|Decorative Lion Head Keystone|
|Location of Keystone-Architectural Arch|
From Wikipedia, the free encyclopedia:
A keystone is the wedge-shaped stone piece
at the apex of a masonry vault or arch, which
is the final piece placed during construction
and locks all the stones into position, allowing
the arch to bear weight.
Although a masonry arch or vault cannot be
self-supporting until the keystone is placed,
the keystone experiences the least stress
of any of the voussoirs,
due to its position at the apex.
|Keystone, Springers, Voussoirs StLouis Brick Building|
From Wikipedia, the free encyclopedia
A voussoir (pronounced /vuˈswɑr/) is a wedge-shaped element,
typically a stone, used in building an arch or vault.
Although each unit in an arch or vault is a voussoir,
two units are of distinct functional importance:
the keystone and the springer.
- The keystone is the center stone or masonry unit
at the apex of an arch.
- The springer is the lowermost voussoir,
located where the curve of the arch springs from the
vertical support or abutment of the wall or pier.
The word is a mason’s term borrowed in Middle English from
French verbs connoting a “turn” (OED). Each wedge-shaped
voussoir turns aside the thrust of the mass above, transferring
it from stone to stone to the springer’s bottom face (‘impost’),
which is horizontal and passes the thrust on to the supports.
Voussoir arches distribute weight efficiently and take maximum
advantage of the compressive strength of stone, as in an arch bridge.
In Eastern Romanesque and Arab architecture the voussoirs are
often in alternating colors, usually red and white.
During the 18th and 19th centuries British bricklayers became
aware that by thickening the vertical mortar joint between regularly
shaped bricks from bottom to top they could construct an elliptical
arch of useful strength over either a standard ‘former’ or over
specially constructed timber false work, (work to be removed following
the construction of the prime). The bricks used in such an arch
are often referred to as ‘voussoirs’.