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1.
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IND
-

2007 0394 GR
-

EN
-

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200707
17

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PROJET

HELLENIC REPUBLIC

HELLENIC MINISTRY FOR THE ENVIRONMENT,

PHYSICAL PLANNING & PUBLIC WORKS

GENERAL SECRETARIAT FOR PUBLIC WORKS

CENTRAL LABORATORY FOR PUBLIC WORKS


























TECH
NOLOGY REGULATION ON

CONCRETE REINFORCEMENT STEEL


TRS 2007


(Draft for Public Scrutiny)































ATHENS 2007


TRS 2007 Draft for Public Scrutiny

Chapter

ii


TRS 2007 Draft for Public Scrutiny

Chapter

iii

CONTENTS




Chapter 1:

GENERAL


1



1.1

Introduction


1

1.2

Field of Application


1

1.3

Objective


2

1.4

Symbols

3

1.5

Units

3

1.6

Definitions

3



Chapter 2: CLASSIFICATION OF STEEL

7



2.1

Distinction of Steel

7

2.2

Technical Categories of Steel Qualities

8

2.3

Shapes of Steel

8

2.4

Marking for Identifying Concrete Reinforcement Steel

8


2.4.1.

Marking for
Identifying Quality Grade

8


2.4.2.

Marking for Identifying the Production Country and Plant

9


2.4.3.

Marking for Identifying Coils Products

10

2.5

Traceability





Chapter 3: CHARACTERISTICS OF STEEL

12



3.1

Geometric characteristics

12


3.1.
1

Nominal Values

12


3.1.2

Surface Geometry

=
Adhes楯n=o敱u楲ements

13

3.2

Mechanical Properties

15


3.2.1

Tensile Properties


15


3.2.2

Shear Strength

16


3.2.3

Bending Strength

16


3.2.4

Fatigue Behaviour

16

3.3

Physical Properties

17

3.4

M
acroscopic Examination of Steel

19

3.5

Chemical Properties

19


3.5.1

General

19


3.5.2

Weldability

20


3.5.3

Chemical Composition of Weldable Steel

21

3.6

Behaviour in Extreme Temperatures

21


3.6.1

Exposure of Steel to Low Temperatures

22


3.6.
2

Exposure of Steel to High Temperatures

23

3.7

Radioactivity

26



Chapter 4:

TEST PROCEDURES AND COMPLIANCE CRITERIA

27



4.1

Introduction

27

4.2

Compliance Tests and Criteria for Domestically Produced Steel

28

4.3

Compliance Tests and Criteria f
or Steel Produced in Other European Union
Countries

28

4.4

Compliance Tests and Criteria for Steel Produced in Third Countries

28

4.5

Sampling Tests of Batch

28


4.5.1

General
-

Application

28


4.5.2

Cross
-
sectional and Reduced Mass Testing of a Bat
ch

29


4.5.3

Surface and Rib Geometry Testing

29


4.5.4

Testing of Tensile Properties


30


4.5.5

Buckling Testing

31


4.5.6

Chemical Composition Testing

31


4.5.7

Strength Testing of Cruciform Spot Welding on Meshes

31


4.5.8

Fatigue Strength
Testing

31


4.5.9

Visual Inspection and Corrosion Testing

32



Chapter 5: TRANSPORTING

33



TRS 2007 Draft for Public Scrutiny

Chapter

iv

5.1

General

33

5.2

Staffing Transportation Companies

33

5.3

Storage

33

5.4

Transport


34

5.5

Ordering

34

5.6

Accompanying Documentation

35



Chapter 6:

SHAPING
-

TREATMENT

36



6.1

General Requirements

36

6.2

Companies that Shape Reinforcement Steel

36


6.2.1

Staffing Shaping Companies

36


6.2.2

Basic Operational Requirements

36

6.3

Straightening Reinforcement Steel

37

6.4

Cutting Reinforcement
Steel

37

6.5

Bending Reinforcement Steel

37

6.6

Welding

38

6.7

Testing and Receiving Reinforcement Steel at the Work site

38

6.8

Shaping Reinforcement Steel at Work site

38

6.9

Shaping and Placement Tolerances of Reinforcement Steel

38

6.10

Health an
d Safety of Employees

39



Chapter 7:

PLACING REINFORCEMENT STEEL

40



7.1

Assembly


Retention
-

Support

40

7.2

Coverage


Spacers


Protection of Ends


Surface Steel Reinforcement


40


7.2.1

Coverage

40


7.2.2

Requirements for Spacers

41


7.2.
3

Protection of ends

41


7.2.4

Surface Reinforcement

41

7.3

Joints

42


7.3.1

Overlapping joints


42


7.3.2

Joints with Mechanical Means
-

Bolted


42


7.3.3

Welded Joints

42

7.4

Anchoring

42

7.5

Testing and receiving Placed Reinforcement Steel

4
2

7.6

Safety and Health of Employees

42



Chapter 8: WELDED JOINTS

43



8.1

General

43

8.2

Joint Types

43


8.4.1

General Notes

45


8.4.2

Butt

Joint (end to end) using Arc Welding Techniques

47


8.4.3

Lap Joint

48


8.4.4

Joint with Strips usi
ng Arc Welding
Techniques

49


8.4.5

Cruciform joint

49


8.4.6

Joints with Other Steel Elements

50

8.5

Welding quality Control

52


8.5.1

General

52


8.5.2

Tests and Number of Samples

52


8.5.3

Executing Tests


Evaluating Results

53

8.6

Welding

New Reinforcement to Old Steel

56


8.6.1

General

56


8.6.2

Welding Steel that must be Welded under Special Conditions

57


8.6.3

Welding quality Control Testing

58

8.7

Safety and Health of Employees

58



Chapter 9:

STEEL MESHES

59



9.1

General

59

9.2

Welding for the Production of Meshes

59

9.3

Bending Meshes

59

9.4

Mesh Characteristics

60

TRS 2007 Draft for Public Scrutiny

Chapter

v


9.4.1

Standardised Structural Meshes

60


9.4.2

Non
-
Standardised Structural Meshes

61


9.4.3

Special type Meshes

61

9.5

Dimension Tolerances

62

9.6

Transporting, Shaping, Placing

62

9.7

Safety and Health of Employees

62



Chapter 10:

CORROSION

64



10.1

General

64

10.2

Corrosion Control

65

10.3

Protection of Ends

65





APPENDICES




Appendix 1: AFFECT OF PRODUCTION METHODS AND ALLOY ELEM
ENTS ON
PROPERTIES OF CONCRETE REINFORCING STEEL




Appendix 2: RADIOACTIVITY




Appendix 3: STAINLESS STEEL




Appendix 4:
WELDING METHODS




Appendix 5: SPACERS




Appendix 6: DELIVERY OF PLACED REINFORCEMENT STEEL




Appendix 7: EXISTING STR
UCTURES




Appendix 8: PRE
-
STRESSED STEEL




Appendix 9: SAFETY AND HEALTH OF EMPLOYEES




Appendix 10:
FATIGUE OF CONCRETE REINFORCEMENT STEEL



Chapter 1:
GENERAL


1.1

Introduction


In this regulation, the numbering of the Tables and Figures
fo
llows the same numbering of the relevant Chapters.
Especially for Tables and Figures of the Comments, the letter
C precedes the number.



This Regulation includes the main Text (right
column), the Notes (left column) and the Appendices,
which are for your
information.


The objective of the Notes and Appendices is:



To provide a basic interpretation or explanation of
the general rules and provisions or present data
that contribute to their understanding.



To present practical applications or simplified
rul
es, which may not have a general application but
are applicable for most usual cases.



To correlate each article with other articles of this
Regulation and other Regulations, Standards,
Decisions, Circulars etc, where necessary.


Clumsy mistakes are a se
rious cause of construction
failures.

Therefore, in order to prevent such mistakes, it is
required that the Regulation is applied by trained,
experienced and capable persons.



This Regulation does not guarantee against clumsy
mistakes. The use of this Reg
ulation requires that it is
applied by individuals that have the necessary
technical knowledge and experience.



1.2

Field of Application



This Regulation specifies the minimum general and
specific requirements that concrete reinforcement
steel has to m
eet. The Employer, especially with
regard to a special project, may specify stricter or
additional special requirements.


In the present Regulation, reference is made to the following
standards and regulation texts:


ELOT EN 10080 (2005): Concrete Reinfo
rcement
Steel
-

Weldable Steel


General Requirements


ELOT EN 1421
-
2 (2005): Concrete Reinforcement Steel
-

Weldable Steel


Part 2: Technical Category B500A


ELOT EN 1421
-
3 (2005): Concrete Reinforcement Steel
-

Weldable Steel


Part 3: Technical Categ
ory B500C


ELOT 656 (1981): Symbols used in project technical
studies


ELOT EN 10020 (2000): Specification and
classification of categories of steel


ELOT EN 10025 (2005): Hot
-
rolled products for
construction steel


Part 2: Technical delivery terms for

non
-
alloy construction steel


ELOT EN ISO 15630
-
1 (2003): Steel for the
reinforcement and prestressing of concrete
-

Test
methods

Part 1 Reinforcement bars and wires


ELOT EN ISO 15630
-
2 (2003): Steel for the
reinforcement and prestressing of concret
e
-

Test
methods


Part 2 Welded meshes



Ε
Ν ISO 17660
-
1 (2006)
:

W
el
d
i
ng
-

W
el
d
i
ng of
reinforcing steel, Part 1:

Load
-
bearing welded joints



Ε
Ν ISO 17660
-
2 (2006)
:

W
el
d
i
ng
-

W
el
d
i
ng of
reinforcing

steel,

Part

2
:

N
on
l
o
a
d
-
b
eari
ng
wel
d
e
d jo
i
n
ts


ELOT EN IS
O 13916 (1997): Welding
-

Guideline for
measuring preheat temperature, temperature between
Also, this Regulation integrates provisions of other relevant
regulatory texts through references to dated or non
-
dated
iss
ues, which are placed in the appropriate places in the text.

For the cases of dated issues, the later amendments or
revisions of those will only apply if they are added to the
present Regulation through amendment or revision of same.
For references in non
-
dated issues, the latest issue of the
referred publication will apply (including amendments).

TRS 2007 Draft for Public Scrutiny

Chapter 1:
GENERAL

2

layers, and temperature for maintaining preheating.



EN 1990: Basis of Design (Eurocode 0)



EN 1992
-
1
-
1 (2005): Design of Concrete structures
-

Part 1
-
1: General R
ules and Regulations for buildings
(Eurocode 2)



EN 1992
-
1
-
2 (2005): Design of Concrete structures
-

Part
1
-
2: General Rules: Structural Design Against Fire
(Eurocode 2)



EN 1993
-
1
-
10 (2005): Design of Steel Structures
-

Part
1
-
10: Resistance to brittle
fracture through thickness
properties (Eurocode 3)



EN 1998
-
1 (2005): Design of Structures for Earthquake
Resistance


Part 1: General Rules, Seismic Actions
and Rules for Buildings (Eurocode 8)



Hellenic Regulation on Reinforced Concrete

(EKOS)



Technolo
gy Regulation on Concrete (KTS)



Hellenic Earthquake Regulation (EAK)



ISO 3898 (1997): Bases for design of structures
-

Notations
-

General symbols



ISO 1000 (1992): SI Units



DIN 488 (09
/
1984)
:

Reinforcement

s
t
eel



DIN 50905
-

Par
t
3 (1987)
:

C
orros
i
o
n of
m
etal
s
;

corros
i
on
te
s
ti
ng
;

corros
i
on charac
t
er
i
s
tic
s under non
-
un
i
for
m

and
l
oca
lise
d corros
i
on a
tt
ack w
it
hou
t

m
echan
i
ca
l

s
t
ress


For the other types of reinforcement steel, the provisions of
the present Regulation will be adapted and completed in the
future with respective individual Regu
lations.


Indicatively, the following types of reinforcement
steel are not part of this Regulation:



Bars or pre
-
stressed tendons for pre
-
stressed
elements (see Appendix A8).



Structural steel used for compound elements.


The directives of this Regulati
on can be used as a basis for
designing and constructing projects under special conditions
(e.g. extremely high or low temperatures, extremely
corrosive environment etc) or using special steel (e.g.
stainless steel, steel with special surface treatment), u
nder
the condition that the directives will be amended or
completed appropriately in order to take into consideration
the special certifications and requirements.



1.3

Objective


The requirements regarding quality, strength and other
properties of steel
, as well as toughness and fire resistance of
structures are associated with designing projects from
reinforced concrete.



The objective of this Regulation is to specify the
requirements, which must be met by concrete
reinforcement steel that concern the
design and
construction of technical projects made of concrete.

The requirements associated with projects constructed using
steel reinforced concrete concern the production of steel, its
mechanical and other properties, its transportation,
placement, as
well as testing and delivery of the
reinforcement steel.



In order to be thorough, references to types of steel that are
not subject to the objective of the present Regulation such as
steel of older standards (S
t
I, S
t
III,

S220,

S400,

S500,

S400s,

S500s e
tc) as well as special steel (e.g. stainless etc),
are made for the most part in the Appendices.

The current Regulation refers to weldable concrete
reinforcement steels, B500A and B500C according to
ELOT EN 10080, ELOT 1421
-
2, and ELOT 1421
-
3.

TRS 2007 Draft for Public Scrutiny

Chapter 1:
GENERAL

3



1.4 Symb
ols

Table S1
-
1 lists the correlation between the symbols used in
this Regulation and the symbols that are used in ELOT
Standards EN 10080, 1421
-
2 and 1421
-
3, which notably do
not conform to ELOT 656 and ISO 3898 standards.


The symbols used in the present

Regulation are
pursuant to the ELOT EN 656 and ISO 3898
standards. The most commonly used symbols are
listed in Table 1
-
1.

Table S1
-
1

Correlation between the symbols of the present
Regulation with the ELOT EN 10080 standard.



Table 1
-
1

Symbols


Descrip
tion

Present
Regulation


ELOT EN

10080

Steel Yield strength

f
y

R
e

Conventional Yield strength
for 0.2% Permanent
Deformation

f
0.2

R
p0.2

Tensile Strength of Steel

f
t

R
m

Total Strain at Maximum Load

ε
u

A
gt



Symbol


Meaning

Α

Nominal Cross
-
s
ection

Α
act

Actual Cross
-
section

α

Gradient angle of Transverse
rib

α
R

Rib Projection Reduced
Surface

β

Gradient Angle of Transverse
Rib as to the Longitudinal
Axis

b

Width of Transverse Rib

c

Spacing between Transverse
Ribs

C
eq

Carbon equiva
lent

Χ
k

Characteristic Value of size X

d (or Φ)

Nominal Diameter

ε
u

Total Strain (elongation)
under maximum load

ε
5

Strain after fracture, measure
in length 5d at the Neck Area
(according to Standards ELOT
959 and ELOT 971)

Ε

Young’s Modulus

h

H
eight of transverse ribs at tip

f
t

Tensile Strength of Steel

f
y


Yield strength of Steel

f
0,2

Conventional Yield strength
for Remaining Deformation

res
=0.2%)

f
y,act

Actual Yield strength of Steel

f
y,nom

Nominal Yield strength of
Steel

F
s

Shea
r Force

S
f

Shear Factor

Τ

Temperature





1.5

Units


In the present Regulation, the following units are used:



kN, kN
/
m

and

kN
/
m
2

for forces and loads



MPa

(
=

M
N
/
m
2

=

N/
mm
2
) for tension and strength



kg
/
m
3

for density



kN
/
m
3

for special or appa
rent weight.


See respective manual by ELOT:

“SI
: The International
system of Units” /1999



The units used are based on the SI International System of
Units, and are in accordance to Presidential Decree 515/83
and standards ELOT 656 and ISO 1000.



1.6

D
efinitions



Iron (pure).
Pure iron is defined as an alloy with a content
of carbon and other alloy elements of less than 0.05%.


TRS 2007 Draft for Public Scrutiny

Chapter 1:
GENERAL

4

Steel:

Iron
-

Carbon (Fe
-

C) alloy with a carbon content up
to 2% and addition of other elements.

Reinforcement Steel:
Stee
l with circular or actual circular
cross
-
section for concrete reinforcement.

Reinforcement steel with ribs:

Reinforcement steel with at
least two rows of transverse surface ribs uniformly
distributed along its length.


Smooth Reinforcement steel:

Reinforc
ement steel with a
smooth surface.


Reinforcement steel with embossed grooves:
Reinforcement steel with specific grooves, uniformly
distributed along its length.


Profiles (Structural Steel):

Construction steel with different
cross
-
sections.


Drawing:
Cold

treatment of a steel bar or wire, which is
drawn through the appropriate mould, resulting in the
reduction of its diameter and subsequent increase in
strength.


Rolling:

Formation procedure that is done in heat or in cold
of a metal object with the use of

counter
-
torque rotating
cylinders.


Control batch:
Quantity of concrete Reinforcement steel of
the same cross
-
section, originating from the same cast, in
straight bar or coils that have been produced from the same
production plant and are provided for ins
pection at any time.


Nominal diameters:
Standardised diameters for concrete
reinforcement steel accepted by the present Regulation.


Structural design is based on the nominal diameter and the
nominal cross
-
section.


The actual cross
-
section is used to te
st the strain tolerances
of the nominal cross
-
section. The other compliance tests are
based on the nominal cross
-
section. The actual cross
-
section
is calculated based on a bar section with a length of l and
mass m and density d, of the steel in question, a
ccording to
the ratio:

Α
ac
t
=127.4
m
/
l


Nominal cross
-
section:

The surface area of the entire circular
cross
-
section with a diameter equal to the nominal diameter.


Actual cross
-
section:
The surface area of the hypothetical
circular cross
-
section with an equ
al length and weight with
the given sample.


Nominal mass:

Mass per unit length, measured by the
nominal cross
-
section and density of steel (which is
considered equal to 7850 kg/m
3
).


where
:

Α
act

the actual cross
-
section in
mm
2

m

mass in

g

l

length in
mm.


The actual diameter is calculated according to the actual
cross
-
section.

In the event of ribbed steel, the direct
measurement with a calliper is not precise.




The reduced surface projection area of the reinforcement
steel bars’ ribs:

The ratio of the
sum of the surface areas of
the projections of all the ribs on a vertical level on the bar’s
longitudinal axis as to the length of the bar on its nominal
circumference which is specified by the nominal diameter
(see fig. 3
-
4).


For resistance units, the t
ypical value that is taken is usually
the percentile p=95% (or 90%), whereas for force units, the
percentile p=5% (or 10%).

The lower end of the single
-
sided
confidence interval is specified as probability “a”.

According
to the present Regulation the value

of probability “a” is equal
Typical magnitude value:
The magnitude value, give or
take, from which percentage p of all values is expected to be
calculated during a hypothetical control with unlimited
samples.

In the context of the present Regulat
ion, the typical
value is defined as the value above which there is a
TRS 2007 Draft for Public Scrutiny

Chapter 1:
GENERAL

5

to 90%.


possibility “a” to find a percentage q of the values.
=
=
The minimum value is applied to the compliance criteria for
units that are referred to with a typical value.


Minimum value:

Value

under which no testing result should
be found.

The maximum value is applied to the compliance criteria for
units that are referred to with a typical value.


Maximum value:

Value over which no testing result should
be found.



Conventional yield strength
:
The stress that corresponds to
permanent deformation after unloading, equal to ε
re
s
=0.2%.



Tensile strength:
Tension at maximum load.


Ductility is a material property, whereas plasticity is a
structural property of reinforced concrete. Steel ductilit
y is
one of the requirements for a reinforced concrete structure to
have plasticity.


Ductility:
In context to the present Regulation, the term is
used to express the ratio of the area of plastic deformation as
to the area of elastic deformation of a reinf
orcement steel bar
that is tested for tensile strength. Usually measured as the
ratio of strain at maximum load as to the yield strain.


In the English language ductility and plasticity have the same
meaning.

In many occasions, instead of the term ductil
ity the
term plasticity is mistakenly used for reinforcement steel.


Plasticity:

The ability of a body or a cross
-
section or area of
an element made from reinforced concrete to respond to
major elastic deformation without significant reduction in its
load
bearing properties.


Thermal transition is defined in different regulatory texts as:




The curve point on the fracture work


temperature
curve.




The temperature at which the impact surface appears
brittle at a certain percentage (usually 50%).




The
temperature at which the impact force has a certain
value (e.g. 27J).


Transition temperature:
The temperature at which
significant change is observed in the fracture characteristics
of a material, with the main change being its conversion
from ductile to
brittle.



Chemical deterioration:

Change of the chemical
composition of a section of a material.


Corrosion:

Any spontaneous, induced, electrochemical in
nature, chemical or mechanical, deterioration of the metal or
alloy surface, which leads to a loss o
f material and other
consequences.



Uniform corrosion:

The corrosion during which the
surface of the metal or alloy is covered by a uniform layer
of corrosion or an almost uniform dissolution of the surface.



Pitting corrosion:
Corrosion during which a

corrosion
product is formed selectively and locally, on the surface of
the metal or alloy, or the metal or alloy is selectively and
locally dissolved.



pH:

The logarithm of the reciprocal of hydrogen
-
ion
concen
tration (Η
+
).


The meshes that are mentioned in the present Regulation are
welded. For simplicity’s sake, hereinafter the term “mesh”
will be used instead of “welded mesh”.
=
=
Welded mesh or plain mesh:

Flat sheet consisting of
longitudinal and vertical cro
ssing bars at right angles, of the
same or different technical category, with the same or
different diameter, and which have been welded at the plant
at all the nodal points by automated machines. In general,
meshes are produced in rectangular sheets of di
fferent sizes.
They are distinguished between structural (standardised and
non standardised), and special type meshes.

TRS 2007 Draft for Public Scrutiny

Chapter 1:
GENERAL

6



Structural mesh:
Mesh with two directions of strength of
which the longitudinal and vertical bars are of the same
technical category w
ith a specific ratio of diameters and
specific distance between bars in both directions.



Standardised structural mesh:
Structural mesh which is
manufactured according to specific physical characteristics,
and is available in stock.



Non
-
Standardised s
tructural mesh:
Structural mesh
which is manufactured with special physical characteristics,
which have been agreed between the manufacturer and the
user.


These meshes are used either in their original form or (more
commonly) after bending and shaping th
em as shear and/or
tightening reinforcement steel.

In the second case they are
also known as “jackets” or beam or column meshes.
=
=
Special type mesh:

Mesh which is built according to the
properties that have been requested by the user. It is usually
a mesh
with a single direction of strength that uses B500C
grade bars for the primary direction and bars from welded
steel for the secondary direction, which are useful only for
holding the bars in the main direction.



Lattice girder:
Two
-
dimensional or three
-
d
imensional
metal configuration that has one upper footing, one or more
lower footings and continuous or non
-
continuous transverse
bars that are welded to the meshes. The transverse meshes
may be connected with the lower footings and mechanical
joints.



S
tandardised mesh:

The mesh, which is manufactured
according to specific technical delivery terms and is
available in stock.


Non
-
standardised mesh:

Mesh manufactured with physical
characteristics and properties that have been specified by the
user.


Shear
factor

(cruciform weld):

The ratio of the force that
causes shear fracture of the weld as to the force that
corresponds to the nominal yield strength of the bar that
receives the load (f
y
,nom
x A).


Natural aging:
Changes in mechanical properties of
concr
ete reinforcement steel that occur at a slow rate in
ambient temperatures, and faster at higher temperatures.

These changes lead to increased yield strength values and at
a smaller extent to tensile strength, as well as to a reduction
in fracture deformati
on. Cold worked steels are sensitive to
aging.


According to ELOT Standards EN 10080, for certain types of
steel (e.g. cold worked, coils etc) artificial aging precedes
testing their mechanical properties.

Artificial aging of concrete reinforcing steel:
P
rocedure
simulating the effects of natural aging, which is done by
heating (usually at 100
ο
C for 60
m
i
n).



Phase:
Structurally distinguished area in a material system
The characteristics and properties of the material in its
interior and up to the limits of its areas are not altered under
normal conditions.



Chapter 2:

CLASSIFICATION OF ST
EEL



2.1 Distinction of Steel



Concrete reinforcement steel is distinguished as follows:



2.1.1

According to the production method as:




Hot rolled, without any additional thermal or thermo
-
mechanical treatment of any type (non
-
tempered
steels).

Hot roll
ed tempered steel, also known as Tempcore or
Thermex have been available almost exclusively since the mid
-
90s.




Hot rolled, followed by an immediate subsequent
thermal treatment (tempered steel).

These types of steel, depending on the production method,

may
have:



Different behaviour under extreme temperatures (see Par.
3.6)



Different type of stress
-

strain diagrams (see Figure C3
-
1a
and C3
-
1b of paragraph 3.2.1.)



Different yield strength in compression compared to
tension.



Different ductility.

C
old working is applied after increasing steel strength (due to
the applied hardening). Cold worked steel may have a
significant decrease in its ductility (due to aging effects), as
well as reduced strength following exposure to high
temperatures, for examp
le after a fire or welding (see also Par.
3.6). Cold worked steel by torsion of the original product is not
produced any more.


As a rule of thumb, one cannot distinguish cold from hot rolled
steel just by looking at them macroscopically (laboratory
testin
g is required).




Cold treated with drawing or rolling of the original
product that comes from hot rolling (cold drawn
steel) or with torsion of the original product that
comes from hot rolling (cold treatment steel by
torsion) or by combining both of the

above.



Steel without ribs are not covered by Standards ELOT 1421
-
2
and ELOT 1421
-
3 and are not the objective of this Regulation.


2.1.2

According to surface form as:




Smooth steels with circular cross
-
section.





Steels with high adhesion embossed
ribs.


Steels with indentations are not the objective of this Regulation
and their use is not allowed by EKOS.




Bars with indentations (embossed grooves).



B500A class steel according to ELOT 1421
-
2 is classified as
low ductility steel and it is allow
ed to be used only for the
production of standardised structural meshes and lattice girders
up to a diameter of F8.


2.1.3
According to ductility as:




Low ductility steels.


The ELOT standards 1421
-
2 1421
-
3 as well as decision No.
9529/645 (Government G
azette 649/B/24
-
5
-
06) of the Minister
of Development do not specify normal ductility steels.




Normal ductility steels.


B500C steels according to ELOT 1421
-
3, are classified as high
ductility steels, which meet the extended requirements for
earthquake r
esistant behaviour of structures as provided for by
EKOS and Eurocodes.




High ductility steels.


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Chapter 2:

CLASSIFICATION OF ST
EEL

8


See also Par. 3.5.

The use of weldable (under certain conditions) steels is not
allowed. However, in Par. 8.6 and Appendix A7 there is
reference to these s
teels used almost exclusively in
construction until the mid 1990s and which are seen in
evaluations and modifications of existing structures.
Bibliography refers to these types of steels as non
-
weldable.
However, considering that non weldable steels (depen
ding on
their chemical composition as stated in Par 8.6) under certain
conditions may be actually welded, therefore the term
“weldable under conditions” has replaced the term “non
weldable.”
=
=
2.1.4
According to weldability as:




Weldable steels




Non
-
wel
dable steels or weldable under conditions.



2.1.5

According to their corrosion resistance, as:




Common steels that are iron
-
carbon (Fe
-
C) alloys
including other alloy elements in small contents.


Stainless steel is not an objective of this Regulation.

However,
their use may be deemed necessary in the event of special
projects or projects in extremely corrosive environments.

Appendix A3 mentions special categories of stainless steel,
which could be used under the conditions stated therein.




Stainless
steels, which are iron alloys with minimum
content in Chromium (Cr) at 12%.

These steels are
corrosion resistant. Their toughness in a corrosive
environment is greater if they contain alloy elements
such as Nickel (Ni), Molybdenum (Mo), Titanium (Ti)
etc.



2.2

Technical Categories of Steel Grades
.




Weldable steels are part of this Regulation and are
distinguished in the following technical categories:

For both these classes of steel, the nominal (typical) yield
strength value f
y
,nom

is 500 MPa.




Β
5
00Α according to ELOT 1421
-
2



Β
500C according to ELOT 1421
-
3



2.3

Shapes of Steel


Concrete reinforcement steel is delivered in the following
shapes:



Straight bars



Coils



Straightened products

The following products are marketed in Greece:



Struc
tural meshes (two directions of strength) that meet the
technical properties and requirements of standards ELOT
EN 10080, ELOT 1421
-
2 and ELOT 1421
-
3. As to their
physical characteristics (e.g. geometry, sheet dimension
etc) they are distinguished between
standardised and non
-
standardised.




Special types of meshes (single direction of strength) that
are intended mainly for bending or curving (jackets, cages
etc).

The bars of the main direction of these meshes must
meet the requirements of standards ELOT E
N 10080 and
ELOT 1421
-
3 and the present Regulation.


Special provisions and recommendations for the meshes that
are mentioned in Chapter 9.






Meshes (also see Chapter 9).

Lattice girders are not wide spread in the Greek market.

Their
requirements that
are stated in standards ELOT EN 10080,
ELOT 1421
-
2 and ELOT 1421
-
3.




Lattice girders.


2.4

Marking for Identifying Concrete
TRS 2007 Draft for Public Scrutiny
Chapter 2:

CLASSIFICATION OF ST
EEL

9

Reinforcement Steels



2.4.1

Marking for identifying quality grades



The marking for identifying the quality by a grade of
concrete rei
nforcement steel is done with a different
configuration of the transverse ribs on the surface of the
bar.


According to ELOT 1421
-
2.


B500A grade steels have at least two rows of transverse
consecutive ribs on their surface in the same direction
and paral
lel to one another as seen in Fig. 2
-
1.





Figure 2
-
1

Rib configuration of B500A grade steel


According to ELOT 1421
-
3.


B500C grade steels have on their surface two rows of
transverse consecutive ribs at opposite directions. In each
row, the consecuti
ve ribs have alternating angle of gradient
as to the longitudinal axis of the bar as seen in Fig. 2
-
2.






Figure 2
-
2

Rib configuration of B500C grade
steel


Appendix A7 of the present Regulation refers to the most
common markings for different quality

classifications, which
were used in Greece until February 2007.




2.4.2

Marking for identifying the
production country and plant


ELOT standard 10080 provides more forms of this numeric
marking system.


Greek industries, also use an additional recognit
ion symbol for
the manufacturer apart from the mandatory marking system
that is described.


Identifying the country and the production plant of the
concrete reinforcement steel is usually done through a
numerical system of straight
-
transverse ribs between
thicker transverse ribs that are repeated (per 1.0m to
1.5m approximately) on one row of the bar’s transverse
ribs.



Two consecutive reinforced transverse ribs are the
symbols indicating the beginning of the marking, as well
as the reading direction (fie
ld A, see Fig. 2
-
3).


See Standard ELOT EN 10080.


The country of production is written after the beginning
of the marking (field B, see Fig 2
-
3).

The number of ribs
indicating the country of origin (country code) is listed in
Table 2
-
1.


For countries w
ith the same code (field B), the production
plants must have a different code number (field C).

The production plant markings follow (field C, see Fig 2
-
3), which is done with normal transverse ribs placed
TRS 2007 Draft for Public Scrutiny
Chapter 2:

CLASSIFICATION OF ST
EEL

10


Appendix A7 of the present Regulation refers to the code
numbers of Greek industries as well as of foreign production
plants whose products have been imported
in Greece from time
to time.


between the thicker ones.

If the production plant number
has two
-
digits (10 and multiples of 10 are not allowed)
the
n it is symbolised with two groups of transverse ribs
between the thicker ones, of which the first group gives
the first digit and the second group the second digit of
the product plant code, as shown in Fig. 2
-
3 and 2
-
4.



Table 2
-
1

Marking the productio
n country (field B)
according to ELOT EN 10080


Country

Country
Code

Austria, Germany,
Poland, Slovakia, Czech
Republic

1

Belgium, Switzerland,
Luxemburg, Netherlands

2

France, Hungary

3

Italy, Malta, Slovenia

4

United Kingdom,
Ireland, Iceland

5

Denmark, Estonia,
Belarus, Lithuania,
Norway, Sweden,
Finland

6

Portugal, Spain

7

Greece, Cyprus

8

Other countries

9



A. Start

B. No for


C. No of manufacturer/


country: 3


factory: 7


Figure 2
-
3

Marking example for identifying production
plant an
d country of B500A grade steel.





A. Start

B. No for


C. No of manufacturer/



country:
2


factory: 10+4 = 14


Figure 2
-
4

Marking example for identifying production and
country of B500C grade steel.



2.4.3

Marking for identifying coil products


The ELOT EN 10080 standard provides additional forms of
marking for recognising products and coils.


In the case that the reinforcement steel is in coil form, then
the same marking is applied, as described above, with the
addition of a symbol for identify
ing product form. This
symbol is an additional, thicker transverse rib at the
beginning of the marking (field A of Fig. 2
-
5 and 2.6).




TRS 2007 Draft for Public Scrutiny
Chapter 2:

CLASSIFICATION OF ST
EEL

11

A. Start

B. No for


C. No of manufacturer/


country: 2


factory: 7


Figure 2
-
5

Marking example for identifying B500A
steel
originating from a coil





A. Start

B. No for


C. No of manufacturer/


country: 2


factory: 10+4 = 14


Figure 2
-
6

Marking example for identifying B500C steel
originating from a coil



For coils that are sent for further processing
(manufacturing
of structural meshes etc) the productions
plant’s marking refers to the manufacturer who gave the
product its final mechanical properties.


This case concerns aligned bars, meshes of all types, lattice
girders as well as other shaped products (e.g. jacket
s, cages,
stirrups etc).


Products originating from processing must have a tag,
firmly fixed for identifying the company that gave them
their final shape.



2.5

Traceability



The production country, the production and/or processing
plant, the quality g
rade, the product's shape and the cast
number must be recognisable and traceable for all delivered
and transported batches of concrete reinforcement steel.


See also Par. 5.6.

The producer must have a procedure that meets this
requirement regarding the pr
oducts it manufactures.





Chapter 3:

CHARACTERISTICS OF STEEL



3.1

Geometric Characteristics



3.1.1

Nominal Values


According to standards ELOT 1421
-
2 and ELOT 1421
-
3.


The nominal diameters are listed in Table 3
-
1.

T
he same
table also lists the fie
ld of application as well as the
nominal cross
-
section, the nominal mass, and the
tolerances as to the nominal mass for each nominal
diameter.


Table 3
-
1

Nominal diameters, nominal cross
-
sections, nominal mass and tolerances as to nominal mass
-

Field of a
pplication


Nominal
Diameter
(mm)

Field of application

Nominal
diameter
(mm2)

Nominal
mass/ metre
(kg/m)

Mass
Tolerances
/ metre
(%)

Bars

Coils and
straitened
products

Welded meshes
and lattice girders

B500C

B500Α

B500C

B500Α

B500C

5.0


X


X


19.6

0.154

±6

5.5


X


X


23.8

0.187

±6

6.0

X

X

X

X

X

28.3

0.222

±6

6.5


X


X


33.2

0.260

±6

7.0


X


X


38.5

0.302

±6

7.5


X


X


44.2

0.347

±6

8.0

X

X

X

X

X

50.3

0.39
5

±6

10.0

X


X


X

78.5

0.617

±4.5

12.0

X


X


X

113

0.888

±4.5

14.0

X


X


X

154

1.21

±4.5

16.0

X


X


X

201

1.58

±4.5

18.0

X





254

2.00

±4.5

20.0

X





314

2.47

±4.5

22.0

X





380

2.98

±4.5

25.0

X





491

3.85

±4.5

28.0

X





616

4.83

±4.5

32.0

X





804

6.31

±4.5

40.0

X





1257

9.86

±4.5



B500A grade coils are exclusively intended for the
manufacturing of meshes and lattice girders.




The bar length, coil weight and relevant

tolerances will be
agreed upon between the buyer and the manufacturer as
specified by standard ELOT EN 10080, Paragraph 7.3.3.
and 7.3.4.


For non
-
standardised meshes as well as special type meshes,
the requirements and relevant tolerances will be agreed

upon
between the buyer and the supplier (see Chapter 9).

The dimension requirements and tolerances of standardised
structural meshes are specified by Standard ELOT EN
10080, Paragraph 7.3.5, and Chapter 9 of the present
TRS 2007 Draft for Public Scrutiny
Chapter 3:

CHARACTERISTICS OF STEEL

13


Regulation.


Similarly, for non
-
s
tandardised meshes, the requirements and
relevant tolerances will be agreed between the buyer and
supplier.


For standardised meshes, the dimension requirements and
tolerances must comply with Standard ELOT EN 10080,
Paragraph 7.3.6.



3.1.2

Surface Geometry


Adhesion
Requirements


Steels with ribs are characterised by their surface
geometry, which dictates their adhesion to the concrete.


The geometric features of the ribs are specified in standards
ELOT 10080, 1421
-
2 and 1421
-
3. The measurement of these
feat
ures and the calculation of the reduced projection surface
α
R
, of the ribs is done according to Standard ELOT EN ISO
15630
-
1.


The geometric characteristics must meet the requirements
of Paragraph 3.1.2.1.

In particular, if one of the characteristics: dist
ance of ribs
'c', angle of gradient of ribs ‘b’ and rib height 'h', does not
meet the requirements, then the ribs’ reduced surface
projection,
α
R
, must be calculated and must meet the
values of table 3
-
2 (see Paragraph 3.1.2.2).



3.1.2.1 Individual geome
tric characteristics of ribs



Concrete reinforcement steels with ribs have at least two
rows of parallel transverse ribs uniformly distributed on
each side of the product’s surface and at equal distance
throughout both rows. Longitudinal ribs may be adde
d, but
are not mandatory.


The transverse ribs resemble the shape of a crescent and
they smoothly merge into the core of the product
.


The projection of the transverse ribs extends on the
vertical level of the longitudinal axis of the bar at least
75% over

the circumference of the bar, which is calculated
from the nominal diameter d (see Fig 3
-
1).






Figure 3
-
1

Cross
-
section of bar



Τhe transverse rib flank inclination ‘a’ should be equal to
or over 45o, and must be radiused at the transition between

the rib flank the core of the bar (see Fig. 3
-
2).


75
.
0
2
1


d
s
s


TRS 2007 Draft for Public Scrutiny
Chapter 3:

CHARACTERISTICS OF STEEL

14



[key:
τ
ο
µ
ή

A
-
A = section A
-
A]


Figure 3
-
2

Angle of gradient ‘a,’ height 'h,' and
睩摴栠wbD映瑲a湳癥牳e⁲楢
=
=
=
The angles of pitch ‘b’ of the transverse ribs relating to the
shaft of the bar should b
e between 35
ο

to 75
ο

(see Fig 3
-
3).





B500A steel



B500C steel


Figure 3
-
3

The angles of gradient ‘B’ and distance ‘c’ of
the transverse ribs (for section A
-
A see fig. 3
-
2)


The width b, the side ribs will be approximately 0.1 d (see
figure 3
-
2).


Th
e height ‘h’ of the transverse ribs at the tip will be from
0.03 d to 0.15 d and spacing ‘c’ will be from 0.4d to 1.2d
(see Fig. 3
-
2 and 3
-
3).



Provided that the longitudinal ribs do exist, their height
should not exceed 0.15d.



3.1.2.2

Reduced project
ion surface



When the calculation of the ribs’ reduced projection
surface is requested
α
R
, (see Paragraph 3.1.2), then the
value should be greater than the value given in Table 3
-
2



Table 3
-
2

Minimum value of the ribs' reduced
projection surface
α
R


Nominal
Diameter

(mm)

5
-

6

6.5
-

8

10


12

α
R,min

0.039

0.045

0.052

0.056




The
calculation of the ribs’ reduced projection surface will
be done according to the following equation (see also Fig.
3
-
4):

TRS 2007 Draft for Public Scrutiny
Chapter 3:

CHARACTERISTICS OF STEEL

15




where:



is the surface of the rib’s longitudinal section


hs

is the average height of each

section with a length
Δ1 of a transverse rib which has been divided in p parts

(l
R
=p∆l)

β

is the ribs' angle of gradient as to the bar’s axis.

d

is the bar’s nominal diameter

c

is the distance between the ribs

k

is the number of series of transverse ribs

m

is the number of rib angles in a row

n, j, i, are the summation variables.




[Key: Καμπόλη μήκους 1r =
Arc length 1r

τοµή A
-
A = section A
-
A
]

Figure 3
-
4

Determination of the ribs' reduced pro
jection
surface
α
R


The mechanical properties of concrete reinforcement steel are
specified in standards ELOT EN 10080, ELOT 1421
-
2 and
ELOT 1421
-
3, whereas their specifications are given according
to ELOT EN ISO 15630
-
1 and ELOT EN ISO 15630
-
2.


3.2

Mechanical Properties



3.2.1

Tensile Properties


The tensile strength limits that the mechanical properties
of concrete reinforcement steel must meet are given in
Table 3
-
3.


In Figure C3
-
1a a typical stress
-

strain diagram under tension
is given for concret
e reinforcement steel class B500C.


The values of yield strength f
y
, listed in Table 3
-
3 are
typical for 95% of cases. The values of total strain under
maximum load,

ε
u
, for ratio f
t
/
f
y

and ratio f
y
,
ac
t
/
f
y
,nom

listed
TRS 2007 Draft for Public Scrutiny
Chapter 3:

CHARACTERISTICS OF STEEL

16

in table 3
-
3 are typical for 90% of cases.



The values f
y

and
f
t

are calculated according to the nominal
cross
-
section.


The lack of obvious yield strength (see Figure C3
-
1b) is
usually due to:

-

cold d
eformation

-

details of chemical composition etc.


When there is no distinctive yield strength limit, the
conventional yield strength limit f
0.2

will be determined.


Property

Technical Quality Grade

Β500Α

Β500C

Yield strength,
f
y

(
M
Pa)

≥500

≥500

Rat
io of the actual to
the nominal value of
yield strength
f
y,act
/f
y,nom

_

≤1.25
=
Ratio of tensile to
yield strength f
t
/f
y

≥1.05
(≥1.03
for d<6mm)

≥1.15 ≤1.35

Total Strain
(elongation) under
maximum load ε
u
(%)

≥2.5
(≥2 for
d<6mm)

≥7.5


The total strain
at maximum load
ε
u

and the strain after
fracture
ε
5
, (according to the revoked standards ELOT 959
and ELOT 971), are measured at different points on the
sample and do not constitute comparable units.



Table 3
-
3
The tensile strength limits of the mechanica
l
properties of steel according to ELOT 1421
-
2 and ELOT
1421
-
3 (Typical values)



Subnote

ε
u,pl
: plastic deformation under maximum load

ε
u
: total deformation under maximum load

ε
u,el
: elastic deformation with respect to maximum load


Figure C3
-
1a

Typic
al stress


strain diagram for steel Case of
visible yield strength.



TRS 2007 Draft for Public Scrutiny
Chapter 3:

CHARACTERISTICS OF STEEL

17



Figure C3
-
1b

Specifying the yield strength of steel.

Case of non
-
visible yield strength.




3.2.2

Shear Strength


However, according to Eurocode EN 1992
-
1
-
1/2005 the shear
factor
for structural meshes is specified at 0.30. Moreover, and
according to EKOS (Par. 3.1.5) in order for a transverse
welded bar to be calculated in the anchoring length, then the
shear factor must be at least 0.30 (Par. 9.4).


For structural meshes, Standard

ELOT EN 10080 specifies
that the welding points of the crossing bars should bear a
force equal to a shear factor of at least 0.25. For other types
of meshes, special requirements are given in Chapter 9.



Paragraph 7.2.4.2 of Standard ELOT EN 10080 is ap
plied
for meshes.



3.2.3

Bending Strength


Concrete reinforcement steel must meet the requirements
of Paragraph 7.2.6.2 of Standard ELOT EN 10080, when
submitted to buckling test.



3.2.4

Fatigue Behaviour


More data on fatigue are given in Appendix A1
0.


In general, according to Standards ELOT EN 10080 and
ELOT 1421
-
3, concrete reinforcement steel should
withstand a specific number of cycles of repeated axial
tensile strain with tension ranging form
σ
m
i
n

to

σ
m
a
x
,
sinusoidal alternating with a fluctuati
on range of

:

2
σ
A

=
σ
m
ax

-
σ
m
i
n


Fatigue testing in not carried out on B500A grade steels.


Fatigue testing is applied to B500C grade steels.


Eurocode EN 1992
-
1
-
1 specifies a percentage of 90%.


B500C grade concrete reinforcement steel should
withstand f
atigue testing of 2x10
6

loading cycles with the
following characteristics:



Maximum tension
σ
m
a
x
=300
M
Pa.



Range of tension fluctuation 2
σ
Α
=150
M
Pa.



The load variation frequency is less or equal to 200Hz.



The minimum free end length of the sample shoul
d be
14 d and certainly not less than 140 mm.


TRS 2007 Draft for Public Scrutiny
Chapter 3:

CHARACTERISTICS OF STEEL

18


Welded bars and meshes made of B500C grade concrete
reinforcement steel must withstand fatigue testing of 2x10
6

loading cycles with the following characteristics:



Maximum tension
σ
m
a
x
=300
M
Pa



Range of te
nsion fluctuation 2
σ
Α
=100
M
Pa



The load variation frequency is less or equal to 200Hz.



The minimum free end length of the sample should be
14 d
long

and certainly not less than 140 mm, where d
long

is the nominal diameter of the test bar.



The sample must

have a section of transversely welded
bar with a minimum length of 5d
trans
on both sides of
the weld, where

d
trans

is the nominal diameter of the
transversely welded bar.


Figure C3
-
2

Change in stress with respect to time for fatigue
testing




3.3

Phys
ical Properties



The physical properties of light or non
-
alloy steels with
low carbon content, such as concrete reinforcement steel,
are similar to those of pure iron.

The values given below
are for pure iron, except for the cases that explicitly refer
t
o steels and can be used for calculations concerning
concrete reinforcement steel.



Values up to 210 GPa have been measured.


The Young’s modulus E is affected by temperature, and
significantly reduced at high temperatures.
Indicative values are
given in

table C3
-
1
(from

G.E.

Dieter, «Mec
h
a
n
ical Metall
u
r
g

,
McGrawHill,
London, 1988).


a)

Elasticity modulus, E


At a temperature of 20
ο
C the value that is taken is 200 GPa.


Table C3
-
1

Effect of temperature on elastic modulus


Temperature

ο
C

20

204

427

537

649

Ε
, (GPa)

200

186

155

134

124




b)

Elasticity modulus in shear, G, and expansion
modulus, K

The values for shear modulus ra
nge from 76 to 82 Gpa and the
bulk modulus from 160 to 169 Gpa. The elastic modulus in
shear stress is referred also to in bibliography as shear modulus
or slip modulus.


The elasticity modulus in shear is measured at 80 GPa and
the expansion modulus at 16
5 GPa.



c)

Poisson ratio, ν


Values from 0.27 to 0.33 have been stated for the Poisson ratio
with an average of 0.30 as the most acceptable for practical
applications.

For practical applications, a value of 0.30 can be used.



d) Iron phases and Curie temperatu
re


R.E. Reed
-
Hill, "Physical M
e
tallurgy Principles", 2n
d

Ed.,
D.
Van Nos
t
rand, New York, 1973,

page

454.


The phases of pure iron with respect to temperature are
given in Table 3
-
4.


For steel phases see Appendix A1.


Temperature Curie i.e. the temperat
ure after which iron
looses its magnetic properties, ranges between 755°C and

791°C, and is more typical at 769°
C.


Tension

2
σ
Α

Period T

Time

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CHARACTERISTICS OF STEEL

19


Temperature
region

Status

Phase

Symbol

Over boiling
point

gas

gas

g

Melting Point


Boiling Point

liquid

liquid

l

1400
ο
C
-
Melting
Point

Solid

Body centred
cubic

δ
=
910
ο
C
-
1400
ο
C

Solid

Face centred
cubic

γ
=
Below 910
ο
C

Solid

Body centred
cubic

α


Melting Point ranges between 1536 and 1539°C and Boiling
Point from 2740 to 2860 °C.


Table 3
-
4

Phases of pure iron



e)

Othe
r properties


In reality, steel density changes slightly depending on
chemical composition and treatment.


For the calculations, steel density will be considered equal
to 7850kg
/
m
3
.


Table C3
-
2 lists the specific heat values at different
temperatures.


T
he average value of specific heat between 0°C to 100°C is
456 J kg
-
1
K
-
1


Table C3
-
2 gives precise values for the linear expansion factor
at different temperatures.


Steel’s linear expansion factor between 0°C to 100°C can
be considered for calculations eq
ual to 10 * 10
-
6

°C
-
1
.


Thermal conductivity for pure iron in the temperature region
of 0
-
100°C has an average value of 78.2 W
m
-
1
K
-
1
. Regarding
steel, the thermal conductivity values at different
temperatures are lower (see table C3
-
2) because of its
stru
cture.


Steel’s thermal conductivity at 20°
C can be considered
equal to
51.9 W
/
m
K
for calculations
.


Table C3
-
2 lists the specific resistance of steel at different
temperatures.


Steel’s specific resistance at 20°C ranges from
15.9μ

c
m

to

16.3μ

c
m.


Table C3
-
2
Physical properties of steel in relation to temperature


Temper
ature
°
C

Density
g/cm
3

Specific
Heat


J kg
-
1
K
-
1

Linear
Expansion
Factor

x 10
-
6

C
-
1

Thermal
Conduct
ivity

W

m
-
1
K
-
1

Specific
Resistance
μ

cm


20


7.84
-
7.86

43
5
-
444

12.18

51.9

15.9
-
16.3

100


477
-
494

12.18

51.1

21.9
-
22.6

200


520
-
528

12.66

49.0

29.2
-
29.6

400


599
-
611

13.47

42.7

48.2
-
48.7

600


699
-
754

14.41

35.6

74.2
-
75.8

800


791
-
950

12.64

26.0

109.4
-
110.0

1000


657

13.37

27.2

116.7
-
119.4




f)

Optical pr
operties of steel


Table C3
-
3 lists the grey matter emission capability factor ε,
and the material’s reflectivity R, as a function of wavelength
λ, for non
-
oxidised steel.

It is noted that reinforcement steel,
due to its production method is slightly oxidised (light coat of
iron oxi
de F
e
3
O
4
) and therefore its optical properties are
different from those of table C3
-
3.


Due to average reflectance at all wavelengths, non
-
oxidised steel has a light metallic grey tone.


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CHARACTERISTICS OF STEEL

20

Table C3
-
3

Optical properties of non
-
oxidised steel

λ

(μm)

ε

R (
%
)

1.0

0.41

-

0.6

0.48

58

0.5

0.49

-




3.4

Macroscopic Examination of Steel


There are other preparations that may be used for
chemical reaction. One of the most known is Nital,
which is the product from the solution of 1.5
-
5ml of
1.4mol/l nitric acid i
n 100ml ethyl alcohol.


Steel can be examined macroscopically by grinding and
chemically treating a vertical section on the longitudinal
axis of a bar in order to determine if the bar has been
thermally treated (Hot rolled tempered steel).


After polishin
g a vertical section of the longitudinal axis
of a bar, it is dipped in Nital for approximately 5 to 30
seconds, depending on the type of steel. The distinction
of martensite and its restructuring products (se Appendix
A1) from the remaining metal cast has
, in essence,
remained without paint during the thermal treatment (e.g.
paint according to Tempcore, Thermex etc), can be done
in a very short time and without special means (see
Figure F3
-
3). This can explain the specific mechanical
and physical propertie
s of steel as well as its behaviour
as to corrosion.





Figure C3
-
3

Cross
-
section of a steel bar (tempered)
after being dipped in Nital




3.5

Chemical Properties



3.5.1

General


According to ELOT EN 10020 standard.


Concrete reinforcement steels
belong to the light or non
-
alloy steel group.


In general, for non
-
alloy steel there are no special
requirements for tempering behaviour or purity, with
regard to non
-
ferrous inclusions. The oxides
CaO, M
g
O,
Si
O
2
,

A
l
2
O
3
,

M
nO,

FeO, P
2
O
5
, and the compounds
FeS,
Mn
S are considered non
-
metallic inclusions and are in
essence steel impurities.




The term deoxydation is defined as the reduction of
dissolved/active oxygen in liquid steel.


The production procedure (metallurgic method) and the
type of deoxydation

of the steel is subject to the
manufacturer’s judgement.


Steel’s durability against time is not only affected by its
chemical composition but also from other factors, such
as environmental effects and the presence of remaining
stress that are due to the

production method (cold rolling,
The limitation of Paragraph 3.5.3 regarding chemical
composition guarantee weldability and durability o
ver
time for concrete reinforcement steel.



Martensite

Bai
nite

Ferrite
-

Perlite

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CHARACTERISTICS OF STEEL

21

over
-
hardening due to the great depth of hardening). In
general it can be said that:



Hot rolled steel is tougher than tempered or cold
rolled steel.



The less amounts of impurities present, such as
Sulphur (S), Nitrogen

(N) and Phosphorous (P) the
more durable the steel will become (see Appendix
A1).



The less roughness the surface has, the more durable
the steel is.



3.5.2

Weldability


Weldability is a composite property, which refers to the
ability to weld using existing technology, and is affected
by factors such as:



The metallurgy of the base metal and the welded
meta
l.



Welding methods and techniques.



Joint type



Any thermal treatment before and after welding.



Possibly any other specialised factors.


Weldability is the ability of steel to be welded according to
project requirements so that the arising joint sat
isfies the
design requirements.



Steels are distinguished as to their weldability in the
following categories:


The allowed welding methods and respective joint types
for weldable steel are stated in chapter 8.




Weldable, of which their weldability is

guaranteed by
their chemical composition (see Paragraph 3.5.3)



Weldable under conditions, of which their weldability
can be guaranteed by proper design and is tested with
special tests (see Paragraph 8.6).


In existing structures, the following types o
f steel may
exist:



S500s and S400s concrete reinforcement steel,
which are weldable



S500, S400 and S220 concrete reinforcement steel,
which are weldable under certain conditions



Braided steel, StI and StIII steel.


From the early 1970’s to the mid 19
90’s, S400 steel was
used almost exclusively (see Appendix A7). In
paragraph 8.6 a special reference is made with regard to
the requirements and the welding methods of older and
newer steel.


Concrete reinforcement steels B500A and B500C that are
specified

in Standards ELOT 1421
-
2 ad ELOT 1421
-
3,
respectively, are weldable.



3.5.3

Chemical Composition of Weldable Steels


The role and importance of additional chemical elements
in the behaviour of concrete reinforcement steel is
described in Appendix A1.


According to Standard ELOT EN 10080, steels are
considered weldable when their content in carbon (C),
Sulphur (S), Phosphorus (P), Nitrogen (N), Copper (Cu),
as well as the equivalent value of
C
e
q
, does not exceed the
relevant values listed in Table 3
-
5.


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22


M
n:
Manganese

V: Vanadium

C
r: Chromium

Ni
:
Nickel

M
o:
Molybdenum

C
u: Copper

The equivalent value of
C
e
q
,

is calculated according to the
following equation:


C
e
q
=C+Mn/6+(Cr+M
o
+V)/5+(Ni+C
u
)/15,


where the symbols of the chemical elements indicate the
pe
rcent mass content (% m.) as specified by the chemical
analysis.


Temperature
region

Status

Phase

Symbol

Over boiling
point

gas

gas

g

Melting Point


Boiling Point

liquid

liquid

l

1400
ο
C
-
Melting
Point

Solid

Body centred
cubic

δ
=
910
ο
C
-
1400
ο
C

Solid

Face centred
cubic

γ
=
Below 910
ο
C

Solid

Body centred
cubic

α




Table 3
-
5

Maximum allowed values for chemical
composition (content % m.) according to ELOT EN 10080.


There is an internati
onal debate regarding which
elements bind nitrogen as well as the quantities required
for that to happen. Indicatively, the following elements
are mentioned: Ti,

Zr,

H
f,
V
,

Nb
,

Ta
,

B
,

A
l

and

W
.

Appendix A1 lists the ratios for quantifying such
binding for
which, however, there is no international
agreement. Standard EN 10025 states that the Nitrogen
content may be greater than the maximum value
(0.013%) and that no measurement is required if Al
content is greater than 0.02%.


(1)

Higher nitrogen values are
allowed provided that there are
adequate quantities of elements that can bind it (see
Appendix A1).


(2)

Exceeding the maximum value of carbon by 0.03% per
mass is allowed under the condition that the equivalent
values of carbon are reduced by 0.02% per ma
ss.



3.6

Behaviour in Extreme Temperatures


Exposure to temperatures reaching 500 °C may occur in
the life span of a construction made from reinforced
concrete (e.g. due to fire). Exposure to temperatures
ranging between 500°
-
700°C occurs more rarely. I
f such
a heating occurs then other factors besides temperature
should be evaluated (exposure time, chemical
composition, steel treatment etc.). Temperatures over
700°
C

(
and up to 1,200°
C
) have no practical interest for
constructions made with reinforced co
ncrete, considering
that concrete disintegrates completely at those
temperatures.


Temperatures below 0°C and over 200°C, approximately,
can be considered as extreme temperatures for concrete
reinforcement steels. Changes in the mechanical properties
of st
eels, but also in the concrete and its adhesion to steel
may occur in regions of extreme temperatures. After the
steel returns to ambient temperature, certain changes either
remain, or partially or entirely disappear.


Moreover, it is quite possible that
other phenomena may
appear e.g. creep, stress relaxation, and change in
microstructure of the phase and material components.


The properties that are primarily affected by temperature
changes are yield and tensile strength and deformation.



The behaviour

of steel in extreme temperatures can be
affected by:



Exposure temperature.


Exposure time is considered as the actual time the
structure remained at the temperature in question.




Exposure time.


See Par 3.6.2



The composition or production method.

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23




The changes that occur are examined below:




Due to exposure of steel to low temperatures (Paragraph
3.6.1.)

and




Due to exposure of steel to high temperatures (Paragraph
3.6.2.)


The combined forces (according to EKOS Chapter 6)
that must be exami
ned during the exposure of steel to
extreme temperatures are:



The basic combined forces, e.g. for cases of special
constructions that are exposed for a long period of
time either to extreme temperature (steam electric
plants, heated floors of reactors, e
tc) or to low
temperatures (tanks for liquefied gas, cooling
chambers, regions that have ice for extended periods
of time).



Circumstantial combination of forces such as in the
event of fire.

The behaviour of steel during its exposure to high
temperatures

affects the fire
-
safety of structures and in
particular the users’ ability to exit the building as well as
endangering the safety of fire fighters.


The behaviour of steel after its exposure to extreme
temperatures will be taken into consideration during
structural evaluation and repair or reinforcement after a
fire.


Both cases examine the behaviour of steel during its
exposure to extreme temperatures as well as it behaviour
after it has returned to ambient temperature.



3.6.1

Exposure of steel to low t
emperatures



3.6.1.1

Behaviour of steel during its exposure to low
temperatures


In general there are no reliable quantitative data
regarding the reduction of fracture deformation, as a
measure of estimating fracture or fracture resistance, as a
functio
n of temperature.

Indirectly, this reduction is
related to the transition temperature, which is defined as
the temperature at which the steel’s fracture
characteristics are significantly changed, with most
important one being that fractures become more bri
ttle
than ductile.


During the exposure of steel to low temperatures, its
fracture deformation is reduced (brittleness) whereas no
significant changes in yield and tensile strength are
observed.


According to Eurocode EN 1993
-
1
-
10, the definition of a
duc
tile or brittle fracture is made based on the absorbed
fracture energy in a Charpy impact test, of a standard
sample with a V notch (fracture resistance test). The
fracture energy absorption test depends on the steel’s
temperature (se Figure C3
-
4).
The tra
nsition temperature
(
Τ
27
J
) is defined as
the temperature at which the absorbed
fracture energy
, Α
ν
(
Τ
), becomes less than 27J.



TRS 2007 Draft for Public Scrutiny
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CHARACTERISTICS OF STEEL

24


Figure C 3
-
4

Ratio between the absorbed impact
energy and temperature (1

: low region, 2 transitional
region, 3: high region)
.



For steel made according to previous standards, the
following exceptions are made:



For steel with a carbon content <0.22% (e.g. St I
-

S220) the transition temperature is in general lower than
-
25°
C.

In particular, what applies for B500A steel, also

applies for S500s steel.




For steel with a carbon content of 0.40% (e.g. St III


S4000 and St IV


S500) the transition
temperature is slightly below 0°
C
.


For stainless steel, the transition temperature is below
-
100°
C (see Appendix A3).


In general,
steel’s transition from ductile to brittle fracture
is observed at temperatures below 0°
C
.

In particular for
B500A and B500C grade concrete reinforcement steels,
the transition temperature (
Τ
27
J
) is below
-
30°
C
.


The above transition is irrespective of the

exposure time.



3.6.1.2
Behaviour of steel after its exposure to low
temperatures


This happens because during exposure to low
temperatures, no changes occur to the material's
microstructure (crystals, phases, components).


The changes stated in Parag
raph 3.6.1.1 are withdrawn
after the steel returns to the usual ambient temperatures.



3.6.2

Exposure of steel to high temperatures



3.6.2.1


Behaviour of steel during its exposure to high
temperatures


For cold worked steel, the effect of temperature