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Public Works Research Institute, Japan

Outline of Design Manual for Seismic Retrofitting of Existing Pile Foundations with High Capacity Micropiles. Public Works Research Institute, Japan Takeshi UMEBARA Jiro FUKUI

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Public Works Research Institute, Japan

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  1. Outline of Design Manual for Seismic Retrofitting of Existing Pile Foundations with High Capacity Micropiles Public Works Research Institute, Japan Takeshi UMEBARA Jiro FUKUI Masahiro ISHIDA

  2. Design and Execution Manual for Seismic Retrofitting of Existing Pile Foundations with High Capacity Micropiles Contents of the manual: Part 1 Design Manual Part 2 Execution Manual

  3. Contents of the Design Manual Chapter 1 : General Chapter 2 : Materials Chapter 3 : Surveying Chapter 4 : Basic items for design Chapter 5 : Basic items for seismic retrofitting Chapter 6 : Verification at normal time, during strong wind, and during level 1 earthquake Chapter 7 : Verification during level 2 earthquake Chapter 8 : Structural details

  4. Points of the Design Manual (1) Scope (2) Basic principles for seismic retrofitting design (3) Verification at normal time, during strong wind, and during level 1 earthquake (4) Verification during level 2 earthquake

  5. Points of the Design Manual (1) Scope (2) Basic principles for seismic retrofitting design (3) Verification at normal time, during strong wind, and during level 1 earthquake (4) Verification during level 2 earthquake

  6. Scope This manual covers the design of seismic retrofitting of existing pile foundations using high capacity micropiles. * This items not stipulated in this manual have to be referred to the following design specifications etc. 1) Specifications for Highway Bridges, JRA 2) Reference Documents concerning the Retrofitting of Existing Highway Bridge Foundations, JRA

  7. Points of the Design Manual (1) Scope (2) Basic principles for seismic retrofitting design (3) Verification at normal time, during strong wind, and during level 1 earthquake (4) Verification during level 2 earthquake

  8. Basic principles for seismic retrofitting design (2) The seismic retrofitting design of an existing pile foundation shall be performed, as necessary, with consideration two levels of design earthquake motions: Two levels of design earthquake motions Level 1 earthquake motion : Earthquake motion with a high probability of occurring during the service life of the existing bridge Level 2 earthquake motion : Strong earthquake motion with a low probability of occurring during the service life of the existing bridge

  9. Points of the Design Manual (1) Scope (2) Basic principles for seismic retrofitting design (3) Verification at normal time, during strong wind, and during level 1 earthquake 1) Verification items 2) Bearing capacity estimation equation (4) Verification during level 2 earthquake

  10. Verification Items at Normal Time, during Strong Wind, and Level 1 Earthquake (1) Pile head reaction force ( allowable bearing capacity) (2) Horizontal displacement ( allowable horizontal displacement) (3) Stresses generated in each member of the foundation ( allowable stresses)

  11. Verification Items at Normal Time, during Strong Wind, and Level 1 Earthquake (1) Pile head reaction force ( allowable bearing capacity) (2) Horizontal displacement ( allowable horizontal displacement) (3) Stresses generated in each member of the foundation ( allowable stresses)

  12. Ultimate push-in Bearing capacity Footing Rcu Pile head part (1) Frictional resistance is considered only in the anchored part. (2) Bearing capacity of the tip is not considered. Unanchored part Stress distribution in pile body Pile length Distribution of frictional resistance Bearing layer Steel pipes anchored part Ultimate friction strength Anchored part Steel pipes unanchored part Grout Max. skin frictional resistance fi Fundamental Assumptions of Bearing Capacity Estimation

  13. Bearing capacity estimation equation Ru = U SLi fi Where: Ru : ultimate bearing capacity of HMP determined by the ground (kN) U : circumference of the anchored part (m) U=p*D D : borehole diameter (m) Li : thickness of the layer consideringthe skin friction (m) fi : maximum skin friction of the layer considering the skin friction (kN/m2) * The value of “fi” is the average value of the friction strength shown in a “Design and Execution Specification for Ground Anchor” ,JGS.

  14. Points of the Design Manual (1) Scope (2) Basic principles for seismic retrofitting design (3) Verification at normal time, during strong wind, and during level 1 earthquake (4) Verification during level 2 earthquake 1) Verification items 2) Calculation model (for calculating the sectional force, pile head reactions, and the displacement in a pile foundation)

  15. Verification Items during Level 2 Earthquake • The strength of the foundation • (The pile foundation does not reach the yield conditionof • the foundation by applying horizontal capacity of the pier.) • Even in case of the pile foundation reaches the yield condition, • if the bridge pier has adequate horizontal capacity, • 1) The response ductility factor • and response displacement of the foundation • (2) Liquefaction assessment • (3) Each member of the foundation • (sectional forces generated in each member  strengths of the member)

  16. Vo KVE KVE Mo Ho HMP Existing pile KHE Calculation model The pile foundation with a rigid frame structure supported by the ground resistance considering the non-linearity. Calculation model of a pile foundation retrofitted by HMP

  17. Axial resistance property of a pile Pile head reaction P (kN) Upper limit of push-in bearing capacity PNU tan-1 KVE Pile head axial disp. d (m) PTU Upper limit of pull-out bearing capacity Axial resistant property Calculation model of a pile foundation retrofitted by HMP

  18. Resistant Property at a Right Angle to the Axis of a Pile Upper limit of horizontal subgrade reaction pHU horizontal subgrade reaction pH (kN/m2) tan-1 KHE Horizontal displacement dH (m) Axial resistant property at a right angle to the axis of a pile Calculation model of a pile foundation retrofitted by HMP

  19. Resistant Property at a Right Angle to the Axis of a Pile HMP Front row of existing piles Existing piles Load direction Front row Rear row Existing piles HMP Front row Front row Others Others Sandy ground 1.0 0.5 1.0 0.5 Raito of the upper limit of horizontal subgrade reaction in each row of piles

  20. Bending moment – curvature relationship of HMP Fully Plastic Moment Y’ My’_HMP Y Bending moment M (kN･m) My_HMP Y : yield Y’ : full plastic fy fy’ Curvature f (1/m) Bending moment – curvature relationship of HMP Calculation model of a pile foundation retrofitted by HMP

  21. Yield of a pile foundation Foundation Yield Horizontal seismic coefficient Pier column Displacement at the action location of the superstructure’s inertia

  22. Yield of a pile foundation The yield of a pile foundation retrofitted by HMP is generally the time when one of the following stage is first reached. (1) The bodies of all existing piles plasticize. (2) The bodies of all HMP plasticize. (3) The pile head reaction of a row of piles (existing piles or HMP) reaches the upper limit of the push-in bearing capacity.

  23. Thank you for your attention.

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