Unusual problem for my course and struggling

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Discussion Overview

The discussion revolves around a mechanical engineering problem involving the design of a boom AC supported by a steel bar and a pin. Participants are tasked with determining the required thickness of the bar and the diameter of the pin based on given loading conditions and safety factors. The scope includes technical reasoning and problem-solving related to structural mechanics.

Discussion Character

  • Homework-related
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant presents the problem and provides known data, including loading conditions and safety factors for the bar and pin.
  • Another participant reminds the original poster that the forum is not a homework service and encourages them to show their efforts.
  • A participant expresses confidence in their solution for part a but struggles with part b, indicating they have calculated a thickness of 12mm for the bar.
  • A later reply critiques the clarity of the original poster's submission and suggests using equilibrium principles to analyze the forces acting on the hinge at C.
  • The original poster questions whether their answer of 12mm is incorrect, indicating uncertainty about their calculations.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the correctness of the original poster's calculations, particularly regarding the thickness of the bar and the approach to solving part b. Multiple viewpoints and suggestions are presented without resolution.

Contextual Notes

There are indications of missing assumptions and potential confusion regarding the notation used in the problem. The original poster's calculations and the method for determining the pin's diameter remain unresolved.

Mechanical94
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A boom AC is supported by a rectangular steel bar BD, and it is attached to a bracket at C by a high-strength steel pin. Assume that the pin at B is adequate to sustain the loading applied to it, and that the design critical components are the bar BD and the pin at C. The factor of safety against the failure of BD by yielding in uniaxial tension is 3.0. The factor of safety against a shear failure of the pin at C is 3.3. Determine the required:


a) Thickness, t of the rectangular bar BD, whose width is b; and, b) Diameter, d, of the pin at C.

known data

P = 10 kN,
L = 3 m,
h = 2 m
Bar BD: b = 25 mm,
shear stress = 250 MPa
Pin C: = 400 MPa
 

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In case you missed it when you read the Terms & Conditions, PF is not a homework service. You must put forth some effort in order to receive help.
 
this is my efforts on this question i believe i have part a correct in this however i can't piece together how to do part b in it
 

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Mechanical94 said:
this is my efforts on this question i believe i have part a correct in this however i can't piece together how to do part b in it

That's fairly hard to read. We prefer that you type your work into the forum posts (preferably with Latex, but at least type in the equations). If you could take a closer picture of your figure (or scan it), that would be a help too. Thanks.
 
hopefully these photos are clearer, i got an answer of 12mm for the thickness and cannot get a solution to part b
 

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The dimensions used in your answer don't match with the symbolic notation used in the question. You could try using the property that when a body is acted upon by three forces that are in equilibrium, then they must all meet at one point (otherwise there is a turning moment). You could use that property to determine the force on the hinge at C. Even if you don't do it that way, the method I suggest acts as a check on the method you do use.
 
so my answer of 12mm was incorrect?
 

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