Segmental arch

{{Short description|Type of arch with a circular arc of less than 180 degrees}}

File:Segmentbåge.png

A segmental arch is a type of arch with a circular arc of less than 180 degrees.{{cite book|last=Harris|first=Cyril M.|title=Illustrated Dictionary of Historic Architecture|location=New York|publisher=Dover Publications|date=1983|page=[https://archive.org/details/illustrateddicti00cyri/page/485 485]|isbn=9780486244440|url=https://archive.org/details/illustrateddicti00cyri|url-access=registration}} It is sometimes also called a scheme arch.{{cite book|last=Smith|first=Percy Major|title=Rivington's Building Construction|location=Abingdon, Oxfordshire, U.K.|publisher=Routledge|page=6|date=2015|isbn=9781317742432|url=https://books.google.com/books?id=kCvtCwAAQBAJ}}

The segmental arch is one of the strongest arches because it is able to resist thrust.{{cite book|last=Kreh|first=Richard T.|title=Masonry Skills|location=Stamford, Conn.|publisher=Cengage Learning|date=2015|isbn=9781285426839|page=401|url=https://books.google.com/books?id=4Vw8AwAAQBAJ}}{{clarify|date=March 2024}} To prevent failure, a segmental arch must have a rise that is equal to at least one-eighth the width of the span. Segmental arches with a rise that is less than one-eighth of the span width must have a permanent support or frame beneath the arch to prevent failure.

The segmental arch is very old (the versions were cut in the rock in Ancient Egypt {{circa}} 2100 BC at Beni Hasan). Since then it was occasionally used in Greek temples,{{sfn | Woodman | Bloom | 2003 | loc=Segmental}} utilized in Roman residential construction,{{sfn|DeLaine|1990|p=417}} Islamic architecture, and got popular as window pediments during the Renaissance.{{sfn | Woodman | Bloom | 2003 | loc=Segmental}} The closed-spandrel Pont-Saint-Martin bridge in the Aosta Valley in Italy dates to 25 BC.{{cite book|last=O'Connor|first=Colin|title=Roman Bridges|location=Cambridge, U.K.|publisher=Cambridge University Press|date=1993|isbn=9780521393263|page=171}} The first open-spandrel segmental arch bridge is the Anji Bridge over the Xiao River in Hebei Province in China, which was built in 610 AD.{{cite book|last=Temple|first=Robert K.G.|title=China: Land of Discovery|location=Wellingborough, Northamptonshire, U.K.|publisher=Stephens|date=1986|isbn=9780850598582|pages=69–71}}

Segmental arches were most commonly used in the 12th-14th centuries, later practically replaced by the low four-centred arch.{{sfn|Audsley|Audsley|1881|p=24}} Some use continued, in the 20th century mostly in residential construction over doorways, fireplaces, and windows.

File:Saqqara - Pyramid of Djoser complex - Heb-sed Court - chapel.JPG|Vaulted building using a decorative segmented arch at the Heb-sed court in Saqqara (restored, {{circa}} 2650 BC)

File:Puente de Alconétar, Cáceres Province, Spain. Pic 03.JPG|Segmental arch of the Alconétar Bridge (1st-2nd century AD)

File:OstianInsula.JPG|Segmental arches in an Ostian insula

File:Anji Bridge, Zhao County, 2020-09-06 05.jpg|Anji Bridge