Page 1
DESIGN OF STEEL STRUCTURES
INTRODUCTION: Advantages and Disadvantages of Steel structures, Loads and Load
combinations, Design considerations, Limit State Method (LSM) of design, Failure criteria for
steel, Codes, Specifications and section classification.
Why Structural Design Courses?
Anyone managing the construction process needs a basic understanding of the engineer’s
environment and the basic understanding of how a structure behaves. Constructors must be able
to address a number of technical questions at the project site including structural issues that
sometimes are not addressed by the design professionals. Since the safety of construction
workers as well as the strength and stability of structures during the construction phase is of
paramount importance, construction mangers need this knowledge.
Structural Design
• Definition: Determination of overall proportions and dimensions of the supporting
framework and the selection of individual members.
• Responsibility:The structural engineer, within the constraints imposed by the architect
(number of stories, floor plan,..) is responsible for structural design
• Safety (the structure doesn’t fall down)
• Serviceability (how well the structure performs in term of appearance and deflection)
• Economy (an efficient use of materials and labor)
Alternatives
• Several alternative designs should be prepared and their costs compared
Page 2
DESIGN OF STEEL STRUCTURES
INTRODUCTION: Advantages and Disadvantages of Steel structures, Loads and Load
combinations, Design considerations, Limit State Method (LSM) of design, Failure criteria for
steel, Codes, Specifications and section classification.
Why Structural Design Courses?
Anyone managing the construction process needs a basic understanding of the engineer’s
environment and the basic understanding of how a structure behaves. Constructors must be able
to address a number of technical questions at the project site including structural issues that
sometimes are not addressed by the design professionals. Since the safety of construction
workers as well as the strength and stability of structures during the construction phase is of
paramount importance, construction mangers need this knowledge.
Structural Design
• Definition: Determination of overall proportions and dimensions of the supporting
framework and the selection of individual members.
• Responsibility:The structural engineer, within the constraints imposed by the architect
(number of stories, floor plan,..) is responsible for structural design
• Safety (the structure doesn’t fall down)
• Serviceability (how well the structure performs in term of appearance and deflection)
• Economy (an efficient use of materials and labor)
Alternatives
• Several alternative designs should be prepared and their costs compared
Types of Load
• Dead Loads (permanent; including self-weight, floor covering, suspended ceiling,
partitions,..)
• Live Loads (not permanent; the location is not fixed; including furniture, equipment, and
occupants of buildings)
• Wind Load (exerts a pressure or suction on the exterior of a building)
Types of Load Continued
• Earthquake Loads (the effects of ground motion are simulated by a system of horizontal
forces)
• Snow Load (varies with geographical location and drift)
• Other Loads (hydrostatic pressure, soil pressure)
Types of Load Continued
• If the load is applied suddenly, the effects of IMPACT must be accounted for.
• If the load is applied and removed many times over the life of the structure, FATIGUE
stress must be accounted for
Design Specifications
• Provide guidance for the design of structural members and their connections.
• They have no legal standing on their own, but they can easily be adopted, by reference, as
part of a building code.
• American Concrete Institute (ACI 318-99) Building Code Requirements for Structural
Concrete
• National Design Specifications for Wood Construction by American Forest and Paper
Association.
Structural Steel
• Steel is an alloy of primarily iron, carbon (1 to 2%) and small amount of other
components (manganese, nickel, …)
• Carbon contributes to strength but reduces ductility.
Steel Properties
• The important characteristics of steel for design purposes are:
o yield stress (F
y
)
o ultimate stress (F
u
)
o modulus of elasticity (E)
o percent elongation (e)
o coefficient of thermal expansion (a)
Page 3
DESIGN OF STEEL STRUCTURES
INTRODUCTION: Advantages and Disadvantages of Steel structures, Loads and Load
combinations, Design considerations, Limit State Method (LSM) of design, Failure criteria for
steel, Codes, Specifications and section classification.
Why Structural Design Courses?
Anyone managing the construction process needs a basic understanding of the engineer’s
environment and the basic understanding of how a structure behaves. Constructors must be able
to address a number of technical questions at the project site including structural issues that
sometimes are not addressed by the design professionals. Since the safety of construction
workers as well as the strength and stability of structures during the construction phase is of
paramount importance, construction mangers need this knowledge.
Structural Design
• Definition: Determination of overall proportions and dimensions of the supporting
framework and the selection of individual members.
• Responsibility:The structural engineer, within the constraints imposed by the architect
(number of stories, floor plan,..) is responsible for structural design
• Safety (the structure doesn’t fall down)
• Serviceability (how well the structure performs in term of appearance and deflection)
• Economy (an efficient use of materials and labor)
Alternatives
• Several alternative designs should be prepared and their costs compared
Types of Load
• Dead Loads (permanent; including self-weight, floor covering, suspended ceiling,
partitions,..)
• Live Loads (not permanent; the location is not fixed; including furniture, equipment, and
occupants of buildings)
• Wind Load (exerts a pressure or suction on the exterior of a building)
Types of Load Continued
• Earthquake Loads (the effects of ground motion are simulated by a system of horizontal
forces)
• Snow Load (varies with geographical location and drift)
• Other Loads (hydrostatic pressure, soil pressure)
Types of Load Continued
• If the load is applied suddenly, the effects of IMPACT must be accounted for.
• If the load is applied and removed many times over the life of the structure, FATIGUE
stress must be accounted for
Design Specifications
• Provide guidance for the design of structural members and their connections.
• They have no legal standing on their own, but they can easily be adopted, by reference, as
part of a building code.
• American Concrete Institute (ACI 318-99) Building Code Requirements for Structural
Concrete
• National Design Specifications for Wood Construction by American Forest and Paper
Association.
Structural Steel
• Steel is an alloy of primarily iron, carbon (1 to 2%) and small amount of other
components (manganese, nickel, …)
• Carbon contributes to strength but reduces ductility.
Steel Properties
• The important characteristics of steel for design purposes are:
o yield stress (F
y
)
o ultimate stress (F
u
)
o modulus of elasticity (E)
o percent elongation (e)
o coefficient of thermal expansion (a)
Standard Cross-Sectional Shapes
Refer steel table
Design Philosophies
• Allowable Stress Design Method (ASD)
• Load and Resistance Factor Design (LRFD)
A member is selected such that the max stress due to working loads does not exceed an
allowable stress.
• It is also called elastic design or working stress design.
o allowable stress=yield stress/factor of safety
o actual stress ? allowable stress
LRFD –Load and Resistance Factor Design
• A member is selected such that its factored strength is more than the factored loads.
o S(loads x L factors) ? resistance x R factor
• Each load effect (DL, LL, ..)has a different load factor which its value depends on the
combination of loads under consideration.
Load Factors
• The values are based on extensive statistical studies
o DL only 1.4D
o DL+LL+SL (LL domin.) 1.2D+1.6L+0.5S
o DL+LL+SL (SL domin.) 1.2D+0.5L+1.6S
o In each combination, one of the effects is considered to be at its “lifetime” max
value and the others at their “arbitrary point in time “ values.
Resistance Factor
• The resistance factors range in value from 0.75 to 1.0 depending on the type of resistance
(tension, bending, compression, ..)
• These factors account for uncertainties in material properties, design theory, and
fabrication and construction practices.
History
• ASD has been the primary method used for steel design since the first AISC
specifications was issued in 1923.
• In 1986, AISC issued the first specification for LRFD.
• The trend today is toward LRFD method, but ASD is still in use.
Page 4
DESIGN OF STEEL STRUCTURES
INTRODUCTION: Advantages and Disadvantages of Steel structures, Loads and Load
combinations, Design considerations, Limit State Method (LSM) of design, Failure criteria for
steel, Codes, Specifications and section classification.
Why Structural Design Courses?
Anyone managing the construction process needs a basic understanding of the engineer’s
environment and the basic understanding of how a structure behaves. Constructors must be able
to address a number of technical questions at the project site including structural issues that
sometimes are not addressed by the design professionals. Since the safety of construction
workers as well as the strength and stability of structures during the construction phase is of
paramount importance, construction mangers need this knowledge.
Structural Design
• Definition: Determination of overall proportions and dimensions of the supporting
framework and the selection of individual members.
• Responsibility:The structural engineer, within the constraints imposed by the architect
(number of stories, floor plan,..) is responsible for structural design
• Safety (the structure doesn’t fall down)
• Serviceability (how well the structure performs in term of appearance and deflection)
• Economy (an efficient use of materials and labor)
Alternatives
• Several alternative designs should be prepared and their costs compared
Types of Load
• Dead Loads (permanent; including self-weight, floor covering, suspended ceiling,
partitions,..)
• Live Loads (not permanent; the location is not fixed; including furniture, equipment, and
occupants of buildings)
• Wind Load (exerts a pressure or suction on the exterior of a building)
Types of Load Continued
• Earthquake Loads (the effects of ground motion are simulated by a system of horizontal
forces)
• Snow Load (varies with geographical location and drift)
• Other Loads (hydrostatic pressure, soil pressure)
Types of Load Continued
• If the load is applied suddenly, the effects of IMPACT must be accounted for.
• If the load is applied and removed many times over the life of the structure, FATIGUE
stress must be accounted for
Design Specifications
• Provide guidance for the design of structural members and their connections.
• They have no legal standing on their own, but they can easily be adopted, by reference, as
part of a building code.
• American Concrete Institute (ACI 318-99) Building Code Requirements for Structural
Concrete
• National Design Specifications for Wood Construction by American Forest and Paper
Association.
Structural Steel
• Steel is an alloy of primarily iron, carbon (1 to 2%) and small amount of other
components (manganese, nickel, …)
• Carbon contributes to strength but reduces ductility.
Steel Properties
• The important characteristics of steel for design purposes are:
o yield stress (F
y
)
o ultimate stress (F
u
)
o modulus of elasticity (E)
o percent elongation (e)
o coefficient of thermal expansion (a)
Standard Cross-Sectional Shapes
Refer steel table
Design Philosophies
• Allowable Stress Design Method (ASD)
• Load and Resistance Factor Design (LRFD)
A member is selected such that the max stress due to working loads does not exceed an
allowable stress.
• It is also called elastic design or working stress design.
o allowable stress=yield stress/factor of safety
o actual stress ? allowable stress
LRFD –Load and Resistance Factor Design
• A member is selected such that its factored strength is more than the factored loads.
o S(loads x L factors) ? resistance x R factor
• Each load effect (DL, LL, ..)has a different load factor which its value depends on the
combination of loads under consideration.
Load Factors
• The values are based on extensive statistical studies
o DL only 1.4D
o DL+LL+SL (LL domin.) 1.2D+1.6L+0.5S
o DL+LL+SL (SL domin.) 1.2D+0.5L+1.6S
o In each combination, one of the effects is considered to be at its “lifetime” max
value and the others at their “arbitrary point in time “ values.
Resistance Factor
• The resistance factors range in value from 0.75 to 1.0 depending on the type of resistance
(tension, bending, compression, ..)
• These factors account for uncertainties in material properties, design theory, and
fabrication and construction practices.
History
• ASD has been the primary method used for steel design since the first AISC
specifications was issued in 1923.
• In 1986, AISC issued the first specification for LRFD.
• The trend today is toward LRFD method, but ASD is still in use.
Advantages of LRFD
• It provides a more uniform reliability in all structures subjected to many types of loading
conditions. It does not treat DL and LL as equivalent, thereby leading to a more rational
approach.
• It provides better economy as the DL make up a greater percentage on a given
structure. Because DLs are less variable by nature than live loads, a lower load
factor is used.
This may lead to a reduction in member size and therefore better economy
STEEL AS A STRUCTURAL MATERIAL
1.1General
Structural steel is a material used for steel construction, which is formed with a specific
shape following certain standards of chemical composition and strength. They can also be
defined as hot rolled products, with a cross section of special form like angles, channels and
beams/joints. There has been an increasing demand for structural steel for construction purposes
in the United States and India.
Measures are been taken by the structural steel authority for ready availability of structural
steel on time for the various projects. The people at every level are working hard to realize the
purpose of producing steel on time, like, service centers, producers, fabricators and erectors
along with the general contractors, engineers and architects are all working hand in hand. Steel
has always been more preferred to concrete because steel offers better tension and compression
thus resulting in lighter construction. Usually structural steel uses three dimensional trusses
hence making it larger than its concrete counterpart. There are different new techniques which
Page 5
DESIGN OF STEEL STRUCTURES
INTRODUCTION: Advantages and Disadvantages of Steel structures, Loads and Load
combinations, Design considerations, Limit State Method (LSM) of design, Failure criteria for
steel, Codes, Specifications and section classification.
Why Structural Design Courses?
Anyone managing the construction process needs a basic understanding of the engineer’s
environment and the basic understanding of how a structure behaves. Constructors must be able
to address a number of technical questions at the project site including structural issues that
sometimes are not addressed by the design professionals. Since the safety of construction
workers as well as the strength and stability of structures during the construction phase is of
paramount importance, construction mangers need this knowledge.
Structural Design
• Definition: Determination of overall proportions and dimensions of the supporting
framework and the selection of individual members.
• Responsibility:The structural engineer, within the constraints imposed by the architect
(number of stories, floor plan,..) is responsible for structural design
• Safety (the structure doesn’t fall down)
• Serviceability (how well the structure performs in term of appearance and deflection)
• Economy (an efficient use of materials and labor)
Alternatives
• Several alternative designs should be prepared and their costs compared
Types of Load
• Dead Loads (permanent; including self-weight, floor covering, suspended ceiling,
partitions,..)
• Live Loads (not permanent; the location is not fixed; including furniture, equipment, and
occupants of buildings)
• Wind Load (exerts a pressure or suction on the exterior of a building)
Types of Load Continued
• Earthquake Loads (the effects of ground motion are simulated by a system of horizontal
forces)
• Snow Load (varies with geographical location and drift)
• Other Loads (hydrostatic pressure, soil pressure)
Types of Load Continued
• If the load is applied suddenly, the effects of IMPACT must be accounted for.
• If the load is applied and removed many times over the life of the structure, FATIGUE
stress must be accounted for
Design Specifications
• Provide guidance for the design of structural members and their connections.
• They have no legal standing on their own, but they can easily be adopted, by reference, as
part of a building code.
• American Concrete Institute (ACI 318-99) Building Code Requirements for Structural
Concrete
• National Design Specifications for Wood Construction by American Forest and Paper
Association.
Structural Steel
• Steel is an alloy of primarily iron, carbon (1 to 2%) and small amount of other
components (manganese, nickel, …)
• Carbon contributes to strength but reduces ductility.
Steel Properties
• The important characteristics of steel for design purposes are:
o yield stress (F
y
)
o ultimate stress (F
u
)
o modulus of elasticity (E)
o percent elongation (e)
o coefficient of thermal expansion (a)
Standard Cross-Sectional Shapes
Refer steel table
Design Philosophies
• Allowable Stress Design Method (ASD)
• Load and Resistance Factor Design (LRFD)
A member is selected such that the max stress due to working loads does not exceed an
allowable stress.
• It is also called elastic design or working stress design.
o allowable stress=yield stress/factor of safety
o actual stress ? allowable stress
LRFD –Load and Resistance Factor Design
• A member is selected such that its factored strength is more than the factored loads.
o S(loads x L factors) ? resistance x R factor
• Each load effect (DL, LL, ..)has a different load factor which its value depends on the
combination of loads under consideration.
Load Factors
• The values are based on extensive statistical studies
o DL only 1.4D
o DL+LL+SL (LL domin.) 1.2D+1.6L+0.5S
o DL+LL+SL (SL domin.) 1.2D+0.5L+1.6S
o In each combination, one of the effects is considered to be at its “lifetime” max
value and the others at their “arbitrary point in time “ values.
Resistance Factor
• The resistance factors range in value from 0.75 to 1.0 depending on the type of resistance
(tension, bending, compression, ..)
• These factors account for uncertainties in material properties, design theory, and
fabrication and construction practices.
History
• ASD has been the primary method used for steel design since the first AISC
specifications was issued in 1923.
• In 1986, AISC issued the first specification for LRFD.
• The trend today is toward LRFD method, but ASD is still in use.
Advantages of LRFD
• It provides a more uniform reliability in all structures subjected to many types of loading
conditions. It does not treat DL and LL as equivalent, thereby leading to a more rational
approach.
• It provides better economy as the DL make up a greater percentage on a given
structure. Because DLs are less variable by nature than live loads, a lower load
factor is used.
This may lead to a reduction in member size and therefore better economy
STEEL AS A STRUCTURAL MATERIAL
1.1General
Structural steel is a material used for steel construction, which is formed with a specific
shape following certain standards of chemical composition and strength. They can also be
defined as hot rolled products, with a cross section of special form like angles, channels and
beams/joints. There has been an increasing demand for structural steel for construction purposes
in the United States and India.
Measures are been taken by the structural steel authority for ready availability of structural
steel on time for the various projects. The people at every level are working hard to realize the
purpose of producing steel on time, like, service centers, producers, fabricators and erectors
along with the general contractors, engineers and architects are all working hand in hand. Steel
has always been more preferred to concrete because steel offers better tension and compression
thus resulting in lighter construction. Usually structural steel uses three dimensional trusses
hence making it larger than its concrete counterpart. There are different new techniques which
enable the production of a wide range of structures and shapes, the procedures being the
following:
• High-precision stress analysis
• Computerized stress analysis
• Innovative jointing
The structural steel all over the world pre-dominates the construction scenario. This material
has been exhaustively used in various constructions all over the world because of its various
specific characteristics that are very much ideally suited for construction. Structural steel is
durable and can be well molded to give the desired shape to give an ultimate look to the structure
that has been constructed. There is a mention of The Super dome situated in the United States
and The Fukuoka Dome of Japan; both speak the unique language of the unique capabilities of
the structural steel.
1.2 Types of structural steel:
Various types of structural steel sections and their technical specifications are as follows:
• Beams
• Channels
• Angles
• Flats
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