ARCHES

Simple Definition of arch. : A usually curved part of a structure that is over an opening and that supports a wall or other weight above the opening. : The raised area on the bottom of the foot that is formed by a curved section of bones. : Something that has a curved shape.
Types of arches based on shape, material of construction, workmanship and number of centers are discussed here. An arch is constructed in curved shape due to which loads from above is distributed to supports (pier or abutment).
Types of Arches
Arches are classified based on:
1.   Shape
2.   Number of Centre’s
3.   Workmanship
4.   Materials of construction
Types of Arches based on shape:
Based on the shape of construction arches are classified into 10 types and they are discussed below.
Flat Arch
·        For flat arch, the intrados is apparently flat and it acts as a base of equilateral triangle which was formed by the horizontal angle of 600 by skewbacks.
·        Even though the intrados is flat but it is given that a slight rise of camber of about 10 to 15 mm per meter width of opening is allowed for small settlements.

·        Extrados is also horizontal and flat. These flat arches are generally used for light loads, and for spans up to 1.5m.




Segmental Arch

·       This is the basic type of arch used for buildings in which Centre of arch lies below the springing line.In segmental arch, the thrust Transferred in inclined direction to the abutment.
      
    Semi-Circular Arch 
      The shape of arch curve looks like semi-circle and the thrust transferred to the abutments is perfectly vertical direction since skewback is horizontal. In this type of arch, the Centre lies exactly on the springing line.
Horse Shoe Arch

Horse Shoe Arch is in the shape of horse shoe which curves more than semi-circle. This is generally considered for architectural provisions.
Pointed Arch

The other name of pointed arch is Gothic arch. In this type of arch two arcs of circles are met at the apex hence triangle is formed. This may be either isosceles or equilateral.

Venetian Arch

Venetian arch is also pointed arch but its crown is deeper than springing’s. It contains four Centre’s, all located on the springing line.

Florentine Arch
Intrados of arch is in the shape of semi-circle and rest of the arch is similar to Venetian arch. It has three Centre’s, all located on the springing line

Relieving Arch


Relieving arch is constructed above flat arch or on a wooden lintel to provide greater strength. In case of relieving arch, we can replace the decayed wooden lintel easily without disturbing the stability of structure. The ends of this arch should be carried sufficiently into the abutments.

Stilted Arch

Stilted Arch consists of a semi-circular arch with two vertical portions at the springing’s. The Centre of arch lies on the horizontal line through the tops of vertical portions.

Semi-Elliptical Arch

This is a type of arch of semi-ellipse shape and having three or five Centers


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