Finding the unknown forces at two supporting pins

  • Thread starter ptguard1
  • Start date
  • #1
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Homework Statement



In a simple truss where P = 8 kip, find the unknown forces D_x, D_y, C_x, and C_y then determine the average normal stress in each member.

Description of truss:

I cannot copy an image due to the source it is coming from, so here is my attempt at a description

A triangle with arms AB (going up and to the right (5 feet)), BD (going down and to the right(5 feet)), and DA (going to the left connecting back with A (8 feet)). Member BE cutting straight down the middle of the triangle (3 feet). Member BC parallel with member ED and equal length of 4 feet. Pins at C and D. The force P is applied downward at point A and the force 0.75P is applied downward at point E.




Homework Equations





The Attempt at a Solution



I know that in a 2D problem you can only have three unknowns to find the forces. I am able to find C_x and D_x to be 29.3 kip (D_x in the negative x direction), but cannot remember how to find the y values.
 

Attachments

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Answers and Replies

  • #2
993
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I am having difficulty downloading the attachament.
 
  • #3
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I went ahead and made a rough sketch on paint
 
  • #4
nvn
Science Advisor
Homework Helper
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ptguard1: The force in truss members is always axial. Therefore, you know C_y = 0.
 
  • #5
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What do you mean by an axial force?
 
  • #6
nvn
Science Advisor
Homework Helper
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ptguard1: The direction of the resultant (i.e., total) force in each truss member is always along the longitudinal centerline of each truss member. A force along the longitudinal centerline of a member is called an axial force.
 
  • #7
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I just discovered that I actually didn't need to find the forces at each pin in order to solve the overall problem, but thank you for the information.
 

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