For rolled I-beams and channels designed by working-stress methods, the permissible axial tensile and compressive stresses in mild steel shall not exceed which value?

Introduction / Context:Before limit-state design, steel members were commonly designed using working-stress methods with specified allowable stresses. For mild steel rolled sections (I-beams and channels), permissible stresses in axial tension and compression are fractions of yield stress, ensuring adequate safety under service loads.

Given Data / Assumptions:

• Mild steel yield stress assumed ≈ 2500 kg/cm2 (≈ 250 MPa).
• Allowable stress in axial tension/compression ≈ 0.6 * fy in working-stress design.
• Question asks for the cap used for rolled I-beams and channels in service conditions.

Concept / Approach:

Using 0.6 * fy for axial stress gives an allowable ≈ 1500 kg/cm2. This conservative limit accounts for variability, residual stresses, and serviceability under repeated loading.

Step-by-Step Solution:

Verification / Alternative check:

Contemporary limit-state design expresses capacities differently; however, legacy MCQs referencing working-stress values consistently cite ≈1500 kg/cm2 for mild steel axial stress limits.

Why Other Options Are Wrong:

• 1400 kg/cm2: Overly conservative relative to the standard allowable.
• 1650 or 1800 kg/cm2: Closer to bending compression/tension allowables; high for axial service stress.
• 2000 kg/cm2: Too high for working-stress axial design in mild steel.

Common Pitfalls:

• Confusing axial allowable stress with bending allowable stress values.
• Mixing limit-state capacities with working-stress allowables.

Final Answer:

1500 kg/cm2