Lecture -2 Introduction to Steel Structures
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Transcript of Lecture -2 Introduction to Steel Structures
N-W.F.P. University of Engineering and Technology
Peshawar
1
Design of Steel Structures CE-411
By: Prof Dr. Akhtar Naeem [email protected]
N-W.F.P. University of Engineering and Technology
Peshawar
2
By: Prof Dr. Akhtar Naeem [email protected]
Lecture 02: Introduction to Steel Structures
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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Topics to be CoveredWhat is Steel?
Mention of Iron in Holy Quran
Steel Making process
Treatments and processes affecting steel properties
Mechanical properties of Structural Steel
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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What is Steel?Steel is an alloy in which iron is mixed with
carbon and other elements.
An Alloy is a homogeneous mixture of two or more elements, at least one of which is a metal, and where the resulting material has metallic properties.
An Alloy usually has different properties (sometimes significantly different) from those of its components.
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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Iron is mentioned in the Holy Quran 6 times:
1. Surah Bani Israil (17:50)
2. Surah Al Kahf ( 18: 96)
3. Surah Al Anbiya.. (21:22)
4. Surah Saba (34:10)
5. Surah Qaf (50:22)
6. Surah Al-Hadid (57:25)
Mention of Iron in Holy Quran
CE-411: Lecture 02 Prof. Dr. Akhtar Naeem Khan 6
Mention of Iron in Holy QuranAl-Hadeed (Sura 57:25)
We have indeed sent Our messengers with clear proofs, and sent down with them the book and the balance, so that people may uphold equity. And we sent down iron in which there is strong power, and benefits for the people; and (We did it) so that ALLAH knows who helps Him and his messengers without seeing (Him). Surely ALLAH is Strong, Mighty.
CE-411: Lecture 02 Prof. Dr. Akhtar Naeem Khan 7
Steel Making Process
http://www.tatasteel.com/products-and-processes/processes/steel-making-process.asp
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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Chemical Reactions in Blast Furnace
Iron (III) Oxide + Carbon Monoxide Iron + Carbon Dioxide
Fe2O3(s) +3 CO(g) 2 Fe(s)+3 CO2(g) (At 1500o C)
Calcium Carbonate Calcium Oxide + Carbon Dioxide
CaCO3(s) CaO(s)+CO2(g)
This oxide helps to remove some of the
acidic impurities from the ore
Steel Making Process
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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Calcium Oxide (g) + Silica (s) Calcium Silicate (l)
CaO(s) + SiO2(s) CaSiO3 (l)
The metal that leaves the Blast Furnace contains between 4%
and 5% Carbon and is brittle. This carbon and other impurities are removed in the next step.
Steel Making Process
Chemical Reactions in Blast Furnace
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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Removal of Impurities by Oxidation
o The Bessemer process named after its Inventor Henry Bessemer who invented the process in 1855
o The key principle is removal of excess carbon and impurities by injection of oxygen through molten iron
o Oxidizing excess carbon and impurities also keeps the metal molten.
Steel Making Process
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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Making Steel Rolled ShapesSteel Making Process
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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Treatments and Processes Affecting Steel Properties
o Quenching
Quenching refers to heating steel to below a critical temperature, holding that temperature and then rapidly cooling it in a desirable medium such as air water or oil to obtain desired hardness property.
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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Treatments and Processes Affecting Steel Properties
o Tempering
Tempering refers to heating steel above a critical temperature, then cooling it rapidly to freeze it in a very hard state followed by rewarming it to an intermediate temperature to give a hardness suitable for the job intended.
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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o Annealing
Heating (usually up to 1150o F) followed by cooling of steel in solid state to relieve the residual stresses and to enhance ductility.
Treatments and Processes Affecting Steel Properties
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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o Killed Steel
It indicates that the steel has been completely deoxidized by the addition of an agent such as silicon or aluminum, before casting, so that there is practically no evolution of gas during solidification. These are characterized by a high degree of chemical homogeneity and freedom from porosity.
Treatments and Processes Affecting Steel Properties
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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o Rimmed Steel
A low-carbon steel containing sufficient iron oxide to give a continuous evolution of carbon monoxide while the ingot is solidifying. Incomplete oxidation allows the metal at the top of the ingot to remain liquid while solidifying in formation of a bottom and side rim of virtually pure iron of considerable thickness virtually free of voids. Sheet and strip products made from rimmed steel ingots have very good surface quality.
Treatments and Processes Affecting Steel Properties
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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o Work Hardening
An increase in strength and hardness attained by stressing the steel to cause plastic deformations at lower temperatures.
Treatments and Processes Affecting Steel Properties
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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Effect of Carbon percentage on Steel Properties
o Carbon has a major effect on steel properties. Carbon is the primary hardening element in steel. Hardness and tensile strength increases as carbon content increases up to about 0.85%.
CE-411: Lecture 02 Prof. Dr. Akhtar Naeem Khan 19
Type of Steel %age of Carbon
Mild Steel Up to 0.25%
Medium Carbon Steel 0.25% to 0.45%
High Carbon Steel 0.45% to 1.50%
• Adding metals such as nickel, chromium, and tungsten to iron produces a wide range of alloy steels, including stainless steel and high speed steels.
Effect of Carbon percentage on Steel Properties
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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Mechanical Properties of Structural Steels
o Most widely used standards for structural materials are American Society for Testing & Materials (ASTM) Standards.
o ASTM specifications for structural steels generally identify the Process by which steel is to be made, chemical composition, and tensile requirements.
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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Mechanical Properties of Structural Steels
CE-411: Lecture 02 Prof. Dr. Akhtar Naeem Khan 22
o Yield strength is usually taken to be that stress which leaves the specimen with a permanent set of 0.2% when specimen is unloaded or stress corresponding to 0.5% elongation (strain)
Mechanical Properties of Structural Steels
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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o Yielding is a discontinuous phenomenon.
o In tension test it begins with sudden appearance in specimen of one or more narrow slip bands called Flow Lines.
o Slip bands are plastic regions separated by completely elastic regions.
Mechanical Properties of Structural Steels
Lecture 01 Prof. Dr. Akhtar Naeem Khan
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Stiffness: The resistance of structural component to deformation.
• Material• Length• X-Section
Mechanical properties of structural steel
Lecture 01 Prof. Dr. Akhtar Naeem Khan
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Stiffness: Variation with Geometry and Material.
Mechanical properties of structural steel
Lecture 01 Prof. Dr. Akhtar Naeem Khan
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Stiffness: Variation with Geometry and Material.
Mechanical properties of structural steel
Lecture 01 Prof. Dr. Akhtar Naeem Khan
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Strength: The max load which a structure or structural component can resist.
Toughness: The ability of a structure or structural component to absorb energy.
Fatigue is a progressive, localized permanent damage under fluctuating repeated stress.
Mechanical properties of structural steel
Lecture 01 Prof. Dr. Akhtar Naeem Khan
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Mechanical properties of structural steel
Lecture 01 Prof. Dr. Akhtar Naeem Khan
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Material A is more Stiffer but less Tougher than Material C
Material A has more strength than Material C
Mechanical properties of structural steel
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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o Specification A6 outlines general requirements for Rolled Steel plates, shapes, sheet piling, and Bars for structural use.
o Specification A370 outlines the procedures for Mechanical testing of steel products.
o Standard specimen called Coupons cut from shapes, are used in tensile test to establish properties of material.
Mechanical Properties of Structural Steels
CE-411: Lecture 02 Prof. Dr. Akhtar Naeem Khan 31
Composition & Property ASTM A36 Mild (low-carbon) steel
ASTM A572 Grade 50 steel
MinimumProperties
Ultimate Tensile Strength, psi 58,000 - 79,800 65,000 min
Yield Strength, psi 36,300 50,000 min.
Elongation 20.0% 18% min
Chemistry Iron (Fe) 99% 98%
Carbon (C) 0.26% 0.23%
Manganese (Mn) 0.75% 1.35%
Copper (Cu) 0.2% --
Phosphorus (P) 0.04% max 0.04%
Sulfur (S) 0.05% max 0.05%
Silicon -- 0.4%
Vanadium and Columbium -- 0.02 – 0.15
Mechanical Properties of Structural Steels
CE-411: Lecture 02 Prof. Dr. Akhtar Naeem Khan 32
Comparison of Mechanical Properties Wrought Iron and Steel
Property Wrought Iron Steel
Elastic Modulus
190Gpa
(27Mpsi)
190 – 210 GPa
(27-30 Mpsi)
Yield Strength 210 MPa
(30ksi)
280-1600 MPa
(40-232ksi)
Ultimate
Strength
340 Mpa
(49ksi)
340- 1900 MPa
(49-275ksi)
% Elongation 35 3- 40
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Types of Steel ShapesStandard Rolled Shapes
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Properties of Steels Used for Buildings and Bridges
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Properties of Steels Used for Buildings and Bridges
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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Properties of Steels Used for Buildings and Bridges
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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Uses of Various Steels
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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Uses of Various Steels
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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Primarily occur as:
Chord Members in trusses:
In diagonal bracing in bracing systems;
Cable elements in suspension roofs, main cables of
suspension bridges and suspenders.
Types of steel structuresTension Members
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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Typical Tension Members
Types of Steel Shapes
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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Primarily occur as: Columns in buildings; Chord Members in trusses and diagonal members
in end panels of trusses Stability is an important consideration in design and
behavior of compression members Area is generally spread out to maximize Radius of
Gyration
Types of steel structuresCompression Members
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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Typical Compression Members Types of Steel Shapes
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Primarily loaded transverse to the longitudinal axis and resist loading by flexure
X-sectional area is located as far from the neutral axis as is practical
Commonly W shapes are used in most cases
For deeper beams I-shaped sections made by welding plates are commonly used
For smaller loads and spans open-web joists are commonly used
Instability due to lateral Torsional Buckling is an important consideration
Types of steel structuresBeam Members
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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Typical Beam Members Types of Steel Shapes
CE-411: Lecture 02 Prof. Dr. Akhtar Naeem Khan 45
Typical Beam Members (Contd.)
• Economical & popular for Roof & floor framing.• Bar joist are supported by bearing walls or steel girders.• Floor of thin concrete reinforced in both directions with
rebars or welded wire fabric.
Open-Web Steel Joist
Types of steel structures
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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Difference between W and S shapes
W shape: Have wide flanges, efficient in resisting moments so used primarily as beamsS shape: Have wide webs, efficient in resisting shear (used in the past as railway tracks)
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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Symbolic Representation of Various shapes
W30x90:
W represents shape of the section, I section in this case
30 is the depth of the section in inches
90 is the nominal weight in lb per ft
L3x2x1/2
L represents shape of the section, angle
3 is the length of one leg, inches
2 is the length of the other leg, inches
½ is the thickness of the angle, inches
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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Classical Skeleton framing
Steel truss
Rigid frames
Arches
Domes
Cable supported Roofs
Types of steel structures
CE-411: Lecture 02 Prof. Dr. Akhtar Naeem Khan 49
Classical system supported by beams, girders and columns.
Beams: W or S shapes, Channel shapes for roof purlins.
Columns: generally W shapes
Classical skeleton framing
Types of steel structures
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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Classical skeleton framing
Types of steel structures
CE-411: Lecture 02 Prof. Dr. Akhtar Naeem Khan 51
Triangular rigid structure
Most common double pitched roof trusses:
Fink & Pratt.
Most common flat trusses: Pratt &Warren
Steel trusses
Types of steel structures
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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Steel trusses
Types of steel structures
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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No span limit
Often prefabricated
Used with wood or steel purlins to support the roof.
Bracing: if resting on masonry walls:
Diagonal bracing in alternate bays
Continuous struts(angles, channels)
Steel trusses
Types of steel structures
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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Truss Bridge
Built-up Members
Steel trusses: Example of steel truss with built up members
Types of steel structures
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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Steel trusses
Types of steel structures
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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• For large unobstructed floor areas and ceiling heights.
• Spans generally 40ft to 100ft• Members are connected by bolting and welding• Members: W shapes or web plates fillet welded to
flange plates• Connection to foundation with a base plate(bolted)
Rigid Frame
Types of steel structures
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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Types of steel structures Rigid Frame
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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Types of steel structuresBraced Frame
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Used in field houses, exhibition halls,… with span over 300ft
Most common type: three hinged arch
Types of steel structures Steel arch structures
Lecture 01 Prof. Dr. Akhtar Naeem Khan
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Types of steel structures Steel arch structures
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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Lateral bracing;
Diagonal bracing in curved surfaces between arches
Lateral bracing of ribs with purlins or trussed purlins.
Types of steel structures Steel arch structures
CE-411: Lecture 02 Prof. Dr. Akhtar Naeem Khan 62
Used for large circular areas: Assembly halls, gymnasium, field houses….
Spans up to 400ft in diameter
Structural members:Perimeter (Tension ring)
Domes and rings are supported by columns braced laterally or by bearing walls
Purlins supports the roof deck and span between ribs
Types of steel structures Steel Domes
CE-411: Lecture 02 Prof. Dr. Akhtar Naeem Khan 63
Types of steel structures Steel Domes
Lecture 01 Prof. Dr. Akhtar Naeem Khan
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Types of steel structures Steel Domes
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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Chicago O’Hare International Airport Restaurant
• Reinforced concrete compression ring 190’dia
• Ring is supported on 26 RCC columns 58ft above ground
• Tension ring W-shape 13’ dia
• Sag of cables 10.5’
• Ends of cables are anchored to the two rings
• Roof deck: precast RCC slabs 3.5” thick which fit between cables with projecting ends of reinforcement hooking over the cables.
Types of steel structuresCable supported roof
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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Types of steel structuresCable supported roof
Lecture 01 Prof. Dr. Akhtar Naeem Khan
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Types of steel structures Cable supported roof
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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Eiffel Tower, Paris
The World’s tallest structure at times(990ft).
Was originally built to last 20 years.
Examples of Famous steel structures
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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James R. Thompson Center, Chicago
The building is enclosed by 17 story curtain walls.
The diameter of rotunda is 160ft
The rotunda projects as a cylinder and its top resembles a drum without a dome slanting towards plaza.
Office spaces are between rotunda’s walls and outer skin
Examples of Famous steel structures
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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The Geodesic Dome at Walt Disney World
Spaceship earth is a huge golf ball, standing 180 ft.
The structure is designed to withstand wind speeds of 200 mph
Structure: steel framing clad with faceted aluminum panels, and stands on 3 pairs of steel legs.
Site was mostly swamp, filled with much, organic material with 95% water content.
As a solution, 2.5 million cubic yards of soil was removed and replaced by clean material
Examples of Famous steel structures
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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Indoor Football Facility,University of Illinois, Urbana
The roof structure is semi-parabolic dome
A large single arched box truss spans the length of the field and supports 1/2 of roof load.
Examples of Famous steel structures
CE-411: Lecture 02 Prof. Dr Akhtar Naeem Khan
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• 110 Stories Tall• Total Height = 1725 ft • Based on revolutionary Bundled Tube Design• Rigid outer walls act as walls of hollow tube• There are 9 tubes in all• The number of tubes reduces with height• Designed by late Fazl-ur-Rehman from Bangladesh• Supported by 114 piles
Examples of Famous steel structures