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Outline of Design Manual for Seismic Retrofitting of Existing Pile Foundations with High Capacity Micropiles. Public Works Research Institute, Japan Takeshi UMEBARA Jiro FUKUI - PowerPoint PPT Presentation
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Outline of Design Manual for Seismic Retrofitting of Existing Pile Foundations wit
h High Capacity Micropiles
Public Works Research Institute, Japan Takeshi UMEBARA Jiro FUKUI Masahiro ISHIDA
Contents of the manual : Part 1 Design Manual Part 2 Execution Manual
Design and Execution Manual for Seismic Retrofitting of Existing Pile Foundations
with High Capacity Micropiles
Chapter 1 : General Chapter 2 : MaterialsChapter 3 : SurveyingChapter 4 : Basic items for designChapter 5 : Basic items for seismic retrofittingChapter 6 : Verification at normal time, during strong wind, and during level 1 earthquakeChapter 7 : Verification during level 2 earthquake Chapter 8 : Structural details
Contents 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
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
Points of the Design Manual
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
Scope
(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
Points of the Design Manual
(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
Basic principles for seismic retrofitting design
(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
Points of the Design Manual
(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)
Verification Items at Normal Time, during Strong Wind, and Level 1 Earthquake
Pile head part
Pile
leng
th
Bearing layer
Steel pipes anchored part
Distribution of frictional resistance
Ultimate friction strength
Rcu
Grout
Max. skin frictional resistance fi
Ultimate push-inBearing capacity
FootingUn
anch
ored
par
tAn
chor
ed p
art St
ress
dist
ribut
ion
in p
ile b
ody
Steel pipes unanchored part
(1) Frictional resistance is considered only in the anchored part. (2) Bearing capacity of the tip is not considered.
Fundamental Assumptions of Bearing Capacity Estimation
Bearing capacity estimation equation
Ru = U Li fi
Where: Ru : ultimate bearing capacity of HMP determined by the ground (kN) U : circumference of the anchored part (m) U=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 (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.
(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)
Points of the Design Manual
(1) The strength of the foundation (The pile foundation does not reach the yield condition of 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)
Verification Items during Level 2 Earthquake
Calculation model
Calculation model of a pile foundation retrofitted by HMP
HMP
Existing pile
VoMoHo
KVE KVE
KHE
The pile foundation with a rigid frame structure supported by the ground resistance considering the non-linearity.
Axial resistance property of a pile
Calculation model of a pile foundation retrofitted by HMP
PTU
PNU
Pile head reaction P (kN)
Pile head axial disp. (m)
tan-1 KVE
Upper limit of push-in bearing capacity
Upper limit of pull-out bearing capacity
Axial resistant property
HMP
Existingpile
VoMoHo
KVE KVE
KHE
HMP
Existingpile
VoMoHo
HMP
Existingpile
VoMoHo
KVE KVE
KHE
Resistant Property at a Right Angle to the Axis of a Pile
Calculation model of a pile foundation retrofitted by HMP
Axial resistant property at a right angle to the axis of a pile
Horizontal displacement H (m)
tan-1 KHE
Upper limit of horizontal subgrade reaction pHU
horiz
onta
l sub
grad
e
re
actio
n p H
(kN/
m2 )
HMP
Existingpile
VoMoHo
KVE KVE
KHE
HMP
Existingpile
VoMoHo
HMP
Existingpile
VoMoHo
KVE KVE
KHE
Raito of the upper limit of horizontal subgrade reaction in each row of piles
HMP
Front row Rear row
Existing piles
Load direction
Front row of existing piles
Front row OthersSandy ground 1.0 0.5 1.0 0.5
HMP Existing piles
Front row Others
Resistant Property at a Right Angle to the Axis of a Pile
Bending moment – curvature relationship of HMP
Calculation model of a pile foundation retrofitted by HMP
Bending moment – curvaturerelationship of HMP
Curvature (1/m)Be
ndin
g m
omen
t M (k
N・m)
Y
Fully Plastic Moment
Y : yieldY’ : full plastic
y y’
My_HMP
My’_HMP
HMP
Existingpile
VoMoHo
KVE KVE
KHE
HMP
Existingpile
VoMoHo
HMP
Existingpile
VoMoHo
KVE KVE
KHE
Y’
Yield of a pile foundation
Displacement at the action location of the superstructure’s inertia
Horiz
onta
l sei
smic
coef
ficie
nt
YieldFoundation
Pier column
Yield of a pile foundation
The yield of a pile foundation retrofitted by HMP is generallythe 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.
Thank you for your attention.