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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