Beam deflection boundary condition calculation

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Discussion Overview

The discussion revolves around calculating beam deflection at specific points (x=L/4 and x=L/2) and understanding the boundary conditions related to the slope of the beam. It includes theoretical considerations and interpretations of physical meanings behind the mathematical expressions involved.

Discussion Character

  • Homework-related
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant states that the displacement at x=0 is zero, leading to a constant C2=0, but expresses uncertainty about the boundary conditions.
  • Another participant explains that the slope of the beam is represented by dv/dx.
  • A participant questions the physical meaning of the slope and its value at x=L/2, suggesting that it should not be zero due to the presence of an upward load P.
  • There is a discussion about the relationship between the derivative of moment, shear force, and distributed force, with a participant noting that this may not directly relate to deflection.
  • One participant emphasizes the need to start with deflection and questions the interpretation of the first derivative of a curve.
  • Another participant reiterates the definition of slope in calculus but does not resolve the disagreement about its value at x=L/2.

Areas of Agreement / Disagreement

Participants express differing views on the value of dv/dx at x=L/2, with some asserting it should be zero while others argue that it cannot be zero due to the applied load. The discussion remains unresolved regarding the boundary conditions and their implications.

Contextual Notes

There are uncertainties regarding the physical interpretation of slope and its implications for beam deflection, as well as the assumptions underlying the boundary conditions used in the calculations.

xzibition8612
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Homework Statement



Find the deflection at x=L/4 and x=L/2 for the beam

Homework Equations



See attached pic.

The Attempt at a Solution



So I have the solution derived in class. Only 0<x<L/2 is derived because since the load on the beam is at L/2, the equation is valid for the entire beam since its symmetric (or something like that, if this isn't the correct explanation somebody tell me). My question concerns the boundary conditions. I know that at x=0, the displacement v=0. Hence you get C2=0. Now the second thing:

dv/dx=0 at x=L/2

I have no idea what dv/dx means, why its 0, and why its taken at x=L/2. Any help would be appreciated thanks.
 

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You ever heard of the 'slope' of the beam being discussed in your class? The slope = dv/dx.
 
ok, so what is the slope physically mean? Why is it 0 at x=L/2? It has something to do with the load P? I see that the derivative of moment is shear force, and the derivative of shear force is distributed force. But that has nothing to do with deflection right?
 
Start with deflection. What's the first derivative of a curve represent?
 
the slope, y/x. Why would dv/dx=0 at x=L/2? That makes no physical sense, because at x=L/2 there is a load P upward and it must deflect. Hence dv/dx can't be 0.
 
Last edited:
What's the slope of a curve in calculus class?
 

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