# Structural Analysis Questions and Answers – Determinacy and Stability

This set of Structural Analysis Multiple Choice Questions & Answers (MCQs) focuses on “Determinacy and Stability”.

1. For the validity of principle of superposition, materials should behave in which manner?
a) linear-elastic
b) non-linear-elastic
c) Non-linear- inelastic
d) Linear- inelastic

Explanation: They should behave in a linear elastic manner so that, Hooke’s law is valid.

2. If in planar system, X parts/members are there with Y no. of forces, then condition for statically determinacy is:-
a) Y < 3X
b) Y > 3X
c) Y = 3X
d) None of the mentioned

Explanation: There can be at max. 3 equilibrium equations for each part.

3. If Y > 3X (X and Y are from the above question) then, the system is:-
a) Statically indeterminate
b) Statically determinate
c) Can’t say
d) Depends on other conditions

Explanation: As there can be at max. 3X equations, at least one of the forces will be unsolvbale.

4. If in a planar system, only 2 reaction forces are acting, then the system is:-
a) Essentially unstable
b) Essentially stable
c) Can’t say
d) None of the mentioned

Explanation: If no. of reactions is less than 3 in any planar system, then the system is essentially unstable.

5. If all the reactions acting on a planar system are concurrent in nature, then the system is:-
a) Can’t say
b) Essentially stable
c) Essentially unstable
d) None of the mentioned

Explanation: The system can rotate about the point of concurrency. So, it is essentially unstable.
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6. If 4 reactions are acting on a beam, then the system is:-
a) Unstable & indeterminate
b) Stable & indeterminate
c) Stable & determinate
d) Can’t say

Explanation: 4 reactions mean that the system is definitely indeterminate. But stability would depend upon the nature of forces acting on the planar structure.

7. If a system has more equations of equilibrium than no. of forces, then the system is:-
a) Improperly constrained
b) Partially constrained
c) Stable
d) Solvable

Explanation: In these cases, system is unstable and unsolvable and is termed as partially constrained.

8. How many cases out of the following are improperly constrained?
Parallel forces, concurrent forces, perpendicular forces, only moment
a) 1
b) 2
c) 3
d) 4

Explanation: parallel and concurrent are improperly constrained.

9. If a structure has total 10 joints, then what should be the minimum no. of joints in which equilibrium equations should be concurrently satisfied for stability?
a) 7
b) 8
c) 9
d) 10

Explanation: For stability, equilibrium equations should be satisfied concurrently at each and every joint of the structure.

10. If a structure has 2j – r no. of members, then it will be:-
a) stable
b) unstable
c) depends upon structure
d) depends upon magnitude of load

Explanation: In these cases, structures can be stable as well unstable.
Here, j represent no. of joints and r represents no. of external forces.

11. If a truss consists of a non-triangular element, then it will essentially be unstable.
State whether the above statement is true or false.
a) true
b) false

Explanation: In these cases, instability is the most probable occurrence, but there are a lot of examples which are unstable.

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