Editing Arch bridge (section)

=== Advantages of simple materials ===
[[File:MonroeStreetBridgea.jpg|thumb|550px|Falsework [[centering]] in the center arch of [[Monroe Street Bridge (Spokane River)|Monroe Street Bridge]], [[Spokane, Washington]]. 1911.]]
[[File:Vanha kivisilta DSC08273 C.JPG|thumb|The old stone arch bridge over the [[Kerava River]] in [[Kerava]], [[Finland]]]]
Stone, brick and other such materials are strong in [[compression (physical)|compression]] and somewhat so in [[shearing (physics)|shear]], but cannot resist much force in [[tension (mechanics)|tension]]. As a result, masonry arch bridges are designed to be constantly under compression, so far as is possible. Each arch is constructed over a temporary [[falsework]] frame, known as a [[centring]]. In the first compression arch bridges, a [[Keystone (architecture)|keystone]] in the middle of the bridge bore the weight of the rest of the bridge. The more weight that was put onto the bridge, the stronger its structure became. Masonry arch bridges use a quantity of fill material (typically compacted rubble) above the arch in order to increase this dead-weight on the bridge and prevent tension from occurring in the arch ring as loads move across the bridge. Other materials that were used to build this type of bridge were brick and unreinforced concrete. When masonry (cut stone) is used the angles of the faces are cut to minimize shear forces. Where random masonry (uncut and unprepared stones) is used they are mortared together and the mortar is allowed to set before the falsework is removed.

Traditional masonry arches are generally durable, and somewhat resistant to [[settlement (construction)|settlement]] or undermining. However, relative to modern alternatives, such bridges are very heavy, requiring extensive [[foundation (architecture)|foundations]]. They are also expensive to build wherever labor costs are high.