Masaru Hoshiya Musashi Institute of Technology

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

2. IWM2002 The purpose of research • Design optimizationfor 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. IWM2002 Today’sTopics • 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) 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 IWM2002

6. Current design (failure mode Ⅰ～Ⅲ) IWM2002 (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 IWM2002

7. IWM2002 Partial factor design method(1) (6) (7) (8) (9) Z,Zi≧0, safe Z,Zi≦0, failure SD: dead load SE: earthquake load

8. IWM2002 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. IWM2002 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. IWM2002 : αR1 bond perimeter friction : αR2 end bearing capacity Mechanical Characteristicsof failure mode Ⅰ Bond length of the pile L(m) Sensitivity Coefficients Vs. Bond Length

11. IWM2002 Mechanical Characteristicsof 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. IWM2002 Mechanical Characteristicsof 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. IWM2002 Comparison of safety index β Histogram of Safety Index β1 Histogram of Safety Index β2 Histogram of Safety Index β3

14. IWM2002 Dependability of resistances (sensitivity coefficient α) Characteristic valueRc1* Characteristic valueRc3* Sensitivity Coefficients Vs. Sensitivity Coefficients Vs.

15. IWM2002 Comparison of Current design code and PFD Method Comparison of βa andβa’

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.