I-lúčim

Existujú dve štandardné I{0}}formy lúčov:

• Rolled I-beam, formed by valcovanie za tepla, valcovanie za studena or vytláčanie (depending on material).

• Doskový nosník, formed by zváranie (or occasionally skrutkovanie or nitovanie) taniere.

I-beams are commonly made of konštrukčná oceľ but may also be formed from hliník or other materials. A common type of I-beam is the valcovaný oceľový nosník (RSJ)—sometimes incorrectly rendered as vystužený oceľový nosník. britský and európskych noriem also specify Universal Beams (UBs) and Universal Columns (UCs). These sections have parallel flanges, as opposed to the varying thickness of RSJ flanges which are seldom now rolled in the UK. 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-trámy—I-beams engineered from wood with drevovláknitá doska and/or laminované dyhové rezivo—are also becoming increasingly popular in construction, especially residential, as they are both lighter and less prone to warping than solid wooden trámy. Existujú však určité obavy, pokiaľ ide o ich rýchlu stratu sily pri požiari, ak nie sú chránené.

Dizajn na ohýbanie 

Najväčšie napätie (${\displaystyle \sigma _{xx}}$) v ohybovom nosníku sú v miestach najďalej od neutrálnej osi.

A beam under bending sees high stresses along the axial fibers that are farthest from the neutrálna os. Aby sa predišlo poruchám, väčšina materiálu v nosníku musí byť umiestnená v týchto oblastiach. V oblasti blízko neutrálnej osi je potrebné pomerne málo materiálu. Toto pozorovanie je základom prierezu I-priečneho lúča-; neutrálna os prebieha pozdĺž stredu stojiny, ktorá môže byť relatívne tenká a väčšina materiálu môže byť sústredená v prírubách.

The ideal beam is the one with the least cross-sectional area (and hence requiring the least material) needed to achieve a given modul sekcie. Since the section modulus depends on the value of the moment zotrvačnostiÚčinný lúč musí mať väčšinu materiálu umiestnenú čo najďalej od neutrálnej osi. Čím ďalej je dané množstvo materiálu od neutrálnej osi, tým väčší je modul prierezu, a preto možno odolávať väčšiemu ohybovému momentu.

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 ${\displaystyle \sigma _{\mathrm {max} }}$ and the maximum expected bending moment is ${\displaystyle M_{\mathrm {max} }}$, potom je požadovaný modul prierezu daný vzťahom³

• ${\displaystyle S={\cfrac {M_{\mathrm {max} }}{\sigma _{\mathrm {max} }}}={ \cfrac {I}{c}}}$

where ${\displaystyle I}$ is the moment of inertia of the beam cross-section and ${\displaystyle c}$ is the distance of the top of the beam from the neutral axis (see teória lúčov for more details).

For a beam of cross-sectional area ${\displaystyle a}$ and height ${\displaystyle h}$, the ideal cross-section would have half the area at a distance ${\displaystyle h/2}$ above the cross-section and the other half at a distance ${\displaystyle h/2}$ below the cross-section.³ For this cross-section

• ${\displaystyle I={\cfrac {ah{2}}{4}};S=0.5ah}$

Tieto ideálne podmienky však nemožno nikdy dosiahnuť, pretože materiál je potrebný v tkanine z fyzikálnych dôvodov, vrátane odolnosti voči vybočeniu. Pre široké-prírubové nosníky je modul prierezu približne

• ${\displaystyle S\cca 0,35ah}$

ktorý je lepší ako ten, ktorý dosahujú pravouhlé nosníky a kruhové nosníky.

Problémy 

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, krabicové nosníky and other types of stiff sections are used in preference to the I-beam.

Tvary a materiály (USA) 

Hrdzavý nitovaný oceľový I-nosník

V Spojených štátoch je najčastejšie spomínaným I-lúčom tvar širokej-príruby (W). Tieto nosníky majú príruby, ktorých vnútorné plochy sú na väčšine ich plochy rovnobežné. Medzi ďalšie I-nosníky patria americké štandardné (označené S) tvary, v ktorých vnútorné plochy pásnic nie sú rovnobežné, a H-pilóty (označené HP), ktoré sa zvyčajne používajú ako pilótové základy. Široké-tvary prírub sú dostupné v triede ASTM A992,⁴ 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), with 50,000 psi (340 MPa) the most common

• A588: Similar to A572

• A992: 50,000–65,000 psi (340–450 MPa)

Ako väčšina výrobkov z ocele, aj I-nosníky často obsahujú nejaký recyklovaný obsah.

Normy 

Nasledujúce normy definujú tvar a tolerancie oceľových profilov I-:

európske normy 

• 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

Manuál AISCupraviť

The Americký inštitút pre oceľové konštrukcie (AISC) publishes the Steel Construction Manual for designing structures of various shapes. It documents the common approaches, Návrh prípustnej pevnosti (ASD) and Návrh faktorov zaťaženia a odporu (LRFD), (starting with 13th ed.) to create such designs.

Iné 

• DIN 1025-5

• ASTM A6, americké štandardné lúče

• BS 4-1

• IS 808 – Dimensions hot rolled steel beam, column, channel and angle sections

• AS/NZS 3679.1 – Australia and New Zealand standard⁵

Označenie a terminológia 

Široký-lúč I-príruby.

• In the Spojené štáty, steel I-beams are commonly specified using the depth and weight of the beam. For example, a "W10x22" beam is approximately 10 in (254 mm) in depth (nominal height of the I-beam from the outer face of one flange to the outer face of the other flange) and weighs 22 lb/ft (33 kg/m). Wide flange section beams often vary from their nominal depth. In the case of the W14 series, they may be as deep as 22.84 in (580 mm).⁶

• In Kanada, 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 250 millimetres (9.8 in) 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 33 kg/m (22 lb/ft; 67 lb/yd).⁷ I-beams are still available in U.S. sizes from many Canadian manufacturers.

• In Mexiko, 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 250 mm (9.8 in) 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 33 kg/m (22 lb/ft).⁸

• 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 BIS).^{potrebná citácia}

• In the Spojene kralovstvo, these steel sections are commonly specified with a code consisting of the major dimension (usually the depth){{0}}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 152 mm (6.0 in) depth 152 mm width and weighing 23 kg/m (46 lb/yd) of length.⁹

• In Austrália, 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 460 mm (18.1 in) deep universal beam that weighs 67.1 kg/m (135 lb/yd)).⁵

Bunkové nosníky 

Bunkové nosníky are the modern version of the traditional "preliačený lúč" which results in a beam approximately 40–60 percent 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 constructions.¹⁰