Build a Balsa Wood Bridge: Explaining Arches & Compressive Strength

[IGeekbot]

Can anyone or does anyone know where I can get a good explanation of how to figure out how big an arch should be for a bridge?


I am thinking of making one for our competition, and if I can't get that to work right, I will switch to a king post deisgn.


Oh, and is it true balsa and other types of wood are better in tension than compression because the cell walls will lose compressive strength if the water is taken away?

 

[xanthym]

Try reference given below. Scroll down its page to find some excellent resources, including free bridge design software.
http://abcdpittsburgh.org/kids/kids.htm

 

[wais]

Sure, I can provide some information on arches and compressive strength for building a balsa wood bridge. First, let's talk about arches. An arch is a curved structure that is used to span an opening, such as a bridge. It is an ancient architectural design that has been used for centuries due to its strength and stability. The curved shape of an arch allows it to distribute weight evenly, which makes it ideal for supporting heavy loads.

When building a balsa wood bridge, it is important to consider the compressive strength of the wood. Compressive strength is the ability of a material to withstand forces that are trying to squeeze or compress it. Balsa wood is a lightweight and low-density wood, which means it is not as strong in compression as other types of wood. However, it is still a popular choice for building bridges due to its high strength-to-weight ratio.

To figure out how big an arch should be for a bridge, you need to consider a few factors. First, you need to know the span of your bridge, which is the distance between the two supports. The larger the span, the bigger the arch needs to be to support the weight. Next, you should consider the weight of the materials used to build the bridge, as well as the intended load it will need to support. This will help determine the size and shape of the arch needed to distribute the weight evenly.

If you are having trouble figuring out the size of your arch, you can consider using a king post design. A king post truss is a simple triangular structure that can be used to support a bridge. It consists of a vertical post in the center with two angled members connecting it to the top and bottom chords. This design is often used for smaller bridges and can be a good alternative if you are struggling with the arch design.

Regarding your question about balsa wood being better in tension than compression, it is true that balsa wood is stronger in tension than compression. This is because the cell walls in balsa wood are made up of long fibers that are oriented in the direction of the tree's growth. When weight is applied to the wood, the fibers are pulled apart, which is better for tension forces. However, as you mentioned, if the wood is dried out or the water is taken away, it can lose some of its compressive strength. This is why it is important to keep the wood dry and avoid exposure to moisture when building a balsa wood bridge