CIV102 Box Girder Bridge
Task: Design and construct a bridge from matboard and contact cement with the highest weight-to-load ratio
In my first year Structures and Materials course, my team was tasked with designing and constructing a bridge from matboard and contact cement. I applied static structure design knowledge from CIV102 and used prior fabrication experience to bridge the gap between theory and application.
Design objective:
1. High failure load
The competitive project was assigned to my Structures and Materials class as a way to apply our knowledge of box girder bridges. With only a few constraints dealing with the dimensions of the structure, the sole objective was clear: to sustain the greatest static load as possible.
This project is an excellent demonstration of iterative design and effective referencing. With critical stresses of the materials known and equipped with methods and formulae for evaluating these values in each design, we evaluated the strengths and weaknesses of each design. Key points were:
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the material is much stronger under tension than compression, so decided on a double-layered top deck pi beam with the bottom deck left open
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shear strength of the glue is weak, so increasing the area of glued surfaces was critical. In pictures it can be seen that all glued pieces contained folded flaps. Small flap patches were even installed for reinforcement
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shear strength of the material is also quite weak, so we installed several web stiffeners, or diaphrams - 12 in total
We also referred to designs from past years and learned about miscellaneous details we were not taught to consider in lectures:
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the glue takes several days to reach its full strength, so we built the bridge almost a full week before testing
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the supports tend the crush the web, so we installed plates to distribute the load
Iterative design was practiced by reallocating material from components with higher failure loads to the predicted weaker components, as these would be the parts that fail first.
Calculated failure load: 1246N
Failure load: 1206 N
(Best load prediction in class of 300)