Editing Arch (section)

==Hinged arches==
{{main|Hinged arch bridge}}
[[File:Rossgrabenbruecke 01 09.jpg|thumbnail|upright=1|Rossgraben bridge ([[Rüeggisberg]]) near Bern, Switzerland, showing the [[Concrete hinge|hinge]] at mid-span of this three-hinged arch.]]

Practical [[arch bridge]]s are built either as a fixed arch, a two-hinged arch, or a three-hinged arch.<ref name="Reynolds's Reinforced Concrete Designer's Handbook, p 41" /> 
The fixed arch is most often used in reinforced concrete bridges and tunnels, which have short spans. Because it is subject to additional internal stress from thermal expansion and contraction, this kind of arch is [[statically indeterminate]] (the internal state is impossible to determine based on the external forces alone).<ref name="Building Structures"/>

The two-hinged arch is most often used to bridge long spans.<ref name="Building Structures" /> This kind of arch has pinned connections at its base. Unlike that of the fixed arch, the pinned base can rotate,<ref>{{cite web|last=Luebkeman|first=Chris H.|title=Support and Connection Types|url=http://web.mit.edu/4.441/1_lectures/1_lecture13/1_lecture13.html|work=MIT.edu Architectonics: The Science of Architecture|publisher=MIT.edu|access-date=3 February 2013|url-status=live|archive-url=https://web.archive.org/web/20121028035620/http://web.mit.edu/4.441/1_lectures/1_lecture13/1_lecture13.html|archive-date=28 October 2012}}</ref> thus allowing the structure to move freely and compensate for the [[thermal expansion]] and [[thermal contraction|contraction]] that changes in outdoor temperature cause. However, this can result in additional stresses, and therefore the two-hinged arch is also statically indeterminate, although not as much as the fixed arch.<ref name="Building Structures" />

The three-hinged arch is not only hinged at its base, like the two-hinged arch, yet also at its apex. The additional apical connection allows the three-hinged arch to move in two opposite directions and compensate for any expansion and contraction. This kind of arch is thus not subject to additional stress from thermal change. Unlike the other two kinds of arch, the three-hinged arch is therefore statically determinate.<ref name="Reynolds's Reinforced Concrete Designer's Handbook, p 41">{{cite book|last=Reynolds|first=Charles E|title=Reynolds's Reinforced Concrete Designer's Handbook|year=2008|publisher=Psychology Press|location=New York|isbn=978-0-419-25820-9 |page=41 |url=https://books.google.com/books?id=hrOfsy89QxkC&q=three-hinged+arch+statically+determinate&pg=PA41|via=[[Google Books]]}}</ref> It is most often used for spans of medial length, such as those of roofs of large buildings. Another advantage of the three-hinged arch is that the reaction of the pinned bases is more predictable than the one for the fixed arch, allowing shallow, bearing-type foundations in spans of medial length. In the three-hinged arch "thermal expansion and contraction of the arch will cause vertical movements at the peak pin joint but will have no appreciable effect on the bases," which further simplifies foundational design.<ref name="Building Structures" />