Comments on: Bridge Joints

By: Alex

Alex — Sun, 27 Nov 2011 08:44:37 +0000

What did you mean when he said “Yes, the sandwich would be stronger than just 1 lap joint. Two chords at the top would not be overkill, but two chords at the bottom might be. This is because the top chord is in compression and the bottom chord is in tension.”

By: tosy

tosy — Sat, 15 Oct 2011 21:35:00 +0000

How do you get the wood to bend?

By: Dylan

Dylan — Wed, 07 Sep 2011 15:37:00 +0000

Just need to know, will this work with towers because I’m making one and I think that the pressure is distributed differnetly. Also is it possible for you to post a picture where a lap joint was actually incorporated into the structure.

By: Garrett Boon

Garrett Boon — Wed, 20 Apr 2011 19:28:00 +0000

Please see my Glue Tips page:
http://www.garrettsbridges.com/building/gluetips/

By: Garrett Boon

Garrett Boon — Tue, 12 Apr 2011 14:08:00 +0000

So you are only allowed to use two pieces of wood for the top chord. Hmm. That takes out the easy way to make your bridge stronger. I’d say to go ahead with your idea.

By: Dombiggers

Dombiggers — Tue, 12 Apr 2011 00:35:00 +0000

Thank you for getting back to me. No, we don’t have a limit on the wieght, However the project must meet a 25% or less load capacity percentage. The bridge will be loaded from the center of the roadway deck with a hanging hook. wieghts will be added till it breaks. I like your idea of the t shape on top, however we’re only allowed to use 2 pieces of wood. I’m now thinking of using 2 pieces in a t shape for the top cord and sandwich the legs on the bottom cord.I want to hold a 100 lbs.(the record on this project is 80lbs) what do you think?

By: Garrett Boon

Garrett Boon — Sun, 10 Apr 2011 15:41:00 +0000

Yes, the sandwich would be stronger than just 1 lap joint. Two chords at the top would not be overkill, but two chords at the bottom might be. This is because the top chord is in compression and the bottom chord is in tension.

I’d also consider making your top chord into a T shape as well. If you have your sandwich as described, glue another 3/16 x 1/2″ stick flat on top of the top chord. That will greatly increase its lateral strength.

Do you have a weight limit for your bridge? How is it going to be loaded?

By: Dombiggers

Dombiggers — Sun, 10 Apr 2011 02:13:00 +0000

I was wondering if i was to sandwich the legs between to two chords at the top and bottom, glue and pin my joints, would that make my bridge stronger than if i just did 1 cord and a lap conection? would the two chords at the top and bottom be over kill? I’m trying to beat the record (80 lbs hanging at center) in my strutures class in college. all the legs, cords and braceing have to be 3/16 x 1/2″ balsa. i’m thinking of going with the warren truss. we are allow to use pin, glue and gusset conections

By: Ware

Ware — Mon, 21 Mar 2011 23:41:00 +0000

Thanks

By: Garrett Boon

Garrett Boon — Mon, 21 Mar 2011 14:25:00 +0000

I haven’t done a lot with toothpick bridges, but it seems to me that lap joints would be the way to go. I’d think that you would want as much overlap in the joints as you can get because the surface area of toothpicks is not much to begin with. I also think that a toothpick would generally be of a higher density than Balsa. That would mean the face ripping off is less of an issue. Granted, I don’t think that toothpicks are high quality wood and there is probably a mixture of densities.