ALAN LI

Objective: To design and create a beam bridge out of mat board, while maximizing the strength to weight ratio.

 

Criteria and Constraints:

• Must span 990 milimeters. 

• Must be able to support several trains weighing  400N total.

• Must have a track width of 95mm

• Must be made from a single sheet of 40'' x 32'' mat board.

• Strength to weight ratio: higher is better.

 

Iterative Process:

 

One of the key components of the bridge was the column, having to support 80% of the total load. While the design of column was a simple box girder that had an estimated bucking load of 3000N, the implementation of the design using matboard was more difficult.

The first iteration had four sides glued together such that the cross section ressembled a pinwheel. However, the cuts in the mat board were not straight enough and there was insufficient contact area for the glue to hold. The column failed at approximately 200N. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The second iteration was made with an edge cutter tool that cut cleanly at a 45 degree angle, increasing the surface area for glue. This increased the maximum load to over 500N, but still resulted in failure due to glue.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The third and final iteration was made by folding a board three times into a box, and gluing an extra reinforcing  strip along the single glued edge. This third iteration was able to withstand over 1000N, at which point we had no heavier weights.

 

The bridge was ultimately successful in carrying the 400N load, but did not meet its expected failure load of 3000N, as there were flaws in the construction of the main span and web, and we did not have enough material or time to perform a second iteration.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Self-Reflection:

 

This project was the main contribution to the refinement of my design philosophy. It made me realize the importance of iteration, which is necessary regardless of how careful you plan, and it introduced many concepts within civil engineering:

 

The nature of civil engineering is that a lot of it is guess-and-check. For example, in the design of reinforced concrete, the distance between the maximum compressive and tensile forces, 'jd', is required in order to find the amount of steel reinforcement needed. However, the value of 'jd' can only be obtained using the amount of steel  This itself is an iterative process, where you make several assumptions in order to begin calculating, and check with the values obtained at end of calculations that the assumptions are correct. If they are not, the process is repeated.

 

 

 

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