Total forming costs may easily be 48 percent of the cost of a concrete wall. This makes it very worthwhile to evaluate a number of form systems to determine which will be most efficient and economical. This article will provide some help in choosing wall forms, but it covers only gang form systems. However, the methods of analysis may be adapted to other forming conditions.
WHEN TO USE GANG FORMS
A gang form, or ganged form as it is sometimes called, is an assembly of prefabricated panels joined to make a much larger unit for convenience in erecting, stripping and reusing. The contractor working on a wall job must first decide whether or not the job requires gang forming. Such factors as the number of reuses, crane availability, concrete finish, architectural features, wall heights and multiple lifts must be studied. Once the decision has been made to use gang forms, the problem becomes one of identifying which of the available systems will enable you to meet the standards set out in the project specifications.
There are four important factors to consider if you are to make a good choice: lateral pressure the forms can take; weight of the forms; cost of form materials; number of ties. These factors are interrelated.
HOW TO USE THE FOUR FACTORS
We have identified four major cost factors to consider in comparative ratings of gang form systems as: tie labor cost; cost of the form material; form assembly labor; concrete placing labor. To create a scoring table for the systems being compared, enter the basic data for each system. Then assign a comparative ranking for each factor. The rankings are then multiplied by an importance factor. Following this procedure will provide an overall rating for each forming system. Using a numerical method to compare gang form systems can eliminate a lot of guesswork.