In influence line diagrams (ILD)
- APoints remain fixed, position of load changesCorrect
- BPoints change, position of loads remains fixed
- CBoth of them change
- DNeither of them changes
Solution
Concept
Fundamental principle of influence line diagrams
Formula
NONE
Step-by-step solution
1. An influence line diagram (ILD) represents the variation of a reaction, shear force, or bending moment at a specific point on a structure. 2. The point or section under consideration remains fixed while a unit load moves across the span. 3. Therefore, in ILDs, points remain fixed while the position of the load changes. Answer: A
Explanation
An influence line diagram illustrates how a structural response at a specific fixed point changes as a unit load moves across a structure. The point under observation remains constant while the position of the moving load changes along the span. Therefore, option A correctly states that points remain fixed while the load position changes.
Why the other options are wrong
B) ILD illustrates structural response at a specific fixed point as the load position moves across the span. C) ILD evaluates structural behavior at a single fixed point under varying load positions, not simultaneous changes of both. D) The load position must vary across the span to construct an influence line diagram.
Shortcut
ILD = Fixed point, Moving load.
Common mistake
Confusing influence line diagrams with structural response diagrams where load positions remain fixed.
Correct answer: A) Points remain fixed, position of load changes