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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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.
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.
i myself prefer to experimment with combining different desingns and i hav held over 100 pounds on a six ounce bridge withmy technique
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!
what is the modulus of elasticity of popsicle sticks
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.
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?
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.
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 
Hello,
We’re trying to make a vertical tower of 70cm in height, 30×30cm base area, and 20×20cm 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 5×5mm 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.
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
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!