Editing Structural engineering (section)

===Trusses===
{{Main article|Truss}}
[[File:McDonnell-Planetarium.jpg|thumb|The McDonnell Planetarium by [[Gyo Obata]] in [[St Louis, Missouri]], USA, a concrete shell structure]]
[[File:gateway arch.jpg|thumb|upright|The 630 foot (192 m) high, stainless-clad (type 304) [[Jefferson National Expansion Memorial#The Gateway Arch|Gateway Arch]] in [[St. Louis|St. Louis, Missouri]]]]

A [[truss]] is a structure comprising members and connection points or nodes. When members are connected at nodes and forces are applied at nodes members can act in tension or compression. Members acting in compression are referred to as compression members or [[strut]]s while members acting in tension are referred to as tension members or [[Tie (engineering)|ties]]. Most trusses use [[gusset plates]] to connect intersecting elements.  Gusset plates are relatively flexible and unable to transfer [[bending moment]]s. The connection is usually arranged so that the lines of force in the members are coincident at the joint thus allowing the truss members to act in pure tension or compression.

Trusses are usually used in large-span structures, where it would be uneconomical to use solid beams.