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.

 
This building on Main Street in Sellersville features many arches above the windows and doors.   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.
 
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.   Fonthill, the home of Henry Chapman Mercer (located next to the Moravian Tile Works), includes many arches above the windows and doors.
     
Gothic arches are pointed arches. St. Stephen's Church in Perkasie, PA, like many churches in the Pennridge area, features many Gothic arches.   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.

 
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.   Inside the building, you can see how the ribs meet in the center of the dome.
 
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.   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.
   
This home in West Rockhill, PA is a geodesic dome. A geodesic dome is basically a half-sphere divided into triangles.   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.

 

 
Two domes or half-spheres combine together to make a sphere for the top of this water tower at Grand View Hospital.   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

A vaulted tunnel with a series of arches aligned next to one another is called a barrel vault. The ribs are sometimes evident depending on the type of structure.

These greenhouses on Telegraph Road in Hilltown Township, PA are made of metal ribs and a flexible plastic fabric.

   
 
This door stoop at Fifth and Callowhill Streets in Perkasie, PA is a short barrel vault.   The ribs are easily seen in this barrel vault made of reinforced concrete (at Moravian Tile Works in Doylestown, PA).
   
The Doylestown Center walkways include a series of barrel vaults.   These new walkway structures were added to an older building.

 

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