I-beams (also known as
H-beams,
W-beams (for "wide flange"),
rolled steel joist (RSJ), or
double-T (especially in
PolishPolish is a West Slavic language and the official language of Poland. Its written standard is the Polish alphabet which corresponds basically to the Latin alphabet with a few additions...
,
SpanishSpanish or Castilian is a Romance language in the Ibero-Romance group that originated in northern Spain and gradually spread in the Kingdom of Castile, evolving into the principal language of government and trade in the Iberian peninsula...
and
GermanGerman is a West Germanic language, thus related to and classified alongside English and Dutch. It is one of the world's major languages and the most widely spoken first language in the European Union. Around the world, German is spoken by approximately 105 million native speakers and also by...
)) are
beamsA beam is a structural element that is capable of withstanding load primarily by resisting bending. The bending force induced into the material of the beam as a result of the external loads, own weight and external reactions to these loads is called a bending moment.- Overview :Beams generally...
with an
I- or H-shaped
cross-sectionIn geometry, a cross-section is the intersection of a body in 2-dimensional space with a line, or of a body in 3-dimensional space with a plane, etc. More plainly, when cutting an object into slices one gets many parallel cross-sections....
. The horizontal elements are
flangeA flange is an external or internal rib, or rim , for strength, as the flange of an iron beam or I-beam ; or for a guide, as the flange of a train wheel; or for attachment to another object, as the flange on the end of a pipe, steam cylinder, etc, or on the lens mount of a camera...
s, while the vertical element is the
web. The
Euler-Bernoulli beam equationEuler-Bernoulli beam theory is a simplification of the linear theory of elasticity which provides a means of calculating the load-carrying and deflection characteristics of beams...
shows that this is a very efficient form for carrying both
bendingIn engineering mechanics, bending characterizes the behavior of a slender structural element subjected to an external load applied perpendicularly to an axis of the element. The structural element is assumed to be such that at least one of its dimensions is a small fraction, typically 1/10 or...
and
shearShearing in continuum mechanics refers to the occurrence of a shear strain, which is a deformation of a material substance in which parallel internal surfaces slide past one another. It is induced by a shear stress in the material...
in the plane of the web.
I-beams (also known as
H-beams,
W-beams (for "wide flange"),
rolled steel joist (RSJ), or
double-T (especially in
PolishPolish is a West Slavic language and the official language of Poland. Its written standard is the Polish alphabet which corresponds basically to the Latin alphabet with a few additions...
,
SpanishSpanish or Castilian is a Romance language in the Ibero-Romance group that originated in northern Spain and gradually spread in the Kingdom of Castile, evolving into the principal language of government and trade in the Iberian peninsula...
and
GermanGerman is a West Germanic language, thus related to and classified alongside English and Dutch. It is one of the world's major languages and the most widely spoken first language in the European Union. Around the world, German is spoken by approximately 105 million native speakers and also by...
)) are
beamsA beam is a structural element that is capable of withstanding load primarily by resisting bending. The bending force induced into the material of the beam as a result of the external loads, own weight and external reactions to these loads is called a bending moment.- Overview :Beams generally...
with an
I- or H-shaped
cross-sectionIn geometry, a cross-section is the intersection of a body in 2-dimensional space with a line, or of a body in 3-dimensional space with a plane, etc. More plainly, when cutting an object into slices one gets many parallel cross-sections....
. The horizontal elements are
flangeA flange is an external or internal rib, or rim , for strength, as the flange of an iron beam or I-beam ; or for a guide, as the flange of a train wheel; or for attachment to another object, as the flange on the end of a pipe, steam cylinder, etc, or on the lens mount of a camera...
s, while the vertical element is the
web. The
Euler-Bernoulli beam equationEuler-Bernoulli beam theory is a simplification of the linear theory of elasticity which provides a means of calculating the load-carrying and deflection characteristics of beams...
shows that this is a very efficient form for carrying both
bendingIn engineering mechanics, bending characterizes the behavior of a slender structural element subjected to an external load applied perpendicularly to an axis of the element. The structural element is assumed to be such that at least one of its dimensions is a small fraction, typically 1/10 or...
and
shearShearing in continuum mechanics refers to the occurrence of a shear strain, which is a deformation of a material substance in which parallel internal surfaces slide past one another. It is induced by a shear stress in the material...
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
torsionIn solid mechanics, torsion is the twisting of an object due to an applied torque. In circular sections, the resultant shearing stress is perpendicular to the radius....
, for which
hollow structural sectionA hollow structural section is a type of metal profile with a hollow tubular cross section. In some countries they are referred to instead as a structural hollow section ....
s are often preferred.
Overview
There are two standard I-beam forms:
- Rolled I-beam, formed by hot rolling, cold rolling or extrusion
Extrusion is a process used to create objects of a fixed cross-sectional profile. A material is pushed or drawn through a die of the desired cross-section...
(depending on material).
- Plate girder, formed by welding
Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes...
(or occasionally boltingalign=right | | | |}Bolted joints are one of the most common elements in construction and machine design. They consist of cap screws or studs that capture and join other parts, and are secured with the mating of screw threads....
or rivetA rivet is a permanent mechanical fastener. Before it is installed it consists of a smooth cylindrical shaft with a head on one end. The end opposite the head is called the buck-tail. On installation the rivet is placed in a punched or pre-drilled hole. Then the tail is "upset" A rivet is a...
ing) plates.
I-beams are commonly made of
structural steelStructural steel is steel construction material, a profile, formed with a specific shape or cross section and certain standards of chemical composition and strength...
but may also be formed from
aluminiumAluminium or aluminum is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al; its atomic number is 13. It is not soluble in water under normal circumstances....
or other materials. A common type of I-beam is the
rolled steel joist (RSJ) - sometimes incorrectly rendered as
reinforced steel joist. British and
European standardThe European Committee for Standardization or Comité Européen de Normalisation , is a private non-profit organisation whose mission is to foster the European economy in global trading, the welfare of European citizens and the environment by providing an efficient infrastructure to interested...
s also specify Universal Beams (UBs) and Universal Columns (UCs). These sections have parallel flanges, as opposed to the varying thickness of RSJ flanges. UCs have equal or near-equal width and depth, while UBs are significantly deeper than they are wide.
I-beams engineered from wood with
fiberboardFiberboard is a type of engineered wood product that is made out of wood fibers. Types of fiberboard include particle board, medium-density fiberboard, and hardboard. Fiberboard is sometimes used as a synonym for particle board, but particle board usually refers to low-density fiberboard...
and/or
laminated veneer lumberLaminated veneer lumber is an engineered wood product that uses multiple layers of thin wood assembled with adhesives. It offers several advantages over typical milled lumber: it is stronger, straighter, and more uniform. It is much less likely than conventional lumber to warp, twist, bow, or...
are also becoming increasingly popular in construction, especially residential, as they are both lighter and less prone to warping than solid wooden
joistA joist, in architecture and engineering, is one of the horizontal supporting members that run from wall to wall, wall to beam, or beam to beam to support a ceiling, roof, or floor. It may be made of wood, steel, or concrete. Typically, a beam is bigger than, and is thus distinguished from, a joist...
s. However there has been some concern as to their rapid loss of strength in a fire if unprotected.
Design
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
columnA column in structural engineering is a vertical structural element that transmits, through compression, the weight of the structure above to other structural elements below. For the purpose of wind or earthquake engineering, columns may be designed to resist lateral forces. Other compression...
s.
I-beams may be used both on their own, or acting
compositelyComposite materials are engineered materials made from two or more constituent materials with significantly different physical or chemical properties which remain separate and distinct on a macroscopic level within the finished structure.- History :The most primitive composite materials were straw...
with another material, typically
concreteConcrete is a construction material composed of cement as well as other cementitious materials such as fly ash and slag cement, aggregate , water, and chemical admixtures...
. Design may be governed by any of the following criteria:
- deflection
In engineering mechanics, deflection is a term that is used to describe the degree to which a structural element is displaced under a load. The deflection of a member under a load is directly related to the slope of the deflected shape of the member under that load and can be calculated by...
- the stiffnessStiffness is the resistance of an elastic body to deformation by an applied force. It is an extensive material property.-Definition:The stiffness, k, of a body is a measure of the resistance offered by an elastic body to deformation .whereIn the International System of Units, stiffness is typically...
of the I-beam will be chosen to minimise deformation
- vibration
Vibration refers to mechanical oscillations about an equilibrium point. The oscillations may be periodic such as the motion of a pendulum or random such as the movement of a tire on a gravel road.Vibration is occasionally "desirable"...
- the stiffness and massIn physics, mass commonly refers to any of three properties of matter, which have been shown experimentally to be equivalent: inertial mass, active gravitational mass and passive gravitational mass...
are chosen to prevent unacceptable vibrations, particularly in settings sensitive to vibrations, such as offices and libraries
- bending failure by yielding
The yield strength or yield point of a material is defined in engineering and materials science as the stress at which a material begins to deform plastically. Prior to the yield point the material will deform elastically and will return to its original shape when the applied stress is removed...
- where the stressIn continuum mechanics, the concept of stress, introduced by Cauchy around 1822, is a measure of the average amount of force exerted per unit area of a surface within a deformable body on which internal forces act...
in the cross section exceeds the yield stress
- bending failure by lateral torsional buckling - where a flange in compression tends to buckle sideways or the entire cross-section buckles torsionally
- bending failure by local buckling - where the flange or web is so slender as to buckle locally
- local yield
The yield strength or yield point of a material is defined in engineering and materials science as the stress at which a material begins to deform plastically. Prior to the yield point the material will deform elastically and will return to its original shape when the applied stress is removed...
- 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
Wide-flange steel materials and rolling processes (U.S.)
In the United States, the most commonly mentioned I-Beam is the wide-flange (W) shape. These beams have flanges in which the planes are nearly parallel. Other I-Beams include American Standard (designated S) shapes, in which 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, which has generally replaced the older ASTM grades A572 and A36. Ranges of yield strength:
- A36: 36,000 psi
The pound per square inch or, more accurately, pound-force per square inch is a unit of pressure or of stress based on avoirdupois units...
(250 MPa)
- A572: 42,000–60,000 psi (290–410 MPa), but 50,000 psi (340 MPa) is the most common
- A588: Similar to A572
- A992: 50,000–65,000 psi (340–450 MPa)
Wide-flange shapes are produced by the
electric arc furnaceAn is a furnace that heats charged material by means of an electric arc.Arc furnaces range in size from small units of approximately one ton capacity up to about 400 ton units used for secondary steelmaking. Arc furnaces used in research laboratories and by dentists may have a...
method and generally contain more than 95% recycled content.
The American Institute of Steel Construction ("AISC") publishes the "Steel Construction Manual" for designing structures of various shapes. It documents the common approaches, ASD and LRFD, (as of 13th ed.) to creating such designs.
Designation and terminology
- 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 10 in (25 cm) in depth (height when the I-Beam is standing on its flanges) and weighs approximately 22 lb/ft (33 kg/m).
- 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 25 cm (10 in) in depth (height when the I-Beam is standing on its flanges) and weighs approximately 33 kg/m (22 lb/ft). I-Beams are still available in U.S. sizes from many Canadian manufacturers.
- 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, ISWB : Indian Standard Wide Flange Beams. Beams are designted 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 BIS
The Bureau of Indian Standards is the national standards organisation of India under the aegis of Ministry of Consumer Affairs,Food & Public Distribution,Govt of India...
)
- 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 152mm depth 152mm width and weighing 23kg per meter length.
External links