Editing Reinforced concrete (section)

==Reinforcement and terminology of beams==
[[File:Rebarbeams.JPG|thumb|right|Two intersecting beams integral to parking garage slab that will contain both reinforcing steel and the wiring, junction boxes and other electrical components necessary to install the overhead lighting for the garage level beneath it.]]
[[File:Fideo o’r trawst concrit olaf yn cael ei osod – Tach 2016 Last concrete beam installation – 2016.webm|thumb|A short video of the last beam being placed on a raised road, part of a new road near [[Cardiff Bay]], [[Wales]]]]

A beam bends under [[bending moment]], resulting in a small curvature. At the outer face (tensile face) of the curvature the concrete experiences tensile stress, while at the inner face (compressive face) it experiences compressive stress.

A '''singly reinforced''' beam is one in which the concrete element is only reinforced near the tensile face and the reinforcement, called tension steel, is designed to resist the tension.

A '''doubly reinforced''' beam is the section in which besides the tensile reinforcement the concrete element is also reinforced near the compressive face to help the concrete resist compression and take stresses. The latter reinforcement is called compression steel. When the compression zone of a concrete is inadequate to resist the compressive moment (positive moment), extra reinforcement has to be provided if the architect limits the dimensions of the section.

An '''under-reinforced''' beam is one in which the tension capacity of the tensile reinforcement is smaller than the combined compression capacity of the concrete and the compression steel (under-reinforced at tensile face). When the reinforced concrete element is subject to increasing bending moment, the tension steel yields while the concrete does not reach its ultimate failure condition. As the tension steel yields and stretches, an "under-reinforced" concrete also yields in a ductile manner, exhibiting a large deformation and warning before its ultimate failure. In this case the yield stress of the steel governs the design.

An '''over-reinforced''' beam is one in which the tension capacity of the tension steel is greater than the combined compression capacity of the concrete and the compression steel (over-reinforced at tensile face). So the "over-reinforced concrete" beam fails by crushing of the compressive-zone concrete and before the tension zone steel yields, which does not provide any warning before failure as the failure is instantaneous.

A '''balanced-reinforced''' beam is one in which both the compressive and tensile zones reach yielding at the same imposed load on the beam, and the concrete will crush and the tensile steel will yield at the same time. This design criterion is however as risky as over-reinforced concrete, because failure is sudden as the concrete crushes at the same time of the tensile steel yields, which gives a very little warning of distress in tension failure.<ref>Nilson, Darwin, Dolan. ''Design of Concrete Structures''. the MacGraw-Hill Education, 2003. p. 80-90.</ref>

Steel-reinforced concrete moment-carrying elements should normally be designed to be under-reinforced so that users of the structure will receive warning of impending collapse.

The '''characteristic strength''' is the strength of a material where less than 5% of the specimen shows lower strength.

The '''design strength''' or '''nominal strength''' is the strength of a material, including a material-safety factor. The value of the safety factor generally ranges from 0.75 to 0.85 in [[Permissible stress design]].

The '''ultimate limit state''' is the theoretical failure point with a certain probability. It is stated under factored loads and factored resistances.

Reinforced concrete structures are normally designed according to rules and regulations or recommendation of a code such as ACI-318, CEB, Eurocode 2 or the like. WSD, USD or LRFD methods are used in design of RC structural members. Analysis and design of RC members can be carried out by using linear or non-linear approaches. When applying safety factors, building codes normally propose linear approaches, but for some cases non-linear approaches. To see the examples of a non-linear numerical simulation and calculation visit the references:<ref>{{cite web|url=http://121.183.206.200:8080/proto.board/abstractArticleContentView?page=article&journal=sem&volume=53&num=4&ordernum=7&site=korsc|archive-url=https://web.archive.org/web/20150402113932/http://121.183.206.200:8080/proto.board/abstractArticleContentView?page=article&journal=sem&volume=53&num=4&ordernum=7&site=korsc|url-status=dead|archive-date=2 April 2015|title=Techno Press|date=2 April 2015}}</ref><ref>{{cite journal |url=http://ijce.iust.ac.ir/browse.php?a_id=563&sid=1&slc_lang=en |title=Energy based structural damage index based on nonlinear numerical simulation of structures subjected to oriented lateral cyclic loading |last=Sadeghi |first=Kabir |journal=International Journal of Civil Engineering |date=15 September 2011 |volume=9 |issue=3 |pages=155–164 |issn=1735-0522 |access-date=23 December 2016}}</ref>