Arch

Definition

An arch is a curved structure designed to span an opening and support loads from above. Compression is the primary cause of internal stresses within an arch. It features an upward-curved centerline axis with a relatively small cross-section and is supported so that the distance between its ends remains constant. Both horizontal and vertical reactive forces are present at each end, with forces acting normal to the arch centerline carried in compression due to its curvature.

Purpose

The purpose of an arch is to:

• Distribute loads evenly, utilizing its curved shape to efficiently transfer weight from the structure above to the supports at either end.
• Provide stability and strength, allowing for larger spans than would be possible with straight beams or lintels.
• Enhance architectural aesthetics with its graceful and functional design.

Examples of Use

1. Architecture and Construction:
   • In bridges, arches support the roadway and distribute the weight of vehicles and pedestrians.
   • In historical buildings, arches are used in doorways, windows, and as decorative elements to enhance structural integrity and visual appeal.
2. Civil Engineering:
   • In aqueducts, arches are employed to support the water-carrying channels over long distances.
   • Tunnel entrances often use arches to distribute the weight of the earth above and prevent collapse.
3. Modern Structures:
   • Stadiums and large sports arenas use arches in their roof designs to span vast open spaces without internal supports.
   • Arches are incorporated into contemporary buildings and bridges for both structural efficiency and aesthetic value.

Related Terms

1. Keystone: The central, topmost stone in an arch, locking the other stones into position.
2. Voussoir: A wedge-shaped element, typically a stone, used in constructing an arch.
3. Spandrel: The triangular space between the curve of an arch and the rectangular frame enclosing it.
4. Abutment: The structure supporting the ends of an arch or bridge, preventing the arch from spreading.
5. Buttress: A support built against or projecting from a wall to reinforce it or to support the weight of an arch.

Notes

• The effectiveness of an arch relies on the proper distribution of compressive forces; incorrect construction can lead to tension forces that may cause failure.
• Arches have been used throughout history in various cultures, from ancient Roman aqueducts to Gothic cathedrals, demonstrating their timeless utility and beauty.
• The materials used in arch construction can vary, including stone, brick, concrete, and steel, each offering different advantages in terms of strength and flexibility.
• Modern engineering often employs computer models to optimize arch designs, ensuring maximum load-bearing capacity and stability.