A1: Miller

Design Goal:

The West Point Bridge Design competition is about creating a sturdy bridge at the lowest cost. In the real world bridges need to be made safe but yet as cheap as possible to fit the budget. My goal was to build a bridge spanning a 24meter gap as cheaply as possible without it breaking during a load test. The load test simulates a truck driving across the bridge. In order to do this I will pick a series of trusses to support the bridge. Each individual part of a truss will be examined to see if it is stressed by tension or compression forces. A solid bar is stronger against tension forces and hollow tubes are stronger against compression forces. It is also important to try to make each piece as small as possible. This is able to be done by getting the force on each piece as close to one as possible. At one the piece will break.

2-D Drawing:

Truck Test in the Middle of the Bridge:

Load Test Results:

Changes to the Bridge During Design:

During the designing of the bridge several changes were made. I adjusted the sizes of each piece according the the forces acting on them. I also changed the center truss section. Originally I had a connection point in the center of the square at the middle with 4 small bars coming out from it to each corner. I found it was cheaper to replace this with 2 bars instead. I like to design the trusses on the bottom and I tried putting an "X" shape in the center of each square as the bracing. I found that a small vertical piece from the roadway to the center of the "X" helped tremendously with the support of the roadway.

Bridge Design Cost:

The bridge I designed costs $222,377.07. I believe this is a pretty good price for a bridge of this size. Some design changes in the truss system would possibly be able to lower this cost. I think it would be possible to design a bridge under $220,000 with additional time and truss analysis.

What I've Learned:

Using WPBD has allowed me to see how trusses can be analyzed and how different pieces are affected by the dead and live load the bridge bears. I learned that it is important to get a working bridge before I start to modify the sizes of braces and structural pieces. It is easy to increase the cost of the bridge. I found simple truss systems work well and are cost efficient. In another design I would like to try new building materials for pieces to see if I can use different materials to help lower the cost as well.