Drawing Bending Moment & Shear Force for a Beam w/ Constant Moment

In summary, the conversation is about drawing a correct bending moment diagram and shear force diagram for a beam with a constant moment. The rule for bending moment is that the value at a certain point is the area under the shear force diagram from the starting point to that point. This rule also applies to a constant moment, where the moment creates a discontinuity on the bending moment diagram. For a clockwise moment, it goes up and for a counterclockwise moment, it goes down. For a uniformly distributed load, the bending moment equation is Mx = (Ay)(x) - (wx^2)/2, but if there is a constant moment at a point, it should be added or subtracted depending on the direction of the moment.
  • #1
frozen7
163
0
Can anyone draw me a correct Bending moment diagram and shear force diagram for this beam?
i have drawn the shear force diagram for this case but I do not know how to draw the bending moment disgram for this case because this question involve a constant moment. Normally the rule for bending moment is the value of bending moment at certain point is the area under shear force diagram from the starting point to that certain point. Can this rule applied on this question as well? I felt the bending moment diagram is quite strange if follow this rule for this question. Can anyone help me?
Thanks.
 

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  • #2
Hello, the only thing a couple or moment does for the bending diagram is create a "discontinuity" (more like a derivative doesn't exist at said point), just like the loads do on the shear diagram. If the moment is clockwise it goes up (adds to the area [method]), and if its counterclockwise it goes down (substract to the area [method]).
 
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  • #3
Does it mean when there is a constant moment at point b, then we should either add or substract that value of constant moment in that point (either draw a straight line goes up or goes down)?
 
  • #4
frozen7 said:
Does it mean when there is a constant moment at point b, then we should either add or substract that value of constant moment in that point (either draw a straight line goes up or goes down)?

exactly what i said above.
 
  • #5
One more thing have to be confirmed.
For uniformly distributed load, Mx = (Ay)(x) - (wx^2)/2 (where x is the distance from staring point to x, Ay is the reaction force at the starting point and w is the force per unit length and Mx is the bending moment)
Let say if there is a constant moment which is 50N/m at point a ,then Mx become Mx = (Ay)(x) - (wx^2)/2 +50 ??
 
  • #6
frozen7 said:
One more thing have to be confirmed.
For uniformly distributed load, Mx = (Ay)(x) - (wx^2)/2 (where x is the distance from staring point to x, Ay is the reaction force at the starting point and w is the force per unit length and Mx is the bending moment)
Let say if there is a constant moment which is 50N/m at point a ,then Mx become Mx = (Ay)(x) - (wx^2)/2 +50 ??

Yes +50 if its clockwise.
 

1. What is a bending moment and shear force in a beam?

A bending moment is a measure of the internal force or stress that occurs within a beam when it is subjected to an external load or force. It causes the beam to bend or deform. Shear force, on the other hand, refers to the internal force that is parallel to the cross-section of the beam and is caused by an external load acting perpendicular to the beam's length.

2. Why is it important to calculate the bending moment and shear force for a beam?

Calculating the bending moment and shear force for a beam is important because it helps engineers and designers determine the structural integrity of the beam. It allows them to understand how the beam will behave under different loads and helps them make informed decisions about the type and amount of support needed for the beam.

3. What are the key factors that affect the bending moment and shear force in a beam?

The key factors that affect the bending moment and shear force in a beam include the type of load applied to the beam, the length and shape of the beam, and the type of support or constraint at each end of the beam.

4. How do you draw a bending moment and shear force diagram for a beam with constant moment?

To draw a bending moment and shear force diagram for a beam with constant moment, you first need to determine the reactions at the supports and the points where the external load is applied. Then, you can use the equations for bending moment and shear force to plot the diagrams. The bending moment diagram will show the variation of bending moment along the length of the beam, while the shear force diagram will show the variation of shear force along the length of the beam.

5. What are the applications of understanding bending moment and shear force in a beam?

Understanding bending moment and shear force in a beam is crucial for the design and analysis of various structures, such as bridges, buildings, and machines. It is also used in the construction industry to determine the size and type of beams needed for specific projects and to ensure the safety and stability of the structure.

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