You can tell that most of these bridges were thrown together. There are a couple nice looking ones. Can you tell that I care about the beauty of the bridge yet?

I wish they gave more information about how many popsicle sticks were used and how much the bridges held.

Thanks to everyone who participated. In order to collect your winnings you must send an email to the contact email on the scoreboard with your name and your PayPal email.

There must be some confusion, as team IMaWIN submitted a design after the cutoff date. This voids that submission. Team Epitome should be in 3rd place.

GarrettsBridges.com is hosting a West Point Bridge Design Local Contest. This local contest starts today and runs to March 1, 2010. All designs must be submitted by Midnight, March 1. This contest is open to anyone under the age of 25.

• First Place Team: $30
• Second Place Team: $20
• Third Place Team: $10

All prize money will be sent by PayPal.

Join for Free

• (1) Register for the West Point Bridge Design Contest at http://bridgecontest.usma.edu/login.htm. If you are not “eligible contestants,” as defined by the WPBDC rules, that’s OK. You can still register in the “Open Competition.” Anyone in the world can enter the Open Competition, though there are no prizes associated with this category.
• (2) On the final page of the web registration system (the same page on which teams are asked to provide their e-mail address and password), you will see a text box labeled, “If you are participating in a local contest organized by your school, a local engineering association, or other organization, enter your Local Contest Code here.” You should enter the Local Contest Code in this text box.
  The Contest Code is GBDC
• (3) The website will check that the code is a valid one and will post a confirmation on the Team Home Page.
• (4) If you already registered and did not enter the Local Contest Code at the time of registration, you can add it at any time by logging into the Team Home Page.
• (5) Once your project or contest is underway, you can view your own Local Contest Scoreboard on the following web page: http://bridgecontest.usma.edu/standings/local/GBDC.htm. This scoreboard will be automatically updated at least every 24 hours after the Qualifying Round begins.

Use the comment form to ask any questions or to talk with other competitors.

A well done introduction to the practical steps of truss design.

Written in 2004. It has 448 pages and has an average of 4.5 star rating on Amazon.

Contains Illustrations.

Here is the link to purchase this book at Amazon:
Design of Building Trusses (Parker/Ambrose Series of Simplified Design Guides)

GarrettsBridges.com will be hosting a local contest this year! The local contest will run from Jan 29 to March 1, 2010. Anyone 25 and under can participate. Stay turned for the contest code. Did I mention that there will be cash prizes for the top three teams?

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.

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.

Shows the failure point in Nic’s Design

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).

Here’s a picture to show the scale:

Let me know what you think!

Cheers, 

Joe.

Here is a balsa wood bridge being tested to failure. You can tell how it breaks, which is pretty cool.