Steel Structures Study Notes
Trimester 1, 2020
INTRODUCTION TO STEEL DESIGN
• Common types of steel sections include:
o Hot rolled
o Standard welded sections
o Cold-formed and welded hollow sections
o Fabricated sections
• Steel structures must perform reliably and be resilient through:
o Live loads
o Dead loads
o Earthquakes
o Wind
o Vibration
• High strength steel is never used in earthquake-prone areas since it is
particularly brittle and has limited stiffness
• Beams are implemented to resist bending moments, columns are included to
minimise axial compression
• The two major design philosophies employed for structural design:
o Allowable stress design (no longer used)
o Limit state design – load and resistance factors
▪ This can comprise of stability, strength and serviceability
design
▪ Design action effect < Capacity Factor * Nominal Capacity
• The value of the capacity factor in limit state design is dependent on the type
of material and the scenario of the eventual design structure (see Table 3.4)
• The four most crucial strength load combinations for the purpose of
CVEN3303 are: 1.35G, 1.2G+1.5Q, 0.9G+W (wind pressure in opposite
direction to gravity), 1.2G+W+c*Q (wind and gravity in same direction)
• For structural design, gravity loads can be distributed across either one-way
or two-way slabs (the number of force distribution directions)
• The four levels of structural design (from greatest to smallest):
o Structure
o Member
o Section
o Element – this may just a small geometry or shape
• The AS4100 – 2016 Standards set out minimum design and fabrication
requirements for steel structures, but do not apply to:
o Elements less than 3mm thick
o Members which have a yield stress of more than 690MPa
o Cold-formed members
o Composite steel-concrete members
o Those to be used in roads, railways or pedestrian bridges
• Note the difference between an action (an applied load which CAUSES
stress) and an action effect (the internal stress or bending moment induced
due to the action)
• The parameters which may affect the design of a structural action include:
, o Origin – which actions occur to the structure throughout its lifetime
o Confidence – ability to predict actions
o Duration – whether occurring over short or long-term
o Distribution – concentrated or evenly distributed across a member
o Return period – rare event or constant frequency
• Failure in steel structures can be local, global or a combination of both
o Buckling is a form of local failure whereas fatigue over time is a global
failure method
• A typical steel frame will consist of beams (horizontal), columns (vertical)
and bracing (any orientation)
• The three forms of connections between steel members:
o Rigid: angle between the members remains equal
o Semi-rigid: slight variation in angle
o Simple: connection acts like a hinge
• The forms of analysis for determining action effects outlined within AS4100
are:
o Elastic analysis
o Plastic analysis
o Advanced analysis
TENSION MEMBERS
• A pin connection means that zero bending moment can be sustained,
whereas a fixed connection allows for bending moments and thus for a lateral
load to contribute towards the bending moment of any horizontal beams
• For two-way slabs, the distributed load will be trapezoidal lengthwise
and triangular along the breadth
• The nominal section capacity (Nt) for a member in tension is the lesser of two
values: 1) yield of gross section OR 2) fracture of net section
• Staggered holes (those not in a linear path) can often lead to conservative
calculations of nominal capacity for a given path, accounted for through:
o Unstaggered Holes: Sum up the diameter*thickness of each hole
o Staggered Holes: Sum up diameter*thickness of each hole less a
zig-zag factor (horizontal distance squared divided by twice the
width distance) multiplied by thickness
• Tensile forces act through the centroid of a beam, therefore an eccentricity
occurs for L-shaped beams where the centroid acts outside of the physical
beam
• Shear lag results in an uneven distribution of stress due to shear occurring
between a member and its end connection
• The correction factor ‘kt’ accounts for the uneven stress distribution caused
by the aforementioned two factors
o A gusset is often used to offset this uneven tension stress distribution
for diagonal truss members
• Snug tightening of bolts means that the bolt was tightened by hand and is still
relatively loose
COMPRESSION MEMBERS
• There are five modes of failure for compression members:
o Yielding – when squash load is reached
Trimester 1, 2020
INTRODUCTION TO STEEL DESIGN
• Common types of steel sections include:
o Hot rolled
o Standard welded sections
o Cold-formed and welded hollow sections
o Fabricated sections
• Steel structures must perform reliably and be resilient through:
o Live loads
o Dead loads
o Earthquakes
o Wind
o Vibration
• High strength steel is never used in earthquake-prone areas since it is
particularly brittle and has limited stiffness
• Beams are implemented to resist bending moments, columns are included to
minimise axial compression
• The two major design philosophies employed for structural design:
o Allowable stress design (no longer used)
o Limit state design – load and resistance factors
▪ This can comprise of stability, strength and serviceability
design
▪ Design action effect < Capacity Factor * Nominal Capacity
• The value of the capacity factor in limit state design is dependent on the type
of material and the scenario of the eventual design structure (see Table 3.4)
• The four most crucial strength load combinations for the purpose of
CVEN3303 are: 1.35G, 1.2G+1.5Q, 0.9G+W (wind pressure in opposite
direction to gravity), 1.2G+W+c*Q (wind and gravity in same direction)
• For structural design, gravity loads can be distributed across either one-way
or two-way slabs (the number of force distribution directions)
• The four levels of structural design (from greatest to smallest):
o Structure
o Member
o Section
o Element – this may just a small geometry or shape
• The AS4100 – 2016 Standards set out minimum design and fabrication
requirements for steel structures, but do not apply to:
o Elements less than 3mm thick
o Members which have a yield stress of more than 690MPa
o Cold-formed members
o Composite steel-concrete members
o Those to be used in roads, railways or pedestrian bridges
• Note the difference between an action (an applied load which CAUSES
stress) and an action effect (the internal stress or bending moment induced
due to the action)
• The parameters which may affect the design of a structural action include:
, o Origin – which actions occur to the structure throughout its lifetime
o Confidence – ability to predict actions
o Duration – whether occurring over short or long-term
o Distribution – concentrated or evenly distributed across a member
o Return period – rare event or constant frequency
• Failure in steel structures can be local, global or a combination of both
o Buckling is a form of local failure whereas fatigue over time is a global
failure method
• A typical steel frame will consist of beams (horizontal), columns (vertical)
and bracing (any orientation)
• The three forms of connections between steel members:
o Rigid: angle between the members remains equal
o Semi-rigid: slight variation in angle
o Simple: connection acts like a hinge
• The forms of analysis for determining action effects outlined within AS4100
are:
o Elastic analysis
o Plastic analysis
o Advanced analysis
TENSION MEMBERS
• A pin connection means that zero bending moment can be sustained,
whereas a fixed connection allows for bending moments and thus for a lateral
load to contribute towards the bending moment of any horizontal beams
• For two-way slabs, the distributed load will be trapezoidal lengthwise
and triangular along the breadth
• The nominal section capacity (Nt) for a member in tension is the lesser of two
values: 1) yield of gross section OR 2) fracture of net section
• Staggered holes (those not in a linear path) can often lead to conservative
calculations of nominal capacity for a given path, accounted for through:
o Unstaggered Holes: Sum up the diameter*thickness of each hole
o Staggered Holes: Sum up diameter*thickness of each hole less a
zig-zag factor (horizontal distance squared divided by twice the
width distance) multiplied by thickness
• Tensile forces act through the centroid of a beam, therefore an eccentricity
occurs for L-shaped beams where the centroid acts outside of the physical
beam
• Shear lag results in an uneven distribution of stress due to shear occurring
between a member and its end connection
• The correction factor ‘kt’ accounts for the uneven stress distribution caused
by the aforementioned two factors
o A gusset is often used to offset this uneven tension stress distribution
for diagonal truss members
• Snug tightening of bolts means that the bolt was tightened by hand and is still
relatively loose
COMPRESSION MEMBERS
• There are five modes of failure for compression members:
o Yielding – when squash load is reached
