# How Do Forces Act on Members in a Pratt Truss Bridge Design?

• giacomh
In summary, the conversation is about designing a pratt bridge for a class project. The design is based on a two-dimensional drawing of one side of the bridge, with horizontal members in compression and vertical members in tension. The diagonal members vary between tension and compression depending on the weight distribution. The possibility of this design is discussed, with the conclusion that it is possible depending on the loading and placement of weight.
giacomh

## Homework Statement

I'm designing a pratt bridge for class that looks like this:
http://www.garrettsbridges.com/photos/pratt-truss-bridge/attachment/pratt-truss-bridge-2/

I have a two dimensional drawing of one side of the bridge.

2. Homework Equations / 3. The Attempt at a Solution

All of my horizontal members on the top are in compression and the bottom are in tension. All of my vertical members except the first one one each side are in compression. My diagonal members vary between tension and compression depending where the weight is placed. Is this possible?

Yes, but it depends on the loading. The end diagonals joining the supports would be in compression. Otherwise I would expect tension in the vertical plane diagonals. Perhaps you need to reword the question or provide evidence for your belief.

## 1. What is a Pratt Truss Bridge?

A Pratt Truss Bridge is a type of truss bridge that uses a series of diagonal members in a "V" pattern to distribute the weight of the bridge evenly. It is known for its distinctive "W" shape and is commonly used for medium to long span bridges.

## 2. What are the benefits of using a Pratt Truss Bridge?

The Pratt Truss design is known for its strength and efficiency. It is able to support heavy loads while using less material compared to other bridge designs. It is also relatively easy and cost-effective to construct.

## 3. What factors should be considered when designing a Pratt Truss Bridge?

When designing a Pratt Truss Bridge, factors such as span length, expected load, and location/terrain must be taken into account. The type of materials to be used, such as wood or steel, also plays a significant role in the design process.

## 4. How is the stability of a Pratt Truss Bridge ensured?

The diagonal members in a Pratt Truss Bridge provide stability by transferring the load from the top of the bridge to the bottom. Additionally, the use of vertical members and a strong foundation helps to distribute the weight evenly and prevent the bridge from collapsing.

## 5. Are there any limitations to using a Pratt Truss Bridge?

While the Pratt Truss design is strong and efficient, it is not suitable for all types of bridges. It is most commonly used for medium to long span bridges, and may not be the best choice for shorter spans or curved bridges. Additionally, the design may not be as visually appealing as other bridge designs.

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