A3: Fitzpatrick

1) Calculations of forces in the truss members using the Method of Joints

Truss bridge being used in calculations



The figure above shows the calculations neccessary to obtain all of the forces on the truss. They are place into an Excel doc for easy accessibility 

2) Truss analysis results

Note that the forces are equally and evenly spread across the bridge



 3) Truss analysis via Bridge Designer

4) In order for the forces on Bridge Designer to match the forces from the method of joints, one must correctly scale the bridges to the same size. If either bridge is longer or shorter than the pther in any way, the results are not going to be the same, because they are simply different bridges

5)

Once again, if this bridge in Bridge Designer is scaled exactly the same as out Knex bridge, the forces on each of the members should be near equal. If the design has been sone correctly, the forces from one side should be symmetrically equal to the forces on the opposite side. While this is usually true, something must have happened when creating this bridge in Bridge Designer, because it continues to show a force of zero on one section of the bridge, which cannot be possible while under a load from the center of the bridge.



6) The method of joints analysis is a good way to maually determine an idea for a load capacity for a bridge. breaking the desgin down into single specific pieces gives one a better chance at not making a mistake. One of the most vital things we can do to assure a better bridge is to use gusset plates with at least 3 joints on them. These joints are stronger than all the others when it comes to the load testing. While these are more epensive than other joints, they are well worth it in the long run. This program is  help when it comes to doing this.