Arch Structures
Arch and Keystone,
Dome, Barrel Vault
ARCH AND KEYSTONE
An arch is a very strong and useful structure.
A true arch is a curved structure. It can span large openings.
It can be built into a wall or from its own base. It is made from
wedge shaped pieces (voussoirs) that lean against each other.
The middle piece, or keystone, holds all the pieces in place;
it is usually larger than the other wedge shapes. The keystone
is the last piece to be put into the structure. A curved support
or scaffold, which is in place during the construction of the
arch, is removed once the keystone is in place; the sturdy arch
then stands on its own.
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| This building on Main Street in Sellersville
features many arches above the windows and doors. |
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Looking closer, we see a series of stones used
to create the arch. The span across the window is then supported on the
brick wall. |
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| The Moravian Tile Works in Doylestown, PA shows
a series of arches in the courtyard area. This building designed and built
by Henry Chapman Mercer is an early example of reinforced concrete. |
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Fonthill, the home of Henry Chapman Mercer
(located next to the Moravian Tile Works), includes many arches above
the windows and doors. |
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| Gothic arches are pointed arches. St. Stephen's
Church in Perkasie, PA, like many churches in the Pennridge area, features
many Gothic arches. |
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Like the true curved arch, the Gothic (pointed)
arch pushes the weight above the structure to the side of the window or
door; the weight is then supported by the wall. |
DOME
A dome is a three-dimensional form on a circle
base. It is usually a half sphere. It can also form other shapes
than a sphere. A dome is made up of a series of equal arches that
span the circle. These are called ribs. All of the ribs meet at
the center of the circle. The top of the dome gets stronger with
more weight on the dome. All of the ribs press against each other
making the structure stronger. The bottom ring is the base that
keeps everything in line so the dome does not collapse.
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| A very large dome is found on the Cathedral
of Saint Peter and Paul (the Roman Catholic Basilica) on the Benjamin
Franklin Parkway in Philadelphia, PA. |
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Inside the building, you can see how the ribs
meet in the center of the dome. |
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| The top of this turret on Broad Street in Lansdale
features an eight sided dome. The ribs can easily be seen on the exterior
of the structure. |
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This Byzantine style dome is found on St. Philip's
Orthodox Church on Clearview Road in Souderton. The ribs are also evident
on this eight sided dome. |
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| This home in West Rockhill, PA is a geodesic
dome. A geodesic dome is basically a half-sphere divided into triangles. |
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This dome located on Old Bethlehem Pike next
to Route 309 (South of Quakertown, PA) is used to store piles of road
materials. This dome structure comes to a point at the top. |
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| Two domes or half-spheres combine together
to make a sphere for the top of this water tower at Grand View Hospital. |
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An elongated dome is found on the top of Philadelphia
City Hall. The building and dome are in the French Second - Empire Architectural
style. The dome includes many decorative elements including the 37 foot
- 27 ton bronze sculpture of William Penn. This sculpture on top of the
building was one of many sculptures created by Alexander Milne Calder
for the building. |
BARREL VAULT
