Tags: howe truss, k-truss, pratt truss, tips, truss design, warren truss
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Truss Design
Learn all the main types of trusses used in real bridges, and see how to apply them to model bridges. Learn the history of each common truss design. This page is designed to help you make an educated decision about what truss design you should use on your bridge.
Common trusses used in engineering:
Warren Truss
Warren Truss
The Warren truss is one of the most simple yet strong designs. This simple design already existed, but what made the Warren unique is that it uses equilateral triangles. Each side of the triangles are the same length. This marked an improvement over the older Neville truss which did not use equilateral triangles.
Go to a more in depth analysis of the Warren Truss.
Pratt And Howe Truss
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- Pratt Truss
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- Howe Truss
The Pratt and Howe trusses are very similar. In fact, the only difference is the direction the slanted members are angled. This changes which members are in compression and tension. On the Pratt truss, the shorter, vertical members are in compression. However, on the Howe truss, the longer, angled members are in compression. Because most materials (especially wood) that model bridge builders use decrease in the ability to resist compression the longer they are, I think the Pratt truss has an advantage.
There are more factors to consider, however. The Pratt and Howe trusses also differ in how they spread the load to the top and bottom chords. The Pratt truss has larger forces on the top and bottom chords than the Howe. Thus. you’d have to use bigger top and bottom chords.
Go to a more in depth analysis of the Pratt Truss.
Go to a more in depth analysis of the Howe Truss.
K Truss
K Truss
The K truss looks very good on paper. It shortens the lengths of the compression members compared to the other trusses. However, one must wonder if it adds additional weight simply because of the number of members. It is really interesting to note the two green members on the K truss, in theory those pieces could be taken off. However, I had to include them to make the truss design program work. This shows only one orientation of the K truss. If I reversed the direction of the K’s, I wonder how much it would change the forces.
Go to a more in depth analysis of the K Truss.
The one thing I don’t like about this truss is the long vertical compression member in the middle of the bridge. If that one member could be shortened or even eliminated, I think the bridge would become more efficient.The K truss would be the hardest of these trusses to build. This is something worth considering. Making a strong joint that would make the most of the switch between compression and tension of the vertical members would be difficult.
If you are interested in learning more about trusses and truss design, check out Truss Fun, Second Edition
how is the structure of trusse in which load has to hang from bottom my truss design is same as shown above
what would be the best truss design for a bridge in which the load is applied from the bottom,. my bridge is the same structure as the above ones , i’m just not sure about the truss design,.
YEAH THE BRIDGES ARE KINDA COOL…. IT WAS A BIG HELP THANKS
wow, this gave us alot of good ideas for school
Thank you so much! My school is entering some groups into a Bridge building competition where all the materials you can use are 3 x 5 note cards and Elmer’s school glue! This website really helped us alot! thank you!
what kind of glue works the best?
. It is the simplest design of the Truss Bridge, with two sides, a bottom, and the railing in simple triangle forms. The bottom of the side of the bridge is 11 inches in length and the top of the side is 10 inches in length. The little rails on the inside of the left and right side of the bridge are 2 inches in length. The bottom of the bridge…… Some of the things I learned in making this bridge were the different jobs involved in the process of actually building a real bridge. You need to have an engineer, an architect, a scientist, and a mathematic. You would need an engineer to help design the bridge. You would need an architect to oversee the construction of the bridge. Also, the architect would prepare information on the structure’s design and specifications, materials and equipment, estimated costs, safety, and construction time. They also make scale drawings and make sure that the bridge meets the building codes and laws. Also, to build a real life bridge, you would need a mathematic. They would make sure that all the little details in the bridge were exact and specific so the bridge was safe, and also look right.
Has anyone else noticed that the K Truss looks like it has arrows in it as well as Ks? Its like an optical illusion! Great Website, and thanks for the tips!
p.s. thanks for the info, this is very helpful
For a science fair i have recently done, i had the warren, pratt and howe trusses all trusses.
the efficiencies in weight held over bridge weight were:
warren – 385.6 reoccurring
pratt – 425
howe – 340
These are not averages of several bridges, and they were only 1 foot long (cause thats what the stores had in stock.)
In this test, they were weighed by hooking a rope to the bottom beam, putting a bucket on the rope, and adding coins to the bucket (and a ten-pound weight).
I hope this answers some questions on which is best (the pratt)
Of course i had 30 pounds of coins.
I am confused about what would be considered tension and what would be considered compression. I understand what the two are but I dont understand how to apply tension and how to apply compression. Heres an example. If you place a truck in the middle of a howe bridge, would that be applying compression tension or a combination of both. How about if you have a bucket dangling under the center of a Howe bridge, would that be applying tension compression or a combination of both.
Best regards,
Allan
i have to biuld a bridge for science fair do you think that popcile sticks would be the way to go , but i also need the bridge to break at some time with in 5-10 minutes. anyone can answer to this i just need some kind of answer.
/:( !!!!
i would also like it if you just posted here on the website!!
please someone respond soon!:D
thank you
p.s. i think that this website could use some more information on the different kinds of bridges and not just on your experiments you should have a viriety of appinions so that people will see two or more sides of the story!! OKAY? DO NOT take this as a insult i just think that it would be better that way , i thnk it would guve you more viewers than what you have now !! just my apinoin but i bet other people agree with me on this matter!! *****
sorry if that sounded wierd
Rose, part of the reason I have the option to leave comments is so people can share their opinions about my bridges or projects they have worked on. I also have an option for people to upload photos of their own bridges, so this site is not just my own work.
Any bridge can break within 5-10 minutes. It depends on how strong it is and how fast you load the bridge.
i made a truss bridge that was 40 cm long. i used the warren truss design. i added vertical suports also though. it was made from popsicle sticks and wood glue. the key is distrubuting the weight evenly. my bridge held over 200 lbs. depending on the materials and how much you have to work with, you should be able to do the same.
Also a determining factor would be exaxtly how the weight is going to be applied to your bridge. i also forgot to mention that my bridge was 10cm wide.
200 pds wow if u want us to believe u say something reasonable 40X10 cant hold 200 pds it would have to be 50 cm high considering u used normal wood glue.
Sorry, but yeah it could certainly hold 200 lbs. He most likely beefed it up with a lot of popsicle sticks. Wood glue is good enough if used properly. I saw a vid on youtube with a simple king post that held so much, they were running out of things to use as weight. It was REALLY strong.
hey josh im tiana and im in yr 7 and we are making bridges and how do you know if it is the write bridge and there is other choices what do you do ??????
When you stated that for a Howe Truss you would have to use larger compression members, were you referring to the diagonal members or vertical members? Thank you for your clarification.
I want to build one project under civil department. its a competition..
I have to build a truss structure using Popsicle. But it will not be tested with vertical load but with horizontal force. Actually judges will attach a string on the top of my Popsicle truss structure which will go over a pulley and will carry a load at the end of the string..
Could anyone plz suggest what structure will be the Best for this very purpose! I need help as soon as possible.. Thnx.
I personally made a warren truss bridge out of popsicle sticks and wood glue. It held over 200 lbs. i cant say that this is the best design to use though. You just need to find which design distributes the wieght most evenly. But i didnt exactly understand how you said the weight would be applied.
so which one would hold the most weight??
that question can really not be answered. there are alot of determinig factors. 1)how the weight is applied. 2)what materials you use. 3)how much materials you have to work with. etc.