Structural Analysis Questions and Answers - Influence Lines

Directions to solve : While writing influence line equations, left most point is always considered as origin and following sign convention is followed.
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1. in influence line diagrams (ILD) :-
a) Points remain fixed, position of load changes
b) Points change, position of loads remain fixed
c) Both of them changes
d) Neither of them changes

Answer: a
Explanation: In ILD we analyze effect of a force or moment on a fixed point by constantly varying point of application of load/moment

2. For drawing ILD, what value of test load is assumed?
a) 1 unit
b) Arbitrary
c) Depends upon structure
d) 0

Answer: a
Explanation: 1 unit load is assumed as calculations are easy then. Actual loads are multiplies with the results obtained to calculate further.

3. ILD of statically determinate beams consists of curve as well as straight lines.
a) True
b) False

Answer: b
Explanation: ILD of statically determinate beams consist of only straight lines.

4.
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AB is of length 1m.
What will be the equation for vertical reaction at point A (RAY)?
a) RAY = 1-X
b) RAY = 2-X
c) RAY = 3-X
d) RAY = 4-X

Answer: a
Explanation: Place unit load at any variable distance X and calculate RAY by conserving moment about point B.

5.
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AB is of length 1m.
What will be the shape of ILD curve for vertical reaction at point A (RAY)?
a) Triangular
b) Circular
c) Rectangular
d) Trapezoidal

Answer: a
Explanation: On plotting the above given equation, shape of curve will come out to be triangular.

6.
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AB = BC = 1m
What will be the equation for vertical reaction at point B (RBY)?
a) RBY = 4X
b) RBY = 2X
c) RBY = 3X
d) RBY = X

Answer: d
Explanation: Take load at any variable distance X and conserve load about point A.

7.
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AB = BC = 1m
Where will be the maximum point of ILD lie?
a) A
b) B
c) C
d) Between A and B

Answer: c
Explanation: On drawing curve based on the above equation, we will find that maximum point will lie at C.

8. Maximum point of ILD always lies at the point at which load is applied.
a) True
b) False

Answer: b
Explanation: False

9. If on ILD analysis peak force comes out to be 2 KN, then what will be the peak force if loading is 2KN?
a) 1 KN
b) 2 KN
c) 3 KN
d) 4 KN

Answer: d
Explanation: Peak force will be load multiplied by earlier peak load i.e. 2*2

10. AC= 1m, CB =3 m
C is just an arbitrary point. A is pin support and B is a roller type support.
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What will be the equation of ILD of shear force at point C for CB part?
a) 0.75 – 0.375X
b) 0.75 – 0.475X
c) 0.85 – 0.375X
d) 0.75 – 0.1375X

Answer: a
Explanation: Just assume force at any point between BC and conserve moment about point B.