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

Downloaded From : www.EasyEngineering.net
Economy of Formwork 11
Dimensional Consistency
For concrete structures, consistency and simplicity yield savings,
whereas complexity increases cost. Specific examples of opportunities
to simplify include maintaining constant depth of horizontal
construction, maintaining constant spacing of beams and joists,
maintaining constant column dimensions from floor to floor, and
maintaining constant story heights.
Repetitive depth of horizontal construction is a major cost consideration.
By standardizing joist size and varying the width, not depth,
of beams, most requirements can be met at lower cost because forms
can be reused for all floors, including roofs. Similarly, it is usually
more cost efficient to increase the concrete strength or the amount of
reinforcing material to accommodate differing loads than to vary the
ww.EasyEngineering.n
size of the structural member.
Roofs are a good example of this principle. Although roof loads
are typically lighter than floor loads, it is usually more cost effective
to use the same joist sizes for the roof as on the floors below. Changing
joist depths or beam and column sizes might achieve minor savings
in materials, but it is likely that these will be more than offset by
higher labor costs of providing a different set of forms for the roof
than required for the slab. Specifying a uniform depth will achieve
major savings in forming costs, therefore reducing the total building
costs. This will also allow for future expansion at minimal cost. Additional
levels can be built after completion if the roof has the same
structural capabilities as the floor below.
This approach does not require the designer to assume the
role of a formwork planner nor restricts the structural design to
formwork considerations. Its basic premise is merely that a practical
awareness of formwork costs may help the designer to take
advantage of less expensive structural alternatives that are equally
appropriate in terms of the aesthetics, structural integrity, quality,
and function of the building. In essence, the designer needs only
to visualize the forms and the field labor required to form various
structural members and to be aware of the direct proportion
between complexity and cost.
Of all structure costs, floor framing is usually the largest component.
Similarly, the majority of a structure’s formwork cost is usually
associated with horizontal elements. Consequently, the first priority
in designing for economy is selecting the structural system that
offers the lowest overall cost while meeting load requirements.
Economy of Formwork and Sizes of Concrete Columns
Architects and engineers sometimes follow a practice of reducing the
dimensions of columns every two floors for multistory buildings, as
the total loads will permit. Although this practice permits reduction
Downloaded From : www.EasyEngineering.net