1. Concepts embedded in the draft IS:800 for Compression members
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2. Behaviour of columns and their design
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3. PTF=PEX or PTF=PEY or PTF=PT
TYPES OF COLUMN BEHAVIOUR CG SC x0 y0
Doubly symmetric
PTF=PEX or PTF=PEY or PTF=PT CG SC CG SC x0
Singly symmetric
PTF=PEX+PT or PTF=PEY
Unsymmetric
PTF=PEX+PEY+PT
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4. INTRODUCTION TO THE DESIGN OF AXIALLY LOADED COLUMNS
Teaching Resources for Steel Structures
INTRODUCTION TO THE DESIGN OF AXIALLY LOADED COLUMNS
Dominant factors affecting ultimate strength of practical columns:
Initial imperfection
Eccentricity of loading
Residual stresses
Lack of defined yield point
Strain hardening
l/r ratio
Material Yield stress
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5. INTRODUCTION (Contd…)
Teaching Resources for Steel Structures
INTRODUCTION (Contd…) x
Typical column design curve c fy
Test data (x) from collapse tests
on practical columns
Euler curve
Design curve
Slenderness  (/r)
x x
x x x
x x
200
100
L. Euler
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6. Teaching Resources for Steel Structures
HISTORICAL REVIEW
PERRY ROBERTSON EQUATION
- a factor defining initial imperfection and load eccentricity
=y / r2
If =L/1000 then =0.001 y/r L / r
=   where = for x-x
=0.002 for y-y
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7. Effect of  on the strength of columns
 = 0.001
 = 0.002
= 0.003
 = 0.004
300
250
200
150
Compressive
strength c
(Mpa) fy
100 50 50
100
150
200
250
Slenderness, 
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8. PERRY ROBERTSON APPROACH
Teaching Resources for Steel Structures
PERRY ROBERTSON APPROACH c fy 
Euler curve
Design curve with  = 0.003
200
100
Robertson’s Design Curve
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9. MODIFICATION TO THE PERRY ROBERTSON APPROACH
Teaching Resources for Steel Structures
MODIFICATION TO THE PERRY ROBERTSON APPROACH c  fy       
200
100    
Euler curve      
Design curve with  = (-0)      0
Robertson’s Design Curve
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10. MULTIPLE COLUMN CURVES IN IS:800
 = 0.002
 = =
 = 0.008
(Curve A)
(Curve B)
(Curve C)
(Curve D)
300
250
200
150
Compressive
strength c
(Mpa) fy
100 50 50
100
150
200
250
Slenderness, 
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11. Teaching Resources for Steel Structures
Rolled steel sections
(b) Double Angle
(c) Tee
(d) Channel
(e) Hollow Circular
Section (CHS)
(f) Rectangular Hollow
Section (RHS)
(a) Single Angle
Cross Section Shapes for Rolled Steel Compression Members
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12. EFFECTIVE LENGTH OF COLUMNS
Teaching Resources for Steel Structures
EFFECTIVE LENGTH OF COLUMNS
Column fixed at both ends : e = 0.7 
Column fixed at one end and
hinged at the other : e = 0.85
(Note: These values are NOT the same as those contained in IS: which suggests 0.80  and 0.65  respectively.)
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© IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta

13. EFFECTIVE LENGTHS OF COLUMNS IN A FRAME
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14. DRAFT IS:800 CONTENTS Section 1 General Section 2 Materials
Section 3 General Design Requirements
Section 4 Methods of Structural Analysis
Section 5 Limit States Design
Section 6 Design of Tension Members
Section 7 Design of Compression Members
Section 8 Design of Members Subjected to Bending
Section 9 Member Subjected to Combined Forces
Section 10 Connections
Section Working Load Design Format
Section Design and Detailing for Earthquake Loads
Section Fatigue
Section Design Assisted by Testing
Cont...
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16. SECTION 7 DESIGN OF COMPRESSION MEMBERS
7.1 Design Strength
7.2 Effective Length of Compression Members
7.3 Design Details
7.3.1 Thickness of Plate Elements
7.3.2 Effective Sectional Area
Eccentricity for Stanchions and Columns
Splices
]7.4 Column Bases
Gusseted Bases
Slab Bases
7.5 Angle Struts
Single Angle Struts
Double Angle Struts
Continuous Members
Combined Stresses
Cont...
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17. SECTION 7 DESIGN OF COMPRESSION MEMBERS
7.6 Laced Columns
General
Design of Lacings
Width of Lacing Bars
Thickness of Lacing Bars
Angle of Inclination
7.6.6 Spacing
Attachment to Main Members
End Tie Plates
7.7 Battened Columns
7.7.1 General
Design of Battens
Spacing of Battens
Attachment to Main Members
7.8 Compression Members Composed of Two Components
Back-to-Back Cont...
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18. APPENDIX E
E.1 Method for Determining Effective Length of Columns in Frames
E.2 Method For Determining Effective Length For Stepped Columns
E.2.1 Single Stepped Columns
E.3 Effective Length for Double Stepped Columns
7.1.2 The design compressive strength of a member is given by Pd = Ae fcd
The classification of different sections under different buckling class a, b, c or d, is given below. a b c d
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19. λ = non-dimensional effective slenderness ratio,
The design compressive stress, fcd, of axially loaded compression members
λ = non-dimensional effective slenderness ratio,
fcc = euler buckling stress = 2E/(KL/r)2
Cont...
 = 0.5[1+ ( - 0.2)+ 2]
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20. c 7.6 Laced Columns 7.7 Battened Columns
The effective slenderness ratio, (KL/r)e, of the laced column shall be taken as 1.05 times the (KL/r)0, the actual maximum slenderness ratio in order to account for shear deformation effects.
7.7 Battened Columns
The effective slenderness ratio of battened column, shall be taken as 1.1 times the (KL/r)0, where (KL/r)0 is the maximum actual slenderness ratio of the column, to account for shear deformation effects.
Cont... c
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21. 7.4.2 Slab Bases 7.5 Angle Struts
The minimum thickness, ts, of rectangular slab bases, supporting columns under axial compression shall be
7.5 Angle Struts
Loaded through one leg 
k1, k2, k3 = constants depending upon the end condition
and
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22. STEPS IN THE DESIGN OF AXIALLY LOADED COLUMNS
Teaching Resources for Steel Structures
STEPS IN THE DESIGN OF AXIALLY LOADED COLUMNS
Design steps:
Assume a suitable trial section.
Arrive at the effective area of the column Ae (No Classification)
Arrive at the effective length of the column.
Decide the appropriate column curve
Calculate the slenderness ratio  and factor 
Calculate fcd
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23. STEPS IN THE DESIGN OF AXIALLY LOADED COLUMNS
Teaching Resources for Steel Structures
STEPS IN THE DESIGN OF AXIALLY LOADED COLUMNS
Calculate fcd values along both major and minor axes.
Compute the load that the compression member can resist
Ae fcd
Check
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24. Summary
Concepts which are embedded in the draft IS:800 has been briefly outlined.
The limit state design appears to be a promise and it presents an open ended design route.
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