CVEN9822 Steel and Composite Structures
Semester 2, 2019
School of Civil and Environmental Engineering, UNSW
INTRODUCTION
Course Outline
Tutorials
Tutorial classes start in Week 2
Venue: Mat 310, RedC M032, ChemSc M10
Time: 10.00-11.00 am
History of Steel Structures
(The Iron bridge crosses the
Severn River in England, 1779)
1780 - 1840 Cast Iron.
arch-shaped bridges up to 30m span.
1840 - 1890 Wrought (worked) Iron.
Spans up to 100m.
1870 - 1920 Bessemer Converter (Rolled shapes)
Introduction to Carbon Steel.
1920 - To date Third most popular construction material
after Concrete and Timber.
Structural Steel – Mild Steel
Steel with less than 0.16-0.29% carbon
Economic, Ductile
Box sections
Hot-rolled into standard shapes
Easily fabricated by welding
Standard sections Cell Form Beams
Typical Steel Fabrication Shop
fabrication workshop hot rolling
Floor Beams
Ductility
The most important material characteristic of mild steel is its
ductility.
Ductility is the ability of the material to undergo large strains with
little increase in stress, prior to failure.
The advantages of ductility are:
It can give prior warning of impending failure
It allows energy absorption in dynamic loading or in resisting brittle
fracture
It allows for redistribution of actions, which is usually benign
Properties of mild steel
Stress Not to scale
Upper yield stress
fu
Strain hardening Est
fy
Tensile rapture
Plastic
Elastic E
y st
Strain
Idealised stress-strain relationship for structural steel
N.B. The same stress-strain curve is assumed in compression,
but we shall see that buckling of members and elements in compression
usually prevents high strains from being realised
Idealised Stress-Strain () Diagram
Yielding under biaxial stresses
Mises Yield Criterion
Mohr Circle Construction
Uniaxial
tension
1.0
Pure Uniaxial
shear tension
-1.0 1.0
Uniaxial
compression
-1.0 Maximum distortion-energy
criterion:
f1, f2 – normal stresses f12-f1f2+f2 2+ 32= fy2
– shear stress
Steel Structures Code
Section
Section
Section
Section 5 59
to
4
6,7243& 88
Section
Section
Connections
Engineered
Design
Member AS 4100
Capacity
Section 1ofof
Properties
Method
Timber
of subjected
Connections
Design Capacity
Introduction
Timber to- -
Structural
Products
•nails, screws -
-
of bending
•Bolting
Members - -
scope,
•eng. Properties
Analysis
Australian
•bolts, Standard
coach screws
•plywood
•Welding
Reconfirmed in 2016 Steeldefinitions,
•tension
strength
•shear (f ’)
Structures
connectors,
•Elastic
Including Amendments from •poles
stiffness
notation,
•Section (E)
capacity
•compression
split rings
•Plastic
2012. •glulam
•Modif’n
•Member
units
•combined
•bending
•Member factors
capacity
(N,buckling-
k•Frame
modifies
•LVL strength
buckling
mm,
actions MPa)
Standards Australia
Design approach of AS4100
Based on limit state design
Principal limit states
Strength (ultimate limit state), concerned
with ‘collapse’:
– yielding
– buckling
– overturning
Serviceability limit state, concerned with
‘function’:
– deflection
– vibration
Strength limit state design principles
Define relevant limit states
Determine appropriate actions
Analyse using appropriate methods and
accounting for variability to determine:
Design effects { S* }, and
Design resistance { R }
Ensure no limit state is exceeded
= 0.9 (for steel members, Mu, Vu, Nu)
= 0.6-0.9 (connectors and connections)
DESIGN LOADS - GENERAL
For the design of structural steelwork the following loads and influences
shall be considered:
G - Dead loads, including the weight of steelwork and all permanent
materials of construction, partitions, stationary equipment, and additional
weight of concrete and finishes resulting from deflections of supporting
members, and the forces due to prestressing;
Q – Live loads, including load due to intended use and occupancy of
structures; movable equipment, snow, rain, soil, or hydrostatic pressure;
impact; and any other live load stipulated by the regulatory authority;
T – Influences resulting from temperature changes, shrinkage, or creep of
component materials;
W – Live load due to wind;
E – Live load due to earthquake
Serviceability Limit State
The following conditions may need to be considered:
excessive deflections Appearance, discomfort of occupants,
damage to non-structural members
excessive vibrations (glass/masonry)
Both conditions are associated with stiffness rather than
strength
For many buildings, controlling deflections will also limit
vibrations
Serviceability Limits
Code gives guidance only
(i.e. /L = 1/250, 1/500, etc.)
Main message is - THINK and discuss with client
