PR-2Elevated Temperatures

& High Strength Materials

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Temperature Behaviour

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L = L0 ( 1+α ΔT ) where

α = Coefficient of Expansion = 1 X 10-5 / oC for Steel = 1 X 10-5 / oC for Concrete

ΔT = Difference in Temperature ΔL/ L0 = α ΔT ( Strain ) Example : Ideally,100 oC change in Steel Section gives

0.12% Strain.

Material Behaviour - STEEL

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Stress Strain Curve for Mild Steel

Yield Point & Plastic Range

Material Behaviour - STEEL

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Stress Strain Curves of Steel & Mild Steel

Hooke’s Law

Stress Associated with 0.2 percent Strain is yield Stress

Temperature Behaviour - STEEL

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Proportional Limit

Temperature Behaviour - ANALYSIS

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P – M Relation with Temperature P= Stress X Area = (E x Strain ) X Area

= EA α ΔT M = K E I δ /L2

Where K varies with B.Cs & Joint Stiffness

P & Counteract Each Other With for Temperature Stress

Temperature Behaviour & Codes

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Maximum & Minimum Temperatures are defined as per Region in IS 875 Part V .

Temperature Variation is taken from Mean Temperature to Extremity.(Except Desert Conditions)

Codal Provisions preclude temperature design with Guidelines for Geometry and detailing.

IS 800 Section 3.10.4 Indicates Stress Analysis of Structure for Temperature need not be done if provisions of code are met

Design Excellence

Temperature Behaviour & Codes

IS456 :2000 Section 27 ,45 m Maximum Length for Expansion Joint,Else refer IS 3414

Strength Variation & alloys Enhanced Physical Properties are achieved

mainly by Heat Treatment Process Addition of Elements to steel

What are the physical Properties ? 1) Strength2) Ductility3) Toughness

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Metallurgic processTemperatures o C Lattice Structure Identified As

< 910 BCC ferrite

910 -1400 FCC austenite

1400-1539 BCC δ - ferrite

Body Centred Cubic

Face Centred Cubic

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Crystalline Structural Variation Ferrite Pearlite Austenite

Martensite

Pearlite-Ferrite

Pearlite : Laminated mixture of Ferrite & Cementite

is hard and has low ductility Martensite : Extremely Hard & Brittle

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Cooled RapidlyCooled Slowly

Heating Treatment process

Annealing Normalizing

Quenching & Tempering

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Heat Treatment Process

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Heat Treatment of Steel :

1) Annealing : Steel is Heated above 910 C , held at that temperature ,

slowly Cooled in the Furnace.

2) Normalizing : Like Annealing,but Steel is Cooled at a fast rate in ambient

air temperature.

3) Quenching & Tempering

Quenching ( Oil) : Steel is water quenched at higher cooling rate

Quenching ( Water) : Steel is water quenched at even higher cooling

rate and

 When Martensite is Heated to a temperature of 600 C , it results in steel

with superior strength & ductility . Therefore High Strength steels

obtained with same material

Strength Variation Grain Size & Yield Strength

Fy = Fo + K/√d

Strength is Achieved by additives to Steel1. Carbon Content

2. Micro Alloy ( Carbon Manganese Steels) with Al,V,Mo etc

3. Chromium

Examples FE490 , SAILMA. Carbon Equivalent ( CE ) :

CE of 0.43 & Above May require Preheating in the HAZ( Heat Affected Zone ) for Welds (IIW,1967)

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Structural SteelsType of Steel Carbon Content Uses

Mild Steel Up to 0.1% Steel Sections in buildings , bridges etc

Medium - Carbon Steel

Up to 0.25% Boiler Plates, Structural Steel

High Carbon Steel Up to 1% Sledgehammers,mason tools,Drills,Axes etc

IS 2062 : Structural Steel Specification for Fabrication

IS 8500 : Structural Steel – MicroAlloyed( Medium and High Strength quality)

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Analysis & Design Input IS 800 :2007 Section 16 :Fire Resistance , Young’s Modulus relation with

Temperature. Coefficient of Expansion for Steel above 100 oC Increases to 1.4 X 10-5 / oC

(AISC 360) IS 6533 (Part 2) : 1989 Chimneys – Fy for IS2062 Steel in relation with

temperature, till 400 oC

Example, Yield Strength at 400 oC is considered 0.5X Fy for structural Steel(fy = 250 ) EN 13084 :7 Design of Chimneys – ELEVATED temperature steel properties

If Temperature Resistant Alloy Steels are Used for Elevated temperatures then the mechanical properties are obtained from , A387 Or Equivalent

ASME Boiler & Pressure Code : 2004 part II Section D TABLE Y-1

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BOLTS

For Example : A194M , Nuts are specified For High Temperature Service as :

M72 Grade 2H Heavy Hex nut shall be reheated above critical Range

Quenched in a suitable Medium ,

And then tempering at a temperature not less than 455 oC .____Design Excellence

BOLT ASSEMBLY

High Temperatu

re

A193M

BOLTS

A194M

NUTS

F436MWASH

ER

BOLT ASSEMBL

YHigh

Strength

A490M

BOLTS

A563M

NUTS

F436MWASH

ER

Structural Steel Bolts , NUTS & WASHERS for HIGH STRENGTH & HIGH TEMPERATURES

A193M - Specification for Alloy-Steel and Stainless Steel Bolting Materials for High-Temperature Service

A194M - Specification for Carbon and Alloy Steel Nuts for Bolts for High Pressure or High Temperature Service, or Both

A320M - Specification for Alloy-Steel and Stainless Steel Bolting Materials for Low-Temperature Service

A325M - Specification for Structural Bolts, Steel, Heat Treated 830 MPa Minimum Tensile Strength

A490M - Specification for High-Strength Steel Bolts, Classes 10.9 and 10.9.3, for Structural Steel Joints

A563M - Specification for Carbon and Alloy Steel Nuts F436M - Specification for Hardened Steel Washers

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Codal References

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References AISC 360 -10 :Specification for Structural Steel Buildings

Appendix 4 BS 5950 : PART 8 Fire Resistance for structural steelwork EN 1993-1-2:2005 : Structural Fire Design Behaviour of High Strength Structural Steel at Elevated

Temperatures: Ju Chen & Ben Young ;Brian Uy, Journal of Structural Engineering,ASCE,2006

Thank You

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