www.www.buonovino.com

[inchak at tatasteel.com]

When a structure is subjected to earthquake, it receives severe shock
(impact) loading. The ability of the structure to survive the earthquake
depends entirely on its ability to absorb the energy of the impact. In a
RCC structure steel has to do the work of energy absorption without
fracture. It is well known that the area under the engineering stress -
strain curve represents the energy absorbed by the steel before it
fractures. It is therefore, possible to recommend various stipulations to
suitably 'tailor' the stress - strain curve, so that a high ability to
absorb energy is intrinsically assured.

We at Tata Steel have studied various international specifications to
understand how the stress - strain curve is tailored in different countries
and have synthesised all these specifications to come out with a new
offering named as 'Super Ductile Rebars'.

For the purpose of this note we will compare various features of the stress
- strain curve with those specified in IS:1786 (Fe 415 grade), Euro Norm,
ASTM A706 (Gr 60) and the combined Australia and New Zealand code (Gr 500 N
and NE).

1) YIELD STRENGTH (MPa) Min. which decides the design load
IS 1786(Fe 415) - 415
Euronorm - 450
ASTM A706 (GR 60) - 420
Australia / New Zealand (500 N) - 500
Australia / New Zealand (500 NE) - 500
TATA STEEL Super Ductile Rebars - 415

2) YIELD STRENGTH (MPa) Max. Some, but not all specifications put a cap on
the maximum permissible yield strength. The idea is that the bar should not
unduly resist plastic deformation (yielding) thus allowing excessive stress
to build up in the concrete. The various specifications stand thus:
IS 1786(Fe 415) - NA
Euronorm - NA
ASTM A706 (GR 60) - 540
澳大利亚/新西兰(500 N) - 650
Australia / New Zealand (500 NE) - 600
TATA STEEL Super Ductile Rebars - 500

3) ULTIMATE TENSILE STRENGTH (MPa) Min. This value should be appreciably
higher than the yield strength so that the strength of the bar (and,
therefore, its ability to bear load) continuously increases as it deforms
plastically under gross overload conditions. The values for the various
specifications are indicated below:
IS 1786(Fe 415) - 10% higher than YS
Euronorm - 15% higher than YS
ASTM A706 (GR 60) - 550
Australia / New Zealand (500 N) - 8% higher than YS
Australia / New Zealand (500 NE) - 15% higher than YS
TATA STEEL Super Ductile Rebars - 20% higher than YS

4) ULTIMATE TENSILE STRENGTH (MPa) Max. Same comments as for the YS maximum
- point 2 above.
IS 1786(Fe 415) - NA
Euronorm - 35% higher than YS
ASTM A706 (GR 60) - NA
Australia / New Zealand (500 N) - NA
Australia / New Zealand (500 NE) - 40% higher than YS
TATA STEEL Super Ductile Rebars - 50% higher than YS


5) % ut / YS RATIO (Min.). This is point 3 and 4 expressed in another way.
For a given yield strength level it can be easily visualised that the
higher is the UTS to YS ratio the larger becomes the area under the stress
- strain curve.
IS 1786(Fe 415) - 1.10
Euronorm - 1.15 - 1.35
ASTM, (GR 60) - 1.25
Australia / New Zealand (500 N) - 1.08
Australia / New Zealand (500 NE) - 1.15-1.40
TATA STEEL Super Ductile Rebars - 1.20

6) % ELONGATION (Min.). This is the prime measure of the ductility of steel
and therefore, its ability to absorb energy. This number should be as high
as possible. Some specifications do not mention this because they have more
faith in uniform elongation as discussed in the point 7 below.
IS 1786(Fe 415) - 14.5
Euronorm - 7.5
ASTM A706 (GR 60) - 10 - 12 (depending on size)
Australia / New Zealand (500 N) - NA
Australia / New Zealand (500 NE) - NA
TATA STEEL Super Ductile Rebars - 18%

7) % UNIFORM ELONGATION UPTO MAX. STRESS (Min.). This is an extremely
important measure, which stipulates the elongation that the bar must
demonstrate before it reaches its maximum strength and necking starts. It
can be well appreciated that once the necking starts the steel may elongate
much more. But eventually it WILL break. The position of various
specifications with respect to this parameter is presented below:
IS 1786(Fe 415) - NA
Euronorm - NA
ASTM A706 (GR 60) - NA
Australia / New Zealand (500 N) - 5
Australia / New Zealand (500 NE) - 10
TATA STEEL Super Ductile Rebars - 8

It is well known that sulphur, phosphorous and carbon should be restricted
to make steel tougher. The restriction with respect to these are also
presented below:

% CARBON (Max.)
IS 1786(Fe 415) - 0.30
Euronorm - 0.22
ASTM A706 (GR 60) - 0.30
Australia / New Zealand (500 N) - 0.22
Australia / New Zealand (500 NE) - 0.22
TATA STEEL Super Ductile Rebars - 0.25

% SULPHUR (Max.)
IS 1786(Fe 415) - 0.060
Euronorm - 0.050
ASTM A706 (GR 60) - 0.045
Australia / New Zealand (500 N) - 0.050
Australia / New Zealand (500 NE) - 0.050
TATA STEEL Super Ductile Rebars - 0.040

% PHOSPHORUS (Max.)
IS 1786(Fe 415) - 0.060
Euronorm - 0.050
ASTM A706 (GR 60) - 0.035
Australia / New Zealand (500 N) - 0.050
Australia / New Zealand (500 NE) - 0.050
TATA STEEL Super Ductile Rebars - 0.040

The purpose of this note is to invite opinion from all the experts
participating in this e-conference on this new offering from Tata Steel.


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