# Build a Balsa Bridge to Hold 20 lbs | Advice & Tips

• pasterino
In summary, the conversation discusses the design requirements for a balsa bridge that must hold 20 pounds and have a trapezoid clearance. The minimum length is 14cm and the maximum is 20cm, with a minimum to maximum height of 5-8cm and a width of 3cm. The person sharing their design has 24 feet of balsa to work with and is open to critiques and advice. They are limited to using small sticks of balsa, possibly 1/8 inch thick, for their high school AP Physics B course. The conversation also mentions the possibility of laminating and suggests looking at the balsa-bridge website for designs. The conversation concludes with the suggestion of building an arch and building
pasterino
Im building a balsa bridge for class but I'm struggling to find a design. The bridge must hold 20 pounds and have a trapezoid clearance. the minimum length is 14cm and the max is 20cm, min to max height is 5-8cm. Width must be 3cm. Here is my design so far, I would build two of these faces and connect them with horizontal lengths of balsa. I have 24 feet of balsa so please critique, advise, and even reconstruct my design. Thanks

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... and you are presumably limited to how much balsa you can use? (Otherwise you can just use a thick plank.) Does it only have to support a 20lb weight?

What level is this to be done at? Like a high-school project gets a different kind of answer to a college engineering class.

There are infinitely many designs - consider what happens when you put the balsa plank edge-up: pretty rigid right? You'll need at least two of these with the gap narrower than the width of the test weight. After that you can put anything you like up for the surface ... but I am imagining a std hobby sheet of balsa - if you have a pile of thin sticks it's trickier.

So you see how important the constraints are?

BTW: there is a simple design here which supports 220kg (485lbs).
The same site also has lots of tips and other designs, physics links etc.

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thanks for the reply, I am limited to small sticks of balsa, i believe they are around 1/8 inch but I am not sure. This is for my high school AP physics B course

Find out of laminating is allowed. If it is, this is a way to really increase the strength.

OK - check out the balsa-bridge website for designs - those folk were restricted by weight.
You may like to try making an arch. You can build long beams out of short lengths like building a wall.

At least now you know your design need only be quite short and the load light :)

## 1. How do I choose the right type of balsa wood for my bridge?

The most important factor in choosing balsa wood for your bridge is the weight and strength of the wood. Look for balsa wood with a high strength-to-weight ratio, as this will ensure that your bridge can support the 20 lbs weight. Additionally, make sure that the wood is free of any knots or defects that could weaken the structure.

## 2. What is the best method for constructing a balsa bridge?

There are several methods for constructing a balsa bridge, but the most common and effective method is the truss bridge design. This involves creating triangular truss structures using balsa wood beams, which distribute the weight evenly and provide maximum support for the bridge.

## 3. How important is the glue used in building a balsa bridge?

The type of glue used in building a balsa bridge is crucial, as it can greatly affect the strength and stability of the structure. It is recommended to use a high-quality, fast-drying wood glue specifically designed for balsa wood. Avoid using super glue or hot glue, as they may not provide enough strength for the bridge.

## 4. What are some tips for ensuring my balsa bridge can hold 20 lbs?

In addition to choosing the right materials and construction method, there are a few tips you can follow to ensure your balsa bridge can hold 20 lbs. These include reinforcing key areas of the bridge with extra layers of balsa wood, using lightweight materials for the deck of the bridge, and testing the bridge with incremental weights before adding the full 20 lbs.

## 5. How can I make my balsa bridge more aesthetically pleasing?

While the main goal of building a balsa bridge is to support a weight of 20 lbs, there is also room for creativity and design. You can add decorative elements such as paint, colored string, or even small models to make your bridge more visually appealing. Just be sure to not compromise the strength and structure of the bridge in the process.

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