As per IS 800: 2007, in case of design of steel beams, the permissible bending stress in tension and the permissible bending stress in compression should NOT exceed _______ times of the yield stress (fy) of steel in a plastic and compact section while the beam is laterally supported.
- A0.75
- B0.45
- C0.60
- D0.66Correct
Solution
Concept
In the working stress method of IS 800:2007, the permissible bending stress for a laterally supported beam with plastic or compact section is 0.66 fy.
Formula
fabc = fabt = 0.66 fy
Step-by-step solution
1. The beam is laterally supported, so lateral torsional buckling will not occur. 2. The section is plastic or compact, so local buckling will not limit the stress. 3. As per the working stress method of IS 800:2007, permissible bending stress in tension and in compression = 0.66 fy. 4. So the answer is (D).
Explanation
When a beam is laterally supported and the section is plastic or compact, it can carry a high bending stress. The working stress method of IS 800:2007 allows 0.66 fy in both tension and compression. This value includes a factor of safety of about 1.5.
Why the other options are wrong
A: 0.75 fy is the permissible bending stress for solid round or square bars and solid plates, not for this case. B: 0.45 fy is closer to the permissible stress for bearing or axial compression, not bending. C: 0.60 fy is the permissible axial tension stress, not bending stress.
Shortcut
Bending in a laterally supported compact beam = 0.66 fy (about fy/1.5).
Common mistake
Students confuse 0.60 fy (axial tension) with 0.66 fy (bending).
Correct answer: D) 0.66