ARCHES AND ITS COMPONENTS
DEFINITION
An arch is a structure constructed in curved shape with wedge shaped units (either bricks or stones), which are joined together with mortar, and provided at openings to support the weight of the wall above it along with other superimposed loads. Because of its shape the loads from above gets distributed to support (pier or abutment).
MEANING
The brick or stone blocks are formed with circular shapes on the door or window or opening with the purpose of resisting the pressure of the upper load. So, the circular frame that is specifically created by brick or stone blocks is known as the arch. It is arranged both sides support of the opening. The objective of the Arch is to bear its own weight as well as other upper body weight on both side support.
COMPONENTS OF AN ARCH
The following are the different components of arches and terms used in arch construction:
1. Intrados
The inner curve of an arch is called as intrados
2. Extrados
The outer curve of an arch is called as extrados
3. Soffit
The inner surface of an arch is called soffit. Soffit and intrados are used synonymously
4. Voussoirs
The wedge shaped units of masonry which are forming an arch is called as voussoirs.
5. Crown
The highest part or peak point of extrados is called crown.
6. Keystone
The wedge shaped unit which is fixed at the crown of the arch is called keystone.
7. Spandrel
If two arches are constructed side by side , then a curved triangular space is formed between the extrados with the base as horizontal line through the crown. This space is called as spandrel.
8. Skew back
This is an inclined surface or splayed surface on abutment, from which arch curve starts or ends.
9. Springing Points
The imaginary points which are responsible for thw springing of curve of an arch are called as springing points.
10. Springing Line
The imaginary line joining the springing points of either ends is called as springing line.
11. Springer
The first voussoirs at springing level which is immediately adjacent to the skewback is called as springer.
12. Haunch
The lower half of the arch between the crown and skewback is called haunch.
13. Arcade
The row of arches in continuation is called arcade.
14. Ring
The circular course forming an arch is called as arch ring. An arch may be formed by one ring or combination of rings
15. Impost
The projecting course is provided on the upper part of a pier or abutment to stress the springing line. This course is called impost.
16. Pier and Abutment
The intermediate support of an arch is called as pier. The end support of an arch is called as abutment.
The arch provides the following benefits :-
1. It provides a robust abutment.
2. It is applied in a greater extent.
3. It is most suitable where the weight is bigger.
4. The structure is applied to enhance the look of any construction.
Arches are compressive structures. There are no tensile stresses in these structures due to its basic geometry. They are self-supporting and stabilized by the force of gravity acting on their weight to hold them in compression. This makes them very efficient and stable, capable of larger spans, and supporting greater loads than horizontal beams.
By
Ms. M. Darneshree
Assistant Professor
Dpt of IDD
