By working on this project for Engineering 209, Bonnie and I were able to use methods and other techniques that we were taught in class to calculate the forces that are applied to the pins when an object with a weight of 20 pounds is placed in it.  We also used other Engineering classes such as EGR 101 AutoCAD and EGR 103 MathCAD to make our project as complete as possible.  We used AutoCAD to draw the assembly drawing, the dimension drawing, and the free-body diagram.  We used MathCAD to create our force analysis.

In order to do our force analysis we assumed that the chair was pinned to the ground by the back leg and we also assumed that the front leg had a roller under it.  This allowed us to take a moment about the back leg to solve for the forces.  The forces in the x-direction are all equal to each other because there is no applied horizontal force.  We can determine this because we know that the chair has no moving parts, therefore it must be in equilibrium.

Determining the stresses of the chair was very interesting.  We picked one screw, that seemed to have the most forces acting on it, and we also picked the front leg, so that we could determine the internal stress of both.  The internal stress of a screw is given by the formula (lambda equals the internal shear stress divided by the area).  We found the value of the internal shear stress by taking the sum of the forces in the x-direction, which gives us the value of the shear stress.  The internal stress for the member (leg) was a little more difficult.  We used the method of bending moments to determine the internal shear stress.