Steel bridges are diverse structures categorized by their design, load-bearing mechanisms, and materials. Here's an organized overview of the main types, highlighting their characteristics and applications:

1. Suspension Bridges

Structure: Uses cables anchored to towers or abutments to support the deck. Steel is prominent in cables, towers, and anchorages.

Features: Ideal for long spans (over 500 meters), with flexibility to withstand dynamic loads.

Examples: Golden Gate Bridge (USA), Akashi Kaikyō Bridge (Japan).

Advantages: Efficient for very long spans, aesthetic appeal.

2. Beam Bridges

Subtypes:

Box Girder: Hollow steel sections for torsional strength; used in highways and railways.

Example: Millau Viaduct’s approach bridges (France).

Plate Girder: I-beams or rectangular plates for shorter spans (up to 100 meters).

Example: Urban highway overpasses.

Simple Beam: Horizontal steel beams supported by piers.

Features: Straight, rigid decks; cost-effective for mid-length spans.

3. Truss Bridges

Structure: Triangular frameworks (Pratt, Warren, Howe, Baltimore trusses) to distribute loads efficiently.

Features: Lightweight, strong, and suitable for railroads and roads.

Examples: Brooklyn Bridge (USA, hybrid suspension-truss), Iron Bridge (UK).

4. Cantilever Bridges

Structure: Deck extends horizontally from supports on both ends, balanced by counterweights.

Features: Reduces material use for long spans; common in railroads.

Examples: Forth Bridge (Scotland), Quebec Bridge (Canada).

5. Arch Bridges

Subtypes:

Tied-Arch: Deck is tied to the arch below for stability (e.g., Sydney Harbour Bridge, Australia).

Fixed-Arch: Traditional arch with vertical supports.

Features: Aesthetic and efficient for medium spans; steel allows larger arches.

6. Cable-Stayed Bridges

Structure: Cables run directly from towers to the deck, reducing cable numbers compared to suspension bridges.

Features: Moderate to long spans (200–800 meters); modern and sleek appearance.

Examples: Millau Viaduct (France), Oriental Pearl Tower Bridge (China).

7. Movable Bridges

Subtypes:

Drawbridges: Raised vertically via counterweights.

Bascule Bridges: Rotated horizontally on a pivot (e.g., Tower Bridge, London).

Swing Bridges: Rotated 90° for ship passage.

Features: Steel mechanisms for reliable operation; essential in busy waterways.

8. Floating Bridges

Structure: Steel pontoons or floats support the deck on water.

Features: Temporary or permanent solutions for soft soil or water crossings.

Examples: pontoon bridges in military or emergency use.

9. Hybrid Bridges

Subtypes:

Steel-Concrete: Steel frames with concrete decks (common in highways).

Steel-Wood: Light steel trusses with timber decking (pedestrian use).

Features: Combines materials for cost, weight, and sustainability benefits.

10. Pedestrian Bridges

Structure: Lightweight steel trusses, cable nets, or walkways.

Features: Narrow, durable, and often aesthetically designed.

Examples: Manhattan’s High Line (USA), London’s Garden Bridge (UK).

Key Advantages of Steel:

Strength-to-Weight Ratio: Ideal for spanning large distances.

Durability: Resists corrosion with modern coatings.

Flexibility: Adapts to dynamic loads (e.g., earthquakes, wind).

Sustainability: Recyclable and energy-efficient in production.

Each type suits specific environments and requirements, leveraging steel’s versatility to meet engineering challenges.