Which of the following beams is likely to have a point of contraflexure?
Try it first: pick an option, then read the explanation.
Correct answer: C. Beam with overhangs
Asked in SSC JE 03/03/2017 (Evening)
Detailed Explanation
A point of contraflexure exists only where the bending moment changes sign. Under ordinary downward loads, check which beams have both sagging and hogging regions.
Why “Beam with overhangs” Is Correct
A cantilever under downward load is hogging throughout; a simply supported beam is sagging throughout — no sign change in either. A beam with overhangs hogs over the supports and sags in the span, so the BM crosses zero — option (c).
Why the Other Options Are Wrong
- A. Cantilever beam: A cantilever under downward loads hogs everywhere — one sign only.
- B. Simply supported beam: A simply supported beam under downward loads sags everywhere.
- D. None of these: The overhanging beam does have contraflexure points.
Key Point
Overhanging, fixed and continuous beams have contraflexure; SS beams and cantilevers (downward loads) do not.
Key Concepts for Students
- A couple on a SS beam can create a contraflexure point.
- Fixed beams with UDL have two points, 0.211L from each end.
- Short overhangs may not create contraflexure if the span moment stays positive throughout.
Practice more: this is question 41 in Bending Moment and Shear Force MCQs – Part 3. Try the whole set and check every answer instantly.