By applying the static equations ΣH = 0, ΣV = 0 and ΣM = 0 to a determinate structure, we may determine:
Try it first: pick an option, then read the explanation.
Correct answer: D. All options are correct
Asked in SSC JE 27/01/2018 (Evening)
Detailed Explanation
A structure is statically determinate when the equations of equilibrium alone are enough to find all the unknown forces. In a plane there are three: ΣH = 0, ΣV = 0 and ΣM = 0.
Why “All options are correct” Is Correct
First, applying the three equations to the whole structure gives the support reactions. Then, cutting the structure at any section and applying the same equations to one part gives the shear force and bending moment at that section. So all three quantities can be found — option (d).
Why the Other Options Are Wrong
- A. Supporting reactions only: Reactions are found, but so are shear forces and bending moments.
- B. Shear force only: Shear force can be found, but so can reactions and moments.
- C. Bending moments only: Bending moments can be found, but so can reactions and shear forces.
Key Point
Determinate structure: statics gives reactions, SF and BM everywhere.
Key Concepts for Students
- Indeterminate structures need compatibility equations as well.
- Degree of indeterminacy = unknown reactions − available equations (externally).
- Free-body diagrams of cut parts give internal forces.
Practice more: this is question 4 in Force Analysis MCQs – Part 1. Try the whole set and check every answer instantly.