Question about Truss Analysis (Statics)

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SUMMARY

The discussion centers on truss analysis in civil engineering, specifically regarding the determination of zero force members in a concurrent 2D force system. The user, Kyle, questions the validity of a solution involving the equilibrium equations Fy = 0 and Fx = 0, particularly concerning the diagonal member T and the connection between joints 8 and 9. Kyle asserts that the equilibrium equations suggest that member 8->9 cannot be zero, indicating a potential error in the teaching assistant's solution. The analysis highlights the importance of correctly identifying zero force members in truss structures.

PREREQUISITES
  • Understanding of truss structures and their components
  • Knowledge of equilibrium equations in statics
  • Familiarity with zero force member identification techniques
  • Basic proficiency in 2D force systems analysis
NEXT STEPS
  • Study the principles of zero force members in truss analysis
  • Learn how to apply equilibrium equations in 2D force systems
  • Explore advanced truss analysis techniques using software tools like SAP2000
  • Review case studies on common mistakes in truss analysis
USEFUL FOR

Civil engineering students, educators in statics, and professionals involved in structural analysis will benefit from this discussion, particularly those focusing on truss design and analysis methodologies.

ktw
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Homework Statement
Whoops.. accidentally wrote everything in the solution box! Please see below.
Relevant Equations
Fx=0, Fy=0
Hi, I am a civil engineering student currently taking Statics. We are doing truss analysis in the class right now; and I know that this joint is marked as correct.
20191101_202114.jpg
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However, I don't see how this is even possible. I begin by considering this a concurrent 2D force system, Fy = 0 & Fx = 0. The equilibrium equation for Fy is -P + (1/√5)√5 * P + (1/√5)T = 0 ; where sin(θ) = (1/√5) and T is the diagonal that is following the line 8->5. I do not understand how the value of T can equal zero and then the member connecting joint 8 to joint 9 can also be zero; considering this would imply that (2/√5)√5P + 0 = 0 using the equilibrium equation Fx = 0. I understand zero force members and I do not think member 8->9 can be visually determined to be zero. Could anyone shed some light on this for me?

Thanks, Kyle
 
Last edited:
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Looking at this closely.. there's no way that the solution is correct. My TA must have been mistaken. Thanks for looking at my question
 

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