material and sectional properties - steel

7/29/2019 Material and Sectional Properties - Steel

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STEEL


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Widely Used Construction Materials:


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Only certain material properties are of interest to us here specifically, those that have some bearing on the

structural behavior of the elements under consideration.


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now ng ow a ma er a samp e

contracts or elongates as it is stressed

its performance in an actual structure.

o on y s s u ma e s ress orstrength) indicated, but also a measure

elasticity), its linear (and presumably

behavior, and its ability to absorb


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near re a ons p e ween s ress

and strain is an indicator of elasticits original shape after being stressed

Structures are expected to behave

loads; but plastic behavior,

characterized by permanentdeformations, needs to be consideredwhen ultimate, or failure, loads are

.


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curve is the modulus

of elasticit E that is, the changein stress, f , divided

strain, . For linear materials:

.

=


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Incredibly high strength andmodulus of elasticity (indicatedby the slope of the curve) ofsteel relative to concrete and

wood. The information about the

strength and ductility of thethree materials in tension

.

Concrete has very littlestrength in tension and fails in

both tension and compression.

Wood has high tensile strength,

also fails in a brittle mannerwhen stressed in tension; incom ression, however, wood

shows ductile behavior.


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to the proportional limit

A peak value, the upper yield point, is quickly reached,point

The stress then remains constant, even though the. ,

the test specimen continues to elongate as long as theload is not removed, even though the load cannot beincreased. This constant stress re ion is called the ieldplateau, or plastic range.

At a strain of approximately 12 times the strain at yield,strain hardenin be ins and additional load andstress) is required to cause additional elongation (andstrain). A maximum value of stress is reached, afterwhich the specimen begins to neck down as the stress

, .


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ductile behavior of

steel because of itsa y o un ergolarge deformationsbefore fracturing.

Ductility can bemeasured by theelon ation definedas:

.


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Ductility is important in a structural member because itallows concentrations of high stress to be absorbed and

redistributed without causing sudden, catastrophic failure.


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stress that lies between theproportional limit and the upper

yield point. Up to this stress, thespecimen can be unloaded withoutpermanent deformation; theunloading will be along the linear

,

path followed during loading. Thispart of the stressstrain diagram iscalled the elastic range.

Beyond the elastic limit, unloadingwill be along a straight line parallel

to the initial linear part of the,

permanent strain. For example, ifthe load is removed at point A inthe figure, the unloading will be

along line AB, resulting in thepermanent strain OB.


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v r u r r ru ur ,including strength and ductility, are

determined b its chemical com osition. Steel is an alloy, its principal component

being iron.

no er componen o a s ruc ura s ee s,although in much smaller amounts, iscarbon which contributes to stren th butreduces ductility.

Other components of some grades of steel, , ,chromium, molybdenum, and silicon.


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r : mostly iron and carbon, with less than 1% carbon

- iron and carbon plus other components (usually

less than 5%)

increasing strength, which is accomplished at theexpense of a reduction in ductility

g -a oy or spec a y s ee s:

similar in composition to the low-alloy steels butwith a hi her ercenta e of the com onentsadded to iron and carbon

These steels are higher in strength than the plaincarbon steels and also have some s ecial ualit

such as resistance to corrosion


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designation assigned them by the American Society forTesting and Materials (ASTM). This organization

their composition, properties, and performance, and itprescribes specific tests for measuring these attributes

mild steel designated as ASTM A36, or A36 for short. Other commonly used structural steels are ASTM A572

Grade 50 and ASTM A992. These two steels are very similar in both tensile properties

and chemical composition, with a maximum carbon content

of 0.23%.


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o -ro e s ee s apes con a n res uastresses even before they are loaded.These are caused by the uneven cooling

of the shapes after they are rolled at

(1093C). The exposed flanges andwebs cool and contract sooner than theweb flange intersections; the

then inhibited by the adjacent areaswhich have already cooled, so they areforced into tension as theysimultaneousl com ress the areas thatcooled first.

The typical pattern of residual stresses

within a wide-flange cross section isshown in the fi ure.

Residual stresses have an impact on theinelastic buckling of steel columns, sincepartial yielding of the cross section

than would be the case if the residualcompressive stresses locked into thecolumn were not present.

section, with + indicating tensionand indicating compression


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o

Hot-rolledo Cold-formed (report/presentation)

Panels and decks


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molten steel is taken from the furnace and

oured into a continuous castin s stem wherethe steel solidifies but is never allowed to coolcompletely

squeeze the material into the desired cross-sectional shape

deformed with no resulting loss in ductility

durin the rollin rocess, the member increasesin length and is cut to standard lengths (usuallya maximum of 65 to 75 feet)


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W-shape

S-shape Angle

Structural Tee


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AMERICAN INSTITUTE OF STEEL CONSTRUCTION (AISC)MANUAL


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also called a wide-flange shape

consists of two parallel flanges separated by a single web has two axes of symmetry commonly used for both beams and columns within steel-

framed structures

typical designation would be W18

50 W indicates the type of shape 18 is the nominal depth parallel to the web 50 is the weight in pounds per foot of length.

nominal depth is the approximate depth expressed inwhole inches

All W-shapes of a given nominal size can be grouped intofamilies that have the same depth from inside-of-flange toinside-of-flange but with different flange thicknesses

have parallel flange surfaces, making it somewhat easier tomake connections to other structural elements


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similar to the W-sha e in havin two arallel flan es asingle web, and two axes of symmetry

difference is in the proportions:

the flanges of the S. the outside and inside faces of the flanges of the W-shape

,S-shape slope with respect to the outside faces

example of the designation is S18 70 n ca ng e ype o s ape

the two numbers giving the depth in inches and theweight in pounds per foot

formerly called an I-beam


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- -

Typical designation would be L6 6 34 or L6 4 58

the three numbers: the lengths of each of the two legs as measured

, ,of the leg

and the thickness, which is the same for both legs

for the unequal-leg angle, the longer leg dimension isalways given first

t oug t s es gnat on prov es a o t edimensions, it does not provide the weight per foot


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has two flanges and a web, with only one axis of symmetry

carries a designation such as C9 20 notation is similar to that for W- and S-shapes, with the

web and the second number the weight in pounds per

linear foott e ept s exact rat er t an nom na

inside faces of the flanges are sloping, just as with the

Miscellaneous Channelsfor example, the MC10 25are similar to American Standard Channels


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produced by splitting an I-shaped member at middepth sometimes referred to as a split-tee

prefix of the designation is either WT, ST, or MT,w r .

WT18 105 has a nominal depth of 18 inches and awei ht of 105 ounds er foot and is cut from aW36 210

ST10 33 is cut from an S20 66 MT5 4 is cut from an M10 8. The M is for

miscellaneous. The M-shape has two parallel

either the W or S categories


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used for bearing piles

,approximately the same width

and depth, and equal flange and

are desi nated in the samemanner as the W-shape; for

,


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, ,

sections classified as a bar if width of rectangular shape is 8

classified as a plate if the width is more than 8 inches

usual designation for both is the abbreviation PL (for,by the thickness in inches, the width in inches, and thelength in feet and inches; for example, PL 38 5 3-

bars and plates are formed by hot-rolling


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designation is HSS can be produced either by bending plate material into the desired shape

an we ng t e seam or y o -wor ng to pro uce a seam ess s ape shapes are categorized as steel pipe, round HSS, and square and

rectangular HSS

Steel pipe is available as: standard, extra-strong, or double-extra-strong, with designations such as Pipe 5

Std., Pipe 5 x-strong, or Pipe 5 xx-strong, where 5 is the nominal outer diameter ininches

different strengths correspond to different wall thicknesses for the same outerdiameter. For nominal outer diameters > 12 inches the desi nation is the outerdiameter and wall thickness in inches, expressed to three decimal places; for

example, Pipe 14.000 0.375. Round HSS are designated by outer diameter and wall thickness,

expressed to three decimal places; for example, HSS 8.625 0.250quare an rec angu ar are es gna e y wo ou s e mens ons

and wall thickness, expressed in rational numbers; for example, HSS 7 5 38


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needed to satisfy design requirements that areespecially severe

-sectional elements cover plate is welded to one or both flanges of a W-shape

that is being rehabilitated or modified for some useother than the one for which it was designed

enough (cross section does not have enough area ormoment of inertia) then plate girders can be used I-shaped sections, with two flanges and a web box sections, with two flanges and two webs (components

can be welded together and can be designed to have exactlythe properties needed)

double-angle shape, a pair of angles placed back-to-back double-channel shape (either American Standard or Miscellaneous

Channel)


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material such as sheetsteel or plate into the

heating only relatively thin

resulting shapes aresuitable only for light

advantage of this

product is its versatility,

conceivable cross-sectional shape can


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epor ers:

ABAYON, MARK

van ages nbuilding construction

ABELA, MIA cold-formed steel

ABULAG, SHERLOU constructionMethods of forming:

AGGABAO, GERALD

GACUTAN

Cold roll forming

Press brake operation

ALFILER, MARJORIEANNE PADILLA

Ben ing ra eoperation


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Steel is subject to corrosion if not protected and loss ofstrength and stiffness at high temperatures if not fireproofed.While these are extremely important material properties, the

issues have been addressed within the architectural designprocess.

material and sectional properties - steel

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