An arch is built primarily using wedge-shaped blocks, known as voussoirs, to create a self-supporting structure.
The Foundation of Arch Construction: Voussoirs
Arch construction heavily relies on the principle of the wedge. The essential component of an arch is the voussoir.
- What are Voussoirs? Voussoirs are wedge-shaped blocks, wider at the top and narrower at the bottom. This shape is critical for the arch's structural integrity.
Building the Arch: Step-by-Step
Here's how an arch is typically constructed:
- Support Structure: A temporary structure, often called a centering, is built to support the voussoirs while the arch is being assembled.
- Placement: Voussoirs are placed side by side, starting from the springers (the lowest point on each side of the arch) and working toward the center.
- Key Stone: The final voussoir, called the keystone, is placed at the very top of the arch. It is often slightly larger than the other voussoirs and helps to lock the arch together.
- Removal of Support: Once all the voussoirs are in place and the keystone is inserted, the centering is carefully removed. The arch now supports itself due to the wedging action of the voussoirs.
How Wedging Works
The wedge shape of the voussoirs plays a vital role. Each block transfers a portion of its weight to the blocks beside it, and ultimately to the abutments (the supports at each end of the arch). The weight and shape create a compression force that pushes the voussoirs together, thus making the arch strong and stable.
Practical Considerations
- Material Choice: Arches can be made from various materials including stone, brick, and concrete.
- Arch Shapes: There are different types of arches such as semicircular, pointed, and segmental arches, each having its specific characteristics and uses.
Conclusion
Arch construction is an age-old technique that depends on the simple yet effective principle of using wedge-shaped voussoirs to distribute weight and create a self-supporting span.
