Analysis of Structures (Method of Sections)

[timeforplanb]

Homework Statement

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

(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.

 

[SteamKing]

The link to your diagram is broken.

 

[timeforplanb]

The link to your diagram is broken.

looks okay to me.

 

[PhanthomJay]

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.