported by the formwork in addition to its own
weight include the weight of the concrete and the reinforcing bars. The weight of ordinary
concrete, including the reinforcing, is taken as 150 lb/ft 3 . The weight of the formwork,
which is frequently neglected in the design calculations, may vary from 3 or 4 psf up to 12
to 15 psf.
The vertical live load to be supported includes the weight of the workers, the con-
struction equipment, and the storage of materials on freshly hardened slabs. A minimum
load of 50 psf of horizontal projection is recommended by ACI Committee 347. 1 This fig-
ure includes the weight of the workers, equipment, runways, and impact. When powered
concrete buggies are used, this value should be increased to a minimum of at least 75 psf.
Furthermore, to make allowance for the storage of materials on freshly hardened slabs (a
very likely circumstance), it is common in practice to design slab forms for vertical live
loads as high as 150 psf.

Lateral Loads

For walls and columns, the loads are different from those of slabs. The semiliquid con-
crete is placed in the form and exerts lateral pressures against the form, as does any liquid.
The amount of this pressure is dependent on the concrete weight per cubic foot, the rate of
placing, the temperature of the concrete, and the method of placing.

1 ACI, Committee 347, Guide to Formwork for Concrete (ACI 347 R-94) (Detroit: American Concrete
Institute), 33 pp.