Swinging bridges, often a type of suspension bridge, are typically constructed by hanging a walkway or deck from robust main cables anchored at either end.
Key Components of a Swinging Bridge
The construction relies on several primary elements working together to create a stable yet flexible crossing:
- Main Cables: These are the primary load-bearing elements. As referenced, the main cables can be formed from parallel strong wires that are aerially spun in place during construction, or they can be prefabricated wire ropes brought to the site. These cables span the gap the bridge crosses and are securely anchored to the ground or towers on either side.
- Deck: This is the walking surface of the bridge. The deck's weight, along with the weight of anyone on the bridge, is transferred to the main cables.
- Suspender Ropes: These are strong ropes (or sometimes rods or wires) that run vertically or near-vertically from the deck level to the main cables. They suspend the deck, distributing its load along the length of the main cables.
- Stiffening Elements: While the main cables carry the primary load, the deck might be prone to excessive movement or swaying. The deck can be stiffened by a truss or by girder elements beneath it. These elements help the bridge maintain its shape, distribute loads more evenly, and resist wind forces or swaying caused by movement on the bridge.
The Basic Construction Process
While complex engineering is involved in larger suspension bridges, the fundamental principle for a swinging bridge is creating a suspended pathway.
- Main Cable Installation: First, the main cables are installed across the span and securely anchored. This might involve building towers or simply anchoring into solid ground on either side, depending on the bridge's size.
- Suspender Attachment: Strong suspender ropes are attached at intervals along the main cables.
- Deck Assembly: The deck sections are then lifted and attached to the lower ends of the suspender ropes.
- Stiffening (Optional but Common): If required, truss or girder elements are integrated with or attached beneath the deck to provide rigidity.
This method allows for bridges that can span significant distances without requiring extensive support structures from below, making them ideal for crossing valleys or rivers. The inherent flexibility of the suspension design is often why they are referred to as "swinging" bridges, as they can sway slightly.
