A3: Miller

1) Calculations of forces for the truss members using the Method of Joints.

Truss Bridge used for the Method of Joints

This shot shows the calculations done in excel to determine the forces on each member.

2) Results of Analysis
Forces Acting on Each Member

Members symmetrical to one another have the tension and compression force acting upon them.

3) Replication of Bridge Analysis done in Bridge Designer

4) In order for the hand analysis to show the same results as the Bridge Designer calculations the bridge must be scaled to the same size.  In Bridge Designer each individual square is 2"x2".  The drawing that I did in the Bridge Designer does not have the same lengths as the hand drawn one I did the calculations for.  It does however have very similar results.

5)

The forces in the KNEX bridge will be fairly similar to the forces calculated by the bridge designer analysis.  The member lengths are a little different and there are less sections than the real bridge.  The forces felt by the 2 middle sections should be relatively realistic when compared to the KNEX bridge.  The 2 outside sections are showing unrealistic numbers.  While this is not the full bridge formation it should give us the general idea we need to help improve our bridge design.

6) Using the method of joints analysis allows the determination of tension and compression on individual members of a bridge for a given load.  Using this information it is possible to apply the KNEX connection strenghts to determine a failing load for the bridge.  The connectors with 3 members attached to them have the highest pull out force at an average of 35.6lbs.  Connectors with only 2 members attached suffer almost a 10lbs. decrease in strength which leaves them at 26.5lbs.  The weakest attachment to a connector is 1 member.  The pull out force for this is 20.7lbs.  With this data it is obvious that connectors should be loaded with at least 3 members to assure the highest pull out force.  There is also a possibility to determine pieces that are not giving the bridge any structural support by analyzing the results of calculations and using the pull out test information.  These pieces can be removed to decrease cost.