Truss Analysis: Find Forces on Members

[FairyChatMan]

Truss Analysis :(

Homework Statement

Find the force on each of the members and tell if it is tension of compression.

Homework Equations

M = fd $$\sum$$Fx and Fy = 0

The Attempt at a Solution

Well, my professor said to us that the first thing to do is to compute for the reactions on the pin. After that, start using Free body diagram on one of the pin, and continue to complete the truss.

Here's what I did...

I set point D as pivot... then
$$\sum$$M = 8A - 16cos55 - 12cos55 = 0
A = 2.0075 N upward

But shouldn't the summation of all forces be zero? By having A = 2.0075 and an unknown Rxn on D (which obviously will point upward), the system won't be in equilibrium because cos35 + 1.5cos35 = 2.0479 N.

Just help me getting the correct Reactions on point A and D and i'll be able to solve this problem.. thanks..

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[pongo38]

How many reaction components are there at A?

 

[PhanthomJay]

Homework Statement

Find the force on each of the members and tell if it is tension of compression.

Homework Equations

M = fd $$\sum$$Fx and Fy = 0

The Attempt at a Solution

Well, my professor said to us that the first thing to do is to compute for the reactions on the pin. After that, start using Free body diagram on one of the pin, and continue to complete the truss.

Here's what I did...

I set point D as pivot... then
$$\sum$$M = 8A - 16cos55 - 12cos55 = 0
A = 2.0075 N upward

that should be M = 16A - ...etc

But shouldn't the summation of all forces be zero? By having A = 2.0075 and an unknown Rxn on D (which obviously will point upward), the system won't be in equilibrium because cos35 + 1.5cos35 = 2.0479 N.

if you sum forces in y direction, A_y -1(sin35) -1.5(sin35) +D_y =0, plug in value for A_y and solve for D_y.

Just help me getting the correct Reactions on point A and D and i'll be able to solve this problem.. thanks..

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looks like you had a math typo, some trig errors,and you missed a variable when summing y forces = 0. You can check your work by summing moments about A to solve for D_y.