A3 - WETZEL

Truss Overview:

Free Body Diagram & Calculations:

Replication of Analysis in Bridge Designer:

In order to make the results of the hand analysis correspond to the online Bridge Designer program, some simple scaling was used. While using Bridge Designer, I mentally set each grid square to be 3"x3". Because my bridge constraints set the bridge length to be 36", that meant 18 squares on the grid would correspond to the length of my hand-drawn bridge. The height, needing to be 10", I scaled at about 3.3 squares on the Bridge Designer grid. This enabled me to use Bridge Designer to see if my own calculations were right about this bridge by creating angles similar to the ones I used. As long as the triangles composing my bridges corresponded, the tension and compression forces would also correspond. I was happy to see that the results calculated by Bridge Designer were very closely related to the results I'd calculated myself.


Knex Bridge Designer Analysis:

Just as I've done for the hand and computer analyses of the small bridge, I've now designed the Knex bridge using the Bridge Designer program. In order to scale the draft's calculations to the actual bridge, I will need to measure the actual bridge and set a value for each square on the grid in the program. After we test the bridge and see the weight it fails under, I will be able to scale the real load with the one I've used in the designer to determine the stress on the Knex bridge when it is holding a specific load.

Given the testing information about Knex joints, I might use this analysis as a guideline for the Knex bridge. I can say that, theoretically--and based on the computations of the Bridge Designer--the bridge will be able to hold x amount of weight when there are y joints. But if I optimize the strength of the joints by having more chords meet in a single joint, the bridge should be able to hold more than the program suggests. The testing information about Knex shows that a joint is stronger when more member meet at it. At the same time, the Bridge Designer's unique formula "members + 3 = 2*nodes" leads users to do the same thing: have multiple members meet at a single node. By following this pattern, my group and I should be able to increase the strength of our bridge enough for the cost to strength ratio to benefit from the modifications.