Building an arch bridge involves constructing each side of the arch simultaneously and supporting them until they meet in the middle, at which point the arch becomes self-supporting.
The construction of the arch itself is a crucial step in building this type of bridge. Here's a breakdown of the process:
The Core Construction Method
- Building Outward: The key method involves constructing the arch from both sides of the span simultaneously.
- Temporary Support: As each side of the arch is built outwards toward the center, it requires temporary support. According to construction methods, each side of an arch is built out toward the other, supported by temporary cables above or by falsework below until the ends meet.
- Temporary Cables: These are used to suspend sections of the arch as they are built, particularly common for steel arch bridges.
- Falsework: This refers to temporary structures (like scaffolding or centering) built from wood or steel beneath the arch to support its weight and shape during construction. This is a traditional method used for masonry, concrete, and steel arches.
- Meeting in the Middle: Construction continues from both sides until the two halves of the arch meet precisely at the crown (the highest point).
- Becoming Self-Supporting: Once the two sides meet and the final keystone (or connecting element) is placed, the arch is able to bear weight and becomes inherently stable due to the compression forces distributed along its curve. At this point the arch becomes self-supporting, and the cables or falsework are removed.
- Removing Supports: With the arch capable of supporting itself, the temporary cables or falsework that held it up during construction are carefully dismantled and removed.
Beyond the Arch
Once the arch is complete and self-supporting, the remaining parts of the bridge structure are added, which may include:
- Adding spandrel walls or columns above the arch.
- Constructing the deck or roadway surface.
- Installing railings and other finishing elements.
This method ensures that the arch is built safely and precisely, allowing it to perform its function of efficiently transferring loads to the bridge supports at each end.
