1. Masaru Hoshiya Musashi Institute of Technology
IWM2002
Probability Study for a High-Capacity Micropile Bearing Mechanism
Masaru Hoshiya Musashi Institute of Technology
Yoshinori Otani Hirose & Co., Ltd.

2. The purpose of research
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The purpose of research
Design optimization　for the HMP
The uncertainty of each composition parameter (characteristic of ground condition , material , load)
Current design Code (draft)
（Allowable Stress Method）
Partial Factor Design Method

3. Today’s Topics Probabilistic analysis of bearing mechanism for HMP
IWM2002
Today’s Topics
Probabilistic analysis of bearing mechanism
for HMP
Effectiveness of Partial Factor Design Method

4. Structure , failure modes of HMP
IWM2002
Steel
Pipe
Bearing
Stratum
Core
(deformed
re-bar)
Grout
Fig.1
Structure of HMP
Fig.2
Failure modeⅠ
Fig.3
Failure mode Ⅱ
Fig.4
Failure mode Ⅲ

5. Current design(1) (1) IWM2002 IWM2002
　　 (1)
r: revision coefficient for the safety factor by the difference in how to estimate ultimate bearing capacity
n: safety factor
　　　　 　 　　　 (2)
RC1: ultimate friction bearing capacity
RC2: steel pipe compressive strength
RC3: sum of non-steel pipe anchorage ultimate compressive strength
and steel pipe bond ultimate friction resistance
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6. Current design (failure mode Ⅰ～Ⅲ)
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(3)
R1: bond perimeter friction
R2: end bearing capacity
　　　 　　(4)
R3: ultimate compressive strength
of steel pipe grout
R4: ultimate compressive strength
of re-bar and steel pipe
　　 　　 　 (5)
R5: ultimate compressive strength of non-steel pipe grout
R6: ultimate compressive strength of re-bar
R7: bond perimeter friction of steel pipe
Casing Plunge Length LC
Bond Length L
Bearing
Stratum
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7. Partial factor design method(1)
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Partial factor design method(1)
(6)
(7)
(8)
(9)
Z,Zi≧0, safe
Z,Zi≦0, failure
SD: dead load
SE: earthquake load

8. Partial factor design method(2)
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Partial factor design method(2)
(10)
(11)
(12)
Rj*: characteristic value of resistances
(j=1～7)
SD*: characteristic value of dead load
SE*: characteristic value of seismic load
φRj,γSDi, γSEi:partial factor

9. Partial factor design method(3)
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Partial factor design method(3)
(13)
(14)
(15)
αRjT,αSDiT,αSEiT: standard sensitivity coefficient for each resistance,dead load,
seismic load
βiT: target safety index for Zi
kRj , kSDi , kSEi: coefficient which connect mean and standard sensitivity factor of
the resistances , dead load ,seismic load
VRj ,VSD ,VSE: 　　 coefficient of variation for the resistances ,dead load ,seismic load
(16)

10. Mechanical Characteristics of failure mode Ⅰ
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Mechanical Characteristics　of failure mode Ⅰ
: αR1 bond perimeter friction
: αR2 end bearing capacity
Bond length of the pile L(m)
Sensitivity Coefficients Vs. Bond Length

11. Mechanical Characteristics of failure mode Ⅱ
IWM2002
Mechanical Characteristics　of failure mode Ⅱ
αR3:ultimate compressive strength of steel pipe grout
αR4:ultimate compressive strength of re-bar and steel pipe
compression strength of the grout fG (N/mm2)
Sensitivity Coefficients Vs. Compression Strength of Grout

12. Mechanical Characteristics of failure mode Ⅲ
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Mechanical Characteristics　of failure mode Ⅲ
:αR5 ultimate compressive
strength of non-steel pipe grout
:αR6 ultimate compressive
strength of re-bar
:αR7 bond perimeter friction of
steel pipe
Casing plunge length of the steel pipe Lc(m)
Sensitivity Coefficients Vs.
Casing Plunge Length of Steel Pile

13. Comparison of safety index β
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Comparison of safety index β
Histogram of Safety Index β1
Histogram of Safety Index β2
Histogram of Safety Index β3

14. Dependability of resistances (sensitivity coefficient α)
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Dependability of resistances (sensitivity coefficient α)
Characteristic value　Rc1*
Characteristic value　Rc3*
Sensitivity Coefficients Vs.
Sensitivity Coefficients Vs.

15. Comparison of Current design code and PFD Method
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Comparison of Current design code and PFD Method
Comparison of βa and　βa’

16. IWM2002
Conclusion
Partial Factor Design method can achieve optimization of ＨＭＰ designs by taking into consideration the probability and dependability of the parameter which constitutes each limit state.