Finding the bending moment for maximum stress

In summary, the conversation discusses using My/I to find the maximum bending stress for a beam. The problem is not clear, but it involves finding the bending moment for a beam with multiple points of load and reaction points. The sum of all moments must equal zero, but the conversation suggests constructing a shear diagram to find the bending moment diagram and then identifying the maximum bending moment. The maximum bending moment is the value furthest above or below the zero axis, or the absolute value from the x axis.
  • #1
Jameseyboy
25
1
Hi,

I am looking to use My/I to find the maximum bending stress for a beam

My problem is I don't know how to find the bending moment- the reason why:

The beam has more than one point of load, aside from the reaction points. (Pin joint cantilever beam)

The sum of all moments equal 0 so I don't know how or which bending moment to use.
 
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  • #2
Your problem is not clear. Perhaps there is a diagram showing the beam and loading which you can post?

In any event, if the beam is in equilibrium, the sum of all moments will equal zero. However, you are looking for the moments which are internal to the beam. If you have the reactions of the beam, construct the shear diagram, and from this, you can construct the bending moment diagram. Once you have done this, the max. BM should be clear.
 
  • #3
Ahh ok, so I can physically get the answer from the BMD? Is this typically when it crossed the x axis? Then the actual value is THAT particular moment on the beam disregarding the other ones?

Sorry to be so vague
 
  • #4
The maximum BM is just that: it's the value which lies the furthest above or below the zero axis. The points where the shear force is zero are also points where the BM is a maximum or minimum, since dM(x)/dx = V(x), according to Euler beam theory.
 
  • #5
Right. So it's not the value I.e. Going from +2 to -2 meaning 4 ---> it's actually the absolute value from the x axis- so '2'?
 
  • #6
Correct.
 
  • #7
Fantastic. Cheers
 

1. How do you calculate the bending moment for maximum stress?

The bending moment for maximum stress is calculated by multiplying the force applied to an object by the distance from the point of application to the point of maximum stress.

2. What is the significance of finding the bending moment for maximum stress?

Finding the bending moment for maximum stress is important because it helps engineers and designers determine the maximum stress that a structure or object can withstand, ensuring it is strong enough to withstand the forces that will be applied to it.

3. What factors affect the bending moment for maximum stress?

The bending moment for maximum stress is influenced by the shape, size, and material of the object or structure, as well as the location and magnitude of the applied force.

4. How does the bending moment for maximum stress impact the design of structures?

The bending moment for maximum stress is a critical factor in the design of structures as it helps engineers determine the appropriate size and shape of the structure to ensure it can withstand the expected forces and stresses.

5. Can the bending moment for maximum stress be reduced or eliminated?

The bending moment for maximum stress can be reduced by using stronger or more durable materials, changing the shape or size of the structure, or by redistributing the applied forces. However, it cannot be completely eliminated as some level of stress is necessary for a structure to be functional.

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