Overview of Structural Design and Detailing of Large Diameter Drilled Shafts (Caltrans Practice)

1. Overview of Structural Design and Detailing of Large Diameter Drilled Shafts(Caltrans Practice) Amir M. Malek, PE, PhD Senior Bridge Engineer (Technical Specialist) Office of Bridge Design Services California Department of Transportation ADSC/CALTRANS CIDH Pile Workshop Spring 2008

2. Outline • Types of Large Diameter Shafts and Comparison • Design Highlights and Review of LRFD Requirements • Communications of Structural and Geotechnical Designers for LRFD of Shafts • Highlights of Seismic Design and Detailing Requirements per Caltrans Seismic Design Criteria (SDC) • Case Study ADSC/CALTRANS CIDH Pile Workshop Spring 2008

3. Applications and Types • Used for high seismic loads also where small footprint is desirable • Most effective where hard layer (rock) is reachable • Used with/without casing • Types I & II per SDC classification Type-I : More ductile performance, advantageous for short columns Type-II : Easier post-event repair, shaft enlargement of at least 18” (24” under study) to contain inelastic action to the column(SDC 7.7.3.5) ADSC/CALTRANS CIDH Pile Workshop Spring 2008

4. Test of 6’ diameter Type-I Shaft at UCLA ADSC/CALTRANS CIDH Pile Workshop Spring 2008

5. Test of 6’ diameter Type-I Shaft at UCLA ADSC/CALTRANS CIDH Pile Workshop Spring 2008

6. Types of Large Diameter Drilled Shafts (Caltrans SDC) ADSC/CALTRANS CIDH Pile Workshop Spring 2008

7. LRFD & Seismic Design Highlights • Structural Designer provides Factored Loads for applicable Limit States • Geotechnical Designer will provide tip elevations based on Compression, Tension, and Settlement also Factored Nominal Resistance for Service, Strength and Extreme Event Limit States (LRFD) • Structural Designer performs Stability Analysis and provides tip elevation for Lateral Loads • Structural Designer analyzes, designs and details the shaft for Seismic Demands according to Caltrans SDC • Scour, Liquefaction and Lateral Spreading are considered in design (if applicable) ADSC/CALTRANS CIDH Pile Workshop Spring 2008

8. Review of LRFD Requirements • Consider Service, Strength and Extreme Event Limit States for Geotechnical and Structural Design of the Shaft • Follow MTD3-1 for Communications and Transfer of Information between SD and GS as summarized in the following Tables ADSC/CALTRANS CIDH Pile Workshop Spring 2008

9. Preliminary Design Data Sheet(to be provided by SD) ADSC/CALTRANS CIDH Pile Workshop Spring 2008

10. General Foundation Information(to be provided by SD) ADSC/CALTRANS CIDH Pile Workshop Spring 2008

11. Foundation Design Loads(to be provided by SD) ADSC/CALTRANS CIDH Pile Workshop Spring 2008

12. Lateral Stability (BDA Chapter 12) Available Software: LPILE, W-FRAME, or SAP ADSC/CALTRANS CIDH Pile Workshop Spring 2008

13. General Seismic Design Highlights (Requirements that may be affected by size/type of the shaft) • Geometrical/Structural Irregularities • Demand and Capacity • P-Δ Effect • Displacement Ductility Limitation • Minimum Local Displacement Ductility Capacity ADSC/CALTRANS CIDH Pile Workshop Spring 2008

14. Geometrical/Structural Irregularities: Balanced Stiffness of Bents (SDC 7.1.1) Balanced Frame Geometry (SDC 7.1.2) • Demand vs. Capacity (SDC 4.1.1) • P-Δ Effect (SDC 4.2) • Displacement Ductility Demand Limits (1.5-3/5 for bents supported by the shafts, per SDC 2.2.3) • Minimum Local Displacement Ductility Capacity Limits (SDC 3.1.4.1) ADSC/CALTRANS CIDH Pile Workshop Spring 2008

15. Structural Analysis for Demand Assessment • Use Expected Material Properties • Determine Column/Shaft Plastic Moments from Section Analysis • Use Mo=1.2Mp • Use Push-over Analysis and Find Shear and Moment Demands at Collapse ADSC/CALTRANS CIDH Pile Workshop Spring 2008

16. Mo Vo Demand Calculation (Single Column Bent) Mo ADSC/CALTRANS CIDH Pile Workshop Spring 2008

17. Seismic Demand Calculation (Multi-Column Bent) Mo Type-I ADSC/CALTRANS CIDH Pile Workshop Spring 2008

18. Seismic Demand Calculation (Multi-Column Bent) Mo Type-II ADSC/CALTRANS CIDH Pile Workshop Spring 2008

19. Structural Design of the Shafts • MneTypeII >= 1.25 MDemand (SDC 7.7.3.2) • VnTypeII >= VDemand (SDC 3.6.7) • Shear capacity is calculated as a ductile member using SDC 3.6 requirements (for Type-II assume µd=1) ADSC/CALTRANS CIDH Pile Workshop Spring 2008

20. Detailing Requirements • No Splice Zones (SDC 8.1.1) Plastic hinge region and areas of MD>My • Ultimate Splices (SDC 8.1.2) Ductile members outside “No Splice Zone” • Service Splice (MTD20-9) Capacity Protected Members like Bent Cap • For Hoops and Spirals in Ductile Members Use Ultimate Splices, Except: No splices in spirals used in “No Splice Zones” (end anchorage has been used to improve constructability) ADSC/CALTRANS CIDH Pile Workshop Spring 2008

21. Case Study (Type-II) Top of the Pile Boundary Conditions: V & M (V=150 kips, M=3,750 k-ft) ADSC/CALTRANS CIDH Pile Workshop Spring 2008

22. Liquefied Layer ADSC/CALTRANS CIDH Pile Workshop Spring 2008

23. Typical ADSC/CALTRANS CIDH Pile Workshop Spring 2008

24. Typical ADSC/CALTRANS CIDH Pile Workshop Spring 2008

25. Typical ADSC/CALTRANS CIDH Pile Workshop Spring 2008

26. Typical ADSC/CALTRANS CIDH Pile Workshop Spring 2008

27. Scour Included ADSC/CALTRANS CIDH Pile Workshop Spring 2008

28. Summary (Method-I) ADSC/CALTRANS CIDH Pile Workshop Spring 2008

29. ADSC/CALTRANS CIDH Pile Workshop Spring 2008

30. Thank You ADSC/CALTRANS CIDH Pile Workshop Spring 2008