Diploma work Presentation Master Structural Engineering Budapest University of Technology and Economics By Eng.Mohanad haba

1. by
HABH MOHANAD
June 19/2017
The effect of the holes on the buckling behaviour
of thin-walled members
BUDAPEST UNIVERSITY OF TECHNOLOGY AND ECONOMICS

2.  Review of literature
 Buckling analyses and Comparisons
 The use of the so called (constrained finite element method
)
 Re-analyzing of sections with different holes from the
literature
 Compare the results of cFEM with the classical methods.
 parametric studies
 The effects of the holes on the buckling behaviour of thin–
walled members.
 Using cFEM to analysis sections with single hole
 parametric studies considering holes parameters (size,
position and shape)and evaluate the results.
The plan

3. Why we study the effect of the holes on the buckling
behaviour of thin-walled members
 Thin-walled members contain different types of holes.
 The holes will influence the elastic buckling behavior
 The effect of the holes still unhandled or only partially
handled in the current design standards.
 Constrained finite element method (analysis of the elastic
buckling behaviour) proposed.

4. (DSM/EWM)
Critical elastic load
of buckling modes
The strength
Design of Thin walled-cold formed steel sections
Buckling modes.
• Local buckling
• Distortional buckling
• Global buckling ( Flexural / flexural torsional)
• Others
Numerical methods
 Review of literature
FEM
Divides the members in both
transvers and longitudinal directions
Single element strip in the longitudinal
direction of the section
Sections with and without holes Sections without holes
Can not decompose the pure modes
(Unconstrained)
Can decompose the pure modes
(Unconstrained and constrained)
FSM
ANSYS , ABAQUS CUFSM, CFSM

5. D. Moen and B.W. Schafer 2008
• Experimental study
• Numerical analysis
• ABAQUS
• Comparisons
 Review of literature

6. C. D. Moen and B. Schafer 2009
• Elastic buckling of thin plates with holes in compression or bending)
• simplified approximation for the critical load with the use of CUFSM
• Reducing the thickness of the plate in the strip of the holes for (L and D)
And the weighted average for the (G)
Develop the simplified method for including Columns & beams with different
holes
Comparisons
Casafont 2012 & Smith 2014
• Analyzed Pallet rack columns the simplified + CUFSM and FEM.
• Compared
 Review of literature

7. J. Cai and C. D. Moen 2016
• Elastic buckling analysis of thin-walled structural members with
rectangular holes using generalized beam theory
• Results are compared with FEM.
Global buckling example Distortional buckling example
 Review of literature
• Most of the simplified methods have some drawbacks .

8. Methods of buckling analysis (Advantages and disadvantages)
FEM
Divides the members in both
transvers and longitudinal directions
Single element strip in the longitudinal
direction of the section
Sections with and without holes Sections without holes
Can not decompose the pure modes
(Unconstrained)
Can decompose the pure modes
(Unconstrained and constrained)
FSM
ANSYS , ABAQUS CUFSM, CFSM
Divides the members in both
transvers and longitudinal directions
Sections with and without holes
(Unconstrained and constrained)
cFEM
cFEM
 .
 .
 .
 .
 Review of literature
Shear and torsion
 .

9.  Choosing different perforated sections with different
properties from the literature.
 Remodeling and reanalyzing the sections with using the two
options of cFEM software.
 Unconstrained FEM (mixing modes allowed).
 Constrained FEM ( mixing not allowed, each modes exactly
pure ).
 Comparisons .
 Results .
Buckling analyses and Comparisons

10. Sections Applied :
I. Vertical steel pallet rack columns
II. C-sections with slotted web perforations
III. C-sections with circular holes of the web
I II III
Buckling Analyses and Comparisons

11.  (Unconstrained cFEM – Classical FEM)
- First-Lowest Buckling modes.
- Higher buckling modes (Distortional, Local and Global) buckling
modes.
Buckling Analyses and Comparisons

12. - E.g. Unconstrained of higher buckling modes of sections with (shape 2).
- The differences ~1% perfect.
- Some difference higher than 1% .
Buckling Analyses and Comparisons

13.  (Constrained cFEM – classical FEM)
- (Local, Distortional and Global) buckling modes.
- (G+S),(G+SG) ,(D+S) and (D+SD) have been analyzed.
- The effect of (v=0.3, v=0) have been considered.
- e.g.
Pure
(L)
Pure (D)
Pure (G)
Buckling Analyses and Comparisons

14.  (Constrained cFEM – classical FEM).
- (Distortional, Local and Global) buckling modes.
- With (v=0.3, v=0),(G+S) and (D+S) always converge with ( g and
d).
- Strongly agreed with previous studies (G and D) are never pure.
- cFEM gives perfect results.
Buckling Analyses and Comparisons

15.  4500 models with single hole have been performed and analyzed.
 parametric study for all the buckling modes are perform
considering
 Constant parameters :
- (C – section, Length, cross-section, material properties, B.c).
 Variable parameters :
- The applied loads (6 types).
- Holes shapes ( Square, Rectangular, Circular and Oval)
- Size of the holes .
- Holes positions.
 Solid section analyzing.
 The results are compared and evaluated.
Parametric study

16.  Constant parameter:
- Length = 1200 mm,
- Web depth = 200 mm
- Flange width = 50 mm
- Thickness = 2 mm
- E=210GPa
- v= 0.3
- B.c (p-p) free to warp
 Variables parameter:
- Types of lodes
- 15 position/ hole
- 25 sizes /(straight and curved) hole edges
Parametric study

17. Load
Hole
Shape
Size
Position
Critical buckling load of each mode Relations
The effect of changing (size , shape and positions) holes compared with solid
Examples :
Critical load are compared between :
-(circular/square) (rectangular1/Oval 1, rectangular2/ Oval 2)
- (Fcre – Size of)
- Point load, down
word.
- (a) In B1
- (b) In C4.
- (σcrd) – Positions).
- Compression
- (a) Square hole
- (b) Circular hole.
Parametric study

18. - Shape and area of removed material.
A1
Example:
- Global buckling modes , Uniform load, acting downward.
A5
Parametric study

19.  Some Conclusions :
- Holes can decrease and increase the critical load
- Every thing depend on every thing
- Curved edges and straight edges holes almost identical
- The tendencies of each buckling mode are different depending on the hole
parameters
- Lowest difference between the max. increasing and min decreasing in case of G
- The highest differences are in case of L and D
- Positions and size of the maximum and minimum critical load summarized
in database tables.
- Max and Min. average difference of the critical load compared with section
without hole.
Parametric study

20. Q1/ How can the theoretically applied boundary conditions be elaborated in
practice?
Relatively close to the Euler column buckling.Euler column buckling
Difficult to be in reality
Based on the compression experimental testCompression tests

21. Q2/ What do you think about the modeling method you used around the
holes? What is the effect of element sizes of the zigzag edges?
109.03
109.04
109.05
109.06
109.07
109.08
109.09
109.1
1 2 3 4 5 6 7 8
Criticalloadoflocal
buckling.
Discretization
510.8
511
511.2
511.4
511.6
511.8
512
512.2
1 2 3 4 5 6 7
Criticalloadofglobal
buckling.
Discretization

22. Q3/ A very systematic research was done about the critical loads but what do
you think what is the effect of the changes of critical loads to the design
resistance?
The critical buckling load related to the critical load resistance
Fcr FD,R
- We have not considered design resistance.
- Due to hole: critical load can increase or decrease
- Resistance by a design method (e.g., EC3 or DSM): (probably) follow the
tendency of critical load
- Resistance in reality: ?

23. Thanks for your attention