Length & Bending Stress: How Does Beam Length Impact Stresses?

In summary, if you have a beam or something, and apply a moment at one end, the bending stress is given by M*y / I, where I is the moment of inertia of the beam.
  • #1
studentoftheg
17
0
if you have a beam or something, anchored at one end and apply a moment at the other end, then the bending stress is given by M*y / I, where I is the moment of inertia of the beam. what affect does the length of the beam (i.e. the distance between the anchor and the end of the beam, where the moment is applied) have on the stresses generated?
 
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  • #2
Look at the definition of a moment and then equation for bending stress.

Thanks
Matt
 
  • #3
Thanks Matt, OK well maybe I'm not picturing this correctly in my head. I know that a moment = force x distance (from point of interest), but in my example there is an applied moment to the end of the beam (irrespective of the length of the beam). As I stated above, the bending stress is M*y / I. Now the moment of inertia of the beam isn't affected by the length of the beam, and obviously neither is the distance from the neutral axis (y). So, if say a moment of 100kNm is applied to a beam that is anchored at one end, then the stress doesn't appear to be affected by the length of the beam (it is M*Y/I), which I'm thinking has to be wrong?
 
  • #4
The higher the moment the higher the stress. The longer the beam, the higher the moment.

Thanks
Matt
 
  • #5
Right, I see now. So the resultant moment at the anchor will increase as you increase the length of the beam. I was picturing it wrong...
Thanks again
 
  • #6
Your welcome.

Matt
 
  • #7
studentoftheg said:
if you have a beam or something, anchored at one end and apply a moment at the other end...

CFDFEAGURU said:
The longer the beam, the higher the moment.

Be careful about what you really mean here. If you apply a moment (i.e. two forces that produce a couple), the moment is constant along the length of the beam.

If you apply a shear force, that creates a bending moment which does depend on the length of the beam.
 
  • #8
Yes, that is correct. Due to the length factor, I was figuring a force was being applied to create a moment load at the anchor.

Thanks
Matt
 

1. How does beam length affect bending stress?

The longer the beam, the greater the bending stress. This is because a longer beam has a larger moment of inertia, which means it is more resistant to bending. However, a longer beam also has a larger deflection, which can lead to higher stresses at certain points along the beam.

2. What is the formula for calculating bending stress in a beam?

The formula for calculating bending stress is 𝜎 = Mc/I, where 𝜎 is the bending stress, M is the bending moment, c is the distance from the neutral axis to the outermost point of the beam, and I is the moment of inertia.

3. How does beam length impact the overall strength of a structure?

The overall strength of a structure is directly affected by the length of its beams. Longer beams have a higher capacity to carry loads, making them stronger and more stable. However, longer beams also tend to be more flexible, which can lead to increased deflection and potential failure under heavy loads.

4. What is the relationship between beam length and deflection?

The relationship between beam length and deflection is directly proportional. This means that as the beam length increases, so does the deflection. This is due to the increased bending stress and lower stiffness of longer beams.

5. How can beam length be optimized to minimize bending stresses?

To minimize bending stresses, the beam length should be optimized based on the specific structural requirements and load conditions. This can involve using shorter beams with larger cross-sections or adding additional supports to reduce the overall length of the beam. Finite element analysis can also be used to determine the optimal beam length for a given structure.

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