Structural Systems and Foundations Flashcards

What is the most common foundation type used for single-family residential construction in the United States?

Answer: Poured concrete footing and foundation wall

Poured concrete spread footings with foundation walls (or slabs-on-grade) are the most widely used residential foundation system in the US due to cost and ease of construction.

What is the primary purpose of a vapor barrier installed under a concrete slab-on-grade?

Answer: To prevent ground moisture from migrating up through the slab

A vapor barrier (typically 6-mil or thicker polyethylene sheeting) blocks soil moisture from wicking up through the concrete slab and causing dampness or flooring failures.

Why must footings be placed below the frost depth in cold US climates?

Answer: To prevent frost heave from shifting the foundation when soil freezes and expands

Footings must extend below the local frost depth so that freezing and thawing soil does not cause upward movement (frost heave) that can crack or shift the foundation.

What does 'soil bearing capacity' refer to in foundation design?

Answer: The maximum load per unit area that soil can support without excessive settlement or failure

Soil bearing capacity is the maximum stress that the soil can withstand under a footing before it shears or settles beyond acceptable limits.

What is a grade beam foundation?

Answer: A reinforced concrete beam at or near grade that transfers structural loads to piers or piles below

A grade beam is a reinforced concrete foundation element that spans between deep supports (piers or piles) and carries wall loads across unstable or expansive soil.

What is the structural role of reinforcing steel (rebar) in concrete foundations?

Answer: To resist tensile forces that plain concrete cannot withstand on its own

Concrete is strong in compression but weak in tension; rebar carries tensile forces caused by bending, shrinkage, and soil pressure, preventing cracking and failure.