Working Stress Design – Permissible Bending Tensile Stress for HYSD Fe 415 Bars in Beams According to classic working-stress practice (IS 456, WSM context), what is the permissible bending tensile stress in high yield strength deformed (HYSD) bars of grade Fe 415 used in a reinforced concrete beam?

Introduction / Context:
The working stress method (WSM) limits the service stresses in steel and concrete to values below yield or crushing, providing a margin of safety against long-term effects. In Indian practice for reinforced concrete, permissible bending tensile stresses for different steel grades are tabulated. This question checks recall of the allowable bending tensile stress for HYSD Fe 415 bars in beams under WSM.

Given Data / Assumptions:

• Steel type: HYSD (high yield strength deformed) bars.
• Grade: Fe 415 (characteristic yield strength ≈ 415 N/mm^2).
• Design philosophy: working stress method (service stress limits).
• Member: reinforced concrete beam (flexure).

Concept / Approach:

In WSM, the permissible bending tensile stress in steel is taken as a fraction of the yield strength to ensure adequate factor of safety and control of serviceability. For Fe 415 HYSD bars, the widely taught and referenced allowable bending tensile stress in beams is about 230 N/mm^2. This value reflects both material properties and the conservative nature of WSM compared with limit state design (LSD), where stresses can reach closer to yield under factored loads.

Step-by-Step Solution:

Verification / Alternative check:

Classic Indian RCC design handbooks and solved examples using WSM consistently adopt 230 N/mm^2 for bending tension in Fe 415 bars. This sits comfortably below fy, in line with the WSM philosophy of allowable stress design.

Why Other Options Are Wrong:

• 190 N/mm^2: Too low for Fe 415 in bending tension; more aligned with lower strength steels or conservative contexts not typical for HYSD Fe 415.
• 140 N/mm^2: Characteristic of mild steel (Fe 250) bending tension in WSM, not Fe 415.
• None of the above: Incorrect since 230 N/mm^2 is listed.

Common Pitfalls:

Mixing WSM values with limit state partial-safety-factor stresses; confusing values for bars in direct tension vs bending; using Fe 250 permissible values for HYSD bars by mistake.

Final Answer:

230 N/mm^2