View source for I-beam

{{Short description|Construction element}}
{{About||the nightclub|I-Beam (nightclub)|the text cursor of a graphical computer user interface|Cursor (computers)}}
{{Use dmy dates|date=March 2023}}
{{Use British English|date=March 2020}}
[[File:i-Beam 002.JPG|thumb|An I-beam used to support the first floor of a house]]
An '''I-beam''' is any of various structural members with an {{ibeam}}- (serif capital letter 'I') or H-shaped [[cross section (geometry)|cross-section]]. Technical terms for similar items include '''H-beam''', '''I-profile''', '''universal column''' ('''UC'''), '''w-beam''' (for "wide flange"), '''universal beam''' ('''UB'''), '''rolled steel joist''' ('''RSJ'''), or '''double-T''' (especially in [[Polish language|Polish]], [[Bulgarian language|Bulgarian]], [[Spanish language|Spanish]], [[Italian language|Italian]], and [[German language|German]]). I-beams are typically made of [[structural steel]] and serve a wide variety of construction uses.

The horizontal elements of the {{ibeam}} are called [[flange]]s, and the vertical element is known as the "web". The web resists [[shear forces]], while the flanges resist most of the [[bending moment]] experienced by the beam. The [[Euler–Bernoulli beam equation]] shows that the {{ibeam}}-shaped section is a very efficient form for carrying both [[bending]] and [[shearing (physics)|shear]] loads in the plane of the web. On the other hand, the cross-section has a reduced capacity in the transverse direction, and is also inefficient in carrying [[torsion (mechanics)|torsion]], for which [[hollow structural section]]s are often preferred.

== History ==
{{Further|Bethlehem Steel}}
[[File:Muhlenberg College.jpg|thumb|[[Mark di Suvero]]'s ''Victor's Lament'' (foreground in red) on the campus of [[Muhlenberg College]] in [[Allentown, Pennsylvania]], is an I-beam sculpture paying tribute to the rich history of [[steelmaking]] in the [[Lehigh Valley]] region of the eastern [[Pennsylvania]].]]
In 1849, the method of producing an I-beam, as rolled from a single piece of wrought iron,<ref>Forsyth, M. Structures and Construction in Historic Building Conservation. p. 179.</ref> was patented by Alphonse Halbou of [[Forges de la Providence]] in [[Marchienne-au-Pont]], Belgium.<ref>{{cite book|url=https://books.google.com/books?id=18-6AAAAIAAJ|page=82|title=International directory of company histories|volume=26|author=Thomas Derdak, Jay P. Pederson|publisher=St. James Press|year=1999|isbn=978-1-55862-385-9}}</ref>

[[Bethlehem Steel]], headquartered in [[Bethlehem, Pennsylvania]], was a leading supplier of rolled structural steel of various cross-sections in American bridge and skyscraper work of the mid-20th century.<ref name="MorningCallSupplement2003">{{Cite magazine |date=14 December 2003 |title = Forging America: The History of Bethlehem Steel |magazine= Morning Call Supplement | publisher = [[The Morning Call]] |url=http://www.mcall.com/news/specials/bethsteel/all-bethsteel-c0p1,0,4389048.story?coll=all-bethsteel-nav | access-date = 24 September 2010 |archive-date = 27 April 2011 |archive-url = https://web.archive.org/web/20110427003302/http://www.mcall.com/news/specials/bethsteel/all-bethsteel-c0p1,0,4389048.story?coll=all-bethsteel-nav | url-status = dead}}</ref> Rolled cross-sections now have been partially displaced in such work by [[Fabrication (metal)|fabricated]] cross-sections.

== Overview ==
[[File:Ibeam.svg|thumb|A typical cross-section of I-beams]]
There are two standard I-beam forms:
* Rolled I-beam, formed by [[hot rolling]], [[cold rolling]] or [[extrusion]], depending on the material.
* [[Plate girder]], formed by [[welding]] (or occasionally [[bolted joint|bolting]] or [[rivet]]ing) plates.

I-beams are commonly made of [[structural steel]] but may also be formed from [[aluminium]] or other materials. A common type of I-beam is the ''rolled steel joist'' (RSJ), sometimes incorrectly rendered as reinforced steel joist. [[British Standard|British]] and [[European Committee for Standardization|European standards]] also specify Universal Beams (UBs) and Universal Columns (UCs). These sections have parallel flanges, shown as "W-Section" in the accompanying illustration, as opposed to the varying thickness of RSJ flanges, illustrated as "S-Section", which are seldom now rolled in the [[United Kingdom]]. Parallel flanges are easier to connect to and do away with the need for tapering washers. UCs have equal or near-equal width and depth and are more suited to being oriented vertically to carry axial load such as columns in multi-storey construction, while UBs are significantly deeper than they are wide are more suited to carrying bending load such as beam elements in floors.

[[I-joist]]s, I-beams engineered from wood with [[fiberboard]] or [[laminated veneer lumber]], or both, are also becoming increasingly popular in construction, especially residential, as they are both lighter and less prone to warping than solid wooden [[joist]]s. However, there has been some concern as to their rapid loss of strength in a fire if unprotected.

== Design ==
[[File:Beam mode 2.gif|thumb|An I-beam vibrating in torsion mode]]
I-beams are widely used in the [[construction industry]] and are available in a variety of standard sizes. Tables are available to allow easy selection of a suitable steel I-beam size for a given applied load. I-beams may be used both as beams and as [[column]]s.

I-beams may be used both on their own, or acting [[composite material|compositely]] with another material, typically [[concrete]]. Design may be governed by any of the following criteria:
* [[Deflection (engineering)|deflection]]: the [[stiffness]] of the I-beam will be chosen to minimize deformation
* [[vibration]]: the stiffness and [[mass]] are chosen to prevent unacceptable vibrations, particularly in settings sensitive to vibrations, such as offices and libraries
* bending failure by [[yield (engineering)|yielding]]: where the [[stress (mechanics)|stress]] in the cross section exceeds the [[yield stress]]
* bending failure by [[Buckling#Lateral-torsional buckling|lateral torsional buckling]]: where a flange in compression tends to buckle sideways or the entire cross-section buckles torsionally
* bending failure by [[Buckling#Local buckling|local buckling]]: where the flange or web is so slender as to buckle locally
* local yield: caused by concentrated loads, such as at the beam's point of support
* [[shear failure]]: where the web fails. Slender webs will fail by buckling, rippling in a phenomenon termed '''tension field action''', but shear failure is also resisted by the stiffness of the flanges
* buckling or yielding of components: for example, of stiffeners used to provide stability to the I-beam's web.

=== Design for bending ===
[[File:Poutre flexion deviee.svg|thumb|Bending torque and resulting stress in case of bi-axial bending of a symmetric beam. The complex bending is the superposition of two simple bendings around the ''y'' and ''z'' axes (small deformation, linear behaviour). The largest stresses ({{math|{{sigma}}{{sub|''xx''}}}}) in a beam under bending are in the locations farthest from the neutral axis.]]
A beam under bending sees high stresses along the axial fibers that are farthest from the [[neutral axis]].  To prevent failure, most of the material in the beam must be located in these regions.  Comparatively little material is needed in the area close to the neutral axis.  This observation is the basis of the I-beam cross-section; the neutral axis runs along the center of the web which can be relatively thin and most of the material can be concentrated in the flanges.

The ideal beam is the one with the least cross-sectional area (and hence requiring the least material) needed to achieve a given [[section modulus]]. Since the section modulus depends on the value of the [[second moment of area|moment of inertia]], an efficient beam must have most of its material located as far from the neutral axis as possible. The farther a given amount of material is from the neutral axis, the larger is the section modulus and hence a larger bending moment can be resisted.

When designing a symmetric I-beam to resist stresses due to bending the usual starting point is the required section modulus. If the allowable stress is {{math|''σ''<sub>max</sub>}} and the maximum expected bending moment is {{math|''M''<sub>max</sub>}}, then the required section modulus is given by:<ref name="Gere" />
:<math>
   S = \cfrac{M_{\mathrm{max}}}{\sigma_{\mathrm{max}}} = \frac{I}{c}
 </math>,
where {{mvar|I}} is the moment of inertia of the beam cross-section and {{mvar|c}} is the distance of the top of the beam from the neutral axis (see [[beam theory]] for more details).

For a beam of cross-sectional area {{mvar|a}} and height {{mvar|h}}, the ideal cross-section would have half the area at a distance {{math|{{sfrac|''h''|2}}}} above the cross-section and the other half at a distance {{math|{{sfrac|''h''|2}}}} below the cross-section.<ref name=Gere>Gere and Timoshenko, 1997, ''Mechanics of Materials'', PWS Publishing Company.</ref> For this cross-section,
:<math>
   I = \frac{ah^2}{4} \,; \quad S = \frac12 a h
 </math>.
However, these ideal conditions can never be achieved because material is needed in the web for physical reasons, including to resist buckling.  For wide-flange beams, the section modulus is approximately
:<math>
   S \approx 0.35 a h
 </math>
which is superior to that achieved by rectangular beams and circular beams.

=== Issues ===
Though I-beams are excellent for unidirectional bending in a plane parallel to the web, they do not perform as well in bidirectional bending. These beams also show little resistance to twisting and undergo sectional warping under torsional loading. For torsion dominated problems, [[box beam]]s and other types of stiff sections are used in preference to the I-beam.

==Shapes and materials in the United States==
[[File:Rostiger Stahltraeger.jpg|thumb|A rusty riveted steel I-beam]]

In the [[United States]], the most commonly mentioned I-beam is the wide-flange (W) shape. These beams have flanges whose inside surfaces are parallel over most of their area. Other I-beams include American Standard (designated S) shapes, in which inner flange surfaces are not parallel, and H-piles (designated HP), which are typically used as pile foundations. Wide-flange shapes are available in grade ASTM A992,<ref>{{cite book
 |url=http://www.astm.org/Standards/A992.htm
 |title=ASTM A992?A992M Standard Specification for Structural Steel Shapes
 |publisher=[[ASTM International|American Society for Testing and Materials]]
 |year=2006
 |doi=10.1520/A0992_A0992M-06A
}}</ref> which has generally replaced the older ASTM grades A572 and A36. Ranges of yield strength:
* '''A36:''' {{cvt|36000|psi|MPa|lk=on}}
* '''A572:''' {{cvt|42000|–|60000|psi|MPa}}, with {{cvt|50000|psi|MPa}} the most common
* '''A588:''' Similar to A572
* '''A992:''' {{cvt|50000|-|65000|psi|MPa}}

Like most steel products, I-beams often contain some recycled content.

== Standards ==
The following standards define the shape and tolerances of I-beam steel sections:

=== European standards ===
* [[EN 10024]], Hot rolled taper flange I sections – Tolerances on shape and dimensions.
* [[EN 10034]], Structural steel I and H sections – Tolerances on shape and dimensions.
* [[EN 10162]], Cold rolled steel sections – Technical delivery conditions – Dimensional and cross-sectional tolerances

=== AISC manual ===
The [[American Institute of Steel Construction]] (AISC) publishes the ''Steel Construction Manual'' for designing structures of various shapes. It documents the common approaches, [[Allowable Strength Design]] (ASD) and [[Limit state design|Load and Resistance Factor Design]] (LRFD), (starting with 13th ed.) to create such designs.

=== Other ===
* [[DIN 1025-5]]
* [[ASTM A6]], American Standard Beams
* [[BS 4-1]]
* [[IS 808]] – Dimensions hot rolled steel beam, column, channel and angle sections
* [[AS/NZS 3679.1]] – Australia and New Zealand standard<ref name=onesteel>[http://www.onesteel.com/images/db_images/productspecs/Hot_Rolled_Cat_Issue5_Feb2010.pdf Hot rolled and structural steel products – Fifth edition] {{webarchive|url=https://web.archive.org/web/20130410021605/http://www.onesteel.com/images/db_images/productspecs/Hot_Rolled_Cat_Issue5_Feb2010.pdf |date=10 April 2013 }} — [[Onesteel]]. Retrieved 18 December 2015.</ref>

== Designation and terminology ==
[[File:i-BeamCrossSection.svg|thumb|The dimension of a wide-flange I-beam]]
In the [[United States]], steel I-beams are commonly specified using the depth and weight of the beam. For example, a "W10x22" beam is approximately {{Cvt|10|in|mm|0}} in depth with a nominal height of the I-beam from the outer face of one flange to the outer face of the other flange, and weighs {{cvt|22|lb/ft}}. Wide flange section beams often vary from their nominal depth.  In the case of the W14 series, they may be as deep as {{cvt|22.84|in|mm|0}}.<ref>AISC Manual of Steel Construction 14th Edition</ref>'

In [[Canada]], steel I-beams are now commonly specified using the depth and weight of the beam in metric terms. For example, a "W250x33" beam is approximately {{Convert|250|mm|in|1}} in depth (height of the I-beam from the outer face of one flange to the outer face of the other flange) and weighs approximately {{cvt|33|kg/m|lb/ft lb/yd}}.<ref>{{cite book
 |title=Handbook of Steel Construction
 |edition=9th
 |publisher=[[Canadian Institute of Steel Construction]]
 |year=2006
 |isbn=978-0-88811-124-1
}}</ref> I-beams are still available in US sizes from many Canadian manufacturers.

In [[Mexico]], steel I-beams are called IR and commonly specified using the depth and weight of the beam in metric terms. For example, a "IR250x33" beam is approximately {{cvt|250|mm|in|1}} in depth (height of the I-beam from the outer face of one flange to the outer face of the other flange) and weighs approximately {{cvt|33|kg/m|lb/ft}}.<ref>''IMCA Manual of Steel Construction'', 5th Edition.</ref>

In [[India]], I-beams are designated as ISMB, ISJB, ISLB, ISWB. ISMB: Indian Standard Medium Weight Beam, ISJB: Indian Standard Junior Beams, ISLB: Indian Standard Light Weight Beams, and ISWB: Indian Standard Wide Flange Beams. Beams are designated as per respective abbreviated reference followed by the depth of section, such as for example ''ISMB 450'', where 450 is the depth of section in millimetres (mm). The dimensions of these beams are classified as per IS:808 (as per [[Bureau of Indian Standards|BIS]]).{{Citation needed|date=September 2016}}

In the [[United Kingdom]], these steel sections are commonly specified with a code consisting of the major dimension, usually the depth, -x-the minor dimension-x-the mass per metre-ending with the section type, all measurements being metric. Therefore, a 152x152x23UC would be a column section (UC = universal column) of approximately {{cvt|152|mm|in|1}} depth, 152&nbsp;mm width and weighing {{cvt|23|kg/m|0}} of length.<ref>{{cite web|url=http://www.corusconstruction.com/file_source/StaticFiles/Construction/Library/BS4Sectionsbrochure.pdf |archive-url=https://web.archive.org/web/20100215100102/http://www.corusconstruction.com/file_source/StaticFiles/Construction/Library/BS4Sectionsbrochure.pdf |archive-date=15 February 2010 |title=Structural sections |publisher=Corus Construction & Industrial |url-status=dead }}</ref>

In [[Australia]], these steel sections are commonly referred to as Universal Beams (UB) or Columns (UC). The designation for each is given as the approximate height of the beam, the type (beam or column) and then the unit metre rate (e.g., a 460UB67.1 is an approximately {{Cvt|460|mm|in|1}} deep universal beam that weighs {{Cvt|67.1|kg/m|0}}).<ref name=onesteel />

== Cellular beams ==
{{Main|Cellular beam}}
[[Cellular beam]]s are the modern version of the traditional [[castellated beam]], which results in a beam approximately 40–60% deeper than its parent section. The exact finished depth, cell diameter and cell spacing are flexible. A cellular beam is up to 1.5 times stronger than its parent section and is therefore utilized to create efficient large [[Span (engineering)|span]] constructions.<ref>{{cite web |url=https://www.kloecknermetalsuk.com/westok/products/westok-cellular-beam/ |title=Cellular Beams - Kloeckner Metals UK |website=kloecknermetalsuk.com |access-date=13 May 2017}}</ref>

== See also ==
* C-beam, also known as a [[structural channel]] or Parallel Flange Channel (PFC)
* [[DIN 1025]] – a DIN standard which defines the dimensions, masses and sectional properties of a set of I-beams
* [[Open web steel joist]]
* [[Reinforced concrete]]
* [[Steel design]]
* [[Structural angle]]
* [[T-beam]]
* [[Weld access hole]]

== References ==
{{Reflist}}

== Further reading ==
* {{Cite book |last=Ashby |first=M. F. |year=2005 |title=Materials Selection in Mechanical Design |edition=3rd |location=Oxford; Boston |publisher=Elsevier Butterworth-Heinemann |isbn=9780750661683}} See chapter 8, sections 8.4 ("Floor joists: wood or steel?") and 8.5 ("Increasing the stiffness of the steel sheet").

== External links ==
{{Commons}}
* [http://www.cisc-icca.ca/ Canadian Institute of Steel Construction website]
* [http://www.aisc.org/ American Institute of Steel Construction website]
* [http://www.imca.org.mx/ Mexican Institute of Steel Construction website]
* [http://www.umass.edu/bmatwt/publications/articles/i_joist.html Wood I-joists]
* [http://www.steelconstruction.org/ British Constructional Steelwork Association website]

[[Category:1849 introductions]]
[[Category:Structural engineering]]
[[Category:Structural steel]]