1. Experimental & Analytical Studies of Drilled Shaft Bridge Columns Sandrine P. Lermitte, PhD Student Jonathan P. Stewart, Assistant Professor John W. Wallace, Associate Professor Civil Engineering, UCLA Kerop Janoyan, Assistant Professor Civil Engineering, Clarkson University 7NCEE July 21-24, 2002

2. Project Objectives Study of shaft – soil interaction –Pile specimens –Cyclic displacements –Large scale –Well instrumented Identify damage states –Plastic hinge Develop/Assess models –P-Y Curves

3. Specimen Information Specimen Design –6 ft Diameter column –36 - #14 Bars (2%) –#8 hoops @ 6” o.c. Instrumentation –200 channels: Load, strain, displacement, soil pressure cells, rotation, curvature

4. Test Overview - Caltrans 40 ft 48 ft 105/405 Interchange - LAX

5. Cyclic Loading 05101520253035404550 -150 -100 -50 0 50 100 150 Number of cycles Lateral Deflection at Top of Column (in) After 9 in displacement, 16 stops per cycles

6. Test Results

7. Load – Displacement Response

8. Shaft/Column Modeling Fiber (section) model Material models (concrete, rebar) Soil modeling –API p-y curves (2 ft pile tests) –Experimentally derived p-y curves Analysis –Pushover, Cyclic (no-gap, gap)

9. Fiber Model Unconfined concrete Confined concrete #14 steel bar

10. 0 1 2 3 4 5 6 7 00.00050.0010.00150.0020.00250.003 Strain (in/in) Stress (ksi) Mean f’ c Mean+/_1 STDEV Material Properties Steel reinforcement Reinforced concrete Fy = 71 ksi Fult =102 ksi Ec f’c = 6.1 ksi Ec = 3,500 ksi

11. Soil Model API relations, Stiff clay

12. Trilinear API p-y Curves 0123 0 1000 2000 3000 4000 y (in.) p (lb/in.) 3 ft Depth 0123 0 1000 2000 3000 4000 y (in.) p (lb/in.) 6 ft Depth 0123 0 1000 2000 3000 4000 y (in.) p (lb/in.) 10 ft Depth 0123 0 2000 4000 6000 y (in.) p (lb/in.) 24 ft Depth

13. Experimental p-y curves.p(z): double differentiating the shaft bending moment distribution, y(z) : single integration of the slope, or a double integration of the curvature

14. 6 in Displ. Level West Pull -48 -42 -36 -30 -24 -18 -12 -6 0 -10-8-6-4-2024 Soil Reaction, p (k/in) Depth, z (ft) 6 in Displ. Level -48 -42 -36 -30 -24 -18 -12 -6 0 -1.6-1.2-0.8-0.400.40.81.21.6 Displacement, y (in) Depth, z (ft) Derivation of experimental p-y curves at different depths Soil Reaction p (k/in.) Displacement y (in.)

15. Experimental p-y curves 00.10.20.30.40.50.60.70.80.91 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 x 10 4 y (in) p (kips) 3 ft below ground 6 ft below ground 10 ft below ground 18 ft below ground 24 ft below ground 30 ft below ground

16. Comparison API vs. Experimental p-y curves 3 ft Depth 0 2000 4000 6000 8000 10000 12000 14000 16000 00.20.40.60.81 y (in) p (lb/in) API Stiff Clay Curve Fitted Test Data Curve

17. 00.050.10.150.20.25 y (in) API Stiff Clay Curve Fitted Test Data Curve 18 ft Depth 0 1000 2000 3000 4000 5000 6000 7000 8000 p (lb/in) Comparison API vs. Experimental p-y curves

18. Trilinear Exp. p-y Curves 012345 0 1 2 x 10 4 y (in.) p (lb/in.) 3 ft Depth 012345 0 1 2 x 10 4 y (in.) p (lb/in.) 6 ft Depth 00.511.52 0 5000 10000 y (in.) p (lb/in.) 10 ft Depth 00.511.52 0 5000 10000 y (in.) p (lb/in.) 30 ft Depth

19. 05101520253035404550 0 100 150 200 250 300 350  top (in) F (kips) F  TOP  GROUND F/2 Pushover Analysis

20. 05101520253035404550 0 100 150 200 250 300 350 Shaft/Column top displacement (in) Lateral Force applied (kips) API p-y Experimental p-y test results Top Force vs Displacement

21. 012345678 0 50 100 150 200 250 300 350 Shaft ground displacement (in) Lateral Force applied (kips) API p-y Experimental p-y test results Ground line Force vs Displacement

22. 012345678 x 10 -4 -50 -40 -30 -20 -10 0 10 20 30 40 Curvature (/in) Height (ft) API Exp Test Curvature Profiles 36 in. top displacement

23. Gap at end of testing

24. DRAG ELEMENT CLOSURE ELEMENT PLASTIC ELEMENT ELASTIC ELEMENT RADIATON DAMPING a) Model A: proposed by Boulanger et al.(1999) b) Model B: “Gap model” proposed DRAG ELEMENT CLOSURE ELEMENT PLASTIC ELEMENT ELASTIC ELEMENT RADIATON DAMPING

25. DRAG ELEMENT CLOSURE ELEMENT PLASTIC ELEMENT ELASTIC ELEMENT -0.8-0.6-0.4-0.200.20.40.60.81 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 -0.8-0.6-0.4-0.200.20.40.60.81 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 y/y max p/p u l t Gap Model -0.8-0.6-0.4-0.200.20.40.60.81 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 y/y max p/p u

26. 80% drag 2 ft below ground -8-6-4-202468 -80 -60 -40 -20 0 20 40 60 80 y(in.) p u l t (kips) P-y response @ - 2 ft 20% drag force

27. Cyclic Response - 20% drag force -50-40-30-20-1001020304050 -400 -300 -200 -100 0 100 200 300 400 Shaft top displacement (in) Lateral Force applied (kips) Gap model 20% drag test envelope

28. -3-20123 -80 -60 -40 -20 0 20 40 60 80 y(in.) p u l t (kips) P-y response @ -2 ft 80% drag force

29. -50-40-30-20-1001020304050 -400 -300 -200 -100 0 100 200 300 400 Shaft top displacement (in) Lateral Force applied (kips) Gap model 80% drag test envelope Cyclic Response - 80% drag force

30. Comparison 80% drag model and test results for 9 in. and 40 in. 0510152025303540 0 10 20 30 40 50 60 70 80 90 Displacement (in) Height (ft) Gap model, 80% drag Actual test response

31. Comparison 80% drag model and test results for 9 in. and 40 in. 00.511.522.533.544.55 x 10 -4 0 10 20 30 40 50 60 70 80 90 Curvature(/in) Height (ft) analytical model with 80% drag force experimental results

32. Summary & Conclusions Test Results 6 ft diameter CIDH shaft/column test –Provide needed data (scale, cyclic loading, M/V, instrumentation) –Behavior and modeling (p-y) Plastic hinge located ~0.5D below ground line Test shaft/column behavior –~20% lateral drift prior to loss of lateral load capacity –Buckling of vertical bars, hoop fracture, vertical bar fracture

33. Summary & Conclusions Analytical Studies Fiber model of shaft/column & p-y curves –API p-y relations are too soft (monotonic) –Experimentally derived p-y curves (monotonic/cyclic) Lateral load capacity of system is over-estimated Yield displacement is under-estimated Peak inelastic curvature is over-estimated Cyclic material models & gap behavior –Nonlinear gap model with elastic/plastic/drag/gap –Drag participation was varied –Excellent agreement (global and local responses) between experimental results and analytical results for 70 to 80% drag participation