The Secret to the Truss Strength!

Truss structures are more common than you think. But why do we use them? Beams seem to work fine right, well yes but there is a catch! The trusses are mostly used in bridges, roofs of venues, some cars and many other places. But how do they work and what is their advantage over beams? In this video, we dive deeper on truss structures and the secret to their efficiency. The video is supplemented by a scaled experiment that practically shows the advantages of the truss.

This video was sponsored by Brilliant

References:
[1] M. Carver, "Tennessee’s Survey Report for Historic Highway Bridges," Ambrose Printing Company, Nashville, Tennessee , 2008.
[2] J. M. Gere and B. J. Goodno, Mechanics of Materials, Cengage Learning, 2013.
[3] R. C. Hibbeler, Structural Analysis, Upper Saddle River, New Jersey: Pearson Prentice Hall, 2015.

[kurtsmith]

On your truss/beam testing table, drill a large hole in the table w/ a 6in holesaw, this would you allow you to load the test beams axially. I suspect the truss may have tested over 25% compared to the beam if the load was purely axial. The higher center of gravity and torsion induced by the rope twisted it significantly and in my opinion it failed prematurely. Great video, regards.

[BReal-EC]

I have been a pressed metal pated wood truss designer (and also engineered wood) for around 30 years now. This was a good video. I was worried your staple connections were too weak as the connections are where the engineering really matters, but they seemed to hold up well. In pressed metal plated wood trusses, when a truss is overloaded it always fails at a joint not in a member. A well overloaded joint actually causes the pressed metal plates to slowly roll out of the wood.

[WilliamDye-willdye]

Well done. The most interesting part for me was the explanation of why it's so important to get all of the members connecting to the gusset to line up on the same point.

[dalegray]

During the course of my career I have recorded nearly a thousand bridges. Many of these were actual pin-connected bridges that did not use gussets. These were usually older railroad bridges from the late 19th and early 20th century. Some have been repurposed as local access bridges, but they are still around. That said, even through I have been immersed in bridge tech information, I learned quite a few new things from your video, always something new to learn. Thank you.

[CplusO]

As a maker and not an engineer you helped me a lot with this description. Thanks

[luzr]

Loved it - especially the work that went into the simulated catastrophe! The pin / convergence point explanation gave me exactly what I need for a roofing solution at home. Many thanks for the clarity you provided.

[TonboIV]

The first example I can think of, of a suspension bridge with a railway on it is the "Seto Ohashi Bridge" in Japan. It's actually a series of bridges, jumping between small islands to link the Japanese main island of Honshu with the large southern island of Shikoku over a total distance of 13km. There are six individual bridges: a truss bridge, two cable stayed bridges, and three suspension bridges, the longest with a 1100m centre span. All bridges are double decked with a highway on the upper deck and railway tracks on the lower deck. Currently it has two narrow gauge tracks, but the bridges were designed to carry four tracks to allow for an eventual Shinkansen line.

[ronkuzyk]

Great demo. You also inadvertently showed why good construction quality is important.

[g.m.]

Make the truss bridge in a way that the load is hanging from a pin joint and not from the middle of a truss (place the joints in a way that one joint is placed exactly in the middle). Thus you can avoid breaking the truss by a bending effect.

[rhamel]

Great demo; we can also so see that the bottom cord failed in tension… this demo is well balanced (picture/formula) linear tension-compression vs bending forces against deflection is a great introduction. There is great thinking and a lot of preparation for this very short fun Eng. lesson. 👍 thank you!

[LTVoyager]

Even if the central axis of all members passes through the same point, the gussets still apply a moment to the members under load, particularly if the deflections are very high. That is why another condition of the pin connection assumption is fairly small allowed deflections.

[what_to_read]

"Amazing work! As an aspiring engineer, you are a true inspiration. Your dedication and commitment to engineering excellence are truly remarkable!"

[bendenisereedy]

Great video. The humble bicycle frame is also a perfect truss structure. The difficulty comes when other forces intervene such as the bending force on the head tube when you apply the front brake. Carbon frame engineers have learned a lot in recent years about laying the carbon mat is such a way that maximum stiffness is achieved with minimum weight and they have also learned how to vary the carbon layup so as to allow controlled flex to prevent an over-stiff ride.

[harriehausenman]

I love the models and since you clearly state the drawbacks and simplifications, I am super fine with crude models (although YOUR woodworking skills still esceed mine BY FAR, obviously 🙂).
And remember, whe can't all be 'Practical Engineering' on the first tries 😉
Thanks for putting all the effort and work in these videos, much appreciated and future engineer generations will thank you 🥳

[jimf]

Doing engineering at Napier in the 70s we were given a sheet of balsa, a tube of glue and a craft knife (Aaargh! student risk assessment kills this idea in 2023!) and challenged to build a bridge across a gap between two benches in the lab. A truss just managed to outperform my box girder. It was a really great exercise. I have used the intuition about the distribution of structurally significant material that developed from that exercise many times since then!

[fantabuloussnuffaluffagus]

7:33 apart from the support for your truss failing before the truss, the way you've loaded the truss with lines running near horizontal out to the table edges guarantees that you won't have a proper vertical load on your truss, and the way you wrapped the line around the bottom chord where it is unsupported also guarantees that the bottom chord is loaded in both bending and shear.

[jh]

That was very insightful, would definitely be great to see more model experiments like this in the future :)

[krishansharma]

Very well explained, cleared a lot of concepts. Really good job!

[hafeeznoormohamed]

Wow thanks for another great video. Enjoyed the experiment--would be cool to see more of those!

[numeroVLAD]

Since you have connected loading string twice to your bridge you created shear and twist. The shear failure is evident, 2 ropes cut you bridge. Put some metal clip first on the bridge then connect rope to the clip to get a better failure modes. To eliminate sideway force use pulleys at the edge of a table and make sure that the structure is centered