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I-beams (also known as H-beams, W-beams (for "wide flange"), rolled steel joist (RSJ), or double-T (especially in Polish and German)) are beams with an I- or H-shaped cross-section. The horizontal elements are flanges, while the vertical element is the web. The Euler-Bernoulli beam equation shows that this is a very efficient form for carrying both bending and shear 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, for which hollow structural sections are often preferred.

Overview
There are two standard I-beam forms:

Rolled I-beam, formed by hot rolling, cold rolling or extrusion (depending on material).
Plate girder, formed by welding (or occasionally bolting or riveting) 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 and European standards 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 deeper.

I-beams engineered from wood with fiberboard and/or laminated veneer lumber are also becoming increasingly popular in construction, especially residential, as they are both lighter and less prone to warping than solid wooden joists. 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 columns.

I-beams may be used both on their own, or acting compositely with another material, typically concrete. Design may be governed by any of the following criteria:

deflection - the stiffness of the I-beam will be chosen to minimise 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 yielding - where the stress 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 - 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,[1] which has generally replaced the older ASTM grades A572 and A36. Ranges of yield strength:

A36: 36,000 psi (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 furnace method and generally contain more than 95% recycled content.[citation needed]

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).[2]
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)

工字钢

工字钢也称钢梁，是截面为工字形的长条钢材。其规格以腰高( h)*腿宽(b)*腰厚(d)的毫数表示，如“工160*88*6”，即表示腰高为160毫米，腿宽为88毫米，腰厚为6毫米的工字钢。工字钢的规格也可用型号表示，型号表示腰高的厘米数，如工16#。腰高相同的工字钢，如有几种不同的腿宽和腰厚，需在型号右边加a b c 予以区别，如32a# 32b# 32c#等。 工字钢分普通工字钢和轻型工字钢，热轧普通工字钢的规格为10-63#。经供需双方协议供应的热轧普通工字钢规格为12-55#。工字钢广泛用于各种建筑结构、桥梁、车辆、支架、机械等

工字钢 HW HM HN H型钢的区别
　　工字钢翼缘是变截面靠腹板部厚,外部薄; H型钢的翼缘是等截面
　　HW HM HN H是H型钢的通称,H型钢是焊制; HW HM HN是热轧
　　HW 是H型钢高度和翼缘宽度基本相等;主要用于钢筋砼框架结构柱中钢芯柱,也称劲性钢柱;在钢结构中主要用于柱
　　HM 是H型钢高度和翼缘宽度比例大致为1.33~~1.75 主要在钢结构中:用做钢框架柱在承受动力荷载的框架结构中用做框架梁;例如:设备平台
　　HN 是H型钢高度和翼缘宽度比例大于等于2; 主要用于梁;
　　工字钢的用用途相当于HN型钢;
　　1、工字型钢不论是普通型还是轻型的，由于截面尺寸均相对较高、较窄，故对截面两个主袖的惯性矩相差较大，因此，一般仅能直接用于在其腹板平面内受弯的构件或将其组成格构式受力构件。对轴心受压构件或在垂直于腹板平面还有弯曲的构件均不宜采用，这就使其在应用范围上有着很大的局限。　
　　2、 h型钢属于高效经济裁面型材(其它还有冷弯薄壁型钢、压型钢板等)，由于截面形状合理，它们能使钢材更高地发挥效能，提高承裁能力。不同于普通工字型的是h型钢的翼缘进行了加宽，且内、外表面通常是平行的，这样可便于用高强度螺桂和其他构件连接。其尺寸构成合理系列，型号齐全，便于设计选用。　
　　3、h型钢的翼缘都是等厚度的，有轧制截面，也有由3块板焊接组成的组合截面。工字钢都是轧制截面，由于生产工艺差，翼缘内边有1：10坡度。Ｈ型钢的轧制不同于普通工字钢仅用一套水平轧辊，由于其翼缘较宽且无斜度(或斜度很小)，故须增设一组立式轧辊同时进行辊轧，因此，其轧制工艺和设备都比普通轧机复杂。国内可生产的最大轧制h型钢高度为800ｍｍ，超过了只能是焊接组合截面。
　　我国热轧H型钢国标（GB/T11263-1998）将h型钢分为窄翼缘、宽翼缘和钢桩三类，其代号分别为hz、hk和hu。窄翼缘h型钢适用于梁或压弯构件，而宽翼缘h型钢和h型钢桩则适用于轴心受压构件或压弯构件。工字钢与Ｈ型钢相比，等重量前提下，w、 ix、 iy都不如h型钢。