For a simply supported beam subjected to a moving point load, what does the influence line for the shear force at a given section represent?
- AThe change in shear force due to the movement of the load across the spanCorrect
- BThe change in bending moment due to the movement of the load across the span
- CThe maximum shear force that can occur at the section
- DThe minimum shear force that can occur at the section
Solution
Concept
Influence line diagram for shear force
Formula
NONE
Step-by-step solution
1. An influence line shows the variation of a structural response (such as shear force or moment) at a specific section as a unit load moves across the beam. 2. It allows engineers to determine the maximum shear force that can occur at that section under moving loads. Answer: A
Explanation
An influence line represents the continuous variation of a structural response at a fixed section as a unit load moves across the span. For shear force, it shows how the internal shear at that specific point changes with load position. Thus, option A is the correct answer.
Why the other options are wrong
B) Option B refers to the influence line for bending moment rather than shear force. D) Option D refers to minimum shear force rather than the maximum shear force capacity at the section.
Shortcut
Influence Line Diagram (ILD) represents the variation of a response quantity as a load moves across the span.
Common mistake
Confusing influence line representations with bending moment influence lines or maximum shear force envelopes.
Correct answer: A) The change in shear force due to the movement of the load across the span