1. Local buckling and section classification
Dr R SENTHIL
ASSOCIATE PROFESSOR
ANNA UNIVERSITY

2. RECTANGULAR PLATES SUPPORTED ON FOUR SIDESNx y z b a A B C D x
Buckling of Plate under Uni-axial Compression

3. Buckling Coefficient, k
PLATES WITH OTHER SUPPORT CONDITIONS
web
(a)
(b)
(c )
(d)
Plate Elements with Different Edge Conditions
(e)
Rotation of free edge
Table 1 Values of k for Different Load and Support Conditions
Load Condition
Support Condition
Buckling Coefficient, k
Uniaxial Compressive Stress (x)
Hinged-hinged
4.00
Fixed-fixed
6.97
Hinged-free
0.43
Fixed free
1.27
Shear Stress (xy)
5.35
8.99

4. BUCKLING OF ONE SQUARE ELEMENT

5. LONG PLATE ELEMENT= ONE SQUARE ELEMENT

6. LOCAL BUCKLING
(a)
(b)
Local buckling of Compression Members

7. 8 times Stronger!
K=4.0
K=0.425

8. Full section capacity eroded by local BucklingM1 M2
Local buckling
Vent
M=M1
M<M2
Full Section Capacity
Full section capacity eroded by local Buckling

9. DESIGN OF PLATE ELEMENTS
Limiting width-thickness ratio to ensure yielding before plate buckling

10. LOCAL BUCKLING
In IS:800 (1984) the local buckling is avoided by specifying b/t limits. Hence we don’t consider local buckling explicitly
However in IS:800(2007) limit state design, the local buckling would be the pivotal aspect for the design of structural components

11. How codes view steel sections?
Un-stiffened element
Stiffened element
Section comprising of a stiffened element and two un-stiffened elements
Channel

12. How can we get maximum stiffened elements
1. Channel section
2. Channel with a simple lip
3. Channel with compound lip
4. Intermediately stiffened
Channel with compound lips

13. UNSTIFFENED OR OUTSTAND ELEMENTS

14. STIFFENED OR INTERNAL ELEMENTS

15. SECTION CLASSIFICATIONMp
Rotation  My y u
Slender
Semi-compact
Compact
Plastic
Section Classification based on Moment-Rotation Characteristics

16. MP MP My
SEMI-COMPACT
PLASTIC MP MP My
COMPACT
SLENDER

17. Sectional Classification for Indian Conditions
Section type
Flange criterion (b/T) 
Web criterion
(d/t) 
Slender
Semi-compact
Compact
Plastic
>15.75
<
<8.92
>126
<82.95 T d B t
b = B/2
<
<
<

19. Section classification of Indian standard rolled ‘I’ beams

20. Summary
Local buckling concepts which are embedded in the IS:800 for beams have been briefly outlined.