In a truss, it is assumed that the members are joined by:
Try it first: pick an option, then read the explanation.
Correct answer: B. Smooth pins
Asked in SSC JE 22/01/2018 (Morning)
Detailed Explanation
Truss analysis by joints and sections rests on a few idealising assumptions.
Why “Smooth pins” Is Correct
Members are assumed to be connected by smooth, frictionless pins. A smooth pin cannot transmit a moment, so — with loads applied only at joints — every member carries only axial force. Rough pins would transmit moments and make members bend.
| Assumption in plane-truss analysis |
|---|
| Members are joined at their ends by smooth (frictionless) pins |
| Loads and reactions act only at the joints |
| Self-weight of members is neglected (or lumped at joints) |
| Each member is straight and carries only axial force (tension or compression) |
Why the Other Options Are Wrong
- A. Rough pins: Rough pins would transmit moments, contradicting truss theory.
- C. Either rough or smooth pins: Only smooth pins fit the assumption.
- D. None of these: Smooth pins is correct and listed.
Key Point
Truss assumption: smooth pin joints + loads at joints → axial forces only.
Key Concepts for Students
- Real gusset-plate joints cause small secondary stresses.
- Self-weight is usually lumped at the joints.
- Members are assumed straight and meeting at a single point at each joint.
Practice more: this is question 21 in Beams and Trusses MCQs – Part 2. Try the whole set and check every answer instantly.