# First Bridge build W Balsa wood **PICS**



## navihawk (Jun 10, 2012)

It is nothing fancy but I had fun doing it and learned a lot. I also identified some mistakes that I made and now I will know what not to do for my next bridge build. I am pretty impressed with the bridge strength though. I suspended a 3 gallon bucket of water (25 LBS) from the middle of the bridge and it had zero deflection. For the weight of my trains this was 20% heavier than my worst case scenario. I was afraid to add any more water because if it broke then all of that work would go to waste but I know it can hold at least that much. Maybe more though but I wasn’t willing to risk breaking it. The Bridge spans 8 ft. and is connected with glue at all joints (Elmer’s Wood Glue). I actually tested tite bond II and Elmer’s wood glue by gluing two balsa wood sticks end with each glue type. Then once they dried, I hung weights from them at 6" away from the joint. Elmer’s joint broke at 22 LBS or 132 (In-LB). The tite-bond joint broke at 13 LBS or (78 In-LB). I was very surprised by this as tite-bond is what most balsa wood bridge builders swear by. In the cross members (top and bottom) I used very small screws and glue. 

Total time to build was about 13 hours but I had to stretch it out over 6 days. I found that after you add three or 4 sets of trusses, you need to let everything dry before you move any further. I kept getting movement out of the previously installed beams. I slapped some cheapo Ace Hardware spray-paint on it although now I wish I would have painted it black but I am very happy with its appearance. 

Later I am going to add some LED lights to the top and bottom. Then I will mount it on the wall to carry the layout I have running around my celling.


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## navihawk (Jun 10, 2012)

Well for some reason the pictures won't work in this forum. I've tried everything I can think of and even read up on the picture sizes in the FAQ section. So I'll just post direct links.

http://i46.photobucket.com/albums/f...te46-1.jpg

http://i46.photobucket.com/albums/f...lete40.jpg

http://i46.photobucket.com/albums/f...lete38.jpg

http://i46.photobucket.com/albums/f...lete28.jpg

http://i46.photobucket.com/albums/f...lete21.jpg

http://i46.photobucket.com/albums/f...plete8.jpg


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## SteveC (Jan 2, 2008)

navihawk

On including images in your replies you might want to review FAQ - As a Standard Member how do I use the Rich-text/HTML Editor? - Including Pictures in Your Replies: Section[/b]


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## vsmith (Jan 2, 2008)

Nicw, but when you hang it will it get attached to the track support or will this be self suspended? I ask because LS trains are heavy and balsa while good in compression can be tricky in tension. Be a shame to have a train come thru the bottom of it.


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## navihawk (Jun 10, 2012)

Hi vsmith,

It will be self-supporting and will not use track support to hold itself up. It is capable of holding the weight of three FA's + the weight of 4 more cars running across it at the same time. I suspended two times that amount of weight that it would ever experience in real life from the center of the bridge and it held with ZERO deflection. I used the tensile strength of the balsa wood and compared it to the amount of stress being derived within this project by using stress = Force/Area. I then designed it around a factor of safety of two. I used enough trusses that axial loaded tension would be effectively redistributed through the structure. It is still holding in a static model with an Aristocraft E-8 and two NYC Heavyweight Pullmans in my office. It would never last outside in the weather. Since it is used indoors I have no worries about its strength but doubt it would last outside more than a year.


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## cubythewater (Jan 14, 2008)

Looks great! Did you use any bridge design software, or did you freehand your design?


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## Garratt (Sep 15, 2012)

navihawk,

Posting photos from photobucket, right click->Copy Image then in anything except the Quick Reply editor, right click->Paste. 
No need to have the frontal lobotomy reading the 'how to do it' section.









How to post photos (the easy way) - Non 1st Class Members 

Andrew


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