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.

There are several ways to test model bridges:

• With a machine
• By pouring sand
• Textbooks
• Pushing down on your bridge

Using a machine

Obviously, if a machine is being used to test your bridge, there isn’t a lot you can do. You can stand watching the destruction of your bridge. Or turn away and cover your eyes with your hands. I would not recommend the latter option. You miss out on the most exciting part of model bridge building.

After spending all that time and effort making your bridge, why not enjoy watching it being crushed? Don’t worry, the bridge can’t feel a thing. You can learn valuable information by watching your bridge break. And unless you happen to capture the event on videotape, you won’t ever be able to see it again.

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

Using textbooks

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.

What is the best way to test a bridge?

Which is the best method? I can’t say for sure. I would say that if you had a machine that pushed down at a slow rate, that would be ideal. Most machines add force to your bridge very quickly, and you may or may not be able to see where your bridge broke.

The sand pouring method is slightly slow if you are using a cup to transfer sand from one container to the one hanging from your bridge. Also, it is hard to make sure that you are pouring correctly and watch your bridge at the same time.

The textbook method is great because of its simplicity. There is very little mess, and textbooks are readily available. However, you have to add the load in chunks, rather than a continuous stream. You won’t get an exact weight held by your bridge.

Using a scale to push down on your bridge is also very simple. But you won’t be able to load your bridge very much. This might be overcome by first putting a bucket on the scale, and filling that with sand or other heavy objects, and then pushing down with your hands.