Outline of Design Manual for Seismic Retrofitting of

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

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

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

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

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

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

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

Basic principles for seismic retrofitting design (2) The seismic retrofitting design of an existing pile foundation shall be performed, as necessary, with consideration two Two levels design earthquake motions levels of 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 oc during the service life of the existing bridge

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

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)

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)

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

Bearing capacity estimation equation Ru = U S Li fi Where: Ru : ultimate bearing capacity of HMP determined by the ground (k. N) U : circumference of the anchored part (m) U=p*D D : borehole diameter (m) Li : thickness of the layer considering the skin friction (m) fi : maximum skin friction of the layer considering the skin friction (k. N/m 2) * The value of “fi” is the average value of the friction strength shown in a “Design and Execution Specification for Ground

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 reactions, (for calculating the sectional force, pile head

Verification Items during Level 2 Earthquake (1) The strength of the foundation (2) (The pile foundation does not reach the yield condition of (3) the foundation by applying horizontal capacity of the pier. ) (4) Even in case of the pile foundation reaches the yield condition, (5) if the bridge pier has adequate horizontal capacity, (6) (7) 1) The response ductility factor and response displacement of the

Calculation model KVE V Hoo Mo KVE HM P Existin g pil e KHE Calculation model of a pile foundation retrofitted by The pile foundation with a rigid frame structure supported by the ground resistance considering the non-linearity.

Axial resistance property of a pile Pile head reaction P (k. N) Upper limit of pushin PNU bearing capacity tan-1 KVE Upper limit of pullout bearing capacity Calculation model of a pile foundation retrofitted by Pile head axial disp. d (m) PTU Axial resistant property

horizontal subgrade reaction p. H (k. N/m 2) Resistant Property at a Right Angle to the Axis of a Pile Upper limit of horizontal subgrade reaction p. HU tan-1 KHEHorizontal displacement d. H (m) Calculation model of a pile foundation retrofitted by Axial resistant property at a right angle to the axis of a pile

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 Raito of the upper limit of horizontal subgrade reaction in each ro Existing piles HMP Sandy ground Front row 1. 0 Others 0. 5

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

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

Yield of a pile foundation The yield of a pile foundation retrofitted by HMP is gener 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 reaches the upper limit of the push-in bearing capaci

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