I built this bridge for the 2005 Fernbank Science Center bridge design event. The bridge spanned 16 inches, weighed 37 grams, and held 346 pounds. That puts its efficiency over 4200! One commenter said, “So if this bridge weighed one pound, it could have held up my car.”

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.”

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 :)

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74 Responses to “Fernbank Project: Strongest Bridge Design”

  1. Danaë - September 5, 2008 at 10:20 am

    I was just wondering if you have ever built an arch bridge? Because I heard that was the strongest bridge design.

  2. Garrett Boon - September 6, 2008 at 11:18 am

    Danae, I have built arch bridges before. The problem with saying that one type or design of a bridge is the strongest is that it changes for each situation. An arch bridge might be the strongest for one situation and a truss bridge for another.

  3. Signowurl - October 1, 2008 at 8:37 pm

    Triangles seem the strongest in most types of bridges.

  4. First Timer - October 13, 2008 at 7:50 pm

    Have you ever considered selling designs for bridges other than popsicle. Like this one or towers?

  5. Garrett Boon - October 14, 2008 at 4:01 pm

    I have thought about it, but I just haven’t put the time into creating a product. The hardest part for me would be to get the design into digital format. Thanks for the input.

  6. Kate - November 2, 2008 at 9:56 am

    I was wondering what type of material would you recommend for building an arch bridge? I cannot get my hands on any basswood… Would balsa be the next best thing or would there be something better out there?

  7. Garrett Boon - November 3, 2008 at 10:24 am

    Kate, the next best thing after Basswood is Spruce. Balsa will work also, but is just harder to bend and is in general not a consistent wood.

    • Shannen - August 21, 2014 at 1:52 am

      Hi. your bridge is amazing…and I think my teacher saw your work and ask as to build our own bridge out of the ff materials; barbeque sticks, glue sticks,5 sheets of bond paper. He gave us the ff:
      span: 30 cm, height- 10 cm.weight,10 cm

      I believe you can pretty help me with how iam going to do my project…What type of bridge would be the best for these materials?

      Please help…i dont know what to do…

  8. Mike - November 6, 2008 at 7:33 pm

    Hi, Your website is amazing and has helped me a lot!

    I am, however, stuck between the crossroads of building an arch or truss bridge. Our balsa wood bridge must span a valley of 20 cm and have an inside deminsion of at least 5 x 5 cm. I’m wondering which structure would be more efficient?

  9. Shane - November 11, 2008 at 3:55 pm

    would you be willing to make instructions on how to build that?
    my teacher bet that i couldn’t hold over 200 lbs but i want to prove him wrong!!

  10. Garrett Boon - November 11, 2008 at 6:34 pm

    I probably won’t be making blueprints for this particular bridge. I think I still have my original plans I used to build the bridge, but right now I am in a different country.

  11. Jason - November 25, 2008 at 8:25 pm

    I was wondering whether the Fernbank Bridge could be successfully replicated with only toothpicks…also, was the weight attached to your bridge at the top of your superstructure…for my project, I believe the weights are suspended from the bottom of the bridge…do you have any advice for how I could accomplish a strong bridge under these parameters? Thanks!

  12. Ali - November 29, 2008 at 8:01 pm

    I was wondering if you used any particular glue, I have to make a bridge for geometry(this weekend cause my teacher is lame and didn’t even give us direction) and we have to be able to have the quarterback of our football team stand on it haha

    thanks so much, this was very helpful!!!

    • Garrett Boon - November 29, 2008 at 8:26 pm

      Ali, I used two types of glue on this bridge. I used both Probond and Weldbond. You can read about them on my glues page:

      • Ali - November 30, 2008 at 2:32 pm

        Thanks, i’m in the process of building my bridge right now, and 16 inches is prettty small it looks a whole lot bigger in the pictures!! We’re using gorilla glue and uhh something i think its called epoxy?? I don’t know, it’s blue and white and you mix them together haha

        we have to only use popsicle sticks, so its very difficult, but your site is soo helpful thanks again!!

  13. mackenzie - December 17, 2008 at 4:21 pm

    right now us the grade sevens have a science fair in january 26 and i have chosen to build a bridge and your website here has helped so much but when those engineers told you that if you had added more diagonal supports your bridge would of lasted was that all they told you..? was that the only flaw you had in your bridge or were there other problems..? I want to have the best bridge possible and i need all the help i can get

    • Garrett Boon - December 20, 2008 at 2:17 pm

      Mackenzie, that is exactly what I was told by the engineers at that event. They suggested that the bridge started to twist and therefore failed by torsion. This probably could have been avoided had I included more lateral bracing throughout the truss.

  14. Jennifer - December 19, 2008 at 2:03 pm

    I’m in Science Olympiad and I will be competing in the Elevated Bridge event. The rules: http://soinc.org/sites/default/files/uploaded_files/ElevatedBridgeBRulesGraphicv2.doc (this is the general rules, i could not find the specific ones). Please take a look at the rules. We must use 1/4 by 1/4 (inches) balsa wood. Do you have any tips or ideas on bridge designs, density of wood, grade of wood, etc.? That would be very helpful. :)

  15. Phil Estrin - December 26, 2008 at 4:47 pm

    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

  16. Sam - January 4, 2009 at 2:06 pm

    This is absolutely amazing. Your website is so helpful and cool!

  17. david - January 8, 2009 at 6:28 pm

    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.

  18. aniaya edwards - January 11, 2009 at 7:42 pm

    I”m not trying to be mean ,but this is not what I’m looking for Garrett although nice pictures.

  19. Prakhar - January 12, 2009 at 10:47 pm

    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.

    • Garrett Boon - January 14, 2009 at 12:09 am

      I am pretty sure this bridge was 4 inches tall.

  20. Maynelljah - January 14, 2009 at 1:57 pm

    NIce bridge guys!!!!!! 😀

    • Maynelljah - January 14, 2009 at 2:11 pm

      We are making a bridge for our class at West Finchester Memorial Academy of Engineering- New England

    • Bob O'Brien - October 21, 2009 at 6:37 pm

      wow i am building a bridge for a university project and this design has helped to an extent amount :)

  21. Prakhar - January 14, 2009 at 9:35 pm

    Thanks! That helped a lot

  22. StampingBoy - January 21, 2009 at 3:41 pm

    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.

  23. Garrett Boon - January 23, 2009 at 9:46 pm

    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.

    • josh - January 27, 2009 at 4:52 pm

      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.

    • Anna K and Lea - February 17, 2009 at 2:00 pm

      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?

  24. lily - January 30, 2009 at 4:25 pm

    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

    • Garrett Boon - February 1, 2009 at 10:00 pm

      This would be classified as a truss bridge.

  25. Billya33 - March 9, 2009 at 9:50 am

    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!

  26. TheNocturnalOne - May 26, 2009 at 3:04 am

    I’ve created a bridge out of balsa using butt joints,cardboard gussets,(and some joints with pva glue,some with hot glue guns) before.It was a complete wuss when it came to testing it. It only held 18lbs before completely collapsing.Compared to your bridge,it would be like an elephant standing next to a pea!

  27. Joey - January 18, 2010 at 9:45 pm

    Unreal! I’d like to try building it myself; I realize this was made in 2005, but if you still have the plans or remember how it was built, could you email me instructions? I can’t tell what size the wood members are.

    Personally, I”d love to take that bridge to an efficiency of over 5000 as well.

    • nick - February 8, 2010 at 6:10 pm

      i think that it looks very cool
      i am building one for my class and i was wondering if you know how far apart each vertical suport was placed
      and are the top l beams two peices of 1/2 inch glued together
      plz reply

  28. Sara - March 2, 2010 at 8:24 pm

    We wanted to use this for our experimental design structure for science olympiad, and I was wondering if you still had the plans, and what you made this out of. please respond.

    • Garrett Boon - March 2, 2010 at 8:35 pm

      Sara, this bridge was made out of Basswood. I do not have the plans anymore.

  29. Anne - March 3, 2010 at 9:07 pm

    we have to do this for 3rd semester science project, only with smaller measurement, and i was wondering what type of glue as used?

    • Garrett Boon - March 4, 2010 at 11:31 am

      Anne, I used two different glues on this bridge, Probond and Weldbond. Both are good choices.

  30. Abhinav Mishra - November 8, 2010 at 12:36 am

    Hi, I have to build a balsa wood bridge for my class. I just had one question.

    I have decided on a Howe Truss bridge, but the slanted members that are on wither end of the roadway. How do I make them? Specifically, how do I make them angled? And strong?

    I know my question may not be clear, its hard to describe on words. If you do know what I am talking about, do I attach them directly to the top of the roadway? Or the side of it? Is it possible to use gusset joints on this type of bridge?

    spans 30cm

    • Garrett Boon - November 8, 2010 at 12:51 am

      Abhinav: If you make your diagonal members on the ends of the bridge connect to the bottom and top of your truss with End Joints, adding a gusset, I think that would work well. This would allow all your other joints to be natural Lap Joints. In your words, attach them to the top of the roadway.

  31. Yenny - January 5, 2011 at 12:44 am

    Do you reccommend binding the pieces? I am using bass wood, but the pieces are quite thin from my perspective. Should I glue two strips together to make it stronger? And if so, are there any parts in particular on the bridge that might not be good to do this?

    • Garrett Boon - January 5, 2011 at 3:06 pm

      Yenny, this is called laminating the wood. Yes, it does make it stronger, but usually not more efficient. This means that it adds more weight than it does strength. I’d recommend you glue your strips of wood into L, T, or even I shapes which will increase their efficiency if done well. The L, T, and I beam shapes are useful for any members of your bridge that are in compression, such as the top chord. Often enough members in compression do not fail because the member itself broke, but rather because the joint failed. I would make sure you are using good joints.

  32. Ryan - February 22, 2011 at 12:47 am

    I saw a bridge today at the TSA Regional conference that held OVER 496 LBS.THe bridge was made of Balsa wood and had a very strong structure.

    • Garrett Boon - February 25, 2011 at 7:03 pm

      Ryan, that sounds like a sweet bridge. Do you know anything more about the bridge? How long was it etc?

  33. Derek - March 4, 2011 at 9:20 pm

    We do bridges every year in math and they weigh under 50 g. and hold in the 1,000. my bridge held around 1,200 last year.

    • Garrett Boon - March 4, 2011 at 10:54 pm

      Hey Derek, what unit is the weight that your bridges held in?

  34. Mike - March 15, 2011 at 11:00 am

    what truss design did u use?

    • Garrett Boon - March 16, 2011 at 4:15 pm

      This bridge used a hybrid truss design. Mostly it was a Subdivided Warren, but went to the Howe Truss on the ends.

  35. Saga - March 15, 2011 at 10:59 pm

    I was wondering, how was the bridge loaded?

    • Garrett Boon - March 16, 2011 at 4:14 pm

      This bridge was loaded from the top with a metal plate that was attached to a hydraulic loading machine.

  36. Steve Amdhome - March 22, 2011 at 2:42 am

    what do you mean by diagonal braces? and how long did it take u?
    i tried to copy your design except with popsicle sticks didnt turn out very well. was kinda crooked and twisted.
    hope i can still beat my class in most durable bridge

    • Garrett Boon - March 22, 2011 at 3:30 am

      Good question. Diagonal bracing here refers to any pieces that would have connected the sides of the bridge on a diagonal. So if I had a piece that was glued on the bottom of the left side and sloped up to the top of the right side of the bridge.

  37. Balsa, Balsa Wood...ha - April 12, 2011 at 7:26 pm

    What kind of truus did you use? A howe, pratt, or warren?

    • Garrett Boon - April 12, 2011 at 10:01 pm

      This bridge used a hybrid truss design. Mostly it was a Subdivided Warren, but went to the Howe Truss on the ends.

  38. Tessa - November 7, 2011 at 5:26 pm

    What kind of popsicle sticks did you use, just regular, or a certain kind. Also, what kind of glue?

    • Garrett Boon - November 7, 2011 at 5:32 pm

      Tessa, I did not use popsicle sticks on this bridge. I used Basswood. I used two types of glue, Weldbond mostly and a little Probond.

  39. Tessa - November 7, 2011 at 7:01 pm

    If this design was used with popsicle sticks would it work?

    • Garrett Boon - November 7, 2011 at 10:22 pm

      Probably, although you might have make some minor modifications.

  40. Paul Colucci - January 22, 2013 at 12:03 am

    K Garrett Boone I’m a 14 year old high schooler and for industrial orentation we are building model bridges that are 10 inches long 2 inches wide and 2 inches tall we are using 1/8 inch thick basal wood and we have 72 inches to work with what would be the strongest bridge design to use

  41. Kylie - March 29, 2013 at 11:47 pm

    Hi there! I have to build a model bridge with atleast a two inch clearance at the bottom. There is going to be a bucket of water hanging from the top, through the bridge and out the other end. Do you have any tips or suggestions as to what type of design I could do? Thanks!

  42. Martin - April 13, 2013 at 7:55 am

    was this easy to make?

  43. Brian Sensenig - October 8, 2013 at 3:27 pm

    Hi! My class is building bridges for art, and I am designing a bridge similar to your fernbank project. I noticed that the engineers said it lacked diagonal bracing. Do you have any suggestions as to how to do this? Thanks!!!!!

  44. Macie - November 3, 2013 at 10:10 pm

    Hello Garrett!
    I was wondering how long did it take you to build that awesome truss bridge!?
    I am a junior in High-school and I have to build the kind same design for my Mechatronics class. I’ll be stealing some ideas from your awesome design. :)
    Thanks in Advance,
    – Macie <3

  45. Nick - January 30, 2014 at 9:45 pm

    Hello, I am taking a Highschool engineering class and I need to build a model truss using balsa wood and whatever else…any suggestions on designs? It’s a contest on who can build the strongest truss. If someone can email me at nickfic343@gmail.com that would be great thank you! -nick

  46. ivan nieto - April 28, 2014 at 1:24 pm

    would you please tell me what materials you used i am doing this as an assingment for my school. the topic is “What makes the worlds strongest bridge?”

  47. MULENGA - June 5, 2014 at 2:15 am

    nice piece of work!!!can any bridge model be made out manila paper?my assignment is to made entirely from manila paper

  48. Sam Witwer - December 2, 2014 at 9:48 pm

    Hey Garrett, I’m Sam, and I was wondering what a good ratio of height to length to width ratio would be for a truss bridge, in general. If you need me to be more specific, then, as an example, let’s assume that we have a Pratt bridge that’s 25 inches long. Do you have any insight on how high or wide it should be then? I’m no expert, so just a general idea would really help me out; if you have enough time.

    • Garrett Boon - December 3, 2014 at 12:14 am

      Sam, I’ve had good success starting with a 1:6 height to length ratio. In general a wider bridge will be more stable but also adds weight. If you are testing the bridge with a load that won’t move around lateral, then a more narrow bridge is fine. But if you are planning on standing on the bridge, you probably want to make it wider. The popsicle stick bridges I make that are 25 inches long are about 3.5 inches wide. This is mostly because of the limitations from using popsicle sticks, but it does seem to work out well.

  49. ashley - December 31, 2014 at 4:45 pm

    Hi I was wondering how you would go about this with measurements that needs to fit under 23 g
    How would you do the height, length, and width measurements and how far apart would you make each vertical line and diagonal line from each other?
    I know you mentioned lateral bracing earlier if the bridge had been loaded on the bottom by a hanger would you have done the lateral bracing on the bottom instead?

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