A New Design Method for Stainless Steel Column Subjected to Flexural Buckling

Transcription

1 Stainless Steel in Structures: Fourth International xperts Seminar A New Design Method for Stainless Steel Column Subjected to Flexural Buckling Shu Ganping Zheng Baofeng School of Civil ngineering, Southeast University Dec , Ascot, UK

2 Contents Introduction Finite element analysis Proposed design method Comparisons Conclusions

3 1. Introduction Research object Flexural buckling of stainless steel columns Motivations Features of stainless steel are not well recognize in current design methods Nonlinear material property A variety of Grades continuously declining Considerable strain hardening

4 1. Introduction Current design methods urocode3 : SI/ASC 8-02 Method proposed by Rasmussen(1997) Method proposed by Hradil(2012) Objective Simple but low accuracy Iterations Iterations Accurate but complex stablish a relatively simple and accurate design method without iterations to predict the flexural buckling strength of stainless steel columns

5 1. Introduction Original idea stablish a database of strength curves of stainless steel columns by using finite element method Select one or two strength curves as base curves xpress base curves in Perry formula stablish a conversion formula to link the base curves and other strength curves Use base curves and a conversion formula to generate other strength curves base curve conversion formula

6 Finite element analysis Software ANSYS 11.0 lement Shell 181 Section SHS Imperfection L/1000 Residual stress Not included Constrains

7 2. Finite element analysis Material model Material model proposed by Gardner with the parameters calculated by using formula proposed by Quach n 0.002( ) n0.2,1.0 (0.008 )( ) t n n0.2,

8 2. Finite element analysis Material model Material model proposed by Gardner with the parameters calculated by using formula proposed by Quach Strength curves e=0.0010, , , , n=3, 4, 5, 6, 7, 8, 9 35 strength curves

9 2. Finite element analysis

10 2. Finite element analysis n e shape of strength curves position of strength curves

11 3. Proposed design method The first try One base curve A simple conversion formula r Pearson Product-Moment Correlation n X i X j X i X i i i j j n X X n X X Tangent Theory N 2 A L/ r t 2 Base curve e=0.002, n =5 Conversion formula b 0,b 0, c c t,b t,c

12 3. Proposed design method Not fit well with the FM strength curves for slender columns

13 Group A Group B 3. Proposed design method The second try Two base curves A conversion formula Cluster analysis Tangent Theory dge Yield Criteria Curve A Curve B

14 3.1 Base curves Cluster analysis Aim Separate the strength curves into two groups according to the similarity of the curve shape Definition of similarity r Pearson Product-Moment Correlation n X i X j X i X i i i j j n X X n X X Result Group A: n=3,4,5 Group B: n=6,7,8,9

15 3.1 Base curves Selection of base curves Base curve Owns the highest Pearson Product-Moment Correlation with other curves in each group Group A: e=0.002, n=4 Group B: e=0.002, n=7 Modified Perry formula of base curves Instead of linear expression of imperfection parameter, the quadratic expression is adopted e , n e , n 7

16 3.2 Conversion formula Aim stablish a relationship between the column slenderness of different grade of stainless steel Theory Material Tangent theory Geometric dge yield criteria Model P Imperfection sin y x 0 v0 l Columns with overall imperfection x v 0 y Max. stress max P A W 1 P v P P 0 0 t

17 3.2 Conversion formula 0 max 0 t 1 P v P A P W P t 1 1 Av A W P 0.2 P A Material c b Slenderness c b Area c= b Section modulus c= b Imperfection c= b Reduction factor c= b 0 0.2, 0,,c t,c 1 c c Av A W P 0 0.2, 0,,b t,b 1 b b Av A W P Column c Column b Base material

18 3.2 Conversion formula c 1 1 0,c 0,b b 0.2,c 0.2,b 2 0,c 2 0,b c b t,c t,b a quadratic equation about and should be calculated by using base curve t,c and t,b should be calculated by using: t n n0 c b

19 3.3 Design steps Determine which group the column belongs to Calculate the approximate reduction factor by using base curve Calculate the conversion slenderness Calculate the final reduction factor corresponding to by using base curve b b

20 4. Comparisons

21 4. Comparisons The proposed strength curves are in good agreement with the FM strength curves

22 5. Conclusions The shape of the strength curve depends more on the strain hardening exponent n, while the position of the strength curve depends more on the nondimensional proof stress e. Cluster analysis has been conducted and the strength curves are separated into two groups. Base curves are expressed in terms of Perry formula with nonlinear imperfect factor A conversion formula is deduced to transform the column slenderness of the normal material into that of base material. The proposed method could provide accurate prediction for stainless steel columns failure in flexural buckling.

23 Thank you for your attention!