They were only glued together at the ends, per specified rules, although we learned later there was an unwritten rule that you could not stack pieces to make a thicker member, so we were penalized slightly..

This next pic shows you the setup for the test: a 5 gal bucket is placed on the bridge & you slowly pour sand in until the bridge breaks. Max weight of 20kg. (my suggestion to dump a 50# bag all at once was not accepted)

We were unaware that the footing for the bridge would be 2″X2″s, & as fate would have it, they hit right in the middle of our trusses. You can see how it is flexing in between trusses along the bottom chord. This was ultimately the failure point. Otherwise, the bridge actually stayed very straight underneath the load.

Here you can see it holding up well:

In the specs for the bridges, the organizers did not specify a minimum height requirement, & 1 of the other teams took this to the extreme & built basically a pallet:

It was a great learning experience for us & has encouraged me to start a club next year where we do little beyond build bridges & towers!

Garrett Adds
Thanks for sharing! It is too bad about the unknown rule about doubling up the sticks. Your lateral bracing on the top and support for the bucket look really good. Another thing that probably would have helped is to have lateral bracing on the ends of the bridge as you look through it. This would stabilize it and help keep it from leaning or falling over sideways. You mentioned that the bridge failed because the supports (2x2s) caused a lot of shear pressure on your bottom chords.

That beam bridge is interesting, and it reminds me of a conversation I had recently with an engineer. He was saying that in real life they try to design bridges so that the mode of failure is gradual, and not sudden. It is hard to do this with model bridges, as most often they look pretty good and before you know it they just explode. But that beam bridge has enough flexibility built into it that you can definitely tell when it is having problems way before it actually breaks. Flexibility is the only plus to using hot glue. I’ve seen a bridge hold up a lot more weight simply because it did not break at the joints due to the flex in the glue than if it had used a harder glue, such as wood glue or white glue.

Loading a bridge by placing weights on top of it has become my method of choice. This is because I have access to a weight set with ample weights to to break any bridge I have created so far. This method is quite and easy, and requires a minimum of equipment. In fact, I do not even need a scale and can simply add up the total of the weights. This allows me to know the running total of force on the bridge, and I can add smaller weights when I think it is close to maxing out.

However, that brings up another point. Unlike the hanging bucket method with sand, I can only add weights in larger increments (2.5 pounds, for example). This means that I may break the bridge without knowing the precise amount it could have held. If I add a 30 pound weight and the bridge collapses, I don’t know if it could have held 25 more pounds or just 1 more pound.

You could substitute free weights with a bucket on top and fill that up with sand or water, but this creates a high center of gravity and you definitely will be cleaning up a large mess when the bridge does break. With anything that you add on top of the bridge, you need to be careful to get out of the way quickly when it breaks. 300 pounds of free weights will not feel good if it lands on your feet.

Instead of free weights you could use any heavy and dense object, such as bricks, heavy textbooks, etc.

You do need to elevate the ends of the bridge in order to get a good test. You can use scrap boards, books, or anything that won’t get crushed by heavy weight.

Pros

• Easy setup
• Minimal equipment
• Fun
• Potentially no dynamic forces

Cons

• Not precise
• Potentially dangerous to feet
• Requires heavy objects

Top Loading Tips

If you are going to test your bridge by putting textbooks on the top, like many people do for popsicle bridges:

• Make sure the first textbook is perfectly centered over the bridge
• Line up all the over textbooks with the first one
• Put each textbook on the bridge gently

If you aren’t going to test your bridge with any of the above methods, here is another simple one.

Take a bathroom scale and place it on the top of your bridge. Simply push down on the scale until the bridge breaks. Of course, only use this method if you think the bridge is not going to hold very much. I will tell you from experience, it gets very hard to push perfectly straight down over 100 pounds. You can end up breaking your bridge pre-maturely by accidentally pushing to one side.

The above photos give you several examples of the hanging bucket method used in real life situations. This method is fairly versatile, and you can adapt it to fit your needs. Please notice that in each of these photos there is a loading block that fits into the bridge, which in turn suspends the bucket with various hardware. You can use this method to load the bridge as shown here, or place the loading block on top of the bridge.

In order to be able to suspend a bucket below the bridge, you have to get the bridge high off the ground. You can use two tables pulled close together, or a table with a removeable leaf. Or you can use a specialized table with a hole cut out in the center made just for this purpose.

Filling the Bucket

Probably the most common weight to fill the bucket with is sand. However, you can use water, weights, gravel, or any other heavy object. Sand is cheap and also is easy to pour, although it can be messy. You definitely have to clean up sand after an event.

The hanging bucket method sometimes creates a problem when loading. The bucket has a tendency to swing from side to side as you fill it up. To counter this, pour your sand or gravel directly into the center of the bucket, don’t worry about trying to fill out the sides. Also, you can steady the bucket with a free hand from yourself or a partner.

Because the bridge is higher with this loading method, you can observe the bridge closely while it is being loaded. Just remember to wear safety glasses to avoid having wood splinters in your eyes.

You never ever want any part of your body to get below the bucket when it is being filled. Keep your fingers and toes well away.

Hanging Bucket Pros

1. Load from deck or top of bridge
2. Use a variety of weights: sand, rock, water, weights
3. Uses inexpensive materials

Hanging Bucket Cons

1. Can be messy
2. Potential for dynamic force causing premature failure

Requirements

1. Loading block, rod, and rope or chain
2. Table or way to lift bridge up for bucket clearance
3. Bucket
4. Sand, small rocks, water, or other heavy and dense objects

Tips for Using Sand

If you have to pour sand into a bucket to load your bridge, here are a few tips:

• Pour quickly but steadily
• Pour into the center of the bucket
• Keep the bucket steady
• Never stick any fingers, arms, feet, or legs under the bucket
• Don’t bump the testing platform

Methods of Testing Bridges

I’ve used and seen a lot of different ways to load model bridges. A lot of people do not want to buy lots of fancy equipment, so they use only what they have available to them. This makes for a lot of creative ideas for testing bridges. I’ll outline some of the ways I’ve seen that work the best.

Hanging Bucket Method

#1 – Hanging Bucket

This is a classic method, and is used for Science Olympiad competitions. The bridge rest on two elevated supports, which could be two tables with a small space between them or one table with a hole cut in it. A loading block is placed either on top of the bridge or inside the bridge and a bucket is suspended below using a eye-bolt, S hook, and some chain. The bucket is then filled up with weight (typically sand, water, or free weights) until the bridge breaks or the maximum load is reached.

———-> Read more about the hanging bucket method

Weights on Top

#2 – Weight on Top

If you do not have access to a hanging bucket system or want to keep the bridge lower to the ground, you can simply load the bridge from the top. This does not work well for arched bridges, as they typically do not have a flat surface to put weights on. Many teachers host a classroom competition to see how many textbooks each bridge can hold. The textbooks are stacked on top of the bridge.

You can use books, free weights (from a weight set), or a bucket filled with weight to load your bridge from the top. Be careful when the bridge does break because if you have a tall pile of weights, whatever they are, they will come tumbling down with a lot of force. Sometimes I have placed cameras around the bridge filming the destruction, and the cameras have come close to being smushed by sliding weights.

———-> Read more about the weights on top method

Stand on a Bridge

#3 – Stand on It

Standing on your bridge is perhaps the ultimate testing method. I love this because if the bridge holds, you were able to create a fully functioning bridge. This is why I am separating the standing method from the other “weight on top” methods. Standing on your bridge gives the best sense of fulfillment and moves your bridge from simply a “model bridge” to a real bridge, even if it is constructed from only balsa wood or popsicle sticks.

However, there are some situations where the human weight method is not appropriate. These cases are usually when you are given a maximum load the bridge should support, which is less than your weight. Also, standing on a bridge is a more dynamic loading than placing weights on top or loading a bucket with sand. It is a lot harder for you to stand still and load the bridge evenly, which causes the bridge to be stressed more in some parts than others. Standing on the bridge can also be dangerous, depending on how high off the ground your bridge is. The lower the better.

———-> Read more about the human weight method

Machine Loading

#4 – Machines

Machines usually make things easier. They can definitely help make testing a model bridge quicker and smoother, while providing an accurate measurement of the weight held. Machines are generally very consistent in how they load bridges, which allows you to not worry about loading error causing premature failure. Also, I think machines let you just sit back and enjoy the pride of your life being crushed, so why not make the most of it? Since you have your hands free, pull out a camera and snap some shots or record a video.

———-> Read more about machine loading

General Loading Suggestions

Efficiency

My time in the Science Olympiad taught me to be very efficient during the testing process. The longer a model bridge has to hold weight, the greater chance that it will fail early. We were given 10 minutes to set up and test our bridge. I spent most of the time setting up the loading block and as little time as possible actually pouring sand. As soon as I starting pouring sand, I didn’t stop or delay at all.

Record the Event

While most handheld cameras do not capture frames quickly enough to really see what is going on, you can still get a good idea of how your bridge failed from watching a video. I recommend always taking a video of the testing. The more angles you can get, the better. I now try to set up three cameras: one broadside view, one looking into the bridge, and one from a higher angle.

What is the Best Way to Test a Bridge?

I’ve shown a lot of different methods, and you want to know which one is the best to use for your bridge. The answer is: it depends. As I mentioned earlier, a machine is probably the most steady and consistent method, but they sure are expensive. I grew up using the hanging bucket method in Science Olympiad, and I can use that method very well and get very consistent results. However, because that takes a while to set up, I am moving to using free weights placed on top of the bridge. This is the method that works the best for me with the equipment that I currently have. You will have to figure out how much time/money you want to invest into testing your bridge and choose a method.

If I have missed anything, or you would like to share your experiences with one of these methods, please leave a comment below.

Local Contest Code

The code is: GBDC

Instructions

(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.”

(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.

(3) The website will check that the code is a valid one and will post a confirmation on the Team Home Page.

(4) If a contestant has already registered and did not enter the Local Contest Code at the time of registration, he or she can add it at any time by logging into the Team Home Page.

(5)You can view the 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.

(6) If you have any problems accessing the Local Contest Scoreboard, or if you have any questions, don’t hesitate to contact me here on this page.

Contest Prizes

• 1st Place: $50
• 2nd Place: $30
• 3rd Place: $20

These cash prizes will be paid out via PayPal.

For tips you can join the facebook fan page for the West Point Bridge Design Contest and follow their twitter page @WPBridgecontest.

Ice Cream Stick Tower

Here is an ice cream stick structure made up from 200 sticks, which carried 30kg. of weight.

Submitted by Sandip Babar.

Questions from Garrett

What glue did you use to build this tower?

Was this just for fun and what inspired your design?

Did you learn anything from building this structure that you could share with the rest of us?

Thanks for sharing!

Here is the link to the main site:

http://bridgecontest.usma.edu/

Is it just me or is the slenderness check new for this year? I did not get much of a chance to play around with the 2011 version, so I am not sure if it is brand new or not. The slenderness check caught me by surprise and is somewhat annoying.

I’d love to hear your comments about the program and how you are doing in the contest.

Beam, Arch, and Suspension Bridge

Have you ever wondered what type of bridge is the strongest? I definitely did, and that is why I created this popsicle bridge kit to compare and contrast three types of bridges to see which one can hold the most weight. This is a very interesting project and was a lot of fun to make and test.

In order to be a scientific test, each bridge is made from similar materials (popsicle sticks and glue, and cord for the suspension bridge), and are the same length. These three bridges also have very similar construction techniques, which allows you to compare each type against each other.

Popsicle bridges are great for school projects and the like because they are very easy to make and a lot of fun to test to failure. Popsicle sticks, unlike toothpicks, are quite strong and allow you to make a solid structure which is capable of holding a lot of weight before collapsing into a thousand pieces. If you are looking to compare different kinds of bridges I highly recommend that you consider this kit.

Included in the kit are all the materials you will need to build these three bridges: a Beam bridge, an Arch bridge, and a Suspension bridge. Each bridge type is different to make and will provide hours of hands-on fun. This kit is designed for simplicity, which makes it great for younger ages. This kit is also created for sincere scientific testing, so students of all ages can benefit from it. Buy your kit today and receive it in the mail in just a few days!

*This kit requires some of the popsicle sticks to be cut. If you do not have a tool to do this already, choose the option to add a craft saw blade.

You can purchase this kit directly from this page or find it in my main store

I like this video because of the commentary. The observers discus their opinions about why each bridge failed (casually) as the video plays. Notice the comment about lateral bracing on the first bridge. Would you agree with them?

Did you catch how the second bridge failed? This would have been an easy fix, and it just goes to say how you should reinforce the loading area on your popsicle bridges. Take the lessons from this video and use on your own models.

I also appreciate this video because the winner shares my name, Garrett. What do you think made Garrett’s bridge so strong?