Permissible Axial Tension – Rolled I-Beams and Channels (Working Stress Context) As per classic Indian working-stress practice for rolled I-beams and channels, what permissible axial tensile stress is commonly adopted (kg/cm^2)?

Introduction / Context:
Before the widespread adoption of limit-state design, many Indian practices used working-stress design for steel. Under this method, permissible (allowable) stresses were specified as fractions of material yield stress. This question checks basic recall of the typical permissible axial tensile stress for rolled I-beams and channels in that system, expressed in kg/cm^2.

Given Data / Assumptions:

• Material: mild structural steel with yield stress around 2500 kg/cm^2.
• Design philosophy: working-stress design (allowable stress approach).
• Member: rolled I-beam or channel subjected to axial tension.

Concept / Approach:

Working-stress design limits the service stress to a specified fraction of yield to provide an implicit factor of safety. A widely taught rule of thumb is 0.6 * fy for axial tension in mild steel under working-stress assumptions, which for fy ≈ 2500 kg/cm^2 yields 1500 kg/cm^2.

Step-by-Step Solution:

Verification / Alternative check:

Historic handbooks and solved examples in working-stress steel design frequently use 1500 kg/cm^2 for axial tension in mild steel members, aligning with the 0.6 fy rule of thumb.

Why Other Options Are Wrong:

• 1800 kg/cm^2: Represents 0.72 fy; too high for the conventional allowable stress.
• 1400 kg/cm^2 and 1420 kg/cm^2: Slightly lower than the standard 1500 and not the commonly taught benchmark value.

Common Pitfalls:

Confusing working-stress values with limit-state design stresses; mixing units between MPa and kg/cm^2; forgetting that permissible stresses vary with material grade and philosophy.

Final Answer:

1500 kg/cm^2