What is Arch in Construction?

In any building, openings are invariably needed in the wall for provision of door, windows, cupboards, admirahs, wardrobes, etc. These openings may be given by the providing either an arch or lintel. Thus, both arch as well as lintel are structural members designed to support the loads of the portion of the wall situated above the openings, and then transmit the load to the adjacent wall portions over which these are supported.

Also Read: Difference Between Beam & Lintel in Structural System
Components of Arch

What is an Arch?

An arch may be defined as a mechanical arrangement of wedge-shaped blocks of bricks or stones which mutually support each other, and in turn, the entire arch is supported at the ends by piers or abutments. The wedge-shaped units (i.e., bricks, stones, or concrete blocks) are so arranged together along a curved line that they balance their own weight by the mutual pressure and exert a vertical pressure only due to its geometry only, which can be sustained safely by supports below.

Also Read: Difference Between Brick Masonry and Stone Masonry
Arch as a Architectural Appearance

Where Arches are Constructed?

Lintels are simple and easy to construct, while special centering / formwork is required for the construction of an arch. However, arches are constructed where,

(i) span is more

(ii) loads are heavy

(iii) strong abutments are available and

(iv) special architectural appearance is required

Also Read: Modern Architecture: Know its Importance & Characteristics!

General Stability of Arches

The stability of arches depends on the friction between surface of wedge-shaped blocks (called voussoirs) and the cohesion of the mortar. The stability of the arches is endangered by one or more of the following:

  • Crushing of the arch material
  • Sliding of wedge-shaped blocks or voussoirs
  • Rotation or overturning about and edge
  • Differential settlement of supports or abutments

To maintain the stability or equilibrium of arches, the following points should be given the consideration.

(A) To prevent the crushing of the arch material (which takes place when the thrust in some part of the arch exceeds the safe crushing strength of the material), the following points are considered.

(i)The size of the voussoirs should be adequate to withstand the anticipated pressure or thrust.

(ii) For small spans, the thickness of the arch ring is kept uniform from crown to the springing. As a rule, the thickness of the ring may be taken either 1/12th of the span or as below. (For brick masonry work in cement mortar, 1:4).

For spans up to 1.5 m – 20 cm

between 1.5 to 4 m – 30 cm

between 4.0 to 7.5 m – 40 cm

Also Read: Ready Mix Mortar for Brickwork, Plaster and Repair Maintenance!  

(iii) For large spans (more than 7.5 m), the thickness of the arch ring may be increased at the springing by about 20% to the thickness at the crown.

(iv) For arch work, only first-class blocks (brick, stones) should be used, and in case of large spans, the arches maybe strengthened by steel reinforcement bar, so that the safe crushing strength is not exceeded.

(B) To safeguard against sliding of one voussoir over other, the following points are considered.

(i) All the bed joints should be perpendicular to the line of least resistance. Normally, they are made normal to the curve of the arch, in which position they are nearly perpendicular to the line of least resistance.

(ii) The depth of the voussoirs should be adequate to resist the tendency of the joints to open and slide upon the another.

Also Read: Joints in Construction: All You Need to Know

(C) To prevent rotation or overturning about the edge, the following points are considered.

(i)The line of resistance or thrust at any section should be within the middle-third of the arch.

(ii) The thickness of the arch and its curve are so designed that the line of resistance at least falls within the section and crosses each joint away from the edge.

(D) To safeguard against the differential settlement of supports or abutments, the following points are considered.

(i) The abutments should be sufficiently strong to resist the thrust of the arch due to self-weight and super-imposed loads. Normally, for abutments of ample size, the segmental arch is strongest whereas for smaller size of supports, semi-circular or pointed arch should be used. Semi-circular arches are the strongest and exert no thrust on abutments or piers.

(ii) Whatever may be the shape of the arch, it should be at least symmetrical to avoid differential settlement of supports.

Also Read: Classification of Loads on Structure

Types of Arches

Different Geometry of Arches

Various types of arches are classified as follows:

(i) Classification of arches according to number of centers to form different shape of an arch

(ii) Classification of arches according to shape formed by soffit or intrados (inner curve of the arch).

(iii) Classifications of arches according to the materials and workmanship employed in their construction.

Also Read: Types of Masonry that can be Used for Construction of your Dream Home

(i) Classification of Arches According to Number of Centers to Form Different Shape of an Arch

(a) One-Centered Arches

Different Types of One Centered Arch

They are of following Types:

  • Semi-circular Arch
Semicircular Arch
  • Segmental Arch (which is less than a semi-circle)
Segmental Arch
  • Horse-shoe Arch (which is more than a semi-circle)
  • Stilted Arch
  • Bull’s eye arch (which is complete circular arch used for circular window to produce architectural effect.)
Round or Bull’s eye Arch

(b) Two-Centered Arches

Two Centered Arch

These arches are of several types but the popular ones are as follows:

  • Blunt or Drop Arch
Blunt or Drop Arch
  • Gothic or Equilateral Arch or Pointed Arch
  • Acute or Lancet Arch
Acute or Lancet Arch

(c) Three-Centered Arches

These arches having three-centers are mainly of two types

  • Elliptical Arch
Elliptical Arch
  • Three Centered Arch

(d) Four-Centered Arch or Tudor Arch

Four Centred Arch or Tudor Arch

(e) Five-Centred Arch

(ii) Classification of Arches According to Shape Formed by Soffit or Intrados

(a) Flat Arch (or Straight, Square or Camber Arch)

Flat Arch

(b) French or Dutch Arch

Flat Arch

(c) Semi-Circular Arch

Semi-Circular Arch

(d) Segmental Arch

(e) Relieving Arch or Discharging Arch

Relieving Arch or Discharging Arch

(f) Pointed Arch (or Gothic Arch)

Pointed Arch

(g) Venetian Arch

(h) Florentine Arch

Florentine Arch

(i) Semi-Elliptical Arch

(j) Horse-Shoe Arch

Horseshoe arch
Round, Lancet and Horseshoe Arch

(k) Stilted Arch

Stilted Arch

(l) Two-Cusped Arch

(m) Corbel Arch

Corbel Arch

(iii) Classifications of Arches According to the Materials and Workmanship Employed in Their Construction

(a) Stone Arches

  • Rubble Arches
Rubble Arch
  • Ashlar Arches
Ashlar Arch

(b) Brick Arches

Brick Arch

Types of Brick Arches are listed Below:

  • Rough Brick Arches
Rough Brick Arch
  • Axed or Rough-Cut Brick Arches
Axed or Rough-Cut Brick Arch
  • Gauged Brick Arches
  • Purpose-Made Bricks Arches
Purpose-made brick arch
  • Concrete Arches
Concrete Arch

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.

Must Read:

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Types of Lintels | Their Uses in House Construction

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