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ttiger2k7
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[PLEASE HELP!] Forces in members of a truss
A barrel vault truss is loaded as shown. Knowing that the length of the bottom chords DF, FH, ..., and QS is 3 ft, determine the force is members IK, JL, and JM.
http://img68.imageshack.us/img68/4817/fyjfhjfgjhfghgx8.jpg
Sum of y-components
[tex]\sum F_{x} = 0[/tex]
x-components
[tex]\sum F_{y} = 0[/tex]
Moment
[tex]\sum M = 0[/tex]
First I did a free body diagram of the entire truss, which gave me three unknowns tosolve for first.
http://img392.imageshack.us/img392/9493/fyjfhjfgjhfgh1ur3.jpg
[tex]\sum F_{x} = 0:[/tex]
[tex]A_{x} = 0[/tex]
[tex]\sum F_{y} = 0:[/tex]
[tex]A_{x} = (1+1.5+1.5+1+1.5+1.5+1) = A_{y} + V_{y}[/tex]
[tex] 9 kips = A_{y} + V_{y} [/tex] ---- (1)
Solving for Moment about A
[tex]\sum M_{a} = 0:[/tex]
[tex]V_{y} (18) = (1.5)(3) + (1.5)(6) + (1)(9) + (1.5)(12) + (1.5)(15) + (1)(18) =[/tex]
[tex]V_{y} = 4.5 kips [/tex] ----- (2)
Then plugging equation (2) into equation (1) I get
[tex]A_{y} = 4.5[/tex]
Then I get stuck. I know I need to pass a section through the truss so I can get two portions, with each including the desired members I am solving for. Then I just draw a FBD and solve for no more than three unknowns.
Homework Statement
A barrel vault truss is loaded as shown. Knowing that the length of the bottom chords DF, FH, ..., and QS is 3 ft, determine the force is members IK, JL, and JM.
http://img68.imageshack.us/img68/4817/fyjfhjfgjhfghgx8.jpg
Homework Equations
Sum of y-components
[tex]\sum F_{x} = 0[/tex]
x-components
[tex]\sum F_{y} = 0[/tex]
Moment
[tex]\sum M = 0[/tex]
The Attempt at a Solution
First I did a free body diagram of the entire truss, which gave me three unknowns tosolve for first.
http://img392.imageshack.us/img392/9493/fyjfhjfgjhfgh1ur3.jpg
[tex]\sum F_{x} = 0:[/tex]
[tex]A_{x} = 0[/tex]
[tex]\sum F_{y} = 0:[/tex]
[tex]A_{x} = (1+1.5+1.5+1+1.5+1.5+1) = A_{y} + V_{y}[/tex]
[tex] 9 kips = A_{y} + V_{y} [/tex] ---- (1)
Solving for Moment about A
[tex]\sum M_{a} = 0:[/tex]
[tex]V_{y} (18) = (1.5)(3) + (1.5)(6) + (1)(9) + (1.5)(12) + (1.5)(15) + (1)(18) =[/tex]
[tex]V_{y} = 4.5 kips [/tex] ----- (2)
Then plugging equation (2) into equation (1) I get
[tex]A_{y} = 4.5[/tex]
Then I get stuck. I know I need to pass a section through the truss so I can get two portions, with each including the desired members I am solving for. Then I just draw a FBD and solve for no more than three unknowns.
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