# Shear force in influence line of beam

• fonseh
In summary, the conversation discusses the change in shear force from -0.5 to 0.5 at point C and the determination of shear force at various locations by applying a unit force at an arbitrary location. The concept of influence lines is also mentioned, with two methods of understanding it - algebraically and by sketching the deflected shape of the beam.
fonseh

## Homework Statement

why at C . the shear force V change from -0.5 to 0.5 ? We wantg to determine the shear force at different location , and a unit force is applied at arbitary location ( measured from A) ...

## The Attempt at a Solution

IMO , there's no upwards force of 1 acting exactly on C , so the shear force will decrease from -0.5 at C to the cantilever end .

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When you apply the virtual load of 1 kN at C, it causes different shear values when analyzing the beam using the right and left segments when cut. Also, note that the magnitude of the influence line at point C from the influence line graph is: 0.5 - (-0.5) = 1 which represents the unit load applied at C.

There are at least two ways of learning about influence lines. The first way is algebraic, as given in the solution quoted. If you have learned about shear force diagrams before coming to influence lines, it is easy to get the two things confused. It is necessary to keep returning to the definition of an influence line to remind yourself that it is NOT a shear force diagram. Part of your question implies you may have taken on this confusion.
The second way of learning about influence lines is to sketch the deflected shape of the beam when a unit displcement is given at the point of interest. In this case, C is the point of interest. So giving the beam a unit displacement in shear at C (0.5 down, and 0.5 up in this case) gives the deflected shape of the beam as shown in the solution. You could (and should) use this approach to check a solution obtained algebraically. This approach also works for other functions such as bending moment (but that will do for the moment!)

## What is shear force in influence line of beam?

Shear force in influence line of beam refers to the maximum force that is applied perpendicular to the axis of the beam. It is a critical factor in determining the structural integrity and stability of a beam.

## How is shear force calculated in influence line of beam?

Shear force is calculated by determining the change in vertical load along the length of the beam. This can be done by plotting the influence line of the beam and finding the maximum value of the shear force at any given point.

## What is the purpose of influence lines in analyzing shear force?

Influence lines are used to visualize the effects of different loads on the shear force in a beam. By analyzing the influence lines, engineers can determine the maximum shear force at different points along the beam and design the structure accordingly to ensure its stability.

## Is shear force the same as bending moment in a beam?

No, shear force and bending moment are two different types of forces that act on a beam. Shear force is the force applied perpendicular to the axis of the beam, while bending moment is the force that causes the beam to bend.

## How does shear force affect the design of a beam?

Shear force is an important factor to consider in the design of a beam as it can significantly affect its strength and stability. Engineers must ensure that the beam is able to withstand the maximum shear force at any given point along its length to prevent structural failure.

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