A2 - WETZEL

The goal of my design was to have a low cost and high strength. Never having designed or tested model bridges before beginning this class, my best idea was to use shorter chords as members of the bridge. Although joints each cost at least $1,000, I decided that their use in between short chords would help make the bridge stronger and tighter once weight was added. By tighter, I mean that I am imagining as weight is added to the bridge's load, the chords will push into the joints and the displacement of the joints will be towards the center of the bridge. As the members move towards the center like so, the stronger, shorter chords will lean into the joints, tightening the joint sections.

Elevation and Plan for the Knex bridge design.

I made sure that the web of the truss was composed entirely of triangles--most of which, in my case, happen to be right triangles. I am hoping that these hold up as well as equilateral triangles may have. My prediction is that if the right angle of one triangle does not have support backing it, it will give out before other parts of the bridge. This is something that I will pay close attention to so I know what the best angles are to use as the groups approach the drafting of their final designs. Something I purposely did not do was make the plan of the bridge out of triangles. I figured that the weight-bearing members all ran vertically, so I did not want to add dead weight to the bridge or raise its cost by webbing its ceiling.

The Truss Bill of Materials

I did my best to keep my design simple so that there would be no useless chords or joints in the price, but I am not yet sure that each chord that I've left will make the bridge strong enough. I was both surprised and glad to see that the total cost of my first Knex bridge design was below $200,000--a price I'd been trying to get my bridge down to in West Point Bridge Design.