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Arches

Arches:-
1. An arch is a structure which is constructed to the span across an opening.
2. It generally consist of small wedge-shaped unit which are join together with mortar.
3.The archers made of steel and R.C.C are built in single unit without the use of wedge-shape unit and they are used for the bridge construction.

Types of arches:-
1. Flat arch
2. Segmental arch
3. Semi-circular arch
4. Semi-ecliptical arch
5. Inverted arch
6. Pointed arch
7. Relieving arch
8. Horse-shoe arch
9.Silted arch
10. Venetian arch
11. Florentine arch 

Flat arch:-
1. The apparent shape of this arch is flat.
2. The Skewback form is angle of 60 degree with the horizontal.
3. An equilateral triangle is formed with one side has intrados 
4. The extrados is kept perfectly horizontal or sometimes ,in order to prevent it from becomes hollow when arch settle.
5. The flat arch are found to be comparatively weak and they are used only for light load and for span up to 1.5 m.

Segmental arch:-
1.The center of the arch is situated below the springing line.
2.This is common type of arch used for building.

Semi-circular arch:-
1.The centre of the arch lies on the springing line.
2.The centre of curve of arch is a semi-ellipse.


Semi-ecliptical arch:-
1. This arch has more than one centre.
2. It shape is that of semi-ellipse.
3. It may have either three centre or five centre.

Inverted arch:-
1. The arch is inverted.
2. This arch is constructed to increase bearing power of soil.

Relieving arch:-
1. This arch is constructed over wooden joist or a flat arch.
2. Relieves the joist or flat arch from carrying the load.
3. The span of the relieving arch will be equal to the clear span of the opening plus twice the bearing of wooden joist 
4. Makes is possible to replace die existing decayed or dameged wooden lintel without disturbing the stability of the existing structure.
Point arch:-
1. This type of arch consists of two curve which are meeting  the apex of triangle.
2. The triangle form may be equilateral or isosceles.
3.In equilateral arch, the centre will be the springing points.
4. In isosceles or Lancet arch, the centre may be on or below the springing line and they may be in between or outside the springing point.
Silted arch:-
1. Has a semi-circular shape attached at a top of two vertical portions.
2.The springing line of arch passes through the tops of vertical portions.


Venetian arch:-
1. The depth of Crown is more than that at a springing line.
2.Has four centres, all located on the springing line.

Florentine arch:-
1.Similar to the Venetian arch except that the intrados has the shape of a semicircular curve.
2.There are three centre for a Florentine arch, all located on the springing line.


Rough arch:-
1. Construction for ordinary uncut bricks.
2. The mortar joints become wider at a extrados then at the intrados.
3.Used where appearance is of secondary important or when it is intended to plaster the face of the arch. 

Axed arches:-
1.Constructed from a brick which are cut to wedge-shaped by means of an axe.
2. The thickness of mortar joints varies from 3 mm to 6 mm.

Rubble arch:-
1. Constructed with rubble stone which dressed by hammer and made roughly to required shape and size of voussoirs.
2. Constructed in 1 arch spring upto a depth of thickness of 380 mm.
3. The thickness is more than 380 mm then the rubble stone are laid into  two rings in the alternate course of header and stretcher.

Gauged arch:-
1. Constructed from a brick which are finally cut by the mean of a wire saw.
2. The surface of brick are finished with file.
3. The mortar joins are very thin has 1.5 mm.
4. Use where the fine finishing of surface is required.

Ashlar arches:-
1. The stone are completely dress and properly shaped.
2. The voussoirs are constructed for full thickness of an arch up to the thickness of 600 mm and then set in fine cement or lime mortar.
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