Seismic assessment of earthquake-resilient low-damage steel frames in OpenSees

1. Seismic assessment of earthquake-resilient low-damage steel frames in OpenSees Theodore Karavasilis Professor of Structures and Structural Mechanics University of Southampton UK 1

2. Outline • Introduction • Yielding devices • Friction devices • Viscous dampers • Post-‐tensioning • Damage-‐free rocking column base • Damage-‐free beam-‐column connection • Seismic assessment • A note on resilience-‐based design: from short-‐term to long-‐term stressors Different technologies employed to resilience-‐based design Damage-‐free self-‐centering configurations for steel joints/connections OpenSees models and techniques

4. Yielding steel structures Plastic deformations and buckling in main structural members • Damage • Residual drifts • Repair costs • Downtime 0 10 20 30 40 50 60 -0.02 -0.01 0 0.01 0.02 Time (sec) Storydrift Residual driftPeak drift Free vibrations

5. Resilience-based design Structuralhealth(%) Time 0 100 50 t0 Repair time • to: occurrence of strong earthquake • Reduction of repair time (the main goal of resilience-based design)

6. Resilience in practice • Strict performance objectives were set by stakeholders • Columns experience uplift and activate viscoelastic dampers • Design: ARUP Resilience in mainstream steel construction?

8. Stainless steel for energy dissipation • Combination of large strength and large fracture capacity 𝑓" 𝑓# 𝜀% 𝐸 Specimen (MPa) (MPa) (%) (MPa) 1 530 752.4 45.7 189,655 2 513 750.9 47.5 181,250 3 518 745.8 47.9 187,500 8

9. Stainless steel hourglass shape dampers To be used as easy to replace energy dissipation elements in steel connections and braces Uniform distribution of plastic bending deformations along their length 9

10. Constant amplitude tests on stainless steel devices Very large fracture capacity

11. Material implemented in OpenSees for yielding devices Original Bouc-Wen Modified Bouc-Wen Includes isotropic hardening (can be different in tension/compression)

12. Verification (analytical and experimental) -10 -5 0 5 10 -2 -1 0 1 2 u (mm) z 5 1 6 2 3 u=9.5 z=1.26 u=6.0 z=1.0 4 u=-6.0 z=-1.09 u=0.0 z=0.0 u=-5.5 z=0.0 A u=-5.8 z=-0.63 u=5.54 z=0.0 -10 -5 0 5 10 -400 -200 0 200 400 u (mm) F(kN) u pl,2 =10.9 u* y,2 =4.9 u pl,1 =5.5 u* y,1 =0.5 A u=-5.8 F=-150 Device with large isotropic hardening

13. 13 Implemented fracture initiation and evolution law • No deterioration up to fracture initiation • Fracture initiation (detected by linear damage accumulation rule – fatigue material in OpenSees) • Strength loss in each cycle based on accumulated plastic deformation after fracture initiation • 20% strength loss corresponds to 70% accumulated plastic deformation capacity after fracture initiation Fracture initiation 20% strength loss FractureCA test Calibration for stainless steel devices

14. Fracture simulation using ABAQUS explicit along with element deletion (to expand the experimental database) 14

16. Friction device Experimental evaluation 270 experimental data points 16 Torque-‐bolt force calibration lawSteel-‐brass friction-‐based damper behaviour Specimen OpenSees Bilinear elastoplastic material with high initial stiffness and low post-‐yield stiffness

18. Viscous damping Established technology 18 Displacement Force )sgn(D ννCF a ××= Available in OpenSees

20. Post-tensioning 20 OpenSees • Initial strain material • Steel 01 material • Iterations are needed to reach the desired post-tensioning force F as shortening of the structure on which post-tensioning is applied results in loss of post-tensioning F Tendons F Post-‐tensioning force

22. Damage-free rocking column base Configuration Short strong column (circular hollow or CFT) Steel base with rounded edges for rocking behaviour with low stress concentration Post-‐tensioned high-‐ strength steel bars Steel Column Friction-‐based dampers 22

23. Damage-free rocking column base Detailing 23

24. Damage-free rocking column base Rocking and forces 24

25. ABAQUS model (Solid elements) 25 Damage-free rocking column base

26. Simplified OpenSees model 26 Constrained nodes Damage-free rocking column base Need to iterate on εο to induce the desired post-‐ tensioning

27. 27 Damage-free rocking column base Comparison of OpenSees and Abaqus models

28. 28 Damage-free rocking column base Experimental evaluation (in progress)

30. Structural details Post-‐tensioned bar Hourglass shape pins Fin plate with slotted holes 30 Damage-free beam-column connection

31. Damage-free beam-column connection 31 Free-body diagrams for connection and floor, and, flag-shape hysteresis

32. Experimental validation of resilience (pre- and post-repair behaviour comparison) -10 -5 0 5 -100 -50 0 50 100 Drift=D/L (%) Appliedforce(kN) 1st run 2nd run Ultimate response K,i= 5kN/mm 32 Damage-free beam-column connection

33. 33 Damage-free beam-column connection FEM models were calibrated and used to identify failure modes not seen in experiments • Beam flange reinforcing plates and beam web transverse stiffeners delay local buckling (drift>7%) • They do increase the fabrication cost!

34. Model for the beam-column connection in OpenSees 34 Damage-free beam-column connection

35. Model for the beam-column connection in OpenSees 35 Damage-free beam-column connection Modified Ibarra – Krawinkler model (Lignos and Krawinkler, 2011) Effect of large compressive forces due to post-‐tensioning? Effect of web transverse stiffeners?

36. Comparison of OpenSees model with experimental results without local buckling 36 Damage-free beam-column connection

37. Comparison of OpenSees, Abaqus, and experimental results with local buckling (monotonic test of Kim and Christopoulos 2008) 37 Damage-free beam-column connection

39. Prototype steel building and seismic-‐resistant frames • MRF • MRF with viscous dampers • SC-MRF with damage-free connections • SC-MRF with damage-free connections/viscous dampers • Viscous damping vs Post-‐tensioning • Quantification of benefits of combining supplemental damping and post-‐ tensioning technologies

40. Pushover analysis

41. Incremental dynamic analysis

42. Repair cost estimation (FEMA P-‐58)

43. Main conclusions of seismic assessment • Viscous damping is more effective than post-‐tensioning for seismic intensities equal or lower than that of the design earthquake • Post-‐tensioning is more effective than viscous damping for seismic intensities higher than that of the design earthquake • Combining post-‐tensioning and supplemental viscous damping achieves repair cost reductions higher than 70% 43

45. Resilience-based design: Short-term vs Long-term stressors Structuralhealth(%) Time 0 100 50 t0 Repair time t0: Strong earthquake (short-term stressor) Structuralhealth(%) Time 0 100 50 t0 Repair time Corrosion Fatigue t0: Detection of damage due to fatigue or corrosion (long-term stressors) 45

46. Steel concrete-composite bridges under long-term stressors 46 Structuralhealth(%) Time 0 100 50 t0 Repair time Corrosion Fatigue

47. Resilience in steel-concrete composite bridges under long-term stressors Journal of Bridge Engineering ASCE 2017 Published patent application Νο WO 2016/135512 A1 47 Structuralhealth(%) Time 0 100 50 t0 Repair time Corrosion Fatigue

48. Financial and technical support 48

49. Thank you! 49

Seismic assessment of earthquake-resilient low-damage steel frames in OpenSees

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Seismic assessment of earthquake-resilient low-damage steel frames in OpenSees