What is an ARCH?

A curved structure for spanning an opening, designed to support a vertical load primarily

by axial compression.

VOUSSOIR-any of the wedge-

shaped units in a masonry

arch or vault, having side cuts

converging at one of the arch

centers.

KEYSTONE- the wedge shaped, often embellished

voussoir at the crown of an arch, serving to lock the

other voussoirs in place.

EXTRADOS- the exterior curve, surface, or

boundary of the visible face of an arch. Also

called back.

ARCHIVOLT-the moulding or band on the face

of an arch following the curve of the intrados.

INTRADOS-the inner curve or surface of an arch forming

the concave underside.

RISE-the height of an arch

from the springing line to the

highest point of the intrados.

SPRING-the point at which an arch, vault, or dome

rises from its support. also called springing

SPRINGER-the first

voussoir resting on the

impost of an arch.

SPANDREL-the triangular-

shaped, sometimes

ornamental area between

the extrados of 2 adjoining

arches, or between the left

or right extrados of an arch

and the rectangular

framework surrounding it.

also spandril.

CROWN-the highest part or point of a

convex construction, as an arch.

HAUNCH-either side of an arch curving

down from the crown to the impost.

IMPOST-the uppermost part of an

abutment, often in the form of a

block, capital, or moulding, from

which an arch springs.

Terminology of stone or brick masonry

SKEW ARCH-an archway

having sides or jambs not

at right angles with the

face of its abutments.

ORDER-any of

several concentric

rings of masonry

forming an arch,

esp. when each

projects beyond

the one below.

LAG-a crosspiece

connecting the ribs in a

centring. Also called

bolster.

CAMBER PIECE-a board used as

centring for a flat arch, slightly

crowned to allow for setting of the

arch. Also called camber slip.

ARCH ACTION-the manner in which an arch transforms the

vertical forces of a supported load into inclined components and

transmits them to abutments on either side of the archway.

ARCH AXIS-

the median

line of an

arched

structure.

LINE OF THRUST-the set of resultants of thrust and weight each

part of an arch imposes on the next lower

one. For bending to be eliminated

throughout an arch, the line of thrust

must coincide with the arch axis.

THRUST-the outward force or

pressure exerted by one part of

a structure against another.

DRIFT-the thrust of an

arched structure on its

abutments, proportional to

the total load and span,

and inversely proportional

to the rise.

RIGID ARCH-an arched

structure of timber,

steel, or reinforced

concrete, constructed

as a rigid body capable

of carrying bending

stresses.

FIXED ARCH-a fixed

frame structure

having an arched

form.

TWO HINGED ARCH-a

two hinged frame

structure having an

arched form.

THREE HINGED

ARCH-a three

hinged frame

structure having

am arched form.

ABUTMENTS-the part of a structure

receiving and supporting the thrust of

an arch, vault or strut.

TIE ROD-an iron or steel rod serving as a structural tie

especially one keeping the lower ends of an arch or

frame from spreading.

Pointed archRound arch

FUNICULAR ARCH-an arched shaped to develop only axial

compression under a given loading. This shape may be

found by inverting the funicular shape for a cable carrying a

similar loading pattern. As with any funicular structure, a

funicular arch is subject to bending if the loading pattern

changes.

An inverted catenary is the

funicular shape for an arch

carrying a vertical load uniformly

distributed along the length of

the arch axis.

The parabola is the funicular

shape for an arch carrying a

vertical load uniformly

distributed over its horizontal

projection.

Flat arch (jack arch)

French arch

Triangular arch

Corbel arch

Equilateral

arch

Lancet arch

Surbased archDrop arch

Rampant arch

Bell arch

Horseshoe

arch

Segmental arch

Roman arch

Categorisation of the

ARCH (form)

Flat arch (jack arch)

Trefoil arch

An arch having a

cusped intrados with

three round or pointed

foils.

Basket handle arch

A three centerd arch

having a crown with a

radius greater than

that of the outer pair

of curves. Also called

anse de panier.

Ogee arch

A pointed arch, each

haunch of which is a

double curve with

concave side

uppermost.

Tudor arch

A four centerd arch

having an inner pair of

curves with a radius

much greater than

that of the outer pair.

Rampant arch

An arch having its one

impost higher than the

other.