Commercial Building Inspector B2Floor ConstructionMedium
A commercial building inspector is reviewing plans for a masonry floor system utilizing precast hollow-core concrete planks. The plans indicate that the planks will be covered with a structural topping. What is the minimum thickness required for this structural concrete topping over the planks, according to the IBC?
- A2 inches (51 mm)
- B1.5 inches (38 mm)
- C1 inch (25 mm)
- D2.5 inches (64 mm)
Show answer & explanationAnswer & explanation
Correct answer: A. 2 inches (51 mm)
For precast hollow-core concrete planks, when a structural concrete topping is used, the IBC (referencing ACI 318) typically requires a minimum thickness of 2 inches (51 mm) for the topping to ensure proper composite action and load distribution.
Why the other options are wrong
- B. 1.5 inches may be acceptable for some non-structural or lightweight toppings, but not for a structural topping over hollow-core planks.
- C. 1 inch is generally too thin for a structural topping over hollow-core planks, potentially leading to inadequate load distribution or composite action.
- D. 2.5 inches would provide sufficient structural performance but is not the minimum required, potentially leading to unnecessary material and weight.
Hollow-Core Plank Topping
A structural concrete topping over precast hollow-core concrete planks is used to create a composite floor system, enhancing load distribution, diaphragm action, and fire resistance.
- Minimum 2 inches (51 mm) thick.
- Required for composite action.
- Provides a level surface and contributes to fire resistance.
- Reinforcement in topping may be required.
Memory trick: Planks need a hat, 2 inches flat, for strength and fire, that's where it's at.