Analysis of Structures (Method of Sections)

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Discussion Overview

The discussion revolves around the application of the method of sections to analyze forces in specific members of a roof truss. Participants are addressing a homework problem that involves determining the forces in members BD, CD, and CE, while also considering reactions at supports.

Discussion Character

  • Homework-related
  • Technical explanation

Main Points Raised

  • One participant describes their approach, assuming a reaction at point F and attempting to take moments to eliminate that reaction from their calculations.
  • The same participant expresses uncertainty about their assumption regarding the reaction at F and mentions difficulties in finding unknown forces.
  • Another participant suggests that the reactions at points A and F should be calculated first by summing forces in the x direction and taking moments about one of the reactions.
  • Multiple participants note that the link to the diagram is broken, which may hinder the analysis.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the best approach to solve the problem, and there are differing opinions on the necessity of calculating reactions before proceeding with the method of sections.

Contextual Notes

There is a lack of clarity due to the broken diagram link, which may limit the ability to visualize the truss and fully engage with the problem. Additionally, the assumptions regarding reactions at point F remain unresolved.

timeforplanb
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Homework Statement


Using the method of sections, determine the force in members BD, CD, and CE of the roof truss shown in the figure
truss.jpg

(the red line is the cutting plane and the green arrows are my assumed directions of the unknown forces)

Homework Equations


summation of moments=0
summation of horizontal forces=0
summation of vertical forces=0

The Attempt at a Solution


i assumed there's a reaction at F (upward), and since i didn't know its value i tried taking the moments at pt. F, N, O to make that reaction disappear. But so far, it doesn't seem like i'll be getting any unknown force anytime soon. please help! am i wrong with my assumption that there's a reaction at F? and also, i tried assuming that there's no reaction at F but i still can't find any unknown force at all.
 
Last edited:
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The link to your diagram is broken.
 
SteamKing said:
The link to your diagram is broken.

looks okay to me.
 
The reactions at A and F should be solved first, by looking at the entire truss and summing forces in x direction = 0 and summing moments about one of the reactions to get the other reaction, etc.
 

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