Which of the following statements is true? A: A roller is provided at one end of a bridge truss to allow thermal expansion. B: A roller provides freedom of deformation in the horizontal plane in case of thermal expansion.
Try it first: pick an option, then read the explanation.
Correct answer: C. Both A and B
Asked in SSC JE 25/01/2018 (Morning)
Detailed Explanation
Long bridge trusses and girders lengthen in summer and shorten in winter. If both ends were held horizontally, that movement would be prevented and large thermal forces would develop. So one end is hinged and the other rests on rollers.
Why “Both A and B” Is Correct
The roller resists vertical load but lets the end slide horizontally. That is exactly the purpose in A, and the freedom of horizontal movement described in B. Both A and B are true — option (c).
| Support | Reactions | Movement allowed |
|---|---|---|
| Roller | 1 (normal to the surface) | Horizontal sliding and rotation |
| Hinge (pin) | 2 (horizontal and vertical) | Rotation only |
| Fixed | 3 (horizontal, vertical, moment) | None |
Why the Other Options Are Wrong
- A. Only A: B is also true — it describes how the roller allows expansion.
- B. Only B: A is also true — that is why rollers are used.
- D. None of these: Both statements are correct.
Key Point
Hinge at one end + roller at the other: the structure stays determinate and free to expand.
Key Concepts for Students
- Thermal strain = αΔT; restrained, it causes stress EαΔT.
- Expansion joints serve the same purpose in decks and pavements.
- A roller support gives one reaction — the structure stays statically determinate.
Practice more: this is question 30 in Bending Moment and Shear Force MCQs – Part 2. Try the whole set and check every answer instantly.