Experimental and Numerical Evaluation of Steel Columns for Performance-Based Seismic Assessment of Steel Moment Frames

Transcription

1 Experimental and Numerical Evaluation of Steel Columns for Performance-Based Seismic Assessment of Steel Moment Frames DIMITRIOS G. LIGNOS, PHD, PE ASSOCIATE PROFESSOR ÉCOLE POLYTECHNIQUE F D RALE DE LAUSANNE (EPFL) International Workshop on Performance-Based Seismic Design of Structures Tongji University, Shanghai, China, October

2 -Acknowledgements ü Ahmed Elkady, PhD Post-Doctoral Scientist, EPFL ü Yusuke Suzuki, PhD Senior Researcher, Nippon Steel & Sumitomo Metal, Japan ü Alexander Hartloper, M.Sc PhD student, EPFL ü Julien Cravero, M.Sc PhD student, École de Ponts, Paris, France 2

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4 Motivation (1) Current Design Practice in North America Steel Moment-Resisting Frames (MRFs) per AISC-2010, CSA-S seismic provisions: ² Design considerations: primarily based on cyclic tests on pre-qualified moment connections (after Northridge 1994). ² Emphasis was mostly on connection performance up to 4% story drift ratios but NOT ON COLUMN PERFORMANCE ² Deep (h > 400mm) and slender (still Class 1 cross-sections) columns are commonly used (weight consideration). Image courtesy of Prof. M. Engelhardt 4

5 Beam-to-Column Connection Tests with Deep Wide Flange Columns h Column Twisting Some Facts: Sources: Chi and Uang (2002), Zhang and Ricles (2006) ² Beam-to-column connections: triggers torsion and out-ofplane bending to the column. ² Torsional properties of wide flange sections tend to produce higher warping stresses in the column (high h/t 3 cf). 5

6 Previous Experiments on Wide-Flange Steel Columns RESEARCHER SECTION SIZE N/N pl,rd LATERAL LOAD Popov et al. (1975) MacRae et al. (1990) Nakashima et al. (1991) Newell and Uang (2006) Cheng, Chen & Nethercot (2013) Suzuki and Lignos (2014) Cravero and Lignos (2016) W8x24 W8x UC 73 (W10x49) W4x13, W5x19, W6x9 W14x132, W14x176, W14x x200x6x4 350x200x4x6 W14x53, W14x61, W14x82, W16x ~ 0.80 Cyclic 0.0 ~ 0.80 Cyclic 0.0 ~ 0.60 Monotonic 0.0 ~ 0.75 Cyclic 0.20 ~ Elkady and Lignos (2015) W24x146, W24x Cyclic Monotonic, Sym. Cyclic, Collapse Sym. Cyclic, Bidirectional, Collapse Small sections Very stocky sections Class 3, 4 Uang et al. (2015) (Part of ATC * Ongoing) + Phase II W24x176, W24x84, W24x131, W24x ~ 0.70 Cyclic 6

7 What Do we Know from Steel Beam Tests? -(Axial Load, P=0) Structural Component Databases for Steel Beams Available From: Plastic Rotation θ p [rad] P/P y =0.20 Source: Lignos and Krawinkler (2011)* Web Slenderness, h/t w 7

8 Motivation (3): Effect of Loading History -Comparisons with Data from Shake Table Collapse Tests Shake table test data Symmetric protocol (Photo Source: E-Defense-2007) 8

9 Motivation (4)-Current State of Practice for Nonlinear Modeling of Steel Columns (ASCE or old FEMA 356) Force Deformation 9

10 Motivation (4): Current State of Practice for Nonlinear Modeling of Steel Columns (ASCE-41-13) - Challenges ² Recommendations are based on cyclic response only (red curve) ² Axial load limit for force-controlled elements may be conservative (Big challenge in seismic retrofit of existing steel buildings) ² Biaxial bending, varying axial load demands (exterior columns) Response of identical columns to different protocols Force Deformation Suzuki and Lignos (2015) If P/P cl 0.50 No plastic deformation Biaxial bending, varying axial loads? 10

11 Motivation (5) Models that Facilitate Collapse Simulations Image Source: NIST GSR Goals for developed column deterioration model: ² To capture the axial load moment interaction (i.e., P-M). ² To capture the cyclic deterioration in flexural and axial strength and stiffness. ² To capture column axial shortening. ² Steel material type versatility. 11

12 Objectives and Scope ² To characterize the stability of steel wide flange columns when subjected to multi-axis cyclic loading. ² Full-scale experimental program ² Corroborating finite element (FE) parametric simulations ² To develop improved seismic design recommendations for steel columns in moment-resisting frames. ² To improve the nonlinear modeling recommendations for steel columns for engineering use within the PBEE framework (Updates in ASCE-41-13). ² Develop high-fidelity column models for collapse risk assessment of steel frame buildings. 12

13 Analyzed Column Sizes for Steel MRFs -FE Preliminary Findings for Specimen Selection Source: Elkady and Lignos (2015)* 13

14 Testing Matrix for Full-Scale Steel Column Testing Test matrix variables were based on preliminary FE analysis of 40+ wide flange and HSS cross sections typical in steel moment-resisting frames Section Size W14x53 Steel Type Loading Number of b f /2t f h w /t w Scheme Specimens Cyclic/Unidirectional 6 W14x Cyclic/Unidirectional 6 A992 W14x Cyclic/Unidirectional 6 Gr. 50 W16x Cyclic/Unidirectional 6 (Equiv. S355) W24x Cyclic/Unidirectional/Bidirectional 4 W24x Cyclic/Unidirectional/Bidirectional 6 HSS-250x9.5 ASTM A Cyclic/Uniaxial 6 HSS-300x16 F y =400MPa 19.0 Cyclic/Uniaxial 6 Total: 46 14

15 Employed Lateral Loading Protocols Symmetric-Unidirectional Collapse-Consistent-Unidirectional X-Drift [% rad] Symmetric-Bidirectional Y-Drift [% rad] X-Drift [% rad] Collapse-Consistent-Bidirectional Y-Drift [% rad] Source: Suzuki and Lignos (2014)* 15

16 Damage Progression Wide Flange Steel Columns: N/N pl,rd = 20% -AISC Symmetric Cyclic Lateral Loading Protocol 16

17 Selected Experimental Findings -Typical Geometric Instabilities Axial shortening Out-of-plane instabilities Y X е z Y X е z Y X е z Source: Elkady and Lignos (2017) 17

18 Selected Experimental Findings -Effect of Boundary Conditions Fixed-Fixed Fixed-Flexible Source: Elkady and Lignos (2017) 18

19 Selected Experimental Findings -Unidirectional (UD)/Bidirectional (BD) loading Moment, M x [kn-m] Due to lateral torsional buckling θ N M δ Due to P-M x -M y UD BD Chord Rotation, θ [rad] Source: Elkady and Lignos (2017) 19

20 Collapse Behavior Characterization -Illustration: Identical Column Specimens, P/P y = 0.30 (Suzuki and Lignos 2015) 20

21 Selected Experimental Findings -Effect of Axial Load (Varying versus Constant) P θ M δ Varying Axial Load Loss of Axial Load Carrying Capacity Constant Axial Load Differential Shortening Source: Suzuki and Lignos (2015) 21

22 Steel Column Finite Element Model (mesh size 25x25mm) Global and local Imperfections Residual stresses peak d / 250 Tension Comp. S4R Shell Element d b f / 0.5d thickness Source: Elkady and Lignos (2015)* 22

23 Steel Column Finite Element Model -Plasticity Model vnonlinear combined kinematic/isotropic hardening material model vcalibration from steel material database (US, Japanese & European steels) Stress, σ [ΜPa] Strain, ε Source: Suzuki and Lignos (2017)* 23

24 FE Model Validation with Component Tests 24

25 FE Parametric Simulations -Proposed Equation for Estimating & Limiting Axial Shortening R 2 =0.873, COV=0.28 Cumulative plastic rotation Web local slenderness Gravity-induced axial load ratio To limit axial shortening to a target 1% of member length, L: Source: Elkady and Lignos (2017) 25

26 Nonlinear Modeling Recommendations for Steel Columns -ASCE Updates (Current ATC-114 Project-Phase 1) Refined Steel Column Models Source: Hartloper and Lignos (2017) 26

27 Proposed Models for Steel Columns -ATC Project: Updates on ASCE 41 Column Modeling Capture variations in strain hardening, ASCE-41-13: assumes constant 0.03 K e Flexure Shear Proposed Backbone Curve Equation R 2 COV Source: Hartloper and Lignos (2017) Test data well represented

28 Proposed Modeling Recommendations for Steel Columns -Comparisons with Steel Column Test Data P g /P y = 0.20 P g /P y = 0.50 Proposed Proposed 28

29 High-Fidelity Deterioration Models for Nonlinear Response History Analysis ² Implemented in the OpenSees simulation platform (not available to public yet). Axial load Lateral displacement y L z Material subclass new material Source: Suzuki and Lignos (2017) Coding in C++ Fixed y z z Force-based formulation (1 element) Seven integration points Midpoint integration HSS-Shapes: 2x8 fibers (Flat) 2x4 (Corner) W-Shapes: 2x8 fibers (Flg.) 2x8 fibers (Web) y 29

30 Proposed Deterioration Model for Steel Columns -Validation with Experimental Data Moment (knm) Experimental Data Simulation Axial Shortening, δ/l Experimental Data Simulation P δ θ Chord M Chord rotation 0 rotation -800 (rad) (rad) Source: Suzuki and Lignos (2017) 30

31 Concluding Remarks 31

32 Acknowledgements 32

33 Thank you for your kind attention! For more information visit: resslab.epfl.ch 33

34 6-DOF System for Full-Scale Testing of Steel Columns Moment Platen 2x1000kN actuators 4000mm 4x1800kN actuators PhD student Specimen: W24x146 (H610x330x16.5x28) 34

35 Current Work: Steel Columns Interacting with RC Footings Hiroyuki Inamasu -September 2016 till now: PhD at EPFL : Masters, Kyoto University Beam-to-Column Connection (Composite action) Embedded Column Base Connection 35

36 Upcoming Testing Program: Steel Columns Interacting with RC Footings Embedded Column Base 36