Editing Through arch bridge (section)

== Tied-arch bridges ==
[[File:Brunelwindsorbridge.jpg|thumb|[[Isambard Kingdom Brunel|Brunel]]'s wrought-iron [[Windsor Railway Bridge]]: both a tied-arch and a through-arch|alt=|left]]
[[File:StanleyFerryAqueductProfile.jpg|thumb|[[Stanley Ferry Aqueduct]], Yorkshire, opened 1839, built in [[cast iron]]. A through-arch, but not a tied-arch|alt=|left]]
Many [[tied-arch bridge]]s are also through-arch bridges. As well as tying the side-loads of the arch, the tension member is also at a convenient height to form the bridge deck, as for a through-arch.

The converse is not true: through-arch bridges do not imply that they are tied-arch bridges, unless they also provide the deliberate tension member that is the key to a tied-arch. Although ''visually'' similar, tied- and untied- through-arch bridges are quite distinct structurally and are unrelated in how they distribute their loads. In particular, [[cast iron]] bridges such as the [[Stanley Ferry Aqueduct]] may resemble tied-arch bridges, but as cast iron is weak in tension they are not structurally a tied arch.