chapter 1 - introduction to steel section

7/27/2019 Chapter 1 - Introduction to Steel Section

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INTRODUCTION TO STEEL STRUCTURE

Prepared by;

Norashidah Abd Rahman


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Steel structure

Engineering structure are required to support loads and resist force and totransfer these loads and forces to the foundations of the structure

Structures are usually 3-D in their extent, but sometimes are 2-D (plates

and shells)or even1-D (lines and cables)

What is structural steel members?

May consist of beam, column (1-D), plate (2-D)etc.

Reduction of a (3-D) to a simpler form


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Structural steel members maybe connected together at joints in a

numbers of ways and by using a variety of connectors Pin, rivets, bolts and welds

Type of structural steel members


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Why steel?

Economical for tall building and large span buildings and bridge due to

its large strength to weight ratio

Steel structure are ductile and robust (can withstand severe loading

such as earthquake). Can easily repaired and retrofitted to carry higher loads

Steel structures, which have bolt connections, can also be reused to

some extent after dismantling

Higher reliability and safety (quality control in production)


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Advantages Disadvantages

High strength/weight ratio General cost

ductility Fire

Isotropic behaviour General maintenance

Rapid construction buckling

Repetitive use

Easy to fabricate


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Steel productions

Steel production can be divided into three stage: 1) Iron production

2)Steel production 3)Rolling process

Steel manufacturing


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Steel section

Hollow section

i.e. circular, square, rectangle

Efficient compression members

Hot finished (Hot rolled section)

Hot rolling done at recrystallization temperature, or the

temperature at which the grain structure of the metal can be

altered

produce products like sheet metal or simple cross sections,

such as rail tracks and I-beams.

Cold formed (Cold formed section)

Cold rolling, done often at room temperature, has the added

effect of work hardening and strengthening the material thus

further improving the materials mechanical properties

cold-rolled products often include similar hot rolled products

like sheets and bars, but are usually smaller


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SHS CHS RHS


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Mechanical properties Tensile test

Modulus of elasticity = 205 000MPa

Tangent modulus at the onset of Strain hardening roughly 1/30 of

the value 6700Mpa

For high strength steels, due to their specific microstructure, thestress-strain curve do not show a sharp yield point but rather they

yield continuously

Stress strain curve for high strength steel


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Tensile test of S355 steel grade

80

6

0

300

100

R20

Coupon test dimension (EN 10002-1:2001 Annex D )


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0

100

200

300

400

500

600

0 2 4 6 8 10 12 14 16 18

Hollow section 200 x 200 x 12.5

Hollow section

200 x 200 x

Stress(N/mm

2)

Strain (mm)


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Nominal yield strengthfyand ultimate tensile strength fudepend on the

steel grade and thickness of the element of the section cross-section

(Table 3.1 of BS EN1993-1-1)

Material properties are taken from product standards (EN10025-2)

Young modulus of steel ,E = 210 000N/mm2

Other steel material coefficient to be used in steel design (Clause 3.2.6 ofEN 1993-1-1)

Shear modulus,

Poissons ratio, v= 0.3

Coefficient of thermal expansion, = 12 x 10-6/0C ( for temperaturebelow 1000C)

2/00081)1(2

mmNv

EG


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Extract from Table 3.1 of BS EN1993-1-1


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Introduction to Eurocode 3 (EC3)

EC0 : Basis of Structural Design

EC1 : Action on Structure

EC2 : Design of Concrete Design

EC3 : Design of Steel Structures

EC4 : Design of Composite Steel and

Structures

EC5 : Design of Timber Structures

EC6 : Design of Masonry Structures

EC7 : Geotechnical Design

EC8 : Design of Structures for Earthquake

Resistance EC9 : Design of Aluminum Structures

Links between the Eurocode


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Eurocode 3 comprises 6 parts;

EN 1993-1 General Rules and Rules for buildings

EN 1993-2 Steel Bridge

EN 1993-3 Towers, Mast and Chimney

EN 1993-4 Silos, Tanks and Pipelines

EN 1993-5 Piling

EN 1993-6 Crane Supporting Structures

Part 1 itself consists of 12 sub-parts:

EN 1993-1-1 General Rules and Rules for Buildings

EN 1993-1-2 Structural Fire Design

EN 1993-1-3 Cold-Formed Members and Sheeting

EN 1993-1-4 Stainless Steels

EN 1993-1-5 Plated Structural Elements

EN 1993-1-6 Strength and Stability of Shell Structures

EN 1993-1-7 Strength and Stability of Planar Plated Structures Transversely Loaded

EN 1993-1-8 Design of Joint

EN 1993-1-9 Fatigue Strength of Steel Structures

EN 1993-1-10 Selection of Steel for Fracture Toughness and through-thickness Properties

EN 1993-1-11 Design of Structures with Tension Components Made of Steel

EN 1993-1-12 Additional Rules for the Extension of EN 1993 up to Steel Grades S700


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Terminology and symbols

Common terms use in Eurocode:

Action = loads, imposed displacement, thermal strains

Effect = internal bending moments, axial forces etc

Resistance = capacity of a structural element to resist bending

momentVerification = check

Execution = construction ( Fabrication, erection, etc )

Eurocode symbols

Eurocode

Subscript

Definition Example

Ed Design value of an effect MEd Design bending moment

Rd Design resistance MRd Design resistance for bending

El Elastic property Wel Elastic section modulus

pl Plastic property Wpl Plastic section modulus


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Geometrical Axes

Types of actions Permanent Actions G,g

Variable Actions Q,q

Accidental Actions A

Major axis y-y

Minor axis z-z

Longitudinal axis of Element x-x


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Classification of Action


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Basic of Structural Design

Limit state design

To ensure that the probability of operating conditions reaching failure

conditions is so low as to be negligible.

Two type of limit state

Ultimate limit state (ULS) load at which the structure will

collapse and at which it can no longer serve its intended function Serviceability limit state (SLS)- load at which the structure is

damage but can still accept additional load. Repaired is usually

required to restore the structure to an acceptable state

The structure is deemed to be satisfactory if its design load effect

does not exceed its design resistance.


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Design load Probable maximum load Factoring the applied load

upwards

Design resistance represent a probable minimum resistancealso

estimated by factoring resistance downward.

Dividing the characteristics resistances by appropriate partialsafety factors

The design value before factoring loading and resistance.

Load obtained by multiplying the characteristic value by the

appropriate partial safety factor

Design value of an Action, Fdis defined in Clause 6.3 of BS EN 1990

krep

repfd

FF

with

FF

Fk characteristic value of action

Frep relevant representative value of the action

f partial factor of action

Either 1.00 or 0, 1or 2


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Recommended value of factors for buildings (Table A.1.1 of EN1990)


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Combination of load

Must determined which combination is the most critical for the structure.

Is discussed in clause 6.4.3 of EN 1990(Combination of actionsfatigue

verifications exclude)

a different and more logical method of combining loads is used in EC3 limit

state method. Strength design is usually carried out for the most severe combination of

action for normal ( termed persistent) or temporary (termed transition)

conditions using


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Approach is applied to the following forms of Ultimate limit state;

EQU = loss of static equilibrium of the structure of any part of it

STR = failure by excessive deformation, transformation of the

structure or any part of it into a mechanism, rupture or loss

of stability of the structure or any part of it

GEO = failure of excessive deformation of the groundFAT = fatigue failure

For the most common set of design situation is given in Table below

Ultimate limit

state

Permanent actions G Variable actions Q

Unfavourable Favourable Unfavourable favourable

EQU 1.1 0.9 1.5 0

STR/GEO 1.35 1.0 1.5 0

chapter 1 - introduction to steel section

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