9 Types of Bridges

Bridges are crucial structures in modern infrastructure, connecting areas separated by obstacles like rivers, valleys, or roads. They come in various designs, each tailored to specific environmental conditions, materials, and spans. Below, we explore the main types of bridges, highlighting how each is uniquely suited to its purpose.

1. Beam Bridge:

Lake Pontchartrain Causeway in Louisiana, USA, is one of the longest beam bridges globally, stretching across Lake Pontchartrain.

Parts: Horizontal beams, piers at each end.

Purpose: The simplest structural form of a bridge, the beam bridge features a straight horizontal beam supported by piers at both ends. The load on the beam bridge is primarily vertical load which is transferred directly to the piers and subsequently into the ground. It is most suitable for short distances.

2. Truss Bridge:

Bollman Truss Railroad Bridge in Savage, Maryland, USA, showcases historical truss design used in railway construction.

Parts: Trusses made of triangular units, deck, piers.

Purpose: The truss structure provides a rigid frame that distributes the load more evenly than a simple beam. Truss bridges can span longer distances than beam bridges because the truss adds considerable stiffness and reduces the bending moments acting on the structure.

3. Arch Bridge:

Ponte Vecchio in Florence, Italy, is a medieval stone arch bridge known for its shops built along it.

Parts: Curved arches, abutments.

Purpose: The arch bears the load and pushes the forces outward along the curve to the abutments at either side. This design is inherently strong and can carry more weight than a beam bridge. The arch bridge is efficient in spanning large areas and looks aesthetically pleasing.

4. Suspension Bridge:

Golden Gate Bridge in San Francisco, California, USA, is one of the most iconic suspension bridges.

Parts: Cables, towers, deck, anchors.

Purpose: The towers hold up the main cables, which in turn hold vertical "suspender" cables that support the deck. This design allows for very long spans needed in wide water or valley crossings. The cables disperse the load through tension forces into the towers and then downward into the ground.

5. Cable-Stayed Bridge:

Millau Viaduct in southern France is the tallest bridge in the world and features a stunning cable-stayed design.

Parts: Cables, towers, deck.

Purpose: In a cable-stayed bridge, the cables attach directly from the tower to the deck at various intervals. This allows for the direct transfer of load through the cables to the towers, which makes it suitable for longer spans than truss bridges but with less material than needed for a suspension bridge.

6. Cantilever Bridge:

Forth Bridge in Scotland is a prime example of a cantilever bridge with a distinctive industrial appearance.

Parts: Cantilever arms, central span, piers.

Purpose: The cantilever arms project into space and are supported only on one end. They are often used in pairs that extend from opposite sides and meet in the middle, sometimes with a simple beam connecting them. This design allows for large spans without the need for piers in the center, making it ideal for situations where the central part of the bridge cannot have supports.

7. Tied-Arch Bridge:

Fremont Bridge in Portland, Oregon, USA, is a notable tied-arch bridge.

Parts: Arch, ties, deck.

Purpose: The arch supports the deck while the ties prevent the arch from spreading outward due to the load. This structure effectively combines the benefits of an arch and a beam and is particularly useful where a traditional arch cannot be supported at the ends.

8. Floating Bridge:

Evergreen Point Floating Bridge in Washington, USA, is the world's longest floating bridge.

Parts: Pontoon sections or barges, anchors, deck.

Purpose: Used primarily in bodies of water with unsuitable conditions for traditional foundations, floating bridges rest on large pontoons or barges that support the deck. These bridges move with the water but are anchored securely to prevent undue movement.

9. Movable Bridge:

Tower Bridge in London, England, is an internationally recognized bascule bridge that opens for river traffic on the Thames.

Parts: Moving mechanism (bascule, swing, or lift parts), counterweights, control towers.

Purpose: Movable bridges are designed to allow boat or ship traffic to pass through. They can be lifted, swung open, or otherwise moved temporarily. While complex in terms of mechanical components, they are essential in navigable waters. 

Bridge Types Based on Mobility

Bridges can also be categorized based on their mobility and the ability to change position to accommodate traffic, both on the road and in the water. Here are the main types of bridges classified by their mobility:

1. Fixed Bridges:

Most beam bridges, arch bridges, and cable-stayed bridges fall into this category. Fixed bridges are the most common type and do not move. They are designed to stay in one place permanently and to handle all loads and environmental conditions without any change in position.

2. Movable Bridges:

These bridges are designed to move to allow navigation or other types of traffic to pass through. Movable bridges can be further classified into several types based on their specific movement mechanisms.

Types:

Bascule Bridges: 

Also known as drawbridges, these use a counterweight to lift the roadway around a horizontal hinge and pivot point.

Swing Bridges: 

These rotate horizontally around a fixed point, usually the center, to open a clear path for boat traffic.

Lift Bridges:

These have a deck that rises vertically while remaining parallel to the deck, using either counterweights or hydraulic systems.

3. Retractable Bridges:

Less common than other movable bridges, retractable bridges (or roll-on bridges) slide backward to clear the way, rather than lifting or swinging. This type is used in situations where there is limited vertical or horizontal space for the typical movements of a movable bridge. The retractable bridge at the old entrance to the Brooklyn Navy Yard is one of the few existing examples.

4. Transporter Bridges:

A less common type, transporter bridges carry a section of roadway across a river or canal. The roadway, or gondola, is suspended from a trolley which runs along tracks on an overhead frame and can move from one side to the other, carrying vehicles and pedestrians while allowing water traffic to pass underneath.

The Newport Transporter Bridge in Wales is one of the few operational transporter bridges left in the world.

Bridge Types Based on Function

Bridges can be classified based on their primary function, which helps to determine their design and structural elements. Here are some common types of bridges categorized by their function:

1. Highway Bridges:

These bridges are designed to carry road traffic, including cars, trucks, and buses. They often need to meet specific standards for load, width, and clearance to accommodate the volume and type of vehicular traffic. The majority of overpasses and flyovers seen on highways are designed as highway bridges, often using beam, truss, or cable-stayed designs.

2. Railway Bridges: 

Specifically designed to support the weight and dynamics of train traffic. Railway bridges often require a very sturdy construction due to the heavy loads and high speeds of trains. Many railway bridges are constructed using the truss or arch design, which provides the necessary strength, such as the iconic Forth Bridge in Scotland.

3. Pedestrian Bridges:

These bridges are designed for foot traffic and sometimes bicycles. They are usually smaller and not built to withstand the heavy loads that vehicle bridges must endure. Safety, accessibility, and aesthetic design are key considerations. Footbridges in parks or between buildings in urban areas, like the Capilano Suspension Bridge in Canada, focus on ease of use and minimal environmental impact.

4. Aqueducts: 

Used to transport water, typically from a natural source to a community or agricultural area. These bridges are part of a water management system and are designed to maintain a specific gradient and protect the water from contamination. Historical examples like the Pont du Gard in France show the use of arch designs to provide both strength and a continuous flow of water.

5. Viaducts: 

A series of bridges connected in a long sequence to traverse a long or wide valley or a series of obstacles. The design usually involves multiple spans supported by piers. The Millau Viaduct in France is a contemporary example where a tall, multi-span cable-stayed bridge crosses a deep valley.

6. Drawbridges: 

These are movable bridges that allow boats and ships to pass by lifting a section of the bridge. They are commonly found in busy waterways and are critical in locations where it's important to manage both road and waterway traffic.

The Tower Bridge in London is a famous historical drawbridge.

Different Bridge Materials

Bridges are constructed using a variety of materials, each chosen for its unique properties such as strength, durability, cost, and aesthetic appeal. The choice of material can significantly impact the design, construction process, maintenance requirements, and lifespan of the bridge. Here are some of the most commonly used materials in bridge construction:

1. Steel:

Ideal for strong, flexible bridges like suspension and truss bridges. It's very strong and can bend without breaking.

2. Concrete:

Common in standard road bridges and arches. It’s very durable and can be shaped easily when wet.

3. Reinforced Concrete:

Used where extra strength is needed without much extra cost. Adds steel bars to concrete, making it stronger against pulling forces.

4. Prestressed Concrete:

Good for longer spans that need to handle more tension. The steel inside the concrete is tightened before the concrete is poured, making it even stronger.

5. Stone:

Used in older or traditional bridges for beauty and durability. It’s naturally strong and long-lasting but varies depending on the type of stone.

6. Wood:

Used for smaller, aesthetic bridges like footbridges. It's easy to work with and looks natural, but it's less durable unless treated.

7. Aluminum and Alloys:

Useful for lightweight or temporary structures and it’s lighter than steel and doesn’t rust.

8. Composite Materials (like fiber-reinforced polymers): 

Increasingly used for parts of bridges that need to be lightweight and resistant to wear. They're strong, lightweight, and don't corrode like metal.

What Influences Different Bridge Designs?

Different bridge designs are influenced by various forces that they must withstand throughout their use. Understanding these forces helps engineers choose the appropriate type and materials for constructing a bridge. Here are the main forces that influence bridge designs:

Compression:

A force that squishes something together.

Impact on Bridges: Important in arch bridges, which push this squishing force from the middle of the bridge down and out to the ends.

Tension:

A force that stretches something apart.

Impact on Bridges: Crucial in suspension and cable-stayed bridges, where the cables are continuously being pulled tight to hold up the bridge's deck.

Bending:

When something straight gets bent.

Impact on Bridges: Beam bridges bend when heavy loads, like cars or trains, move over them. The bridge must be able to bend a little without breaking.

Torsion:

A twisting force.

Impact on Bridges: Can be a problem in bridges when parts of them twist under uneven loads or strong winds, which can cause damage if not properly designed.

Shear:

When parts of a material slide past each other in opposite directions.

Impact on Bridges: Happens where the bridge deck meets supports, and can cause parts to slide out of place if not well secured.

Dynamic Loads:

Loads that change over time, like cars moving over a bridge, wind, or earthquakes.

Impact on Bridges: All bridges need to be built to handle these moving and changing forces safely, especially in areas with lots of traffic, strong winds, or earthquakes.