Solving Equilateral Truss Force w/ Method of Sections

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SUMMARY

The discussion focuses on solving for the forces in each member of an equilateral truss using the Method of Sections. The user initially attempted to analyze the forces by cutting through members AB and AC, rotating the coordinate system by 30 degrees counterclockwise. However, the calculation for force Fbc was incorrect due to neglecting the contributions from member AB. The correct approach involves drawing to scale and applying equilibrium equations accurately to the free body diagram.

PREREQUISITES
  • Understanding of static equilibrium principles (sum Fy=0, sum Fx=0, sum M=0)
  • Familiarity with the Method of Sections for truss analysis
  • Ability to draw free body diagrams accurately
  • Knowledge of vector components and trigonometric functions
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  • Study the Method of Sections in detail for truss analysis
  • Learn how to accurately draw and interpret free body diagrams
  • Practice solving truss problems using static equilibrium equations
  • Explore the effects of member contributions in truss systems
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Engineering students, structural analysts, and anyone involved in civil engineering or mechanical design who needs to understand truss force analysis.

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Homework Statement



Find the force in each member of an equilateral truss. See figure.

Homework Equations



sum Fy=0
sum Fx=0
sum M=0

The Attempt at a Solution



first of all i tryed to cut through AB and AC and i off set the X/Y axis by rotating 30 degrees CCW then i did,

0=Fbc-735cos60

i thought i would get the right answer for Fbc but it is wrong.
Any thoughts?
 

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First of all, try always to draw to scale, in order to avoid distorting the problem. Secondly, when you make a cut, as you have done, replace the cut ends with the forces that are "exposed", in direction if you don't know the magnitude. Then make equilibrium statements about the free body diagram that results, with all the horizontal and vertical components if necessary. In this case, are you able to sketch the triangle of forces at B, more or less to scale? The equation you attempted ignored the contribution from BC.
 
Sorry, that last sentence should have said "The equation you attempted ignored the contribution from AB.
 

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