# Homework Help: Load on Bridge Trusses for Intro to Engineering

1. Apr 18, 2012

### tempneff

1. The problem statement, all variables and given/known data

Calculate the load on each member

2. Relevant equations

$$\sum \tau=0$$ -because it isn't rotating.
$$\sum F =0$$ - because it isn't moving.
$$\tau = Fd\sin \theta$$ - to take the torque at any point

3. The attempt at a solution
I can calculate the torques at each point. I understand that the sums must equal zero. I understand the the concepts of tension and compression and how to get them from the forces at each point.

I have some kind of mental block where I cannot for the love of all that is good and holy relate all that I do understand to the forces at each point.

2. Apr 19, 2012

### PhanthomJay

You can solve for the unknown right support reaction by summing torques = 0 about the left support.
You can solve for the unknown left support reaction by summing torques = 0 about the right support.

You can check your work by making sure that the sum of the reaction forces equals the applied load.

Or you can find the support reactions just from symmetry.

Once you get those reactions, isolate each joint separately , starting at the left support. The sum of forces in the x and y directions must equal 0 at each joint. In a truss, the resultant member forces act along the the direction of the member. Gooooogle on "Method of Joints", for the love of all that is good and holy