In working-stress design of rolled steel beams, the typical permissible average shear stress (units: kg/cm^2) is approximately which of the following values?

Introduction / Context:
Permissible shear stress governs the design of web thickness and stiffening in beams subjected to significant shear near supports. Traditional WSD adopts an allowable average shear stress derived as a fraction of yield stress to maintain adequate safety.

Given Data / Assumptions:

• Mild steel yield stress ≈ 2500 kg/cm^2 (≈ 250 MPa).
• Permissible shear often taken around 0.4 * Fy in older practice.
• Values given are typical exam figures.

Concept / Approach:
Using τ_allow ≈ 0.4 * Fy yields ≈ 0.4 * 2500 = 1000 kg/cm^2. Many handbooks round to a nearby conventional value such as 945 kg/cm^2 for rolled sections, reflecting further safety considerations and standardization across tables.

Step-by-Step Solution:
Adopt Fy ≈ 2500 kg/cm^2 for mild steel.Compute 0.4 * Fy ≈ 1000 kg/cm^2.Select the closest standard permissible value used for beams: 945 kg/cm^2.

Verification / Alternative check:
Older design tables and example problems commonly reference 945 kg/cm^2 for shear in rolled beams, while bending uses ~1650 kg/cm^2, maintaining consistent proportionality to Fy.

Why Other Options Are Wrong:

• 845 and 1025 kg/cm^2: Not the conventional tabulated value for rolled beams.
• 1500 and 1875 kg/cm^2: Too high for shear; closer to bending/tension allowances in WSD.

Common Pitfalls:

• Confusing average shear (V/A_web) with maximum parabolic shear in rectangular webs; WSD limits are typically for average shear in design checks.

Final Answer:
945 kg/cm2.