Free Beam Bending: Find Complete Answer & More

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Discussion Overview

The discussion revolves around analyzing the bending of a beam subjected to a concentrated force, particularly focusing on cases where the force is applied at the center versus off-center. Participants explore the implications of boundary conditions and equilibrium in the context of beam theory, seeking to derive shear, moment, slope, and deflection values.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant describes a beam with a concentrated force at its center, balanced by a distributed downward force, and expresses difficulty in obtaining a complete solution without assuming a deflection value.
  • Another participant suggests considering the beam as balanced on a fulcrum, raising questions about how to approach the problem if the beam is clamped at one end.
  • A participant clarifies that a clamped beam behaves as a cantilever, noting that moment and shear are zero at the free end, while slope and deflection are zero at the clamped end.
  • There is a mention of imposing zero shear and moment at the free ends, but this approach may not hold if the concentrated force is not centered.
  • One participant advises focusing on the simpler case of a centered force before modifying the approach for an off-center force, emphasizing the importance of balancing forces and moments.
  • Another participant proposes modeling the situation as two half-length beams clamped at one end, suggesting the need to account for reactions from the other side.

Areas of Agreement / Disagreement

Participants express differing views on how to approach the problem, particularly regarding the assumptions made about boundary conditions and the treatment of concentrated forces. There is no consensus on the best method to derive the complete answer, and multiple competing approaches are presented.

Contextual Notes

Participants note limitations related to assumptions about deflection values and the implications of symmetry in the beam's loading conditions. The discussion highlights the complexity introduced by off-center forces and the need for careful consideration of boundary conditions.

spovolny
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Consider a beam with an upwards concentrated force applied to its center. This is equilibrated by a distributed downwards force. There are no displacement boundary conditions. I've tried approaching this with simple beam theory, but I can't get a complete answer (shear, moment, slope, deflection) unless I assume a deflection value somewhere. What is the best way to get the complete answer for this problem?

I'm also curious about what happens if the concentrated force is off-center (equilibrium then maintained by applying a moment along with the force). The lack of symmetry complicates things further.
 
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i.e. the beam is balanced on a fulcrum ... how would you normally do this if, say, the beam were clamped at one end?
 
Simon Bridge said:
i.e. the beam is balanced on a fulcrum ... how would you normally do this if, say, the beam were clamped at one end?

I appreciate the quick reply. Clamped at one end means a cantilevered beam, so moment/shear are zero at the free end and slope/deflection are zero at the clamped end. I see how my problem is like a beam on a fulcrum, but I don't want to necessarily say that the center deflection is zero.

I did impose zero shear/moment at the free ends. I also imposed zero slope at the center, but this breaks down if the concentrated force isn't centered.
 
Just stick to one problem at a time - treat the simpler case where the concentrated force is centered and then modify the approach to allow for uncentered force.
This is a statics problem - all forces and moments balance, the main trouble is that the beam bends and you want to know how much by right?
What's wrong with modelling as two half-length beams clamped at one end? You will need to account for the reactions due to the other side.
The main thing is to look at how you would treat that situation.
 

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