Tags: 16 inch span, 300+ pounds, basswood bridge, fernbank bridge
22,297 views in 2012
Fernbank Project: Strongest Bridge Design
I built this bridge for the 2005 Fernbank Science Center bridge design event. This is the strongest bridge I have ever built. The bridge spanned 16 inches, weighed 37 grams, and held 346 pounds. That puts its efficiency over 4200! I had never even come close to getting this amount of strength out of a bridge design before. I was really surprised. One commenter said, “So if this bridge weighed one pound, it could have held up my car.”
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- The award I received
The first time the bridge was tested it did not break. The testing machine was set to only apply 250 pounds. This bridge was too strong for that! Here is the bridge after the second testing:
The secret of a strong bridge design
As you can see, the bridge stayed mostly intact. I talked to a couple engineers at the event and asked them what they thought made my bridge break. One suggested that the bridge failed in torsion, as I did not have any diagonal braces in the bridge. That is definitely a design flaw I will fix if I do this again. I would love to try and break an efficiency of 5000. That would be a strong bridge indeed!
For more information on this competition, see Atlanta Toothpick Bridge Competition. I encourage anyone in the Atlanta area to try and go to this event. It is free and open to all, both young and old. Try your hand at making the strongest bridge. And when you do, send me photos of your bridge 
I was just curious how you made the “L” shaped bracing at the top of your piece. Did you glue it or cut it out of a solid piece? Awesome design!
in which way was the load applied to the bridge? was it from the top or the bottom?
What is stronger a DECK design or a THROUGH design??
i really like this model……..
Gr8 work guys!!!!!!
umm this iss alll soo cooolll !! i kant belive it held out soo muchh.. im gonan try to make one simliar to this but i have one question…. “what type a bridge is this”?? u noe is it a beam bridge, a suspension bridge,and arch bridge ?? or lyk wuttt … it woud be a greatt HELPPP if u kan answer tht.and give me a few more tipz on this…… plz reply ASAPP !! <3 <3 <3 thannxx
This would be classified as a truss bridge.
I designed the Fernbank Bridge with the idea in mind that it would hold a lot of weight, unlike the SciOly bridges. Therefore, I did some things on this bridge I would not do on a SO bridge. The cross bracing on the bottom was mainly for “insurance”.
Unfortunately I have been out of practice building bridges for long enough that I do not remember how to compare the weight and density of the pieces you mentioned off the top of my head.
I would question your statement that butt joints are better for compression. I would suggest that a gusset or double gusset would be the strongest joint.
Good job with your tech class bridge. That is quite impressive.
i made a bridge out of posicle sticks that held 280 lbs. i dont remember exactly how much it weighed. i do know that it was 40cm long by 10cm wide. it looked very similar to this one though.
Dear Garrett,
We are trying to build a bridge for Science Olympiad Division B. We would appreciate if you could give us some tips on how to successfully glue the pieces on the bridge together with super glue. Also, some tips on how to build a SUCCESSFUL bridge would be nice (:
Thank you!!!!!
We are trying to make a bridge similar to this.
What is stronger… X supports, zigzag supports, or straight horizontal pieces?
Thank you again.
Oh, and how wide was this bridge?
Working on SciOly elevated bridge. Using 1/8 square sticks (1.75-2.0 grams per 36″ length). Joined top and bottom chords with butt to butt joints (also 1/8 square but 1.3 1.5 gr per 36″). Noticed that your bridge has face to face joints. Any thoughts? I know face to face is good for tension but butt to butt is better for compression. If I used face to face I could go with 1/32 stripped to 1/8 widths. Also on diagonal bracing for the top is it necessary to make that an “x” or can you zigzag. That eliminates 1/2 the wood. Looking at your bridge, is there a reason for the cross-bracing on the bottom chord? I made a ten inch bridge in technology class last year and put in the cross-bracing but I glued it on to faces to the top of the chord and side of the upright. It weighed ten grams and held 93 lbs. which is also about 4200 efficiency.
Thanks! That helped a lot
NIce bridge guys!!!!!!
We are making a bridge for our class at West Finchester Memorial Academy of Engineering- New England
wow i am building a bridge for a university project and this design has helped to an extent amount
Hey Garret,
Im new to this so can u tell me how tall this bridge is. I’m doing a similar bridge for SciOly
and would love any pointers.
Thanks
I am pretty sure this bridge was 4 inches tall.
I”m not trying to be mean ,but this is not what I’m looking for Garrett although nice pictures.
Aniaya, what are you looking for?
im testing a 30, 45, 60, and 75 degree bridges. They are just truss bridges made up of a bunch of different angles. what would hold the most weight? also tell me the 2, 3, and 4 so that i can keep that in mind for when it comes time for testing.
This is absolutely amazing. Your website is so helpful and cool!
Was this point loaded or spread loaded??? I see no reason why this could possibly be point loaded because throughout the whole bridge it is the same. But then again I could be wrong.
Your brigdes efficency was pretty amazing, and congragulations on achieving such a feat. A few subtle improvements could be made, at least from my angle. Triangles are the strongest non-complex shape for bridges, and you clearly harnessed MOST of their potential in your bridge. Your bridge might have withstood more abuse if the triangle was within your frame, rather then being glued to the externally to the frame. A final point of possible improvement would be the plane of your bridge. Your plane resembles a train track, with two long lines parallel to each other and smaller lines intersecting the long ones perpendicularly. This is smart if the bridge is layed on the ground, but most bridges are suspended in the air, making this platform at a disadvantage. In my unprofessional opinoin i would have used a triangle pattern for the plane, or a double triangle (making the appearance of an X). This tends to be the strongest platform since the squares or rectangles that you made usually cant hold much weight effiecently. Your bridge, once again, is amazing and 4200 effeciency rating is much better then my highest of 3900ish, but that was a default because the judges ran out of wieght to put on, lol. Best of luck to you and everyone else in the future