ADSC/CALTRANS CIDH Pile Workshop Spring 2008 1 Overview of Structural Design and Detailing of Large Diameter Drilled Shafts (Caltrans Practice) Amir M.

ADSC/CALTRANS CIDH Pile Workshop Spring 2008

1

Overview of Structural Design and Detailing

of Large Diameter Drilled Shafts (Caltrans Practice)

Amir M. Malek, PE, PhDSenior Bridge Engineer (Technical Specialist)

Office of Bridge Design Services

California Department of Transportation


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


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)


4

Test of 6’ diameter Type-I Shaft at UCLA


5

Test of 6’ diameter Type-I Shaft at UCLA


6

Types of Large Diameter Drilled Shafts (Caltrans SDC)


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)


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


9

Preliminary Design Data Sheet(to be provided by SD)


10

General Foundation Information(to be provided by SD)


11

Foundation Design Loads(to be provided by SD)


12

Lateral Stability (BDA Chapter 12) Available Software: LPILE, W-FRAME, or SAP


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


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)


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


16

Demand Calculation (Single Column Bent)

MoVo

Mo


17

Seismic Demand Calculation (Multi-Column Bent)

Type-I

Mo


18

Seismic Demand Calculation (Multi-Column Bent)

Type-II

Mo


19

Structural Design of the Shafts

• MneType II >= 1.25 MDemand (SDC 7.7.3.2)

• VnType II >= VDemand (SDC 3.6.7)

• Shear capacity is calculated as a ductile member using SDC 3.6 requirements (for Type-II assume µd=1)


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)


21

Case Study (Type-II)

Top of the Pile Boundary Conditions:V & M (V=150 kips, M=3,750 k-ft)


22

Liquefied Layer


23


24


25


26


27

Case-I Results Competent Not Liquefied

Liquefied (I)

Liquefied (II)

Top Deflection (in.)

0.92 3.4 9.8

12.2

14.4

18.2

Mmax (kip-in.)

(x10-4)

5.3 6.5 7.6

9.2

9.4

11.5

Location of Mmax (ft)

7 14 32

37

42

42

Vmax (kips) 320 268 420

517

420

519

Location of Vmax (ft)

17 32 50

50

55

57

Stable Length (ft)

34 54 65 75

Scour Included


28

Summary (Method-I)


29


30

Thank You

ADSC/CALTRANS CIDH Pile Workshop Spring 2008 1 Overview of Structural Design and Detailing of Large Diameter Drilled Shafts (Caltrans Practice) Amir M.

Documents

sd slide

applicable slide

ucla slide

sap slide

shafts caltrans sdc

overview of structural

foundation design loads

comparison design highlights