Archesand

Dome

Harshil Mehta131010011010

Civil 6th Sem.

What is Arch…?An arch is structure that

spans a space and supports structure and weight above it.

Provides a structure which eliminates tensile stresses in spanning a great amount of open space.

All the forces are resolved into compressive stresses.

Force acting on arch

Elements of arches

Technical Terms Keystone: A keystone is the

wedge-shaped stone piece at the apex of an arch, which is the final piece placed during construction and locks all the stones into position, allowing the arch to bear weight.

Voussoirs: The voussoirs

are the wedge shaped units forming the arch.

Intrados: It is the inner curve of an arch.

Extrados: It is the outer curve of an arch.

Springing stone: The springing stone or springer is the first voussoirs at springing level on either side of the arches.

Crown: Highest point of extrados or highest past of an arch.

Span : Clear horizontal distance between the two supports.

Rise :The vertical distance between the spring line of an arch and the keystone .

Failure of an archEVERY ELEMENT OF ARCH REMAINS IN

COMPRESSION. An arches fail due to: 1) Crushing of the masonry. 2) Sliding of voussoirs. 3) Rotation of some joints about an edge. 4) Uneven settlement of an abutment.

Failure of an archCrushing of the masonry: If the compressive

stress exceeds the safe crushing strength of the masonry unit and mortar , the arch will fail in crushing.

Sliding of voussoirs :To safeguard against sliding of voussoirs past each other due to transverse shear ,the voussoirs of greater height should be provided.

Rotation of some joints about an edge :Rotation can be prevented ,if the line of resistance is kept within intrados and extrados. Also, the line of thrust should be made to cross the joint away from the edge to prevent the crushing of that edge.

Failure of arches

Construction

Masonry work in arch should be carried up from both ends uniformly and keyed in the centre.

Defects in dressing should not be made good by mortar or chips.

The arch work should be kept thoroughly wet. so that no portion of the arch hardens and fully ,sets before the whole arch is completed.

From this consideration, it is desirable to employ a mortar which is slow setting.

Loading of Arches

Loading of arches should be gradual and so

regulated that at least 7 days should elapse

before 50% of design load.

At least 14 days should elapse before 75%of

design load comes on the arch, allowing full

design load only after 28 days of completion of

arch.

Main types of arches

Semi Circular Arch

Segmental arch or arch that is less than a semicircle

Flat arch

•A semi-circular arch is a half circle. This arch has an advantage over segmental arch that side thrust at the support is much less and thus side supports need not be very wide. •A flat arch, which is suitable only for small spans (say up to 1 meter) and light loads, has a horizontal extrados and slightly cambered intrados is employed mainly for spanning door and window openings in ordinary buildings.

DOME

 A dome is an element of architecture that resembles the hollow upper half of a sphere.

Dome structures made of various materials have a long architectural lineage extending into prehistory.

A dome is a rounded vault made of curved segments, meaning an arch rotated around its central vertical axis.

What is DOME..?

 Coffer Cupola Lantern Oculus Pendentive Rotunda Squinch Tholobate Whispering gallery

Elements of dome

Compound Dome Simple Dome

• Masonry domes were provided in the past to serve

as roof cover for large structures, when no other

structural means of bridging large spans were

available.

• With the advent of steel, reinforced concrete and

prestressed concrete, use of domes is not made now,

except on special architectural considerations in

case of monumental, religious and institutional

buildings.

• Construction technique of a dome is more or less

similar to that of an arch.

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