Having trouble calculating reaction forces for this truss.

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SUMMARY

This discussion focuses on calculating reaction forces for a statically determinate truss. Participants emphasize the necessity of using the correct number of equations of static equilibrium, specifically ΣFx=0, ΣFy=0, and ΣM=0, to solve for the reactions. The confusion arises from attempting to calculate four reactions with only two equations, highlighting the importance of understanding the relationship between joints, members, and reactions in truss analysis. Clear communication and legible diagrams are also crucial for effective problem-solving.

PREREQUISITES
  • Understanding of static equilibrium equations: ΣFx=0, ΣFy=0, ΣM=0
  • Knowledge of truss structures and their components (joints, members, reactions)
  • Familiarity with the concept of statically determinate vs. statically indeterminate structures
  • Ability to create and interpret free-body diagrams
NEXT STEPS
  • Study the principles of truss analysis using the method of joints
  • Learn about the differences between statically determinate and statically indeterminate structures
  • Practice solving problems involving reaction forces in trusses with various loading conditions
  • Explore the use of software tools for structural analysis, such as SAP2000 or ANSYS
USEFUL FOR

Engineering students, structural engineers, and anyone involved in analyzing truss systems will benefit from this discussion, particularly those seeking to improve their understanding of static equilibrium in structural analysis.

Comfy
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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
 

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Comfy said:

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:
 
SteamKing said:
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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Comfy said:
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.
 
SteamKing said:
What makes you think this truss is statically determinate? You're still trying to calculate four reactions using only two equations of statics.
I
SteamKing said:
What makes you think this
SteamKing said:
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
 
Comfy said:
I

I have 4 equations Sum of forces in y direction and the
Your last post came out garbled. Can you repeat?
 
SteamKing said:
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?
 
Comfy said:
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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