Slab Form Design

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Concrete forms are engineered structures that are required to sup­port loads composed of fresh concrete, construction materials, equipment, workers, impact of various kinds, and sometimes wind. The forms must support all the applied loads without collapse or excessive deflection. ACI Committee Report 347-1994 defines those applied loads and gives a number of guidelines for safety and serviceability. Based on these guidelines, a number of design tables have been developed for the design of concrete formwork. These tables are useful design tools. However, they do not take into consideration stress modification factors that are provided by the National Design Specification for Wood Construction, NDS 1991. This chapter presents a design procedure for all-wood con­crete slab forms based on NDS 1991 and Plywood Design Specifi­cation 1997.

The objective of the formwork design is to determine the safe spacing for each slab form component (sheathing, joists, stringers, and shores), and ensure that each component has adequate strength to resist the applied pressure without exceeding predeter­mined allowable deflection.