Having trouble calculating reaction forces for this truss.

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  • #2
SteamKing
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Homework Statement


Calculate reaction forces for truss. Truss is attached in picture.

Homework Equations



ΣFx=o
ΣFy=0
ΣM about reaction point=0

The Attempt at a Solution


attached in picture
Unfortunately, the attached images are almost entirely illegible. :frown:

If you want some help, either write out your calculations or post better images. :wink:
 
  • #3
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Unfortunately, the attached images are almost entirely illegible. :frown:

If you want some help, either write out your calculations or post better images. :wink:
This truss is statically determinate now, and should be solvable, right? That is why I don't understand why I am having trouble solving for the support reactions.
 

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  • #4
SteamKing
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This truss is statically determinate now, and should be solvable, right? That is why I don't understand why I am having trouble solving for the support reactions.
What makes you think this truss is statically determinate? You're still trying to calculate four reactions using only two equations of statics.
 
  • #5
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What makes you think this truss is statically determinate? You're still trying to calculate four reactions using only two equations of statics.
I
What makes you think this
What makes you think this truss is statically determinate? You're still trying to calculate four reactions using only two equations of statics.
I have more than 2 equations, I have sum of forces in y and sum of moments about any of the supports. It is statically determinate because 2 (11 joints)=17 members+5 reactions. What do you mean by 2 equations of statics?
truss is statically determinate? You're still trying to calculate four reactions using only two equations of statics.
I have 4 equations Sum of forces in y direction and the
 
  • #6
SteamKing
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I

I have 4 equations Sum of forces in y direction and the
Your last post came out garbled. Can you repeat?
 
  • #7
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Your last post came out garbled. Can you repeat?
I have more than 2 equations, I have sum of forces in y and sum of moments about any of the supports. It is statically determinate because 2 (11 joints)=17 members+5 reactions. What do you mean by 2 equations of statics?
 
  • #8
SteamKing
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I have more than 2 equations, I have sum of forces in y and sum of moments about any of the supports. It is statically determinate because 2 (11 joints)=17 members+5 reactions. What do you mean by 2 equations of statics?
You can write only one equation involving the sum of the forces and one equation summing the moments about one convenient reference point.

You cannot write, for example, one moment equation where you sum moments about point A and another equation where you sum moments about point H.

This beam is statically determinate:


simple-beam-dist-load.png


This beam is statically indeterminate:


upload_2016-5-9_8-26-53.png


Both beams are loaded in a similar fashion, except the latter beam requires an extra equation in addition to the equations of static equilibrium in order to solve for the reactions at the supports. In the case of the latter beam, we must know how the beam deflects under load, and we cannot calculate that unless we know some additional structural details beyond the spacing of the supports.
 

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