Experimental Study on Distortional-Global Interaction Buckling of Stainless Steel C-beams

Transcription

1 Experimental Study on Distortional-Global Interaction Buckling of Stainless Steel C-beams Researcher: Supervisors: Shuang Niu Kim JR Rasmussen & Feng Fan Expert Seminar 2012 Ascot UK

2 Un-stiffened Stiffened Objective To obtain experimental data for distortionaloverall interaction buckling of stainless steel open-section beams Singly-Sym doubly-sym

3 Alloys used Category ASTM EN Austenitic (lean) Duplex S Ferritic S44330 \

4 Overall Test Program Braced ~2m ~2.5m ~3.2m ~4m

5 Test program Material test Specimen design Imperfection measurement Unbraced beam test (member capacity) Braced beam test (section capacity)

6 Material tests Flat coupon (tension) L/D/T Flat coupon (compression) L/D/T Corner coupon (tension)

7 Stress (MPa) Cnr 304-Cnr 443-Cnr Flat-(c) 443-Flat-(c) 304-Flat-(c) Strain (1e-6) nonlinearity anisotropy pronounced strain hardening

8 Stress(MPa) Specimen design 250 f 0.2% (yielding) f crl (local buckling) f crd (dist buckling) 50 design stress to AS/NZS member length (m)

9 relatively small lips, wide flanges

10 Imperfection measurement

11 Unbraced beam tests

12

13

14 Force (kn) Loading stroke (mm) Capacity dropped rapidly soon after reaching ultimate Severe interaction between buckling modes

15 Moment (knm) Moment (knm) Moment (knm) EXP-data 3.0 Mcr-dist 2.0 Mel 1.0 Mpl EXP-data Mcr-dist 1.0 Mel Mpl member length (mm) member length (mm) EXP-data Mcr-dist Mel Mpl member length (mm)

16 Affecting factors Initial rotation of specimen Loading eccentricity Stiffening of Web

17 Braced beam test

18 LVDT frame Loading blade LVDTs

19 Affecting factors in testing conditions All tests failed by gross distortional buckling and yielding

20 Conclusion Material tests: Nonlinearity, anisotropy and profound strain hardening observed in all alloys. Unbraced beam tests: Specially devised rigs offer clearly defined boundary & loading conditions. Successful in gaining distortional-overall interaction buckling, featuring very rapid load shedding in post-peak range. Braced beam tests: All failed by gross distortional buckling and yielding. Affecting factors in tests were identified, which should be accounted for when using the test data, e.g. for FE calibration.

21 Numerical Study on Distortional-Global Interaction Buckling of Stainless Steel C-Beams Researcher: Supervisors: Shuang Niu Kim JR Rasmussen & Feng Fan Expert Seminar 2012 Ascot UK

22 Objectives Develop a refined FE model capable of capturing distortional-global interaction buckling behavior Extend the ultimate strength database beyond the scope of experimental tests Evaluate current design codes for stainless steel (limited to AS/NZS4673 in this presentation)

23 Layout Development of FE model (ABAQUS) Calibration against tests Revised FE model for parametric study Parametric study Evaluation of AS/NZS 4673

24 Development of FE model (ABAQUS) Displacement loading via beam-link system Material definition flat & corner coupons Geometric imperfection as measured Simple support Loading at shear-center Increased thickness simulating stiffeners

25 Load (kn) Load (kn) Sensitivity study (e.g. 304C-4.0m model) Reference 2-Eccentricity-1mm 3-Rotation-1 degree 4-Local-impf-1mm 5-Global-impf-1mm 6-No-Stiffening-on-web 7-Lip-height Horizontal deflection (mm) Section rotation (deg) 1-Reference 2-Eccentricity-1mm 3-Rotation-1 degree 4-Local-impf-1mm 5-Global-impf-1mm 6-No-Stiffening-on-web 7-Lip-height Ultimate load Factor (variation) affect Local imperfection (+0.8mm) -13% Stiffening of web (with or without) -9% Lip Height (+1mm) +8% Initial Rotation (+1degree) -9% Loading Ecc (+1mm) -4% Global imperfection (+1mm) 0%

26 Moment (knm) Calibration against tests Unbraced beam tests C C FE-1 FE Horizontal deflection (mm) 26 tests Average (M Test /M FE ) = 0.98 St.Dev (M Test /M FE ) = 0.04

27 Force (kn) Braced beam tests C-Sec C-Sec-1 FE-Sec-2 FE-Sec Stroke (mm) 6 tests Average (M Test /M FE ) = 1.04 St.Dev (M Test /M FE ) = 0.06

28 Revised FE model for parametric study Unbraced beam model Stiffening of web Loading eccentricity Initial rotation Measured imperfection Simplified imperfection w=? HWL (half-wave-length) Walker theory w =? t s

29 Moment (knm) Moment (knm) Moment (knm) Amplitude equivalent to actual imperfections ActImpd 0.5walker walker member length (mm) ActImpd 0.5walker walker member length (mm) ActImpd 0.5walker walker member length (mm) Average (M walker /M ActImpd ) = 0.87 Average (M 1/2walker /M ActImpd ) = 0.96

30 Sectional Capacity (kn) loading span bending span loading span bracing interval Braced beam model Simple support Lateral restraint Displacement loading Bending span=2*hwl Bending span=3*hwl Bending span=4*hwl Lateral bracing interval (*HWL) bracing interval = 2*HWL (half-wavelength)

31 Parametric study (tested)

32 Evaluation of AS/NZS 4673 Mainly concerned with bending capacity M bx. Data at hand: TEST FE (parametric study results)

33 TEST data --- Design Standard Factors to account for Design Method Stiffening of web Loading eccentricity Not specified Not specified Initial rotation Bi-axial strength check The bi-axial strength check involves considerable conservatism, which affects the accuracy in assessing the term of concern. TEST results are not ideal, in terms of evaluating the design codes. Parametric results eliminate the unintended effects, and are theoretically more suitable for the evaluation.

34 Moment (knm) Initial rotation (degree) Moment (knm) Moment (knm) EXP-data 8.0 My Mcr-local M-dist Mx-0degree 443 Mx-1degree 6.0 Mx-2degree Mx-3degree EXP-data My Mcr-local M-dist Mx-0degree Mx-1degree Mx-2degree Mx-3degree member length (mm) 2101 EXP-data My Mcr-local M-dist Mx-0degree Mx-1degree Mx-2degree Mx-3degree member length (mm) member length (mm) M cr1 global buckling strength of stiffened beam M cr0 global buckling strength of unstiffened beam. C b =1.2 (304 specimens) =1.5 (404 specimens) =1.3 (2101 specimens) Specimen sequence

35 Moment (knm) Moment (knm) Moment (knm) FE-SecCap FE-MemCap Mcr-Loc Mcr-Dist Mu-4673 Mu-4600DSM FE-SecCap FE-MemCap Mcr-Loc Mcr-Dist Mu-4673 Mu-4600DSM s= member length (mm) s= member length (mm) s= member length (mm) FE-SecCap FE-MemCap Mcr-Loc Mcr-Dist Mu-4673 Mu-4600DSM Parametric Study Data

36 Moment (knm) Moment (knm) Moment (knm) 10.0 FE-SecCap 6.0 FE-SecCap FE-MemCap Mcr-Loc Mcr-Dist Mu-4673 Mu-4600DSM FE-MemCap Mcr-Loc Mcr-Dist Mu-4673 Mu-4600DSM s=1.5 (tested) member length (mm) s=1.5 (tested) member length (mm) FE-SecCap FE-MemCap Mcr-Loc Mcr-Dist Mu-4673 Mu-4600DSM s=1.5 (tested) member length (mm)

37 Conclusions A refined FE model was developed which accurately predicted the test specimen behavior and ultimate load Test results were affected by unintended factors. Parametric study yielded results suitable for evaluating design codes AS/NZS 4673 was incapable of capturing the interaction effect between distortional and global buckling for high section slenderness The proposed bracing interval for determining section capacity yielded results comparable with the code predictions

38 The end