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

10 Chapter Two
Downloaded From : www.EasyEngineering.net
of lumber, without ripping, for beam sides and bottoms, and
for other structural members.
It is obvious that a concrete structure is designed to serve specific
purposes, that is, to resist loads and deformations that will be applied
to the structure, and to provide an appearance that is aesthetically
pleasing. However, for such a structure, it frequently is possible to
modify the design slightly to achieve economy without impairing the
usability of the structure. The designer can integrate constructability
into the project by allowing three basic concepts: design repetition,
dimensional standards, and dimensional consistency. Examples of
these concepts, excerpted from ref. [1], are presented in this chapter
to illustrate how economy in formwork may be affected.
ww.EasyEngineering.n
Design Repetition
Any type of work is more efficient if it is performed on a repetitive
basis. Assembly line work in the automobile manufacturing industry
is a good example of achieving efficiency and economy by repetition.
This same concept can be applied to the structural design of concrete
structures. Repeating the same layout from bay to bay on each floor
provides repetition for the workers. Similarly, repeating the same layout
from floor to floor from the lower floor levels to the roof provides
repetition that can result in savings in form materials and in efficiency
of the labor needed to erect and remove forms.
Dimensional Standards
Materials used for formwork, especially lumber and related wood
products such as plywood, are available in standard sizes and
lengths. Significant cost savings can be achieved during design if
the designer selects the dimensions of concrete members that
match the standard nominal dimensions of the lumber that will be
used to form the concrete. Designs that depart from standard
lumber dimensions require costly carpentry time to saw, cut, and
piece the lumber together.
During the design, a careful selection of the dimensions of members
permits the use of standard sizes of lumber without ripping or
cutting, which can greatly reduce the cost of forms. For example,
specifying a beam 11.25 in. wide, instead of 12.0 in. wide, permits
the use of a 2- by 12-in. S4S board, laid flat, for the soffit. Similarly,
specifying a beam 14.5 in. wide, instead of 14 in. wide, permits the
use of two 2- by 8-in. boards, each of which is actually 7.25 in. wide.
Any necessary compensation in the strength of the beam resulting
from a change in the dimensions may be made by modifying the
quantity of the reinforcing steel, or possibly by modifying the depth
of the beam.
Downloaded From : www.EasyEngineering.net