Week 7

In the past week, we tested our bridge that was constructed in week 5.  The test consisted of suspending a bucket from the bridge and loading sand into the bucket until the bridge failed.  Our bridge had a total of 142 members for a total cost of $216,000.  It was able to hold 21.2 pounds before breaking.  The cost per load ratio was $10,189 per pound.  In the previous week, our bridge design failed under the weight of one battery so we were pleasantly surprised when our new design was able to hold 21.2 pounds.  This week we will begin working on our next bridge design that will span 36".  We are planning on using aspects from our previous design as a starting point for this larger bridge.  We are planning on adding more support members to increase the amount of weight that the bridge can hold.  Our main goal is to have the lowest cost per load ratio.  Our biggest accomplishment this week was testing our 24" bridge and analyzing the results to improve the next design.  We did not encounter any major issues this week.  

It was very helpful to be given the information for compression and tension force/strength ratios in West Point Bridge Designer.  These values would be helpful if they were associated with the Knex that were used.  It would also be useful to know the force on the gusset plates and how much force they could withstand. The gusset plates ere the main source of failure int eh Knex test.  If we knew the load on them, the design could be slightly changed to accomplish the greatest amount of force that can be put on the gusset plates.  It would be very challenging to figure out the force/strength ratios because the tension and compression are not extremely apparent like they were in West Point Bridge Designer.  It would also be hard to measure these forces on Knex.  The force on the gusset plates can be taken into account to find the total force acting on each plate.  It would be more complicated than one simple equation because you have to take into account how each plate puts pressure on the surrounding plates and members.