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.

I have not tested this method out myself yet, but I will soon. It take very little prep or materials. All you have to do is soak the wood sticks for a couple days, bend them around a shape, and let it dry. He mentioned putting it on some low heat while drying.

My only question at this point is whether or not it reduces the strength of a popsicle stick. I’m not sure at this point.

Game description:
Construct a bridge and test your building skills. Help your people gather items located on the other side of valley.

How to play?
Build a bridge using your mouse and available budget. When it is done click “Test your bridge”.
Your workers will use it to get items located at the other side of valley, and bring them back to the shop. Your goal is to collect all items in level.

For each level you have limited budget. All money that you won’t use, become your score, so cheaper bridge = higher score.
Money collected in all levels of game will be your total score and will be sent to leader board. You will use those money in challenge mode too.

Building tips:
* There are two types of bridge elemets: “walk” – workers can step on them, “connectors” – used only to connect elemets of the bridge, workers do not collide with them.
* “Connector” elements are cheaper and lighter so use them as much as you can
* Each type of item have different weight and some of them will need stronger bridge then others.
* At the begining of game only wood elements of bridge are available. In further levels, aditional materials will be accessible also, so use them wisely.

Design the Bridge

To start building a popsicle bridge, first you need to come up with a design. Sometimes aspects of the design are set for you if you are building a bridge for a school project or a competition. Often the length of the bridge, as well as how many popsicle sticks you can use are defined by the rules you have been given. Other things, however, are up to you.

If you are just starting out building model bridges, I would recommend you use one of the three most common truss designs. These are the Howe Truss, the Pratt Truss, and Warren Truss. Each of these are very strong designs. Once you have picked out a design, then you can draw out your design to life size on paper, you even draw it out on the computer. The blueprints I have for sale have done all this work for you, and allow you to focus on building the bridge without worrying about how to design a bridge.

Build the Bridge

Now you are ready to build your popsicle stick bridge. Choose your popsicle sticks carefully, because when you buy them from a store some of the sticks in the package will be no good. Choosing a glue to use is also important. Often what I do is build each side of the bridge individually and then join them together. When you are joining the sides, be sure to make the bridge perfectly vertical. If the bridge is leaning at all, then it will be much weaker. I always include lateral bracing to make my bridges stronger.

After you finish your bridge completely, wait enough time to allow the glue to dry completely before you test the bridge. Sometimes you will want to test the bridge immediately, but your bridge will not hold as much weight if you test it before the glue has cured. Be sure to take pictures of your popsicle bridge and send them to me! I would absolutely love to see photos of the bridges you have made. In fact, I have a photo contest going on for the month of January, so be sure to check that out.

Test Your Popsicle Stick Bridge

Testing a popsicle bridge is perhaps the best part of making a bridge. I think so, that is. Perhaps it is something inherent in a boy’s nature to want to see things break and explode, I am not sure. I do know that I love testing my bridges to failure not only to see them fly into millions of pieces, but also to get an efficiency score and to learn how to build a better bridge. You can learn a lot more about testing model bridges on my Testing Tips page.

Testing the Warren

To start out building a model bridge, you have to decide what materials to use. Frequently I use Balsa or Basswood. These two woods are common, and you can find them in most any hobby store. You can also use popsicle sticks, toothpicks, paper, cardboard, and tons of other things. Often I choose to make a balsa wood bridge because they are versatile and fun to construct. What materials you choose will depend on the goal you have for your bridge.

Most competitions tell you what materials you can use, and limit your choice. If you want to build this model bridge to exhibit on your shelf, then you can use materials that have more aesthetic appeal. However, if you are building a bridge to test it to failure, in order to see how much weight it will hold, then you want to use efficient materials.

Once you decide what materials to use, you need to start designing your bridge. Decide how long you want the bridge to be. Are you trying to set the world record for the longest popsicle stick bridge, or are you going for an easy project? You also need to pick out a truss design for your bridge. There are three standard trusses used in engineering, the Warren, Pratt, and Howe. After you pick a design, I find it helpful to draw it to scale on graph paper.

After you have designed your bridge, you need to start construction. Make sure you have all the tools and materials you will need, such as glue, saws or exacto knives, clamps, jigs, wax paper, and such. The glue you choose is important to the strength of your bridge. I recommend Cyanoacrylate Glue. Use your drawing on graph paper as blueprints to build your bridge on. Consider covering your blueprints with wax paper to help keep glue from ruining your drawing. You can do this step in two parts. Make one side of the bridge first, and then remove it from your blueprint. Repeat for the other side, and then join the two sides together to make a bridge.

Now that you have finished your bridge, you can enjoy it. If you are going to test it, remember to wear safety goggles. If you are going to display the bridge, or use it for a model train set, you are good to go.

How Does CA Glue Work?

CA glue is a acrylic resin. It uses water to cure. Yes, water. Other glues rely on the lack of water to cure, but CA glue is the opposite. Usually the natural moisture in air is enough for the CA glue to harden, but this is not always the case.

CA glue works best on porous materials, such as Balsawood or Basswood. In fact, any kind of wood is ideal for CA. Actually, one of the absolute best materials for CA is your skin. No joke, human skin is very porous and has a good amount of moisture built into it. This is why CA glue always seems to instantly bond your fingers together. I have accidentally glued my fingers together many times throughout my building career.

Cyanoacrylate Glue comes in different thicknesses, or viscosities. Thicker CA’s take longer to set, and are heavier. In addition, thicker types tend to leave gaps in the joints. On the other hand, a thin CA glue will soak right into the wood, creating a stronger joint.

Benefits of CA

• Quick Drying
• Can Be Lightweight
• Can Soak Deep Into Joints

Disadvantages of Cyanoacrylate

• CA Glue Is Expensive
• Easy To Glue Your Fingers Together
• CA Goes Bad Relatively Quickly
• It is Easy to Use Too Much
• Has Strong Fumes

CA glue has strong fumes, which some people react against. Please only use CA glue in a well ventilated area. Have a window open in the room where you are working.

Where Can I Get CA Glue?

• Local Hobby Store
• Online

Any hobby store ought to have some sort of CA glue. But you probably can find a better price online, which may or may not include the tax. In fact, here is a link that will take you to Amazon and show you their selection of CA glues from their various sellers:
CA Glue From Amazon

Tips On Using CA

Remember that CA glue bonds easily to human skin? Well, eventually the natural oils in your skin break down the glue molecules and the CA is worn away. Keep this in mind as you are handling the wood that you are using to build your models. As a general rule of thumb, always wash your hands to reduce the oil transfer to the wood you are using. Human oils weaken any glue joint, especially when using CA glue.

Don’t use too much glue. A little goes a long way.

To help CA glue last longer, keep it refrigerated.

To create a stronger joint, roughen up the edges of wood you are gluing with sandpaper.

I have found that if you do glue your fingers to your model, then don’t try to peel your finger off. Instead, rotate your model and twist until your finger comes free. This helps to prevent skin loss.

Additional Resources

Cyanoacrylate Glue and Other Adhesives
What is Cyanoacrylate Glue?
What Good is CA Glue?
Cyanoacrylate

Why Do I Like Basswood So Much?

Basswood has some advantages over Balsa wood. For instance:

• Basswood has significant natural strength. This makes it easier to work with.
• Basswood bends easily. For making arch bridges, this comes in handy.
• Basswood looks nice
• Basswood is relatively consistent from tree to tree in density.

However, Basswood does have some disadvantages. These include:

• Basswood is more expensive than other woods, such as Balsa.
• Basswood is not always readily available.

Basswood Information
Here is another resource about Basswood.

Glue for Basswood

Basswood does not require the use of special glue. I would still follow my recommendations at my Glue Tips page.

Where to Buy Basswood

I would always recommend that you go to a local hobby store to pick up your Basswood. However, if that is not an option, here are some places to buy Basswood online:
Basswood Sheets

Basswood Sticks

To help clear up any confusion when I talk about the “efficiency” or “efficiency score” of the bridges I build. This is a mathematical equation to determine how well a bridge performed.

Simply take the mass that the bridge held, and divide that by the mass of the bridge.

Mass held
________ = Efficiency

Mass of bridge

Some confusion comes up when I weigh the bridge in grams while add weight to the bridge in pounds. These units do not have the same base, and cannot be divided against each other. I usually convert pounds to kilograms (1kg = 2.2 pounds) and then multiply the number of kilograms by 1000 to get grams.

So if my bridge held 54 pounds, I would convert that to kilograms. 54 pounds equals 24.54 kilograms. That equals 24540 grams.

To get the efficiency, I take 24540 and divide that by the mass of the bridge, which was, say, 33 grams. The efficiency score is then 744.