Vật liệu thép theo ASTM

CIE 428 Module A Instructor: Andrew Whittaker
8/21/2002 8:39 AM 1
MODULE A: INTRODUCTION

This module of CIE 428 covers the following subjects
 Specifications for design of steel structures
 Structural steel
 Grades of steel
 Steel shapes
 Properties of structural steel
 Concepts in structural steel design
 Basis of load and resistance factors
READING: Chapters 1 and 2 of Segui

Chapters 1 and 2 of Bruneau et al.
AISC LRFD Manual of Steel Construction, 3rd
Ed.
SPECIFICATIONS
There are two key specifications for the design of steel structures
1. American Institute of Steel Construction (AISC)
 Design of steel buildings and connections
 www.aisc.org

CIE 428 Module A Instructor: Andrew Whittaker
8/21/2002 8:39 AM 2

2. American Association of State Highway and Transportation
Officials (AASHTO)
 Design of steel/reinforced concrete/timber bridges
 www.aashto.org

Other specifications are available from
 American Iron and Steel Institute (AISI)
 Cold-formed steel structures
 www.steel.org
 American Railway Engineering Association
 Steel railway bridges
STRUCTURAL STEEL
History of engineered construction using metals
Iron
 Chief component of steel
 Wrought iron first used for tools around 4000 BC
 Produced by heating ore in a charcoal fire
 Cast and wrought iron used in the late 18C and early 19C
in bridges
CIE 428 Module A Instructor: Andrew Whittaker
8/21/2002 8:39 AM 3

Steel
 An alloy of primarily iron and carbon
 Fewer impurities and less carbon than cast iron
 Began to replace iron in construction in the mid 1800s
 First steel railroad bridge in 1874
 First steel framed building in 1884
GRADES OF STEEL
Numerous grades of steel are available in the marketplace. The
choice is dependent on
 Application
 Yield strength
 Composition
See the summaries on the following sheets from the textbook of

Gaylord et al.
 ASTM A36, A53, A242, A572, A709
 Tensile properties


CIE 428 Module A Instructor: Andrew Whittaker
8/21/2002 8:39 AM 4

STEEL SHAPES
Hot-rolled shapes are produced from molten steel in a furnace that
is poured into a continuous casting where the steel solidifies but
does not cool completely. The partially cooled steel is then passed
through rollers to achieve the desired shape.
Common structural steel shapes are shown below (from Segui).

CIE 428 Module A Instructor: Andrew Whittaker
8/21/2002 8:39 AM 5


A sample designation of a steel shape is
W18x50


Bar, plate and HSS shapes are shown below.
 Hollow steel sections (HSS) are fabricated by either
bending plate material into the desired shape and seam
welding or hot-working to produce a seamless shape


PROPERTIES OF STRUCTURAL STEEL

Stress-strain relationship

CIE 428 Module A Instructor: Andrew Whittaker
8/21/2002 8:39 AM 6
The stress-strain relationship is the best-known characterization of
steel. See the figure below from Segui.

Stress is denoted as f or
σ
, and is calculated as
P
f
A
=

 Engineering stress
Strain is denoted
ε
and is calculated as
L
L
ε
∆
=

CIE 428 Module A Instructor: Andrew Whittaker
8/21/2002 8:39 AM 7
 Engineering strain

The figure above shows 4 ranges of response

 Elastic
 Plastic (yield plateau)
 Strain hardening
 Necking and failure (strain softening)
Many steels are ductile. Ductility is a measure of post-yield
elongation, where elongation is calculated as
0
0
()
f
LL
e
L
−
=

where
f
L =

0
L =

An idealized stress-strain relationship is shown in the figure on the
following page from Segui. The important descriptors are

y
F
: the yield point


u
F
: the ultimate tensile strength
CIE 428 Module A Instructor: Andrew Whittaker
8/21/2002 8:39 AM 8
 E: Modulus of elasticity or Young’s modulus (29,000 ksi)

For high-strength steels, the stress-strain relationships are often
similar to that shown below (from Segui).

Note from the above figure that
 Elastic range
 No well-defined yield point