Probability study for a High-Capacity Micropile Bearing Mechanism

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29 Νοε 2013 (πριν από 3 χρόνια και 10 μήνες)

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IWM2002

Masaru Hoshiya


Musashi Institute of Technology

Probability Study

for

a High
-
Capacity Micropile
Bearing Mechanism

Yoshinori Otani


Hirose & Co., Ltd.

IWM2002



Design optimization

for the HMP

The uncertainty of each composition parameter
(characteristic of ground condition , material , load)

The purpose of research


Partial Factor Design Method

Current design Code (draft)


Allowable Stress Method


IWM2002

Today’s

Topics



Effectiveness

of

Partial

Factor

Design

Method



Probabilistic analysis of bearing mechanism


for HMP

IWM2002

Grout

Bearing

Stratum

Steel

Pipe


Core

(deformed


re
-
bar)

Fig.1


Structure of HMP


Fig.2

Failure mode


Fig.3

Failure mode


Fig.4

Failure mode


Structure , failure modes of HMP

IWM2002

Current design(1)




(1)



r: revision coefficient for the safety factor by the difference in how to
estimate ultimate bearing capacity


n: safety factor








(2)



R
C1
: ultimate friction bearing capacity


R
C2
: steel pipe compressive strength


R
C3
: sum of non
-
steel pipe anchorage ultimate compressive strength


and steel pipe bond ultimate friction resistance

n
rR
R
cu
ca



min
,
,
3
2
1
C
C
C
cu
R
R
R
R

IWM2002

IWM2002


(3)

R
1
: bond perimeter friction

R
2
: end bearing capacity






(4)



R
3
: ultimate compressive strength


of steel pipe grout

R
4
: ultimate compressive strength


of re
-
bar and steel pipe









(5)


R
5
: ultimate compressive strength of non
-
steel pipe grout

R
6
: ultimate compressive strength of re
-
bar

R
7
:

bond

perimeter

friction

of

steel

pipe


4
2
0
0
2
1
1
D
q
L
aD
R
R
R
i
i
C








)
(
85
.
0
1
4
3
2
C
B
BorC
G
G
C
A
A
F
A
f
R
R
R












u
u
B
B
G
G
C
L
aD
A
f
A
f
R
R
R
R


0
2
7
6
5
3
85
.
0
Bearing

Stratum

Bond Length
L

Casing Plunge Length
L
C

Current design (failure mode



)

IWM2002

IWM2002


Partial factor design method(1)


(6)



(7)



(8)



(9)


Z,Z
i

0, safe

Z,Z
i

0, failure

S
D
: dead load

S
E
: earthquake load

E
D
C
C
C
S
S
R
R
R
Z



]
,
,
min[
3
2
1
E
D
S
S
R
R
Z




2
1
1
E
D
S
S
R
R
Z




4
3
2
E
D
S
S
R
R
R
Z





7
6
5
3
IWM2002


Partial factor design method(2)


(10)




(11)




(12)



R
j
*: characteristic value of resistances


(j=1

7)

S
D
*: characteristic value of dead load

S
E
*: characteristic value of seismic load

φ
Rj
,
γ
SDi
,
γ
SEi
:partial factor

*
1
*
1
*
2
2
*
1
1
E
SE
D
SD
R
R
S
S
R
R
γ
γ
φ
φ



*
2
*
2
*
4
4
*
3
3
E
SE
D
SD
R
R
S
S
R
R
γ
γ
φ
φ



*
3
*
3
*
7
7
*
6
6
*
5
5
E
SE
D
SD
R
R
R
S
S
R
R
R
γ
γ
φ
φ
φ




IWM2002


Partial factor design method(3)


(13)



(14)



(15)


α
Rj
T

SDi
T

SEi
T
: standard sensitivity coefficient for each resistance,dead load,


seismic load

β
i
T
: target safety index for Z
i

k
Rj
, k
SDi
, k
SEi
: coefficient which connect mean and standard sensitivity factor of


the resistances , dead load ,seismic load

V
Rj

,V
SD

,V
SE
:


coefficient of variation for the resistances ,dead load ,seismic load



(
16
)

Rj
Rj
Rj
T
i
T
Rj
R
V
k
V



1
1



φ
SE
SEi
SE
T
i
T
SEi
SEi
V
k
V



1
1


γ
SD
SDi
SD
T
i
T
SDi
SDi
V
k
V



1
1


γ
 
)
(
1
i
fi
Zi
Zi
i
P









IWM2002

Mechanical Characteristics

of
failure mode


Sensitivity Coefficients Vs. Bond Length


: α
R1

bond perimeter friction


: α
R2

end bearing capacity

Bond length of the pile L(m)

IWM2002

compression

strength

of

the

grout

f
G

(N/mm
2
)

Mechanical Characteristics

of
failure mode


α
R3
:ultimate compressive strength of steel pipe grout

α
R4
:ultimate compressive strength of re
-
bar and steel pipe

Sensitivity Coefficients Vs. Compression Strength of Grout


IWM2002

Mechanical Characteristics

of
failure mode




R5

ultimate compressive


strength of non
-
steel pipe grout



R6

ultimate compressive


strength of re
-
bar



R7

bond perimeter friction of


steel pipe

Sensitivity Coefficients Vs.

Casing Plunge Length of Steel Pile

Casing plunge length of the steel pipe Lc(m)

IWM2002

1.5     1.6    1.7    1.8    1.9     2.0
0
2
4
6
8
10
12
14
16
1
2
3
4
5
β1
Frequency
0
2
4
6
8
10
12
14
16
1
2
3
4
5
6
β2
Frequency
10.5  11.0  11.5   12.0  12.5  13.0  13.5
1.5     1.6    1.7    1.8    1.9     2.0
0
5
10
15
20
25
30
1
2
3
4
5
β3
Frequency
3.0     3.2    3.4    3.6    3.8     4.0
Histogram of
Safety Index β
1

Histogram of
Safety Index β
2

Histogram of
Safety Index β
3


Comparison of safety index β

IWM2002

Dependability of resistances


(sensitivity coefficient α)

Sensitivity

Coefficients

Vs
.


Characteristic value

R
c1
*

Sensitivity

Coefficients

Vs
.


Characteristic value

R
c3
*

IWM2002

Comparison of Current design
code and PFD Method

Comparison

of

β
a

and

β
a


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.