In reinforced concrete joist floors, how are the forms typically formed?

• A. Inverted Metal or Fiber Glass Forms
• B. Horizontal Wooden Panels
• C. Plastic Sheets
• D. No Forms Used

Answer: (A)

Reinforced concrete joist floors are typically built as ribbed or hollow-core systems, so the formwork is designed to create those hollow spaces between the joists. Using inverted metal or fiber glass forms provides the voids efficiently: the forms are placed between supports with the hollow side facing downward, shaping the underside of the joists as the concrete is poured. This approach gives a precise, consistent void geometry, reduces the amount of concrete needed, and speeds construction because the forms are strong enough to be reused and can remain as permanent void formers or be removed after curing, depending on the system.

Wooden panels would create a solid slab rather than hollow joists and require more lumber and labor. Plastic sheets lack the rigidity and durability to hold their shape under fresh concrete. Having no forms would leave no hollow spaces and result in a heavier, less economical floor.