PEER 2002 Annual Meeting

1. PEER 2002 Annual Meeting Ian Robertson University of Hawaii

2. Objective Development of a load-deformation hysteretic model for slab-column connections of varying dimensions, reinforcement arrangements, gravity loads, and lateral loading routines. Specific reference to “non-ductile” specimens with discontinuous slab reinforcement.

3. RC Floor Systems

4. Punching Shear Failure No Continuity Reinforcement

5. Approach • Task 1: Assemble Web Database • Task 2: Fabricate and test 6 “non-ductile” interior connections • Task 3: Develop backbone curve parameters • Task 4: Develop hysteretic model • Task 5: Validate hysteretic model

6. Non-Ductile Specimen tests • Six specimens fabricated • Three tested with varying gravity load levels Vg/Vo = 0.2, 0.28, 0.47 • Three with varying slab reinforcement ratios r = 0.3, 0.5 & 0.8% top reinforcement • One specimen with bent-up bars

7. Test Setup

8. Varying gravity shear ratio BOTTOM TOP

9. ND1: “Non-ductile” Vg/Vo = 0.2 SLAB PUNCH

10. ND1: Vg/Vo = 0.2 SLAB PUNCH

11. ND4: “Non-ductile”, Vg/Vo = 0.28 PUNCHING FAILURE ZERO RESIDUAL STRENGTH

12. ND4: Vg/Vo = 0.28

13. ND4: Vg/Vo = 0.28

14. ND5: “Non-ductile”, Vg/Vo=0.47 PUNCHING FAILURE ZERO RESIDUAL STRENGTH

15. ND5: Vg/Vo=0.47 TRANSVERSE BOTTOM REINF.

16. Varying Gravity Shear Ratio

17. Bent-up bars TOP BOTTOM

18. Bent-up bars PUNCHING FAILURE RESIDUAL STRENGTH

19. Bent-up Bars

20. Critical Limit StatesforFlat Slab Response

21. FEMA 273 Backbone Curve

22. Limit States No Repair Required Major Reconstruction Repairable Cracking Punching Failure Significant Cracking

23. FEMA 273 Backbone

24. FEMA 273 Backbone

25. Typical Interior Connection

26. Backbone Curve Parameters

27. Initial Stiffness

28. Initial Stiffness • FEMA 273: • Based on gross section modulus of one third slab width (uncracked). • Proposed: • Based on cracked section modulus of one third slab width. for width

29. Peak Lateral Load Capacity

30. Peak Lateral Load Capacity • FEMA 273: • Based on flexural capacity, SMn, of c2+5h slab width, divided by gf • where c2 is the column width perpendicular to the applied lateral load • h is the overall slab thickness • gf is the portion of unbalanced moment transferred by flexure according to the ACI 318 design approach.

31. Peak Lateral Load Capacity • Proposed: • Based on flexural capacity of c2+5h slab width using 1.25fy, divided by gf • Overestimated for heavily reinforced slabs • Neglect reinforcement in excess of r = 0.0065 • Discontinuous bottom reinforcement included proportional to development length beyond face of column.

32. FEMA 356 Modification

33. Peak Lateral Load Capacity

34. Stiffness Degradation

35. Stiffness Model

36. Stiffness Degradation

37. Drift Capacity • FEMA 273: • Specify Plastic Rotation Angle beyond “Yield point”, a

38. Drift Capacity • FEMA 273: • Plastic Rotation Angle, a, depends on Vg/Vo • Vg = Gravity shear acting on slab critical section as defined by ACI 318 • Vo = direct punching shear strength as defined by ACI 318

39. Maximum Drift Level • Proposed Model: • Based on proposal by Hueste and Wight • Maximum drift level related to Vg/Vo • Based on prior test results for connections failing in punching shear Slab Shear Reinforcement • Connections with adequate shear reinforcement will not experience shear failure • Gradual strength decay after peak lateral load

40. Prior test data

41. Drift < 0.5%

42. Pan and Moehle

43. Maximum Drift Level

44. Hueste and Wight

45. Recent data points

46. Proposed Model

47. Residual Strength • FEMA: • 20% of peak lateral load strength • Proposed: • 20% of peak lateral load strength for connections with continuity reinforcement • 0 for connections without continuity reinforcement

48. Example Backbone Output

49. Example Hysteretic Output

50. Model Verification • Comparison with data from tests performed at other universities • Comparison with data from PEER “non-ductile” tests • Verification of the model’s predicted energy dissipation to the measured energy dissipation