Brief description

A modern bridge design consisting of one or more towers (or pylons), from which cables support the bridge deck. It is distinct from a suspension bridge because the cables run directly from the tower to the deck, rather than hanging from a main cable.

Use / Function

• Medium to Long Spans: Ideal for spans longer than cantilever bridges but shorter than suspension bridges (approx. 200m to 1000m).
• Aesthetics: Often chosen for their striking, modern appearance.
• Efficiency: Requires less material than a suspension bridge for medium spans.

Operating principle

The cable-stayed bridge works by tension and compression:

1. Cables (Tension): The cables pull the deck up, transferring the weight of the traffic and the deck itself to the towers.
2. Towers (Compression): The towers support the vertical load from the cables and transfer it to the foundation.
3. Deck (Compression): The horizontal component of the cable force compresses the deck towards the towers.

Unlike an Arch which relies entirely on compression to span a gap, the cable-stayed bridge relies on the high tensile strength of steel cables.

How to create it

1. Foundations: Build strong foundations for the towers (pylons) and the anchorages at the ends of the deck.
2. Towers: Construct the vertical towers (usually reinforced concrete or steel).
3. Deck & Cables: Build the deck outwards from the tower in balanced sections.
   • Install a segment of the deck.
   • Attach the corresponding stay cable to the tower and tension it.
   • Repeat on the other side to keep the tower balanced.
4. Closure: Join the deck sections in the middle.

Materials needed

• Essential:
  • Steel Cable: High-strength strands are critical.
  • Concrete: For towers and deck.
  • Steel: For reinforcement, towers, or deck structure.
• Tools: Heavy cranes, hydraulic jacks (for tensioning cables), formwork.

Variants and improvements

• Harp Design: Cables are parallel to each other.
• Fan Design: Cables all connect to the top of the tower (more efficient).
• Single Tower: Asymmetric designs for specific aesthetic or structural needs.
• Extradosed Bridge: A hybrid between a girder bridge and a cable-stayed bridge, with shorter towers and stiffer deck.

Limits and risks

• Wind: Like suspension bridges, they are susceptible to aerodynamic instability (flutter).
• Cable Vibration: Rain and wind can cause cables to vibrate violently; dampers are needed.
• Complexity: Requires precise engineering to balance the forces during construction.
• Corrosion: The cables are the critical weak point; if they rust, the bridge fails.