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
hey, i dont really understand why is there no load in the middle part of the warren truss. Can anybody help me explain? thx
thanks for the tips. i have to make a balsa wood bridge that will support 15 kilos in the center and the truss designs really helped.
The school I got to St.Peters grade 6s had to build a bridge for Design+Technology and this website has really helped alot thank you!!!
This helped my assignment a great deal,so I offer you my gratitude.
Which truss can support the most weight if done correctly.
thank you for the great info…it helped a lot on my project
I love this site…it gave me a lot of help for our project. Thanks soo much. I just hope that the bridge that my group makes wins. Um, our bridge is meant to be 40 cm long and we have 150 paddle popsticks to complete it. Anyway, thanks a lot again.
this site is very good for the studdy ofmechanics trusses
this is very helpful! i have a project where we need to build model bridges and i think this will help with drafting my design.
this is a good webstie for teens and it gives the motives for kids to learn how to build bridges.
is this Mrs. Goodfellow from CMS???
Why yes, I am from CMS.
hi garret i really like your website can you plese tell me how to glue the members togeather if you cant use nails. shuld i glue them dirrectly on top of each other or next to each other there are three members, i am using the warren truss
I have a study project which uses ‘meranti’ timber instead of steel. The deck is designed to use the plywood. As you know, the more materials I involve in the bridge construction, the more the weight and truss will also involved. So how can I design the truss (the girders as well as piers) so that the bridge can support 4 men life load. The bridge is 2.5 m long, 500mm wide and height. The timber cross section is 12mm x 40mm.
I have an assignment atm and a cart is being moved across the top of the bridge, the bridge must weigh 150g max and we were thinking of using epoxy glue and doing a warren design with vertical supports in all triangles, and the vertical supports and slanted supports would be made of grouped spaghetti wheras the horizontal beams would be made of fettucine, is warren the best design to maximise its ability to hold weight in this instance?
If you have a 5in section of your top chord in compression, which is stronger; a vertical member going from the bottom chord up and bisecting the top chord or save the weight and remove this vertical member and just add more lateral bracing?
hi, im in yr 12 and im currently doing an assignment on bridges
ive built the warren truss bridge with vertical members,
ive had a look at your diagram with the load factors, but im quite confused, you say that the load factors add up to 100% but i dont see how the numbers come together to make 100%
i can only see that when 85% + 15% = 100% at the bottom line, but with the 60% lines i cant figure out how they would add up to give 100% please explain to me =]
Actually, he meant to say that the two black arrows above the bridge represent a single weight, distributed evenly between those two arrows (thus, 2 points at 50% each = 100%), the numbers on the bridge lines are the force amounts(not percentage) most likely, in Newtons. Hope that helps explain things better. There are many free online bridge building games for you to try your own designs and see how they work. I tried a K-truss design in one program from West Point, but the forces were completely reversed. It might have been the program’s physics, but I’m not sure. I had lots of compression at the top and tension at the bottom.