ADSC/CALTRANS CIDH Pile Workshop

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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

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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

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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)

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Test of 6 diameter Type-I Shaft at UCLA
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Test of 6 diameter Type-I Shaft at UCLA
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Types of Large Diameter Drilled Shafts (Caltrans
SDC)
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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)

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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

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Preliminary Design Data Sheet(to be provided by
SD)
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General Foundation Information(to be provided by
SD)
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Foundation Design Loads(to be provided by SD)
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Lateral Stability (BDA Chapter 12) Available
Software LPILE, W-FRAME, or SAP
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General Seismic Design Highlights (Requirements
that may be affected by size/type of the shaft)

• Geometrical/Structural Irregularities
• Demand and Capacity
• P-? Effect
• Displacement Ductility Limitation
• Minimum Local Displacement Ductility Capacity

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• 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-? 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)

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Structural Analysis for Demand Assessment

• Use Expected Material Properties
• Determine Column/Shaft Plastic Moments from
  Section Analysis
• Use Mo1.2Mp
• Use Push-over Analysis and Find Shear and Moment
  Demands at Collapse

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Demand Calculation (Single Column Bent)
Mo
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Seismic Demand Calculation (Multi-Column Bent)
Mo
Type-I
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Seismic Demand Calculation (Multi-Column Bent)
Mo
Type-II
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Structural Design of the Shafts

• MneType II gt 1.25 MDemand (SDC 7.7.3.2)
• VnType II gt VDemand (SDC 3.6.7)
• Shear capacity is calculated as a ductile member
  using SDC 3.6 requirements (for Type-II assume
  µd1)

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Detailing Requirements

• No Splice Zones (SDC 8.1.1)
• Plastic hinge region and areas of MDgtMy
• 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)

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Case Study (Type-II)
Top of the Pile Boundary Conditions V M (V150
kips, M3,750 k-ft)
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Liquefied Layer
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Typical
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Typical
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Typical
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Typical
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Scour Included
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
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Summary (Method-I)
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(No Transcript)
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Thank You