Question about tension and deflection (Mechanics of Material)

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Discussion Overview

The discussion revolves around a homework problem related to the mechanics of materials, specifically focusing on calculating the tension in three rods connected to a rigid bar under a force. Participants explore the necessary equations and methods to approach the problem, including considerations of rigidity and deflection.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant describes the homework problem and expresses difficulty in finding sufficient equations to solve it.
  • Another participant suggests summing moments around different points as a potential method to approach the problem.
  • A further reply questions the participant's understanding of the implications of the bar being rigid, particularly regarding the displacements of points A, C, and E.
  • Another participant clarifies that there are three relevant equations and three unknowns, and prompts the original poster to consider geometric compatibility.
  • A hint is provided to replace the force P with an equivalent force-couple system at the midpoint to aid in solving the problem.
  • The original poster later reports success in solving the problem by changing the unknown P to a known value, allowing for the establishment of a solvable system of equations.

Areas of Agreement / Disagreement

Participants generally agree on the approach to solving the problem, but there are varying interpretations regarding the number of equations and the implications of the rigidity of the bar. The discussion reflects a collaborative effort to clarify the problem without reaching a definitive consensus on all aspects.

Contextual Notes

There is a mention of geometric compatibility as a relevant consideration, which may not have been fully addressed in the original problem statement. The implications of the rigid bar and the behavior of the rods under tension are also points of discussion that remain nuanced.

shinizaki
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Hello everyone, I have some difficulties to solve this question in my homework.

Homework Statement


Picture
http://img714.imageshack.us/img714/7953/picz.png

Rigid bar ACE connected to rod AB, CD, EF which have same material and surface area A. Calculate tension caused by force P in three rods.

2. Homework Equations
Equation :
sigma Fy = 0
sigma M =0
comparison between deflection in A, C, and E


The Attempt at a Solution


I try to solve this question but I can't find sufficient equation to solve it. It have 4 equations and I only find 3. Please help me solve this.
 
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Have you tried summing the moments around different points?
 
You haven't shown your working, but have you considered the property of the bar that it is rigid? What does that imply for the displacements of A, C and E?
 
shinizaki said:
. Relevant equations
Equation :
sigma Fy = 0
sigma M =0
comparison between deflection in A, C, and E
these are your 3 relevant 'equations'
It has 4 equations and I only find 3.
there are 3 relevant equations (as you note; the last is concerned with geometric compatability) and 3 unknowns (the tensions in each rod). What do you mean by four ?(the x direction is irrelevant here). Note that the bar is rigid, but that the rods can extend or compress (which should have been more clearly stated in the problem). Hint: This problem is best solved by replacing the force P with an equivalent force-couple system at midpoint.
 
When I try a few times again, I can solve it at last ! The unknown P I change to one so I have 3 unknowns and 3 equation then revert it back to P. Thanks all^^
 

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