Finding the force exerted on a truss

In summary: So in your final answer, make sure you include a negative sign to indicate the direction is opposite to what you calculated."In summary, The solution to finding the force exerted on member ABCD by the pin at B in figure P4.162 involves using a free body diagram of bars BF and CE, with three unknowns (B_x, B_y, and C), and three equations. The force in bar CE is assumed to be axial and can be either in tension or compression, with the direction being determined by assuming a direction and checking for a negative value in the solution. The final answer should include a negative sign to indicate the opposite direction of the force calculated."
  • #1
Patdon10
85
0

Homework Statement


Find the Force exerted on member ABCD by the pin at B in figure P4.162 (figure is attached)


The Attempt at a Solution


This is also attached. As you can see I solved for everything I could. If I could solve for just one more unknown, I could solve the problem. I just don't see where I could possibly solve for any of them. Can anyone nudge me in the right direction?
 

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  • #2
Patdon10: Hint: Let your free body be bars BF and CE. The unknown external forces on this free body occur at points B and C. This free body has three equations, and three unknowns. You know the force in bar CE is axial.
 
  • #3
What are the 3 unknowns? B_x, B_y, and then just C?
 
  • #4
Yes.
 
  • #5
I'm having trouble getting a grasp on this, how do I know what direction C points in?
 
  • #6
You don't (or you do not need to know). However, you do know C is an axial force, like I said. Regarding whether it is tension or compression, you just assume a direction. Then if its numeric value, in the solution, comes out negative, you know you drew it backwards.
 
  • #7
But what direction would it be? What are my options? because the pin connects to truss AD, does the direction have to go along that truss? or is it along it's own truss - meaning it would simply be up or down.
 
  • #8
F_x = B_x - 1000 = 0
B_x = 1000N

Summation of Fy = B_y - C = 0
B_y = C

M_B = (-0.25)C + (0.73)(1000) = 0
C = B_y = 2920 N

Am I understanding this correctly?
 
  • #9
"The force in bar CE is axial" means the force in bar CE is along (parallel to) bar CE. It is also explained in post https://www.physicsforums.com/showthread.php?t=484381#post3211259".

Your solution in post 8 looks good, except you rounded too much. Generally always maintain at least four significant digits throughout all your intermediate calculations, then round only the final answer to three significant digits.

Keep in mind, you found the force bar AD exerts on bar BF. The question in post 1 asks for the force bar BF exerts on bar AD, which is the opposite.
 
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FAQ: Finding the force exerted on a truss

What is a truss and how does it work?

A truss is a structure composed of interconnected beams or bars used to support weight and resist external forces. It works by distributing the weight and forces evenly across all its members, allowing for a stable and strong structure.

How is the force exerted on a truss calculated?

The force exerted on a truss can be calculated using the principles of statics, which involves analyzing the forces acting on each member of the truss and applying the equations of equilibrium. This allows for the determination of the internal forces in each member and the overall force exerted on the truss.

What factors affect the force exerted on a truss?

The force exerted on a truss is primarily influenced by the load placed on the truss, the geometry of the truss, and the support conditions. The type and direction of the load, as well as the length and angles of the truss members, all play a role in determining the force exerted on the truss.

How does the location of the applied load affect the force exerted on a truss?

The location of the applied load can greatly impact the force exerted on a truss. Placing the load closer to the supports will result in a smaller force exerted on the truss, while placing the load closer to the center of the truss will result in a larger force. This is due to the principles of moments and the distribution of forces within the truss.

How can the force exerted on a truss be optimized?

The force exerted on a truss can be optimized by carefully considering the design and placement of the truss members. By choosing appropriate member lengths and angles, as well as positioning the truss supports strategically, the force exerted on the truss can be reduced and the overall stability and strength can be improved.

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