Articulating Wood bridge
Intro
The main purpose of this project is to design, build, and test a bridge made out of balsa wood and glue in about nine months. The motivation behind this project is that there are many bridges across the United States that need to be prepared. Bridges are a critical part of the transportation industry that helps people cross rivers, canyons, gorges, and rough terrain. Since they are designed to go across these terrains, they are very successful at it. While building this bridge for the project, it must complete the different tasks shown below to be considered a successful build.
​
The task that needs to be fulfilled are:
1. The bridge must hold at least 20kg at its weakest point and deflect as much as 25mm.
2. The bridge must be longer than 400 mm long but no longer than 450mm, and 40mm wide.
3. The bridge must not weigh more than 85g of balsa wood and glue.
4. The pieces of wood that are used for the supports can be more than 30mm wide, and 100mm long.
5. The lifting mechanism must be able to lift the bridge with 10 grams of force and allow a piece of paper to slide underneath it.
6. The bridge must hold a 20 kg load and deflect as most 12.7mm.
7. When building the bridge, the only materials allowed for the body and supports are balsa wood and glue.
8. The bridge must allow a 100 mm long object to pass along the 400 mm bridge without it causing the bridge to collapse.
9. The midsection of the bridge must rise a least 140 mm and maintain it above its original starting point for at least 10 seconds.
10. When the midsection of the bridge starts to rise, it should take no more than 55 seconds to rise and close completely.
11. Must allow a 32mm by 25mm block to pass through on the bridge.
12. The Bridge must be supported only by the two abutments when achieving the other task.
Fig1: Current design of the bridge
Fig 2: Original design of the bridge
Results
After completing the tests, the bridge passed almost all of the tests but one. Table 1 shows the results of the time test. In this test, it was to see if the bridge can raise to 140mm, hold for 10 seconds, and lower to the original position within 60 seconds. According to the table, it took on average of 33.3 seconds to complete the cycle and at an average height of 141.4mm.
The second test, it was tested the torque of the lifting mechanism. This was seeing if the lifting mechanism can move the bridge with a 10 grams force acting upon it. to show that the bridge was lifted a piece of paper was able to slide underneath the bridge with it applied. Table 2 shows the results of 6 trials while Figure 5 shows the trend of it. According to the data, it was able to lift the bridge from 10 grams all the way down to the predicted 7 grams. Trials 5 and 6 were to make sure that the predicted value was true and that the bridge did not move enough to allow the piece of paper to fit underneath it.
​
For the final test was the failure test. this was mainly testing for two criteria of the bridge. the first being that the bridge can hold the 20 kg force acting upon it. While the second criterion was seeing if the bridge will not deflect more than 12.5mm. Table 3 shows the data from this test. This test was the only test that failed. The bridge collapsed at 10.5kg of force acting upon the bridge.
​
Overall, the bridge was able to meet all but one criterion. Even with one of the tests failing, the overall success of the bridge was great. Tt was with in the time frame of that was needed to complete one cycle. The lifting mechanism was designed well enough to allow the bridge to rise with ease. the only part that was not a success was the failure test. This was due to a design flaw of the bridge deck not having support to deflect the force acting upon it. As for the results of these tests, they are accurate and precise due to the multiple trials that were done to see what the average was. These tests are also repeatable due to the common items and procedures that were in place.
Table 1: Results for Time Test
Table 2: Results for Torque Test
Figure 5: Results for Torque Test Chart
