TOPIC 3 STEEL (week 2).pptx

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3 steel

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LEARNING OUTCOME

At the end of this lecture, students should be

able to understand and explain;

i. Type of steel

ii. Properties of steel

iii. Manufacturing process of steel

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COURSE programme OUTCOMEs

CO1:Apply the basic science and

engineering fundamentals to

properties of construction materialsand analyse their properties.

PO1:Ability to acquire and apply

basic knowledge of science,mathematics and engineering

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INTRODUCTION

Steel is the general name given to a large familyof alloys of iron with carbonand a variety ofdifferent elements.

Steel is a material that has wide applications incivil engineering e.g. buildings, bridges, pipelines,water tanks, roof trusses, etc.

In Malaysia, many structures have started to usesteel as the main material.

It also the strongest, the most resistant to ageing,and generally the most reliable in quality.

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Steel is composed of about 98% of iron with the mainalloying elements of carbon, silicon andmanganese.

The yield strength oryield point of a material is definedin engineering and materials science as the stress atwhich a material begins to plastically deform.

Prior to the yield point the material will deformelastically and will return to its original shapewhen the

applied stress is removed.Steel is completely industrialized material and subject toits tight control of its content and the details of itsforming and fabrication. It has additional desirablequalities of:

* Non-combustible

* Non-rotting

* Dimensionally stable with time & moisture change

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MAIN PROPERTIES OF STEEL :

1) Strong under compression and tension compared to concrete &

timber

2) Can resist excessive load due to wind, earthquake, vibration & impact

transfer load.

FACTORS IN SELECTING SPECIFIC APPLICATION OF STEEL :

1) Strength level required

2) Mechanical properties required together with strength

3) Steel making, heat treatment and other plant available

4) Arbitrary local conditions and code of practice

REFERENCES : BS 5950 & BS 4360 (The Structural Use of Steelworkin Building)

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Construction Uses of Steel

Structuralsteelplates, bars, pipes, structural

shapes, etc.

Cold formed steelstuds, trusts, roofing, cladding

Fastening productsbolts, nuts, washers

Reinforcing steelrebar for concrete

Miscellaneousforms, pans, hardware, etc.

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STRUCTURAL STEEL CAN BE DIVIDED INTO 3 CATEGORIES:

1) Framed structures

consists of skeletal framework which carries all the load

The steel members are used to carry:

i) lateral loads when acting as beams and girders

ii) axial loads when acting as struts and ties

The steel frame are made of load bearing elements (e,g. tension

members, columns, beams under combined bending, girder, trussesand axial load)

E.g. beam, girder (girder is a large support beam used in

construction , dome (dome is a common structural element of

architecture that resembles the hollow upper half of a sphere),

trusses

Girder Dome Trusses

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2) Shell-Type structure carries axial stress load

the shell serves a use function in addition to participation in

carrying loads.

The main stress in tension is the containment vessel

E.g. containment vessel used to store liquid, water tank &

storage bin.

Water tank

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3) Suspension-Type structure

Axial tension to support system

Major supporting element is tension cable

Since the tension element is the most efficient way of carrying

load, structures utilization this concept are coming into

increasing use. E.g. cable, suspension bridge.

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TYPE OF STEEL

There is an almost infinite numbers of kinds of steel

available, since it possible to make steel to performunder most known conditions.

The usageof steel: Steel for strength

To resist impact To resist corrosion/abrasion Steel to take & hold a sharp edge Steel to cut other steel

Steel is composed of about 98% of iron with the mainalloying elements of carbon, silicon and manganese. All steels contain carbonand ironbut the description carbon

steel is used where other elements are present in quantitiestoo small to affect the properties.

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TYPE OF STEEL (cont)

The design of steel structures is based primarily on theyield stress or proof stress of the steel but ductility,toughness at normal and weldability are often importantproperties.

* The yield strengthor yield pointof a materialis defined in

engineeringand materials scienceas the stressat which amaterial begins to plastically deform.

* Prior to the yield point the material will deform elasticallyand will return to its original shape when the applied stressis removed.

Weldability is important because welded structures giveweight saving and ease of fabrication compared to boltingand riveting.

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http://en.wikipedia.org/wiki/Materialhttp://en.wikipedia.org/wiki/Engineeringhttp://en.wikipedia.org/wiki/Materials_sciencehttp://en.wikipedia.org/wiki/Stress_(physics)http://en.wikipedia.org/wiki/Plasticity_(physics)http://en.wikipedia.org/wiki/Elasticity_(physics)http://en.wikipedia.org/wiki/Elasticity_(physics)http://en.wikipedia.org/wiki/Plasticity_(physics)http://en.wikipedia.org/wiki/Stress_(physics)http://en.wikipedia.org/wiki/Materials_sciencehttp://en.wikipedia.org/wiki/Engineeringhttp://en.wikipedia.org/wiki/Material


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Steel is derived from 2 raw materials (liquid pig iron and scrap)

Pig ironis raw iron, the immediate product of smeltingiron orewith cokeand limestonein a blast furnace.

Pig iron has a very high carboncontent, typically 3.5%, which makes it

very brittleand not useful directly as a material except for limited

applications.

The iron making blast furnace produces liquid pig iron from the:

Iron

Ore

Limestone

Coke

Air

The scrap used for new steelmaking arises in the steelwork itself (readily

characterized and usually recycled completely).

TYPE OF STEEL (cont)

Iron orelimestone

coke

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2
http://en.wikipedia.org/wiki/Ironhttp://en.wikipedia.org/wiki/Smeltinghttp://en.wikipedia.org/wiki/Iron_orehttp://en.wikipedia.org/wiki/Coke_(fuel)http://en.wikipedia.org/wiki/Limestonehttp://en.wikipedia.org/wiki/Blast_furnacehttp://en.wikipedia.org/wiki/Carbonhttp://en.wikipedia.org/wiki/Brittlehttp://en.wikipedia.org/wiki/Brittlehttp://en.wikipedia.org/wiki/Carbonhttp://en.wikipedia.org/wiki/Blast_furnacehttp://en.wikipedia.org/wiki/Limestonehttp://en.wikipedia.org/wiki/Coke_(fuel)http://en.wikipedia.org/wiki/Iron_orehttp://en.wikipedia.org/wiki/Smeltinghttp://en.wikipedia.org/wiki/Iron


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TYPE OF STEEL

1) CARBON STEEL

a) Low carbon steel

Up to 0.15% Carbon

Soft

Suitable for wire and thin

sheetb) Mild carbon steel

0.150.29% Carbon

Strong

Ductile Suitable for rolling into

sections, sheet and strip

Easily worked and welded

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c) Medium carbon steel

0.30.59% Carbon

For general

engineering purposes

d) High carbon steel

0.61.7% Carbon

Suitable for casting

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Carbon Steel

High Strength Low-Alloy

Steel

Alloy SteelECS 256 UiTM PG 15

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Pig iron scrap

Steel scrap

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4) STAINLESS STEEL

Contains chromium. Classified as:

Martensitic (About 13% chromium)

Ferritic (About 17% chromium) Austenitic (16 - 19% chromium together with 6 - 14%

nickel)

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PROPERTIES OF STEEL

MAIN PROPERTIES OF STEEL :1)Strong under compressionand

tension compared to concrete &

timber

2)Can resist excessive load due to

wind, earthquake, vibration & impacttransfer load.

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STEEL BEHAVIOUR:

Some of the properties of steel which makes it

versatile among construction materials arehigh stiffness and tensile strength, the abilityto be formed into plate, sections and wire,and the weldabilityor ease of welding forconstructional purposes.

Even small differences in the composition of

the steel can have a dramatic effect on itsproperties.

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TENSILE TEST

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The properties of the steel can also be

modified by different mechanical and heattreatments.

The material has high strength in tension and

compressionand is able to undergo large

deformation without fracture. It is a ductile

material.

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STRESS-STRAIN DIAGRAM FOR STEEL

If a rod of steel is subjected to a tensile test, and the

stress (load /cross-sectional area in N/mm2) in therod is plotted against the strain (change in length /

original length), as the load is applied, a graph similar

to that shown would be obtained.

Note that the stress-strain curve is linear upto a

certain value, known as the yield point. This is the

elastic range. Beyond this point the steel yieldswithout an increase in load, although there is

significant strain hardening as the bar continues to

strain towards failure. This is the plastic range.

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STRESS-STRAIN DIAGRAM OF STEEL

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MANUFACTURING PROCESS

1) Primary Steel Making

Refers to the refining processes used to produce liquidsteel.

The aim is to produce a meltof the required composition.

Typical ranges required for structural steels are:

Carbon 0.15 -0.25%

Manganese 0.51.5%

Sulphur & Phosphorus < 0.05%

Types of refining process:

The Bessemer/Thomas process

The open-hearth (Siemens) process

The basic oxygen process

Electric arc steelmaking

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2) Secondary Steel Making

The liquid steel process is not finished when it istapped from the furnace.

It must undergo further treatment, i.e it isnecessary to deoxidize the metal.

This is done by adding manganeseand silicon,which react with dissolved oxygen to forminsoluble particles of oxide.

It may be necessary to adjust the carbon and

manganesecontents to give the grade of steelrequired, because with carbon it will improvesstrengthand manganese gives low temperaturetoughness.

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3)Mechanical Forming Process

Are used to continuously cast materials into the shapes andsizes required.

It can be done either by hot rolling or cold rolling.

i) Hot Rolling

All constructional steel are hot rolled.

These steel are heated to temperature of 12001300C tomake them soft enough to deform and shape.

ii) Cold Rolling

Cold rolling cannot be used to the same degree as hotworking for shaping purposes, because of the increasedstrength of the cold work piece.

Modest reduction can be achieved by rolling to give bettersize tolerances and surface qualities.

Mainly for light weight sections.

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Structural Steel

Hot rolled

structural

shapes

Cold formed

cladding

Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc.

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(Q&A)

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Documents

TOPIC 3 STEEL (week 2).pptx