Formwork - Design of Reinforced Concrete - page 609

20.4 FURNISHING OF FORMWORK

There are companies that specialize in formwork and from whom forms, shoring, and
needed accessories can be rented or purchased. The contractor may very well take bids
from these types of companies for forms for columns, floors, and walls. If structures are
designed with standard dimensions, the use of rented forms may provide the most eco-
nomical solution. Such a process makes the contractor's job a little easier. He or she can
regulate and smooth out the workload of his or her company by assigning the responsibil-
ity and risk involved in the formwork to a company that specializes in that particular area.
Renting formwork permits the contractor to reduce investment in the many stock items,
such as spacers, fasteners, and so forth, that would be necessary if the contractor did all of
the formwork.
If forms of the desired sizes are not available for rent or purchase, it is possible for
the contractor to make forms or to have them made by one of the companies that special-
ize in form manufacture. If this latter course is chosen, the result is usually very high-
quality formwork.
Finally, the forms can be constructed in place. Although the quality may not be as
high as for the last two methods mentioned, it may be the only option available for com-
plicated structures for which the forms cannot be reused. Of course, for many jobs a com-
bination of rented or built-in-place or shop-built forms may be used for best economy.

20.5 ECONOMY IN FORMWORK

The first opportunities for form economy occur during the design of the structure. Con-
crete designers can often save the owner a great deal of money if they take into account
factors that permit formwork economy in the design of the structure. Among the items
that can be done in this regard are the following:

1. Attempt to coordinate the design with the architectural design, such as varying
room sizes a little to accommodate standard forms.
2. Keep story heights as well as the sizes of beams, slabs, and columns the same for
as many floors as possible to permit the reuse of forms without change from floor
to floor. Without a doubt the most important item affecting the total cost of form-
work is the number of times the forms can be used.
3. Make beams as wide or wider than columns so as to make connections simpler.
When beams are narrower than columns, formwork is complicated and expensive.
4. Remember in the design of columns for multistory buildings that their sizes may
be kept constant for a good many floors by changing the percentage of steel used
from floor to floor, starting at the top with approximately 1% steel and increasing
it floor by floor until the maximum percentage is reached. In addition, the
strength of the concrete can be increased as we move down in the building.
5. Keep columns the same size; the more this is done, the smaller costs will be.
Should it be necessary to change the size of a particular column as we move ver-
tically in a building, it is desirable to do it in 2 in. increments—2 in. on one side
of a column on one floor and then 2 in. on the other side on another floor.