How many plies are there in the beam mentioned for the joist span calculation?

• A. 2 plies
• B. 3 plies
• C. 4 plies
• D. 5 plies

Answer: (C)

When sizing a beam for joist spans, the beam’s ability to resist bending comes from its cross‑section. Each additional ply increases the beam’s width, which raises the section modulus and the moment of inertia. That makes the beam stronger and stiffer, reducing both bending stress and deflection under the same loads.

In the given joist span calculation, the beam must be wide enough to meet the required strength and stiffness. Four plies provide the needed cross‑section to carry the load without excessive sag, whereas fewer plies would not meet the criteria. The four‑ply configuration achieves the balance of adequate capacity and practicality for this span.