Model Bridge Design » reader submitted

Hell Gate Bridge 1/4 Scale

high iron models — Mon, 12 Sep 2011 21:24:24 +0000

Bridge is almost complete, features wood deck 4 track main with all hand laid track dimensions are 25 in wide x 27 foot long end to end x 7 foot 6 inches high at center. Weight about 1000 pounds featuring stone covered steel towers and navagation lights.

Here is a picture of the Hell Gate model:

frame work started using steel bars welded together

Garrett’s Thoughts
This is an excellent piece of work. Thank you for sending in this photo of the progress you have made so far. I am definitely looking forward to seeing the finished product. What are your plans for it once it is completed? What inspired you to start building this model bridge?

Dombiggers 1st bridge

dombiggers — Sun, 17 Apr 2011 04:47:45 +0000

As you can see i took your advice on using a t-shape for the bottom cord. Which was really cool, cause it gave me a lip for my cross members. I did sandwich the top cord. I glued lap joints and gusset plates, plus pinned the legs to the cords with small wire nails that I cut to size. The model is 19″ long x 2 1/4″ high. The road way deck is 3″ wide. I didn’t weigh it yet. It spans 18″ with 1/2″ end bearings.

My 1st brigde

Thanks again for all the great info and advice. This project only has to hold 10 lbs. extra credit if it has a 25% or less load capacity percentage. The record in the class on this project is 80 lbs… I’m planning to donate 1$ for every 10 lbs this bridge holds to your web site.

Model Covered Bridge

KerryK — Fri, 18 Mar 2011 17:19:42 +0000

Garrett-
Jobs well done – interesting site and information!
We built a 1/8″ scale model bridge just like the bridges we build for production. We successfully loaded it with 345 pounds with the weight being distributed all the way across the middle. Do you know of a formula where we can figure out that weight capacity for our full scale bridge? We have contacted 3 different engineers in our area who don’t have access to such information.

Model Covered Bridge

Thank you for your time and any helpful resources. (I cannot make the Johns
Hopkins nodes and members work….?)

Rainbow Bridge Company

K-Truss bridge for Wake Tech engineering class

bcmiller2 — Sat, 12 Jun 2010 13:22:41 +0000

This bridge is supporting 191lbs of weight. It didn’t break, that was all the weight we could fit in the trash can. I believe this is close to the maximum load it could hold because the platform the jig is resting on was significantly bowed. The rest of the structure was rock solid. The construction of the bridge is popsicle sticks.

Albury High School Popsicle Bridge record breaker!

davow88 — Mon, 01 Mar 2010 20:10:07 +0000

We run a competition here at Albury High in Australia for our Yr 12 Engineering Studies students involving max. 50 popsicle sticks, PVA wood glue and 2m of extra strong thread. Structures have to span 400mm and are centrally loaded. Here’s a photo of our 2010 winner which weighed in at 69 grams and held 58kgs giving an efficiency using the formula on your website if I used it correctly of around 12000!

Monstrous Popsicle-stick Cantilever bridge

Macsignals — Fri, 01 Jan 2010 08:29:40 +0000

These are some pictures of a bridge I built mainly out of boredom, but also since I have an interest in engineering. It’s a large cantilever bridge, meaning it has two arms that extend beyond their piers that hold up a center suspended span. It’s 10′ 2″ long and as of right now is hanging across my bedroom ceiling. One nice thing about cantilever bridges is how the longer top-chord is in tension, while the shorter, straight bottom chord is in compression.

The bridge was built using both sizes of popsicle/craft sticks held together with high-temperature hot melt glue. In the pictures (on my Photobucket, as WordPress wanted to crop them down too far) you can see the I-beams made out of sticks and made into the chords, diagonals and bracing. Two of the trusses were built by “building up” girders rather than making I-beams. The top-chord lateral bracing is different on the one cantilever arm, as it was built earlier in the year and I came up with the idea for the other bracing in the downtime.

For decoration I added blue LED lights to the bridge.

See more pictures at the Photobucket Album.

Nic’s Popsicle Stick Bridge

Garrett Boon — Sat, 21 Nov 2009 10:29:39 +0000

The design procedure was completed over a 2 week period allowing sufficient time for segment to dry before moving onto the next. Heavy duty pegs were used to fasten the joints that had already been sanded to allow for maximum strength in the joints.

As the design took shape, I made several smaller models and tested the joints to come up with a final design for the joints that would allow for more weight to be added before the joints failed. Failure in the joints would mean that it wasn’t the truss design that caused the failure, but a failure in the construction of the truss.

After allowing 24 hours for the 1 layer truss to dry the pegs were then removed. As the image illustrates the truss consists of one smaller heavily layered triangle and 2 larger reinforced triangles. The top side when under a pinpoint force will be under compression and the bottom tension. The central joint that will be directly under the metal element issuing the force was to be constructed so that the glue joins if they were to fail would not be able to move due to the surrounding sticks creating a ‘nest’ for the failed member.

The original design was to be compiled of 12 layers each consisting of 18-19 sticks. But after weighing the truss structure it was calculated that the truss would have a final weight of over 300grams which would lead to a decrease in efficiency. This was therefore reduced to an 8 layer truss that weighed 220 grams.

When designing the truss care was taken into using sticks that were not only straight but did not contain any knots or weak points, these sticks were discarded.

After the truss was completed all that was needed was to place angled bracing on the truss to stop any bending in the beams under compression. But throughout the whole design efficiency was always key and when bracing was placed on the structure it was placed in selected areas as once again placing sticks in places that was not needed would lead to a decrease in efficiency. Decking was also placed on the end supports to allow for even distribution of force throughout the layers.

The final design structure was 54cm long and 10.5cm wide it had an average depth of 5cm and weighed 220grams.

Nic’s design held a weight of 224kg and had a final efficiency of 1020. It did not shear or snap at any member, but bowed in the second third of member C-E. This member did have angled bracing to stop bowing and this brace did not snap it was only the glue joins in this brace that failed. The truss ballooned out at the point when 2.2kN of force was applied. It was at this point that the test was stopped.

If the experiment was to be completed again I would have braced this area more heavily but from what I had researched I thought the amount of reinforcement already applied would be sufficient as to negate any bowing in this area.

First attempt at a DIY model bridge

JMRewop — Fri, 20 Nov 2009 03:28:53 +0000

It’s taken me just under 48 hours to get this far. Although I wouldn’t say its completely finished.. it’s a good as. I might just polish it off with a lick of paint and other aesthetically pleasing type things.

As you can see, I’ve modelled it on the Pratt Truss. Although, I didn’t do any “real” plans, just rough drawings (no force/load drawings).

Let me know what you think!

Cheers,

Joe.

Double Layer Toothpick Bridge

usmanjavaid — Fri, 28 Aug 2009 03:33:46 +0000

Garrett’s Note:
I am not sure why the author called this a toothpick bridge, as it looks more like Balsa wood. The author did not not give any information about this bridge, which is unfortunate. I would have like to known about why he chose this design, and what the bridge was trying to accomplish.

Spaghetti and Straw Bridge

single mom — Tue, 12 May 2009 16:47:46 +0000

I just wanted to say thank you to everyone who has contributed to this site. After two failed attemps to create a bridge we knew we needed help so we found Garrett’s site. With a lot of reading =P and a little luck we were able to create a straw bridge of our own. It’s not as neat as some of the ones on the site and we used hot glue, from what I have seen here that might be cheating a little. However, we found that it holds 5lbs so far and potentialy more, considering our first bridge broke with a large ball of string as the weight and our second broke with a coke can. I think our success rate was pretty high.

Thanks again!! The best site I have found by far for breaking down the basics of bridge building. My daughter Megan is in 5th grade and she has one of the best bridges out of her entire class thanks to this site. AND for a mom who didn’t do well in physical science I was able to help my daughter create a very sturdy project.

*Note from Garrett*
Using hot glue isn’t cheating at all, it is actually a fairly common choice for glue. It isn’t my first choice because it isn’t as strong as some other glues, but it is also pretty easy to use. And that is what matters more in some cases.