Nominal shear reinforcement in beams: In a reinforced concrete beam zone where the nominal shear stress is less than 5 kg/cm^2, nominal shear reinforcement (stirrups) is provided at a pitch equal to which fraction of the lever arm (z) of the section?

Introduction / Context:
Even when calculated shear demand is small, nominal shear reinforcement is mandated to control diagonal cracking, provide ductility, and confine longitudinal steel. The pitch (spacing) of stirrups is often expressed as a fraction of the effective depth or lever arm z of the section.

Given Data / Assumptions:

• Beam zone with nominal shear stress < 5 kg/cm^2.
• Lever arm z approximately equal to 0.9 d (where d is effective depth), used for practical spacing rules.

Concept / Approach:
Where shear is low, codes permit larger stirrup spacings but still require a minimum amount. A common rule-of-thumb (reflected in many objective-type questions) is to limit the pitch to around 0.5 z in such zones, subject to absolute maximum spacing limits and minimum shear steel requirements.

Step-by-Step Reasoning:
Identify that only nominal shear reinforcement is required.Adopt the guideline pitch ≈ 0.5 z (also cross-check with code max spacing limits such as a multiple of bar diameter or 0.75 d).Provide closed stirrups with adequate anchorage and hook details.

Verification / Alternative check:
Design charts and code clauses for minimum shear reinforcement will generally lead to a similar or slightly more conservative spacing once maximum spacing caps (e.g., 300 mm or 0.75 d, whichever is less) are applied.

Why Other Options Are Wrong:
One-third z: Overly conservative for nominal zones.Full z or 1.5 z: Excessive spacing; risks diagonal cracking and does not meet minimum reinforcement philosophy.

Common Pitfalls:

• Not checking absolute maximum spacing limits in the governing code.
• Ignoring anchorage/hook requirements of stirrups at the compression face.

Final Answer:
one-half of the lever arm