In simple beams, where is the longitudinal steel located to resist tensile stresses?

• A. Near bottom
• B. Near top
• C. Mid-depth
• D. At the ends

Answer: (A)

When a simple beam bends, the top fibers are compressed while the bottom fibers are stretched. Concrete is strong in compression but weak in tension, so the tensile stresses must be carried by steel reinforcement. Placing the longitudinal steel near the bottom puts it in the tension zone where it can resist the bending-induced tensile forces, working together with the concrete above to form a balanced, safe cross-section. In most simply supported spans under positive bending, this means bottom reinforcement; note that near supports with negative moments the top fibers can become tensile and would need reinforcement there as well, but for the main span this bottom location is where the tensile stress is resisted.