A3-O'Callaghan

Free Body Diagram:

Calculations:

Finished Diagram with Forces:

Bridge Designer Analysis of Given Truss:

          Based on the numbers I got through my calculations and then the numbers Bridge Designer gave me, I can honestly say I am a little confused.  My numbers are very similar but not exact, which tells me that I don’t have a different ratio, especially because my top member piece also has a compression of 15 pounds.  My guess is that they used the angle of 60 degrees in Bridge Designer whereas as I used 53.13 degrees and that is why our numbers are slightly different.  I thought I would have to use a scaling technique and match up the ratios, but it has not turned out that way.  

Bridge Designer of Our Bridge:

          Bridge Designer would not let us replicate our actual bridge.  Our bridge does not follow the rule: members +3 =2* nodes.  In order to be able to resemble our bridge somewhat, I made the bridge shorter and it is missing two important members than run vertically on the left sides of the two center squares.  In doing this, I’m not sure how much is different compared to our actual K’nex bridge.  I also don’t know now that these ratios will be correct if we apply them to our own bridge.  I am hoping that these numbers actually somewhat depict how our bridge behaves or else it will not be very helpful.   However, this is a twenty pound load, and if I used the same method that I used for the other bridge, these forces would be pretty accurate.  All of these members are connected in 45 degree angles and I feel like Bridge Designer has an accurate display of what the forces would be on our K’nex bridge if it looked exactly like this.  

         This type of analysis could be helpful when building our K’nex bridge.  I might think about following the rule of member pieces to nodes that Bridge Designer requires.  Also, using the testing information about K’nex joints, I have decided that I definitely want to use as many pieces as possible in a single connector.  It has the highest pull out load and this could potentially increase our cost to load ratio significantly.   This also makes me think that we don’t want to use nodes that have a lot of spots for members to attach to them.  If we did put members everywhere they can attach, our bridge would become extremely expensive.