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Help a Brother Out with Building a Bridge

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JTCasper540_MN
Posts: 742 - Karma: 3,698
Hello NS, I have a project to do and I wanted to ask you guys if you had any input on what i should do, or if you had any tips for me. My project is that I have to build a balsa wood bridge, and I am going to test it with my teacher and partner for its efficiency.

these are basically the rules and what the bridge must have...

1. The bridge must be 30 cm long

2. There must be a road bed which must consist of two pieces of balsa wood which are 2.5 cm apart and has a 5 cm clearance for a hot wheels car to roll across and to hang weight from

3. No vertical supports

4. The wood cannot be treated to change its strength

5. Wood must be bonded together with glue given to us only at joints

6. No splitting or laminating the wood (basically you cannot split the wood or glue it all together to make one board of wood)

So if anyone has any ideas, suggestions or tips please share.
Thanks guys, you're awesome!
Jan 4 2015 4:32PM
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kshaughn
Posts: 509 - Karma: 4,568
My college physics thesis was based on bridges so I might be able to help. I don't know how much balsa wood you will have to use, but I would recommend either a Pratt or Warren (with vertical support) truss bridge. They are pretty easy to build and can support a lot of weight for their size. They are pretty much what all railroad bridges are.


Jan 4 2015 4:42PM
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kshaughn
Posts: 509 - Karma: 4,568
Shit I missed the part where you said no verticals. Definitely go Warren truss then. Mimic my first image but change the pattern of the truss from pratt to warren. Hope that helps.
Jan 4 2015 4:44PM
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JTCasper540_MN
Posts: 742 - Karma: 3,698
kshaughnShit I missed the part where you said no verticals. Definitely go Warren truss then. Mimic my first image but change the pattern of the truss from pratt to warren. Hope that helps.


Everyone, forget number 3, the way it was worded in the packet was a little awkward but I understand it now, and there can be verticals, sorry.
Jan 4 2015 4:49PM
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49566738265
Posts: 0 - Karma: 7,704
Depending on the thickness of your material and your patience, if you can bend the balsa into a semi circle for your main support you can buy a lot of strength without adding material or laminating. Think wagon wheel, and bend slowly moving down the length of the board clamping to a mold. Water will help.

Without seeing what you have in hand, there's not much more to it than trying that or copying a proven bridge design.
Jan 4 2015 4:55PM
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Phil-X-
Posts: 7205 - Karma: 14,399
kshaughnShit I missed the part where you said no verticals. Definitely go Warren truss then. Mimic my first image but change the pattern of the truss from pratt to warren. Hope that helps.


lel i think he meant no vertical piers/piles/towers.

but as someone who's done a little bridge stress analysis and done the whole balsa thing in middle school, he's got it right. The trick to this kinda bridge contest is to make really clean cuts and joints. Use a good amount of adhesive and make sure you don't get air bubbles and shit in there


You could try and figure out some loophole style bridge and rek everyone (in a hand-thrown glider competition I just made a balsa and composite 2.5ft dart which I threw clear across the gym rather then a plane)
Jan 4 2015 5:00PM
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Jump_N_Jib
Posts: 16 - Karma: 5
sounds like a cool project...good luck!
Jan 5 2015 6:11PM
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rigzz
Posts: 1768 - Karma: 147
Love these kind of projects. Show us what you have to work with, it'll be easier for us to help you!
Jan 5 2015 9:46PM
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losh
Posts: 1126 - Karma: 4,695
I love seeing a bunch of threads about like bongs or weed and shot then I click on this and this random group of skiers just knows how to build ducking bridges. I think it's awesome the amount of diversity on this site. BTW show us pics of the finished product.
Jan 5 2015 11:56PM
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cool_name
Posts: 4295 - Karma: 3,131
Just lay the balsa across the gap, and claim cost efficiency because it will be able to support hotwheel cars without any additional bracing, therefore all additional bracing is simply wasted costs

Maybe through some sustainability catch phrases in as well and your saved time from not building a bridge to go skiing
Jan 6 2015 12:10AM
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cool_name
Posts: 4295 - Karma: 3,131
More helpful advice is balsa is strong when going with the grain, but weak when going against it
Jan 6 2015 12:13AM
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msg
Posts: 1108 - Karma: 3,269
these projects were heaps fun cause you got to waste sticks and sticks of hot glue
Jan 6 2015 12:23AM
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JTCasper540_MN
Posts: 742 - Karma: 3,698
here is the finish product...I am very happy with the way the bridge turned out...it weighed 17 grams and held 13.2 kilograms so that is 776 efficiency...it was a little heavier than I expected it to be but it still did really good...I beat a lot of my class mates too! I came in fourth place sooo yeeeah...
Thanks for all of the help guys!!

Jan 18 2015 3:12PM
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