Probably the question I get asked the most is “What bridge design holds the most weight?” or “What bridge design is the strongest?”

The answer to that question is not simple and probably is not going to be what you expect. The truth is, I cannot answer the question. There are too many variables that are not being defined.

What Bridge Design Holds the Most Weight?

Probably the question I get asked the most is “What bridge design holds the most weight?” or “What bridge design is the strongest?

The answer to that question is not simple and probably is not going to be what you expect. The truth is, I cannot answer the question. There are too many variables that are not being defined.

Example:
Is the the Pratt truss or the Warren truss stronger? Actually, the answer is up to you. You can make the Warren truss stronger. Or you can make the Pratt stronger. It depends simply on the strength of the wood you use. You can use 2×4′s to build the Warren, and toothpicks to build the Pratt. Obviously the Warren is going to be stronger in this case.

A Better Question

I think though, many people are trying to ask whether or not one of these trusses has an inherent advantage over the others. In my mind, none of them do. If you look at my truss design page, you will see that each truss spreads a load out differently, but none with an apparent advantage. Conclusion: no bridge design has an inherent strength over another.

However, this conclusion only applies to this general setting. It may be that in a specific situation one bridge design would be better suited than another. It is up to you to examine how each truss works and decide which one to use.

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39 Responses to “What Bridge Design Holds the Most Weight?”

  1. Lil Roy - September 25, 2008 at 11:04 pm

    In a specific case, such as the truss spanning 15 inches with a single constantly increasing force applied directly in the middle (7.5) inches from the ends, which would be the stronger truss, assuming that a limited amount of material is used. I guess the better question is given a specific amount of material, what is the optimum truss design. Also for the truss members, would a round, square or rectangular tubing be stronger, again the material is limited.

    • Thomas - May 24, 2010 at 8:44 pm

      How about the challenge of constructing a bridge designed to hold 100 lbs: span is 18 cm; materials available are 12 popsicle sticks (11 cm each) and 10 toothpicks; a square opening in the center must be part of the design to suspend the 100 lbs of weight. I am currently working on a suspension bridge design…what do you think?

  2. Garrett Boon - September 27, 2008 at 10:26 pm

    Lil Roy, personally I prefer the Pratt truss. I have had good success with it. Do you have to use tubing? Tension members do not need to be anything other than flat pieces of wood. Compression members can be made more efficient if they are in an I or T shape.

  3. tyler - October 3, 2008 at 2:09 pm

    i myself prefer to experimment with combining different desingns and i hav held over 100 pounds on a six ounce bridge withmy technique

  4. IIVII@ST3RZ - November 22, 2008 at 7:26 pm

    Thank you for not specifing a certain bridge because i know that you would be flamed horribly if someone didnt agree with you. I agree with you 100%! Well Done!

  5. ralph - November 27, 2008 at 4:06 am

    what is the modulus of elasticity of popsicle sticks

    • Garrett Boon - November 27, 2008 at 10:37 am

      Ralph, I don’t know the modulus of elasticity of a popsicle stick. But I imagine it is not consistent, because of the total lack of quality control with popsicle sticks. For the most part we don’t even know what wood popsicle sticks are made of. Thus, knowing the modulus of elasticity would not really be helpful. What is more beneficial is simply sorting through and finding the popsicle sticks with the best grain and least deformity.

  6. J. Campbell - January 7, 2009 at 1:30 pm

    i have to construct a bridge that is exactly 7 inches long. i will be given 25 miniature wooden beams that are 7 inches long themselves and i can cut and put the mtogether as i like but i cannot laminate them ( and no not like running them through a lamination machine) using these materials what bridge would have the most strength but would weigh the least?

  7. Paul Wallace - April 2, 2009 at 8:57 am

    Just an observation…The Burr Arch (and King Post) design as used in covered bridges in western Indiana not only allow for distribuation of load, but the archs stiffen the truss and stop twist or deflection that can cause a truss to fail.

  8. technology is boring - October 26, 2009 at 12:00 pm

    how do you make a bridge that supports weight that is made out of pine pieces that has to be 50 inches high less than 20 inches tall and the 20 inches wide please i need this answer by October 29th 2009 or else i will fail :( so can you please help me :)

  9. Pedro Cori - October 29, 2009 at 3:28 pm

    Hello,
    We’re trying to make a vertical tower of 70cm in height, 30x30cm base area, and 20x20cm area at the top (with any shape in between). It should withstand around 80-100kg of force applied vertically down at the top, and must be built with typical 5x5mm model sticks (although they may be made of any wood), glue, and copper wire (good for tension segments). Of course, the lighter the better.
    I’ve been investigating a while, and I’ve found a lot of information about trusses that support horizontal (perpendicular to the longest side) weight on the structures (i.e. bridges and roof supports), but almost nothing on truss structures that can tolerate force applied in this fashion (like a vertical support).
    Do you know what design would best fit this purpose or where I can get any information on the subject? Since the copper wire is much stronger than wood per unit of weight, I was thinking that probably the most efficient tower should have the most tension elements possible and the shortest compression ones, but I’m not sure where to get research that has been done on the matter.
    Any help would be greatly appreciated.

  10. SCTennisboy92 - November 30, 2009 at 8:36 am

    Hello, my class and I are currently in the process of locating a suitable truss for a paramount bridge project . I am trying to find the strongest design with these conditions. The bridge must be able to hold itself up over a span of 6 inches (so it must be longer than six inches of course). Next, i have only 8 different varieties at my disposal, among these are the pratt, curved chord pratt, baltimore, warren (with and without vertical supports), quadrangular warren, lattice, and finally the whipple. Next, including glue and toothpicks, the weight of the truss must amount to less than 20 grams- 10 toothpicks weighing 1.3g and 1 stick of glue weighing approximately 4.2 grams, we may use any type of glue but were given the recommendation of hot glue guns. When the bridge is tested and put under stress, the weights will be placed under the center of the bridge 5 pounds at a time. My group and I tend to be rather competitive and we compete to win. Please if you can sparre the the time reply with any suggestions.

    Thanks,

    A competitive junior who wants to win :)

  11. science girl - December 5, 2009 at 1:31 pm

    i am currently workin on a sciencefair project where i will be constructing 3 different bridges.. i am looking for ideas on 1. what 3 designs i should use.. 2. how should I test them as far as which will be able to hold the most weight. and 3 which supplies i should use, hellp mee!

    • 6th grader girl - May 23, 2010 at 3:00 pm

      i am working on a science project too. i have to design a scale model of a suspencion bridge. but i am not sure how ro build or design a suspension bridge because i am simply a beginner to all of this. what tyoe of equipment should i use?

      • Chika Athena - March 22, 2011 at 11:01 pm

        I think you should use really thin yarn.

  12. 4th grader boy - October 22, 2010 at 4:39 pm

    I am in the 4th grade and have to make a science project about what type of bridge holds the most weight? All new to me and might as well be a language from another planet. Can any one help? Is ther a formula to use?

    • Experimenting Sophomore - October 24, 2010 at 10:04 pm

      The best design would be a cable-stayed bridge-
      Here’s an image:
      http://www.roadtraffic-technology.com/projects/hangzhou/images/7-cable-stayed-bridge.jpg

      However, I am currently doing a project with material that don’t allow this style of bridge or supports in the chasm, so I’m improvising best I can. I originally intended to attempt a suspension bridge, but have since changed it to an eye-looking thing held by triangles that disperse the weight to either side. I wish I had a picture to show you, but our camera is MIA at the moment.

      I do not know the effectiveness of this bridge yet, and won’t until Tuesday, but feel free to give it a try if this is the type of project you’re dealing with as well.

  13. lolsmileyface - May 3, 2011 at 7:35 pm

    Hi im in 6th grade and me and my partner have to build a bridge that is strong lightweight and easy to make it has to be atleast a foot long and under 85 grams we dont no much so we need help on what bridge to make and if you can an image would be nice thanks :)

  14. Brookequinn10 - July 26, 2011 at 6:36 am

    hi im in 5th grade and weve got a project we have to build a bridge and  our teacher will be putting weights on it . what would be the strongest item to use plus whats a good famous bridge to get imformation for :)

  15. Bnjwill97 - October 6, 2011 at 7:14 am

    in 8th grade making a bridge to hold weights 

    • Hannah - October 13, 2011 at 2:07 pm

      thats what im doing right now !

  16. Ashleysn8 - October 17, 2011 at 12:15 am

    i have to make one that’s 11 inches and holds more than 25 lb and i’m in 6th grade

    • adi - November 16, 2011 at 4:26 am

      I created an expirement for my fourth grade science fair that tested both the flat truss and the warred truss using the exact same materials; balsa wood and glue. The flat truss held up 46.3 pounds of water, the warren only held 30.9. They both were across a span of eleven inches and in the end I only had chunks of demolished bridge… :)

      • Kyle - February 6, 2012 at 8:18 pm

        LOL. That would be my result!

        What types of materials can you use to make a drawbridge that can hold the weight of many cars at one time?

        I haven’t been lucky enough to see many drawbridges but up in Portland Oregon they are mostly steel (the parts that raise and lower)
        and concrete at the pillars that hold the bridge up.

  17. Ashley - February 15, 2012 at 7:43 pm

    For my grade 8 scince fair im dioin a project with bridges and i deffiantly suggest the flat truss!

  18. Reed - March 14, 2012 at 9:30 pm

    Im in 8th grade and in industrial tech we are building bridges out of little rods made of balsic wood i need the best type of bridge that would most likely hold the most weight im thinking a cablestayed with 25 pound fishing line.

  19. awsome guy - March 20, 2012 at 9:58 pm

    im in year 7 and i need to build a bridge that has to be 65cm long, 10cm high. it has to be 200 grams it than has to hold the weight of a road that is 750grams and a trolly that has to be 910grams.(it has to be made from dried spaghetti

  20. Irene - March 28, 2012 at 2:02 pm

    Does anyone know the strongest type of truss to use for a bridge that will be supporting a hanging a mass in the centre?

    • Megan - May 1, 2012 at 10:19 am

      Pratt truss…Design simple and build perfect

  21. chloe - April 4, 2012 at 3:47 pm

    Yea.. I’m in eighth grade, and we have to build an at least 80 cm bridge that can hold at least 30 lbs… within 2 weeks.

  22. andy - December 30, 2012 at 5:24 pm

    I think triangles will hold the most weight.

  23. regisellen - February 7, 2013 at 10:57 pm

    Hi i am doing a science experiment and i need to know 1)What kind of bridge holds the most weight.
    2)How much will it hold if i am making it out of popsicle sticks. 3)How many popsicle sticks it will take.4)Is there anthing else i could use besides popsicle sticks.

    P.S.
    It doesn’t matter how many sticks i use i will just buy more thank you and i need to have the answer in about two weeks if this is after the two week mark when you see it don’t worry i will still need some advice -Thank You :) Regisellen Thank you

  24. Ian - March 7, 2013 at 8:25 pm

    I tested the popsicle stick versions of the howe, pratt, warren, and k bridges. The bridge that withstood the most weight was the pratt bridge.

  25. ben sweatland - March 14, 2013 at 11:32 am

    sweatland@peoplepc.com I am a welding student and have to build a brige 22 inches long 3 inches wide out of 1/8th in rod. the bridge will be tested by how much weight that can be hung on the underside before it collapses. I plan on an arch brige but am trying to figure the best truss system to use for strength. any feedback would be greatly appreciated. ty ben

  26. maddie - March 24, 2013 at 10:37 am

    Hi,
    Im in the seventh grade and in Industrial Arts we are building bridges out of balsa wood the bridge can only be 13 inches wide and we have as much balsa wood as we need.
    so what would be the best bridge design for this project?
    (the wieght will be put into a bucket that is attached to the bridge)

  27. Brendan - August 15, 2013 at 3:48 pm

    My friends brother Is in high school, and in 8th grade his science fair project was best bridge design, and I am doing that project, and he told me the best design was the arch bridge. if you an get the wood not to break, you put a piece of wood on the bottom and 2 one on each side, but you make your arched piece longer than the bottom and top, and you have to bend the wood without it breaking, and it is basically a spring. the bottom pole goes down, but the arch takes over, while the bottom is drooping.

  28. science cat's owner - December 5, 2013 at 5:12 pm

    Hi!! I’m a 8th grader an need help on my science project, my bridge needs to hold up to 20lbs an it can’t be taller than 9in. It has to be built out of toothpicks, and school glue. The maximum weight is 10oz, the maximum length is 24”, the width can’t be larger than 2 1/2 ” . Please help!!! I can’t get an idea and I need a jup start!!!!

  29. Amy - January 17, 2014 at 1:31 pm

    Hi!
    I am doing a science fair project on the bridges. Do you know how forces are spread out according to the whipple truss bridge?

  30. Brenda - May 22, 2014 at 8:27 am

    Garrett, we recently did a bridge experiment in scouts using card stock to demonstrate how a regular piece will only hold a little weight but the same piece with the long sides folded up a little will hold a lot more. What is the principle being demonstrated? And more importantly, can you use it in Popsicle stick bridge design??

    Any one can try this using the front or back from an empty cereal box.

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