Structural Analysis Questions and Answers – Influence Lines

This set of Structural Analysis Multiple Choice Questions & Answers (MCQs) focuses on “Influence Lines”.

While writing influence line equations, left most point is always considered as origin and following sign convention is followed.

1. In BMD and SFD :-
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

Explanation: In BMD and SFD, we analyze the structure by fixing loads initially.

2. 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

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

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

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

4. ILD of statically determinate beams consists of curve as well as straight lines.
State whether the above statement is true or false.
a) True
b) False

Explanation: ILD of statically determinate beams consist of only straight lines.
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Following figure is for questions 5 and 5.

AB is of length 1m.
5. 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

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

6. What will be the shape of ILD curve for vertical reaction at point A (RAY)?
a) Triangular
b) Circular
c) Rectangular
d) Trapezoidal

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

Following figure is for questions 7 and 8.

AB = BC = 1m

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

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

8. Where will be the maximum point of ILD lie?
a) A
b) B
c) C
d) Between A and B

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

9. Maximum point of ILD always lies at the point at which load is applied.
State whether the above statement is true or false.
a) True
b) False

Explanation: In the above example above sentence is proved wrong.

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