Balsa Bridge Design

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If  a person needs to build a balsa wood bridge over a ten-inch span, then the person would need a minimum bridge length of at least eleven inches.  The height of a balsa wood bridge usually corresponds to its length.  For every six inches of a bridge’s length, the bridge will need to be one inch in height.  When deciding the height of a balsa wood bridge, there has to be a balance between the upper, lower, and middle beams.  When the bridge is made taller, then the upper and lower beams become lighter; however, the middle beams of the bridge must be made bigger to compensate the new height.  The increase in height also decreases the load of the bridge, and when the load is decreased, then the bridge can be taller.  For a bridge that is at least eleven inches long, then it needs to be at least one-and-a-half inches tall.

Ten twenty-four inch pieces will not be enough to build the bridge.  For my design four of the pieces will be used for the upper and lower parts of the bridge.  The connections at each point of the top beams connect to the bottom beams at two points.  Therefore, it is unlikely that my bridge design will be able to be completed with just ten pieces of balsa wood.

In a top truss design the balsa bridge becomes taller, with the base acting as a support.  This means the bridge can be lighter with the base still retaining its strength.  With a bottom truss design, the bridge is weighted down by all of the trusses that reach downward.  The bottom design is not as efficient because the bridge is more weighted and has the greater possibility of becoming unstable.

                                                          

 

 

 

http://www.garrettsbridges.com/design/bridge-height/

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