18 Different Component Parts of an Arch

18 Different Component Parts of an Arch

Arch is the structure which is constructed over the opening of the windows, doors or cupboard etc. The arch structure is also used in bridge construction. In Ancient time it was the most common structure used in any types of buildings. Arch may be circular, elliptical or any other shaped. It consists of wedge-shaped blocks of stone, bricks etc. It may be made of steel or R.C.C in case of bridge construction. In this article, I am going to share different component parts of an arch and also some technical terms used in arch construction.

1. Abutment:

The abutment is the end support of an arch. In other words, it is the end support of a span on which the arch rests. The abutment may be walls or column in case of buildings, and retaining wall in case of a bridge. An abutment should be designed in such a way that it can easily withstand arch thrust.

2. Piers

Piers also a supporting member of an arch, but it is the intermediate supporting members. Piers are used when series of arch is constructed.

3. Arch ring

It is a course of wedge-shaped blocks, arranged in a curved form and supported on the abutments or piers.

4. Intrados

This is the inner curved surface of the arch.

5. Extrados

This is outer curved surface of the arch, it is also known as back of the arch ring.

6. Soffit

Soffit is the buttom surface of the arch. Indrados and soffit terms are used to indicate same thing.

7. Span of the Arch

Span of the arch is nothing but the clear horizontal distance between the supports.

8. Crown

The Crown is the highest part of an arch. In othe words, it is the height points of the extrados arch.

9. Voussoirs

Voussoirs are wedge-shaped units by which the arch ring is created. These blocks units may be of brick, stone or plain cement concrete. Voussoirs are also called arch blocks.

10. KeyStone

Key stone is also a wedge-shaped block unit but it is larger than the voussoirs. This unit is placed at the highest point of the arch.

11. Skew Back

It is the splayed surface prepared on the top of an abutment or pier, to receive the arch. Arch work actually starts from skewback.

12. Springing Points

These are the points from where the curve of an arch starts. In other words, these are the points at which intrados and skew backs intersect.

13. Springing Line

The springing line is nothing but the imaginary horizontal line joining the two springing points.

14. Springers

It is the first voussoir (or, beginning voussoir) at the springing level on either side of the arch.

15. Depth of the arch

It is the verticle distance between the intrados and extrados of an arch.

16. Haunch

If you imagine a line between crown and skewback, then the portion below the imagined line is known as Haunch.

17. Center of the arch

As its name suggests, it is the geometrical center of the curve of an arch.

18. Rise of the arch

It is the perpendicular distance between the springing line and the heighest point of the below curve(intrados) of the arch.