Static Bridge
My partner and I were instructed to build a bridge from basswood following the criteria listed below. We had many problems spanning from time constraints to miscommunication, but managed to complete a bridge for destructive testing. Our miscommunication laid in the design of the section of the bridge which holds the loading block. I wanted an I-beam made from two large pieces of basswood and a smaller piece of balsa wood in the middle, but I failed to communicate this to my partner so the design shown below is what we ended up with. Below are the official criteria and constraints from the Pennsylvania Society of Professional Engineers Annual Bridge Building Competition:
Materials:
Our project was much less successful than we had hoped, primarily because 1) our glue was not completely dry as we were crunched for time and 2) the design was not exactly what we were aiming for. l did learn a few things about priorities on the other hand. My partner and I were so focused on the previous assignment (truss testing) that we were behind when it came to bridge building. Ultimately, our project was not a complete failure because the bridge had an efficiency of about 145%, but there are certainly many things we could have done better. Below is a picture of our bridge before testing and a video of the bridge breaking (the video was taken in portrait, but is sideways).
Materials:
- The bridge shall be constructed from basswood sticks with 3/32 inch square cross section, which may be notched, cut or laminated in any manner.
- The bridge shall be constructed using the basswood sticks and glue. Any commonly available glue may be used, but the basswood sticks must very obviously be the major component. (Bridges built primarily of epoxy or other glue with sticks as secondary members are not permitted. Wood bridges encased in epoxy or glue are also not permitted.)
- No materials other than glue or basswood may be used. DO NOT paint the bridge.
- To ensure fairness, it is encouraged that only the materials distributed by the competition director be used to construct the bridge.
- The bridge mass may not be greater than 30 grams (Four quarters plus 3 dimes give a mass of about 30 grams).
- The bridge must span a gap of 300 mm (11-13/16 in).
- The maximum allowable bridge dimensions are:
- i. Length: 450 mm (17-11/16 in)
- ii. Width: 80 mm (3-1/8 in)
- iii. Overall Height: 140mm (5-1/2 in)
- iv. Height from Supports to Deck (Load Point): 40mm (1-9/16 in)
- No part of the bridge may extend below the support surfaces.
- The bridge must allow for mid-span loading as described in section 4.
- A “go/no-go” gauge will be used the day of the competition to determine conformance of a contestant's bridge to the dimensional criteria. Bridges not initially meeting the criteria may be altered for conformance prior to the start of the competition at the student's risk.
Our project was much less successful than we had hoped, primarily because 1) our glue was not completely dry as we were crunched for time and 2) the design was not exactly what we were aiming for. l did learn a few things about priorities on the other hand. My partner and I were so focused on the previous assignment (truss testing) that we were behind when it came to bridge building. Ultimately, our project was not a complete failure because the bridge had an efficiency of about 145%, but there are certainly many things we could have done better. Below is a picture of our bridge before testing and a video of the bridge breaking (the video was taken in portrait, but is sideways).