In the case of eccentrically loaded struts, a ______ is preferred.
Try it first: pick an option, then read the explanation.
Asked in SSC JE 03/03/2017 (Morning)
Detailed Explanation
An eccentrically loaded strut carries axial compression plus a bending moment P·e. It needs a large moment of inertia and section modulus about the bending axis, as well as a good radius of gyration against buckling.
Why “composite section” Is Correct
The book's key is composite section: a built-up section (e.g. channels or angles laced or battened together, or a plated section) can be arranged to put material far from the neutral axis, giving a high Z for the moment Pe and a high r for buckling. Note: this question is worded loosely and textbooks differ — some (and many online keys) give "hollow section" for the same reason. We keep the book's answer (c).
| Effect of eccentric load | Section property needed |
|---|---|
| Direct stress P/A | Area A |
| Bending stress Pe/Z | Large section modulus Z |
| Buckling | Large least radius of gyration r |
Why the Other Options Are Wrong
- A. solid section: A solid section keeps much material near the centroid, giving low Z and r per unit weight.
- B. hollow section: Hollow sections are also efficient and some books choose them; the book's key, however, is the composite (built-up) section.
- D. reinforced section: "Reinforced section" is not a standard choice for struts in this context.
Key Point
Eccentric strut → needs high Z and r: built-up/composite (book) or hollow sections; avoid solid sections.
Key Concepts for Students
- Combined stress σ = P/A ± Pe/Z.
- Built-up sections are joined by lacing or battens.
- Textbook keys differ for this question.
Practice more: this is question 32 in Columns and Struts MCQs – Part 3. Try the whole set and check every answer instantly.