CONCRETE LIBRARY OF JSCE NO. 34, DECEMBER 1999
A STUDY ON CRITICAL VALUE FOR DECISION TO REQUIRE REPAIR OF CONCRETE
STRUCTURES
(Translation from Proceeding ofJSCE, No.54-4/V-32, 33-41, August, 1998)
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Tomoaki TSUTSU1\/[I Takayuki NAKAGAWA Manabu MATSUSHHVIA Hiroyuki OHGA
In the maintenance of RC structures, the level of deterioration is judged through visual inspections based on a
maintenance manual. If necessary, a detailed inspection is then carried out in order to determine how to repair or
reinforce the structure. Decision-making with respect to repairs and reinforcement follows the maintenance
manuals of various administrations based on the Standard Specification of the JSCE, JCL and so on.
This study sets out to determine the boundary between whether or not to require repairs or reinforcement of a
power plant’s RC structures. Crack width and peeling are selected as measures of chloride-induced damage. The
critical value for repair is obtained using actual data by inverse calculation based on reliability theory.
Keywords: crack width, peeling oflf concrete cover; decision making ofrepair; least expected cost, reliability theory.
Dr. Tomoaki Tsutsumi is a Senior Research Engineer at the Engineering Research Center of TEPCO, Tokyo,
Japan. He received his Master of Engineering Degree from Tokyo Metropolitan University in 1982. His research
interests include the deterioration of RC structures and inspection methods for damaged RC
structures. He is a member of the JSCE and JCI.
.
Mr. Takayuki Nakagawa is a Research Engineer at Tokyo Electric Power Service Co., Ltd, Tokyo, Japan. He
graduated from Utsunomiya University in 1995. His research interests include the deterioration of RC
structures and the application of mathematical modeling to members sutifering chloride-induced
damage. He is a member of the JSCE and JCI.
A
Dr. Manabu Matsushima is a senior research engineer at Tokyo Electric Power Service Co., Ltd,
Tokyo, Japan. He received his‘Doctor of Engineering Degree from Tokyo Denki University in 1994.
His research interest is the application of reliability theory to concrete members in RC structures.
He is member of the JSCE, JCI, and AIJ.
The late Prof. I-Iiroyuki Ohga was Associate Professor at Tokyo Metropolitan University, Tokyo, Japan. He
received his Doctor of Engineering Degree from Tokyo Institute of Technology in 1989. His research
interests included the deterioration of RC structures and new concrete materials. He was a member of
the JSCE and JCI
1
.INTRODUCTION
Concrete structures have long been regarded as permanent,with a major advantage being low maintenanceover
manyyears. However,it has been observed in recent years that manyconcrete structures are suffering deterioration
for various reasons. As a result, the importance of maintenance and rehabilitation work has becomewidely
recognized again [ 1 ] , [2].
The process for managing concrete structures begins with a judgment of the deterioration level using a simple
visual inspection based on a maintenancemanual.Then, if rehabilitation works is required, a detailed inspection is
carried out The visual judgement as to the whether or not to repair and reinforcement is required is carried out
based on an administration's ownstandards or those of various public associations. The decision is based on
whether or not the performance of the deteriorated structure continues to satisfy the required functionality. The
criteria for judging deterioration level are bearing capacity, durability, serviceability, and appearance. However,the
most important of these criteria are the bearing capacity of membersand cracking along the reinforcement
Bearing capacity can be obtained through structural calculations taking into account the reduced cross section of
reinforcement using data obtained in situ. Static bearing capacity is not reduced by the occurrence of cracks along
the reinforcement because the corrosion products are few whencracking occurs. However,bearing capacity is
reduced because the bond strength of the reinforcement is reduced under repeated positive-negative loading. The
corrosion rateof reinforcement increases with elapsed time after cracking.
Appearanceis judged in terms of cracking due to corrosion products and rust stains. Deformationis judged by
reduced stiffness of membersdue to peeling-off of coverconcrete [3].
Visual inspection of any deteriorationis the usual approach at the first stage, while the detailed, secondary stage
entails investigation of chloride ion density, carbonation depth, and nonedetective test Given the thoroughness of
the detailed stage, these inspections are carried out only after the decision has been madeto require repairs.
According to the results of a questionnaire put to concrete engineers [4] , the decision as to whether or not torequire
repairs mainly depends on concrete cracking and peeling-off. Of secondary importance are exposure of the
reinforcement, corrosion products, rust stain, lack of bearing capacity, leakage of water, and appearance.
These criteria are judged by visual inspection [5] ~~[ 1 5]. For example, according to the Standard Specifications
of the Port and Harbor Bureau,deteriorationis judged using three criteria: the corrosion state of the reinforcement,
concrete cracking,and concrete peeling. The authors have studied use of crackwidth as a criterion for repair and
peeling off[ 1 6]. Miyamoto at al. [ 17] propose equipment for evaluating concrete bridges based on a nemo-fuzzy
expert system constructed using the results of questionnaires completed by inspection engineers.
This method provides for evaluation of visual inspections also of repair intervals while taking cost-performance
into consideration,and this approach will in future prove useful in maintenance and rehabilitation work.However,
there is a need for moredeteriorationdata tobe gathered as in situ data remains scant
In this paper, based on the past results of maintenance and rehabilitation works in practice, the
critical value of chloride induced damage, namely crack width and peeling, at which repairs
became necessary is obtained by inverse calculation using the in situ deterioration data.
2. CRITERIA IN CURRENT STANDARDS
The criteria used to judge the relationship between crackwidth and repair interval differ among various
administrations. Somedo not refer to crackwidth at all. Some treat crackwidth as related to reinforcement
corrosion while others accept no link. Thus, noconsensuscanbe reached amongscholars at present
78
Twocrack width criteria can be considered one for design and one for repair. The critical value for design is
smaller than that for repair [3]. The critical value of crack width at various administrations is shown in Figure 1 [5]
~
[ 15]. Where no value is actually given in the specifications, it is derived by comparisonwith other criteria and
the authors' experience with deterioration inspections. The target structure is a landing pier assumed to be located
in the splash zone.According to this figure, the critical value of crack width lies between 0.2 and 0.4mmin various
administrations [5 ].
The state of peeling at which repair becomesnecessary is shown in Figure 2. The criteria of most administrations
requires repair and reinforcing whenpartial peeling off occurs. In the case of structures, such as bridges where
injury to the general public is a possibility, repairs are requited even whenlight damage occurs to be on the safe
side.
Japan Road Association:
Standard
specification
for measures against
chloride induced damage 5)
J S C E : S t a n d a r d s p e c i f ic a ti o n fo r
d e s ig n a n d c o n s tru c tio n o f m a r in e
c o n c re te s tru c tu re s
Civil Engineering
Research Center:
Project of ministry of constructiondevelopment of durability
technology
for concrete structures 8)
J S C E : S t a n d a r d s p e c i f ic a ti o n fo r
d e s ig n a n d c o n s tr u c tio n o f c o n c re te
stru c tu re s (D e s ig n ) 12)
C e n tra l R e s e a rc h In s titu te o f R a ilw a y
T r a n s p o r t a t io n : S t a n d a r d d e s ig n
sp e c if ic a tio n f o r r a ilw a y c o n s tru c tio n
- C o n c re te s tru c tu re s '
of \j
<
A r c h ite c tu r a l In stitu te o f Ja p a n : C r a c k
m e a s u r e s f o r c o n c re t e b u i ld in g s
(D e s ig n a n d c o n s tr u c tio n )
n
J C I : S t a n d a r d s p e c i f ic a t io n o n
in s p e c tio n , re p a ir , a n d re in fo rc e m e n t
o f c o n c re te s tru c tu r e s
I
I
I
I
I
0 .0
I
I
1 .0
0 .6
0 .4
0 .2
Allowable
crack width w (mm)
Figure 1 Criterion for crackwidth
Civil Engineering
Research Center: Project
of construction-development
of durability
for concrete structures 8)
of ministry
technology
JCI: Standard specification
for inspection,
reinforcement of concrete structures 7)
repair,
and
Investigation
prevention
prevention
of
and
and
Coast Development Technical Center:
marine concrete structure deterioration
reinforcing
-Manual for deterioration
reinforcing
13)
I
bridges
Construction
for repair
Hokuriku Regional Construction Bureau:
Specification
for repair of bridges 9>
I
Hokuriku
Regional
Bureau: Specification
Potentially
Partially
Overall
State of peeling
Figure2 Criterion for peeling
79-
Loss of section
1 .2
3
. DECISION AS TO WHETHER OR NOTTO REQUIRE REPAIR
The deterioration level of a target structure must be evaluated in order to manageits maintenance. Although each
administrationhas its owncriteria for deteriorationlevel, assumptions are based on the characteristics of the target
structure. Typical criteria are as given in investigation of marine concrete structures ondeteriorationprevention and
reinforcing-manual for deterioration prevention and reinforcing-edited by Coast Development Technical
Center[13] , Standard specification for maintenance managementof structures, edited by Central Research
Institute of Railway Transportation [14] , and Inspection specification on road structures edited by Hanshin
Expressway Public Corporation[ 1 5]. In these specifications, concrete cracks,peeled off area, and rust stains are
mainly judged by visual inspection and the results used to determine the deteriorationlevel. Oncethe deterioration
level has been determined, a decision is made according to 1) the importance of the structure, 2) the results of
visual inspection, and 3) budget. Criterion 3) is artificial and varies with social conditions. Criteria 1) and 2) are
universal and can be explained as follows.
The decision as to whether or not to require repair depends on the importance of the structure
and the function of its structural members. The importance of repair can be determined by
considering the function of structural membersin the order 1) column, 2) beam, 3) slab, and 4)
other non-structural members.
Table 1 Maintenance ManagementDiagramusing Visual Inspection
Item s
n
(1) C rack w idth
C rack
p attern } n ot
a ffectin g stru ctu re an d
fun ction .
W h en
crack s affec t
structural fu n ctio n , crack
w id th *2*is w < 0 .0 0 5 C m m .
(2 ) A m ou n to f P eeling
P eelin g w ith d iam eter less
th an 5 0cm an d d ep th less
th an 2 .5 cm .
(3 ) E xp o su re S tate o f E x p o sure of agg reg ate .
A g g regate
(4 ) R u stS tain
(5 )
E x po sure
R einforcem en t
D am ag e L ev el
m
IV
C rack p att ern n o t affectin g C rack w idth affec tin g
structure an d fun ctio n .
b earin g
cap acity
of
E v en if crack w id th m em b ers
w < 0 .00 5m m , pro p agatio n
of crack p rog resse s.
P eelin g w ith d iam eter
o v er 5 0 cm an d d epth o v er
2 .5 cm .
A g g regate to sep arate
sep aratin g offo r like ly
S tates of ag greg ate
affectin g b earin g cap acity
o f m em b ers
W id espread ruststain s
E x p o sure
o f E x p o su re
of
rein fo rc em ent o f stru ctural rein fo rcem en to f stru ctu ral
m em b ers.
m em bers
affecting
b earin g
cap acity
of
m em bers.
*1) Crack not affecting structural members
is not bending or shear crackbut crack parallel to mainbars or crack
dueto drying and shrinking.
*2) Calculation using coverthickness. Generally, the relationship betweencoverthickness and crack width is as
follows;
C o v e r th ic k n e s s t ( m m )
C r a c k w i d th w ,,
S p o tty ruststain s
o f E x p osure
of
rein fo rcem en t of n o n stru cturalm em bers.
P eelin g aff ec tin g b earin g
c apa city o f m em b ers
30
0 .1 0
50
0 .2 0
-80-
70
0 .3 5
Visual inspections are mainly evaluated with respect to a) crack width, b) concrete peeling, c)
rust stains, d) exposure of reinforcement, and e) exposure of aggregate. Of these, deterioration
depends directly on a) crack width and b) concrete peeling while c),d), and e) are subordinate.
These conclusions can be substantiated by statistical
analysis using periodical in situ inspection
data[!7].
An example of the criteria used for visual inspections in a marine environment is shown in Table 1. The
deterioration level is divided into four stages: I : no deterioration, It : slight deterioration, in : mild deterioration,
and IV: severe deterioration [18]. Rehabilitation work is required when the deterioration exceeds in and the
boundary between deterioration levels n and HI is the criterion for repair. Although the decision mainly
depends on crack width and peeling, the need for rehabilitation work maybe judged synthetically from the
importance of the structure and the location of deteriorated members.
4. CRITERIA FOR DETERIORATIONLEVELUSING INVERSE ANALYSIS
Aninverse method using crack width is explained below. Concrete structural membersare divided into four types,
a) column, b) beam, c) wall, and d) slab. Crack width distributions reflecting deterioration levels II and El , as
obtained fromvisual inspections of existing concrete structures located in Tokyo Bay, are shown in Figure 3.
Although the boundarybetween n and IH seems vague, the borderbetween n and ffl can be found. These
data are for cases where only cracking occurs but no peeling. Therefor, an analysis considered both complex
evaluations don't require. The probability density function for each deterioration level is modeled using the crack
width data at deterioration levels E and HI. Since the result is not symmetrical about the meanof the data, a lognormal distribution gives an approximation as shownin the figure 4.
The log-normal probability
density function model f2 (w),
d
[ l9].
efined as Eq.(l)
and Eq.(2)
f2 (w)=
V 27r|7 w
f3 (w)
for deterioration levels II and HI may be
i flnw-A.;
expl
(1)
'2
^'
ou
U D e te ri o r a tio n L e v e l II
8
50
1 D e te ri o r a tio n L e v e l III
40
>>
o
C 30
24
<D
20
0
10
3
0 0
B ,
SS: III I
n
0 .0
0.5
1.0
1.5
fl O E D
2.0
2.5
3.0
0 0
3.5
3 3 0 0 0 0 0 0 4 D
4.0
4.5
5.0
5.5
6.0
Crack Width w (mm)
Figure 3 Crack width of deterioration levels
-81
II and HI (Wall)
2 .0
-ODeterioration Level II
-0-Deterioration Level III
0 .5
1 .0
1.5
2.0
2 .5
3 .0
Crack Width w(mm)
Figure 4Relationship
between f2 (w ) and f3 (w )
Table 2 Mean and Standard Deviation of Each Deterioration Level
Ite m s
D e te ri o ra ti o n le v e l II
C o lu m n
M ean
0 .5 0 ( 1 4 )
S .D .
1 .2 3
C ra ck w id th
B eam
0 .7 5 (2 2 )
w Jm m )
S ab
W ai
0 .0 0 (3 )
0 .8 9 (7 4 )
C o lu m n
B eam
S ab
0 .4 0 ( 1 6 )
0 .3 3 ( 1 7 )
0 .0 5 (1 2 )
W all
0 .4 1 (5 7 )
P e e lin g
A J m 2)
N
M em b er
D e te ri o ra ti o n le v e l IE
M ean
2 .7 7 (2 1)
S .D .
2 .2 1
0 .6 8
3 .3 9 (5 4 )
0 .0
1 .2 4
0 .1 6
1 0 .4 4 (2 4 )
.4 9 (4 7 )
1 .5 4 (9 )
0 .4 9 (3 )
2 .3 7
5 .9 7
0 .1 6
0 .0 4
0 .6 3
0 .8 7 (7 )
3 .2 6 (9 )
1 .1 2
0 .6 7
0 .0 0
0 .3 5
1 .4 8
umberin Q indicates number of data.
f
3 (w)=
Where, A,L and £,L are the coefficients
XL =&HIL -^L2
271&W
exp
(2)
of the log-normal probability
and ^L2 =M 1+-V L representatively.
density function and described as
JIL and aL are the mean and standard
2
( ^J
deviation of crack width at deterioration level L. Suffices 2 and 3 indicate deterioration levels H and HI,
respectively. The value in 0 in Table 2 indicates the number of data obtained in situ. The relationship between
f2(w)
and f3(w)
is shown in Figure 4 using a wall as an example. Deterioration level II may be selected
whenthe crack width is small. On the contrary, deterioration level III is indicated whenthe crack width is large.
The boundary between II and HI is a gray zone that is not easy to divide. Assuming that the crack width at
which repair becomesnecessary is wcr, the probability
-82-
of misjudging a deterioration level of HI when the actual
structure is at deterioration level
II is described
as Eq.(3).
+00
C2(wJ=
Jf2(w)dr
(3)
wcr
In the same way,the probability of judging a deterioration level of II when the target structure is at deterioration
level III is described as Eq.(4)
C3 (wc>
WJrf3(w )dr
o
(4)
Therefore, wcr is chosen as the optimum crack width at which repair becomes necessary when Cj (wcr )
obtained as the summationEq.(3) and Eq.(4) is minimized as shown in following equation:
CT(wJ=
C2(wJ+C3
+00
(5)
Wcr
=Jf2(w)dr+
wcr
The distribution
(wJ
Jf3(w)dr
0
of crack width to require repair is described
as Eq.(6) by conversing
CT (wcr ) to the equation to
take a maximumvalue when CT(wcr ) may be minimized.
fWc>cr )= l -CT (wcr )
The probability
in Figure 5(a)~(d)
distributions
of crack width
and Rgure 6(a)~(d)
(6)
fwcr (w ) and peeled area fAcr (A) obtained in this paper are shown
respectively. C2 (w ),C3 (w ),C2 (A),
and C3 (A) are also shown in the
samefigures.
5. CLASSIFICATION OF REPAIRS
The maximumlikelihood estimator of crack width distribution and peeled area is assumed to coincide with the
decision point as to whether or not to require repair in this paper. Likelihood values obtained using the method
described above are shown in Table 3. Crack width for slabs and peeled area for beams are excluded fromthe
evaluation because of a shortage of in situ data as indicated in the table. Crack width obtained in the above manner
indicates 0.6~1.2 mm,a value larger than the 0.2mmgiven by the Standard Specification for Design and
Construction of Concrete Structures (JSCE; environment severe; cover thickness: 7cm). This value of 0.2mmis
obtained by considering the allowable crack width for design, and its value is chosen on the safe side. According to
the Standard Specification for Inspection, Repair, and Reinforcement of Concrete Structures (JCI) [ 1 1 ] , 0.4mm is
O3
OJ
the allowable crackwidth at which repair becomes necessary and this value is also small even if scatter is
considered. According to the results on peeling, as shown in the table, the value at slab indicates about only 0.3m3.
Critical value at column and wall indicate about 1.Om3.The data at slab can't be reliability as shown in Figure 6(c)
because the whole data at unrepair is nearly zero. Therefore, the results of peeling off at slab are to deal as reference
after this.
The concept behind the classification of rehabilitation
work is non described. The probability distribution
indicating repair is described as Eq.(6). Therefore, assuming that the integral of Eq.(6) over the whole distribution
is 1.0, the risk probability
of crackwidth whether or not to require repair Fwc(w c ) is described
as Eq.(7).
Fw» Jfwcr(wc
)iw
0
(7)
Where, wcrindicates the critical value of crackwidth with risk probability
taken into account The relationship
between crack width wcr and risk probability
Fwc(wc ) is also shown in Figure 8(a)~(d).
The integral of the
whole crack width distribution is adjusted to equal 1.0 when the crack width is 10.0mm and whenthe area of
peeling is 4.0m3. Although the deteriorationvalue mayreach infinity in a mathematical sense, an upper limit value
is assumed in the mannerdescribed earlier in this paper, so the actual phenomenonhas an upper limit Equation (7)
meansthat rehabilitation work is definitely not required at zero and is certainly required at 1.0. Therefore, Eq.(7)
represents the probability of repair being required. Figure 7 indicates that the cumulate probability density function
at walls and beams mayincrease rapidly to 1.0 with crackwidth wcr while it may increase slowly to 1.0 for other
members.
The difference can be explained by the difference in scatter of deteriorationlevels II and HI , as shown
in Figure 5. In case of the cumulate probability density function increasing rapidly to 1.0, the point at which repair
becomenecessary is ill-defined because the overlap is larger and the variation of both distribution is spread. On the
contrary, when it increases slowly to 1.0, the decision is clear because the overlap is smaller and the variation is
narrowed.The critical value of crackwidth and peeling with considering risk probability taken into account is
obtained as follows. Generally, 5% or 1% is statistically permitted when a rare event occurs [20]. It is said that
those values are appropriate to a human sense[20]. 'A 5% risk probability, namely a 95% reliability value, is also
described in the Standard Specification for Design and Construction of Concrete Structures (JSCE) if it is assumed
that the distribution of materials is a normal distribution. A 95% reliability value is accepted in this paper according
to the same argumentThe critical values mentionedabove are the case of severe condition that a membersmaybe
caused immediately by received damage. Onthe other hand, in the case that the bearing capacity of the structure
has deteriorated moderatelydue to chloride-induced damage and unaffected immediately bearing capacity by the
occurrence of deteriorationcracking,the risk probability can take larger than 5% risk probability. Although the
samediscussions are left how to choose the risk probability, a 15% risk probability, namely a 85% reliability value,
is adopted in this paper. The critical values of crackwidth obtained using Figure 7 are shown in Figure 9. The
critical values of peeling obtained using Figure 8 are shown in Figure 10. The crackwidth is 0.3~0.6mmfor a
85% reliability value and the critical values coincide roughly with various administrations (0.2 ~0.4mm) because
various standard specifications for repair are developed in considerationof future deteriorationat the design stage.
1 .04
0 .0
2 .0
3.0
4.0
Crack Width'-w
( a)
2 .0
5.0
.0
6.0
-(mm)
3.0
4.0
A (m2)
(a) Column
Column
4.0
2.0
Peeling
6.0
0.0
8.0
0.2
0.4
0.6
Crack Width w (mm)
0.8
Peeling
(b)B eam
1.0
1.2
1.4
1.6
A (m2)
(b)B eam
à"0 &-CD=i
1
T77T
0 .0
0 .0
5.0
1 0.0
1 5.0
20.0
1 .0
Crack Width w (mm)
(c)
1
.0
0
.0 GO
2.0
Peeling
( c)
Slab
3.0
4 .0
A (m2)
Slab
£
0 .0
0.5
1 .0
1.5
.0
2.0
Crack Width w (mm)
distribution
3.0
A (m2)
(d)Wall
(d)WaU
Figure 5 Probability
2.0
Peeling
of crack width fwcr (w )
-85~
Figure 6 Probability
distribution
of peeled are fAcr (A )
2 .0
4.0
6.0
8.0
10.0
Crack Width we (mm)
Figure 7 Relationship
between Fwc(wc ) and crack width wc
1 .0
2.0
Peeling
Figure 8 Relationship
3.0
4 .0
Ac (m2)
between FAc(Ac ) and peeled area A,,
Table 3 Critical Values
Ite m s
G ar d e W id th
W c(m m )
P e e lin g
A M
C o lu m n
B eam
S lab
0 .8
1 .2
0 .7
0 .4 )
W aU
(2 .0 )*
0 .6
Data in Q for reference only due to shortage at data.
Data marked *for reference due to whole data of deterioration
0 .3 *
1 .3
n nearly equaling to 0.0.
The crack width for an 85% reliability value is 0.5~1.0mm. These values are larger than existing standard
specifications and coincides with the likelihood value (0.8 ~~
1.Omm)obtained from the distribution of crack width
as shown in Table 3. It seems that the critical value in maintenance mutual is in too safety side with considering the
fact that rehabilitation managementin practice has been earnedout well. Consequently, it can be proposed that the
critical value of crack width in actual rehabilitation managementcanbe eased as a result of the argument above.
86-
The area of peeling is 0.4m2 at a 95% reliability value and 0.6~0.7m2 at on 85% reliability value. The critical
value of 0.5m2 at which repairs are necessary, as shown in Table 1, coincides roughly with the critical values
obtained here.
l.O
1.4
ta
｣ 1.2
I 1.0
mft
O 85% R eliab ility V alueTl f Q )
D 95% R eliab ility V alue
s¥
0.8
O
0.6
<u 0.4
｣
｣ 0.2
<
nn
-D
-<D *
o
n
Colu mn
Beam
Slab
Wall
Member
Figure 9 Allowable crack width WCT
u .o
-r 6 ^ 0 .7
O 9 5%
R e lia b ility V a lu e !
D
R e lia b ility V a lu e
85 %
0 .6
ra
<
0 .5
0ｻ
=
CD
n
0 .4
o
0 .3
JO
｣
o
<
) r ¥¥
v ^ ;
0 .2
-fc
u
/^ #
^ ｻ
0 .1
n n
Column
Beam
Slab
Wall
Member
Figure 10 Allowable
6
peeled area A<,
. CONCLUSION
In this paper, based on the past results of maintenance and rehabilitation
works in practice, critical
values of major parameters of chloride-induced damage, namely crack width and concrete peeling at which repairs
becomesnecessary are obtained by inverse calculation using deterioration data obtained in situ.
The following is a summaryof the findings:
(1)
A stochastic model is proposed using the distribution for two deterioration levels II and ffi using existing
investigation data.
(2) The crack width at which repair is required is obtained using the proposed model. A value of 0.0~0.6mmat a
95% reliability level is obtained, and coincides with various current standards. A value of 0.0~~1.0mmat an
85% reliability level is obtained, and coincides with records of past rehabilitation work.
(3) The area of concrete peeling is 0.4m2 at a 95% reh'ability level and 0.6~0.7m2 at an 85%
reliability
level. The boundary value of 0.5m2 between repair being required at not, or
between deterioration levels II and ffi as shown in Table 1, coincides roughly with the
-87-
critical
value obtained in this paper.
REFERENCES
1) Ootuki N., and Sekino T,: Studies on the durability of old concrete structures in HOKAIDO, Proceeding of
JSCE,No.366/V-4,pp.27-37,
1996.2 (in Japanese).
2) Kobayashi, K.: Durability of concrete structures, Proceeding of Japan Concrete Institute,Vol.23, No.2,pp.4-12,
Feb., 1 985 (in Japanese).
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required to repair RC structures, Proceeding of JSCE,No.420/V- 13 ,pp. 1 8 1 - 1 90, 1 990.8 (in Japanese).
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Electric Power Industry, 1992. 10 (in Japanese).
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Structures, 1 977.3 (in Japanese).
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1987.2 (in Japanese).
8) Civil Engineering Research Center: Project of Ministry of Construction -Development of durability technology
for concrete structures, 1 989.5 (in Japanese).
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Japanese).
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