Why must bars be placed at right angles, in two directions on square or rectangle footings?

Why must bars be placed at right angles, in two directions on square or rectangle footings?

• A. They tend to curl
• B. To increase load capacity
• C. To reduce material use
• D. To simplify construction

Answer: (A)

The main idea is that a square or rectangular footing experiences bending in both directions. Concrete tends to shrink and curl or warp as it cures and loads, especially at the edges, if reinforcement only goes in one direction. By placing reinforcing bars in two directions at right angles, you create a grid that resists tensile stresses in both axes, tying the footing together and restraining differential movement. This helps keep the footing flat and reduces crack-related curling. So the two-direction arrangement is about preventing that curling tendency and improving crack control, rather than primarily increasing load capacity, saving material, or simplifying construction.

The main idea is that a square or rectangular footing experiences bending in both directions. Concrete tends to shrink and curl or warp as it cures and loads, especially at the edges, if reinforcement only goes in one direction. By placing reinforcing bars in two directions at right angles, you create a grid that resists tensile stresses in both axes, tying the footing together and restraining differential movement. This helps keep the footing flat and reduces crack-related curling. So the two-direction arrangement is about preventing that curling tendency and improving crack control, rather than primarily increasing load capacity, saving material, or simplifying construction.