This article will answer the question “what is a beam bridge,” explain its advantages and disadvantages and explore design options.
What is a Beam Bridge?
A beam bridge is a bridge type that is composed of beam members to make up the superstructure of the bridge. In the context of pedestrian, trail, or greenway bridges, beam bridges can be an economical solution for footbridges or light vehicle bridges.
A beam bridge may also be known as a stringer bridge. A beam bridge design uses multiple horizontal beam members with abutments/piers located on each end. Usually, these members are a simple span where the members only see bending forces.
Beam bridges include:
- Curbs
- Decking
- Railing
Material Considerations
The design of a beam bridge for pedestrian use will depend on the materials chosen for construction. Options include:
Fiber Reinforced Polymer (FRP)
FRP is a lightweight material that requires minimal maintenance and could have a 100+ year lifespan. Although it does have a higher upfront cost than wood or steel, the maintenance and replacement costs are significantly less than wood or steel.
Steel
Steel is extremely heavy, can span long distances, and has a long lifespan. Steel bridges are difficult to assemble on an interior trail system, leading to higher installation costs.
Wood
Wood is the least expensive option with the shortest lifespan of about 30 years and requires frequent maintenance. Wood boards often need to be replaced every few years due to rot, and some bridges need to be painted every few years. Wood deck boards can also be slippery when wet, which can be dangerous for pedestrians. harmful if the bridge is in a place with heavy foot traffic.
Considerations for FRP Beam Bridges
When using FRP, beam bridges are ideal solutions for short spans, ranging from 10 to 24 feet long.
FRP Beam Bridge – Advantages
Beam bridges can bring people together, connect communities, and help people explore nature. Additional benefits include:
- Access to previously inaccessible lands
- Allow access to stunning views
- Beneficial for short spans
- Can be built quickly with an inexperienced crew
- Can be built almost anywhere
- Increase accessibility to anyone who is disabled
- Can be customized with various rail, curb, and decking options
- Offer year-round access to flooded areas or crossing over ephemeral (seasonal) streams
FRP Beam Bridge – Disadvantages
When selecting a beam bridge, determine the structural design and environmental factors to ensure a beam bridge is the best option for you.
- FRP material properties limit the bridge length
- Limited camber control
FRP Beam Bridge Considerations
To accurately determine if a beam bridge is the best option for your project, consider the following factors.
- Dimensions and strength
- Environmental factors
Dimensions and Strength
You will need to know the total size (height, length, width) and the design loads. Additionally, the following questions will help to determine the bridge design factor.
- Does it need to accommodate foot traffic?
- Does it need to support bikes or vehicles?
- What do the rail heights need to be?
- What will the snow and wind loads be?
Environmental Factors
Ask yourself the following environmental questions.
- Will the bridge cross over a body of water?
- Will the bridge cross over a highway?
- Is a geotechnical analysis needed?
- Does a flood study need to be conducted?
- How difficult will it be to transport bridge parts and tools to the site?
Beam Bridge vs. Suspension Bridge
A beam bridge and a suspension bridge carry weight in very different ways. A beam bridge is a simple structure of horizontal beams on vertical abutments, or piers for longer spans. A suspension bridge hangs its deck from cables in tension, with towers at the abutments.
- What carries the load: on a beam bridge, the beams bear the weight of the traffic. On a suspension bridge, the cables bear it.
- Span: a beam bridge suits short spans; an FRP beam can span 10 to 24 feet. A suspension bridge suits long spans, up to 7,000 feet.
- Materials: a beam bridge can be built from FRP, steel or wood. Suspension bridge cables are made of steel.
- Movement: a beam bridge resists twisting and bending under traffic. A suspension bridge moves, twists and sways under live load.
For parks, hiking trails and remote sites, the simple, easy to assemble beam bridge is often the better fit. A suspension bridge suits busy waterways, mountain regions and long distances. Read our full beam bridge vs. suspension bridge comparison for the pros and cons of each.
Contact Us When You’re Ready for a Quote
The Areté Structures I-Beam Stringer Bridge is an economical solution for your shorter span footbridge or light vehicle bridge needs. When you’re ready for a beam bridge quote, reach out to the Areté Structures team.