Local buckling and section classification Dr R SENTHIL ASSOCIATE PROFESSOR ANNA UNIVERSITY senthilr68@gmail.com

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

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

BUCKLING OF ONE SQUARE ELEMENT

LONG PLATE ELEMENT= ONE SQUARE ELEMENT

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

8 times Stronger! K=4.0 K=0.425

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

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

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

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

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

UNSTIFFENED OR OUTSTAND ELEMENTS

STIFFENED OR INTERNAL ELEMENTS

SECTION CLASSIFICATION Mp Rotation  My y u Slender Semi-compact Compact Plastic Section Classification based on Moment-Rotation Characteristics

MP MP My SEMI-COMPACT PLASTIC MP MP My COMPACT SLENDER

Sectional Classification for Indian Conditions Section type Flange criterion (b/T)  Web criterion (d/t)  Slender Semi-compact Compact Plastic >15.75 <15.75 9.975 <8.92 >126 <82.95 T d B t b = B/2 <9.975 8.92 <126 102.9 <102.9 82.95

Section classification of Indian standard rolled ‘I’ beams

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