Design Considerations for Economical Formwork - Simplified Design of Reinforced Concrete Buildings - page 256

Chapter 9

Design Considerations for
Economical Formwork

9.1 INTRODUCTION

Depending on a number of factors, the cost of formwork can be as high as 60% of the total cost of a cast-in-
place concrete structure. For this reason, it is extremely important to devise a structural system that
will minimize the cost of formwork. Basic guidelines for achieving economical formwork are given in
Reference 9.1, and are summarized in this chapter.

Formwork economy should initially be considered at the conceptual stage or the preliminary design phase of
a construction project. This is the time when architectural, structural, mechanical, and electrical systems are
conceived. The architect and the engineer can help reduce the cost of formwork by following certain basic
principles while laying out the plans and selecting the structural framing for the building. Additional savings
can usually be achieved by consulting a contractor during the initial design phases of a project.

Design professionals, after having considered several alternative structural framing systems and having
determined those systems that best satisfy loading requirements as well as other design criteria, often make
their final selections on the concrete framing system that would have the least amount of concrete and possibly
the least amount of reinforcing steel. This approach can sometimes result in a costly design. Complex
structural frames and nonstandard member cross sections can complicate construction to the extent that any
cost savings to be realized from the economical use of in-place (permanent) materials can be significantly
offset by the higher costs of formwork. Consequently, when conducting cost evaluations of concrete structural
frames, it is essential that the costs of formwork be included.

9.2 BASIC PRINCIPLES TO ACHIEVE ECONOMICAL FORMWORK

There is always the opportunity to cut costs in any structural system. The high cost of formwork relative to the
costs of the other components makes it an obvious target for close examination. Three basic design principles
that govern formwork economy for all site-cast concrete structures are given below.

9.2.1 Standard Forms

Since most projects do not have the budget to accommodate custom forms, basing the design on readily
available standard form sizes is essential to achieve economical formwork. Also, designing for actual
dimensions of standard nominal lumber will significantly cut costs. A simplified approach to formwork
carpentry means less sawing, less piecing together, less waste, and less time; this results in reduced labor and
material costs and fewer opportunities for error by construction workers.