architecture technology: steel

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Politecnico di Torino School of Architecture

STEEL

Acciaio

Fundamentals of Architectural TechnologyProf. Roberto Pagani

Arch. Giulia Bonomi

Arch. Zang Yu


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0 General definitions

METALSmetalli

Of all known elements, metals make up the majority.Within periodic table there are five separate families of metals>Alkali metals

very reactive metals, none of these used in architecture>Alkaline earth metalsmagnesium and beryllium are used as alloyins constitutents

otherwise not used for architectural applications>First transition metals

known for hardness and strength, especially when tungsten,chromium and vanadium are used as alloying agents

>Second transition metalsiron is major architectural element of this group

Nickel is alloyed with copper to produce moneland, with iron andsteel to produce the stainless steels>Third transition metals

all of these play an architectural roleZinc and copper are sought for their superior stability in atmosphericconditions

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0 General definitions

Metals are characterized by a crystalline, compact and homogeneouschemical structure which make them similar to isotropic materials, asthey have same physical characteristics in any direction.

According to their composition they can be divided into:

FERROUS orIRONWORKS

CAST IRON ghisa

STEEL acciaio

SOFT IRON ferro dolce

NOT FERROUS

COPPER rame

ALLUMINIUM alluminio

ZINC zinco

LEAD piombo

crystalline structure

amorphousstructure

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1 Ferrous metals

FERROUS METALSmetalli ferrosi

They are obtained casting in blast furnaces iron stones at 1900C,which are further processed.Ferrous metals include alloys of iron and coal, to which other elementsare added, in order to convey specific characteristics to the material.According to the composition of the alloy, ferrous metals can be dividedinto:

> CAST IRON ghisahigh percentage of carbon --> between 2,06% and 4%obtained directly casting iron stones

> SOFT IRON ferro dolceobtained with a total decarburetion of cast iron in order to reach verylow percentage of iron --> less than 0,1%

> STEEL acciaiogained with a partial decarburetion of cast iron in order to reachmedium percentage of carbon --> from 2,06% to 0,1%it can also contain less than 1% manganese and small amounts ofsilicon, phosphorus, sulphur and oxygen

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Steel can be divided into three more categories:

> Carbon steelsThey contain only carbon and iron and small quantities of impurities.Among these can be included carpentry steels which are normally used inconstruction and which are classified according to their resistance to tensilestrength:

Fe 360 --> ultimate strenght 360 N/mm2



Carbon steels are used also to produce metallic bars for concrete steel.

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1 Ferrous metals


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> Low-alloy steelsaddition to carbon steels of small amounts of alloy elements such aschromium, columbium, copper, manganese, molybdenum, nickel,phosphorous, vanadium, zirconium improves some of the mechanicalproperties.

The two main examples of low-alloy steels are ex-ten steeland corten steelwhich both have:good resistance to tensile stressvery high resistance to corrosiongood possibility to be welt

> High-strength steelsThey contain a quantity of alloy elements above 5%.Additional strength is obtained through a fine-grained crystalline

microstructure as opposed to the course graining of simple carbon steel.Among these can be included stainless steelwhich are very used inconstruction.

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The quantity of carbon in the alloy can affect mechanical properties:the highest the percentage is the hardest and resistant the metal is,despite the loos of ductility, malleability and the possibility to be welt

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PHYSICAL AND MECHANICAL PROPERTIES

Propriet fisiche e meccaniche dei metalli

> ISOTROPYisotropia

>CONDUCTIVITY conducibilit

>FIREPROOF incombustibilit

>High resistance to tensile strenght good resistance to

compression strenght

>DUCTILITYduttilit

> RESILIENCE resilienza

>MALLEABILITY malleabilit

>HARDNESS durezza

2 Properties

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> DUCTILITY duttilit

more commonly defined as the ability of a material to deformeasily upon the application of a tensile force, or as the ability ofa material to withstand plastic deformation without rupture

Ductile materials show large deformation before fracture

STEEL

Young modulus

2.100.000 daN/cm2

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The lack of ductility is oftentermed BRITTLENESS fragilit

Usually, if two materials havethe same strength andhardness, the one that has thehigher ductility is moredesirable

The ductility of many metalscan change if conditions arealtered: an increase intemperature will increaseductility while a decrease intemperature will cause a

decrease in ductility and achange from ductile to brittlebehavior.

2 Properties

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Cold-working also tends to make metals less ductile.

Cold-working is performed in a temperature region and over atime interval to obtain plastic deformation, but not relieving thestrain hardening.

Minor additions of impurities to metals, either deliberate orunintentional, can have a marked effect on the change fromductile to brittle behavior.

The heating of a cold-worked metal to or above the temperatureat which metal atoms return to their equilibrium positions willincrease the ductility of that metal.

> RESILIENCE resilienza

attitude of a material to absorb energy (in the form of elastic orplastic deformation) in a short time.

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2 Properties


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>MALLEABILITY malleabilit

property of metals to be shaped or formed into thin sheets, byhammering or pressure, without breaking

gold, iron, copper and lead are malleable metals

>HARDNESS durezza

Resistance of metal to plastic deformation, usually byindentation.

However, the term may also refer to stiffness or temper, or toresistance to scratching, abrasion, or cutting.

It is the property of a metal, which gives it the ability to resist

being permanently, deformed (bent, broken, or have its shapechanged), when a load is applied.

The greater the hardness of the metal, the greater resistance ithas to deformation.

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PHYSICAL AND MECHANICAL WEAKNESSES

Debolezze fisiche e meccaniche dei metalli

>SHRINKABILITYdeformabilit

> Bad behaviour in case of fire

>Low resistance to CORROSION

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2 Properties


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> ROLLING laminazione

The process of shaping metal by passing it between rollsrevolving at the same peripheral speed and in oppositedirections.In steel there are a number of different types of rolling mill forprocessing the ingot to its finished shape. These are variously

known as Cogging mills, Slabbing mills, Billet mills, Bar mills andStrip mills, which produce plate, sections, bars, sheet and strip.

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3 Processings

hot rollingis the most commonlyused process, durgin which

metal is heaten at 1100 -1300 C in order toimprove its malleabilityand workability


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cold rolling

cold rolling of previously hot rolled strip causes the hardening ofthe material due to the breaking of the crystalline structure.Higher precision can be reached and better mechanical properties

> WIRE DRAWING trafilaturais a metalworking process used to reduce the cross-section of a wire

by pulling the wire through a single, or series of, drawing die(s)

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3 Processings

Drawing is usuallyperformed at roomtemperature, thus classifieda cold working process, but

it may be performed atelevated temperatures forlarge wires to reduce forces


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> EXRTUSION estrusioneis a metalworking process similar to wide drawing consisting inpushing the metals through a die of the desired cross-section, afterheating the bars at 1100 C.

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3 Processings

> FORMINGstampaggio

> BENDING piegatura

> FORGING fucinatura

The cross-sections that can beproduced vary from solid round,rectangular, to L shapes, Tshapes.


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architecture technology: steel

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