PT1.3 - Construction of Bridge

Design rationale


General design 









We are doing a truss bridge for our project. Truss bridges can easily hold up weight but are really heavy due to the amount of materials used. Hence, we have to watch out the number of ice cream sticks we are using to prevent our bridge from becoming too heavy. 


Our bridge consists of a through truss (above the bridge) and a deck truss (below the bridge). Having two trusses, makes the bridge stronger but heavier. This can decrease our efficiency if the bridge is unable to hold a lot of weight. 




Members

The ice cream sticks are arranged in triangles to create a strong structure that transfers the weight from a single point to other areas of the bridge.

A single beam/ ice cream stick undergoes compression and tension.The very top of the beam gets the most compression and the very bottom of the beam experience the most tension. The middle of the beam experiences very little compression and tension.




Base of the bridge

We made a plank for our base but it has some gaps. We feel that by making the base flat like a plank, it increases the bridge's stability. The bridge is 1.2 cm thick and the sides of the main plank is in between 2 ice cream sticks to make it more stable. The ends of the bridge has lesser support than the ends. We also place ice creams sticks in the centre of the base to increase stability.





Anchors of bridge

The ends of our bridge are the anchors of the bridge. The bridge is resting on the platform and we plan to have 2 cm of sticks on each end of the bridge. We think that 2 cm of sticks is sufficient for the anchor of the bridge. If the anchors are too short or just nice, the bridge will not be able to withstand the load. When we placed our bridge on the platform, 4 members of the deck truss (diagonal pieces) were in contact with the platform. We feel that these 4 members will experience a lot of pressure and break when the load is place. Hence, we removed the diagonal members to let the bridge rest on its anchors instead.


Joints of bridge 

We used glue as our joints since it is the only thing we can use to make the bridge. In order to connect the ice cream sticks together, we spread the glue on the flat side of the stick. This makes the bridge stable. If we apply too much glue, the mass of the bridge increases. 


References

(n.d.). Retrieved February 10, 2016, from http://science.howstuffworks.com/engineering/civil/bridge4.htm

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