preliminary estimation of reduction factors in mechanical...
TRANSCRIPT
Paper Number O84
Preliminary estimation of reduction factors in mechanical properties of steel reinforcement due to pitting simulated corrosion
2014 NZSEE Conference
K. Andisheh, A. Scott & A. Palermo
University of Canterbury, Department of civil and natural resources engineering, Christchurch, New Zealand.
ABSTRACT: In recent years, growing attention has been given to the effects of corrosion on reinforced concrete structures. Marine environment and de-icing salt are two causes chloride-induced corrosion. Basically, there are two types of steel reinforcement corrosion called general and pitting corrosion. In real corroded reinforced concrete (RC) structures, a mix of the general and pitting corrosion usually takes place. Corrosion decreases the mechanical characteristics of steel reinforcing.
In this study, reduction factors of mechanical properties of steel reinforcement have been estimated through experimental monotonic tensile tests to take into consideration of eccentricity caused by pitting corrosion. Reduction factors have been defined to estimate the effect of corrosion on the reduction in mechanical properties of corroded steel bars. The reduction factors indicate the percentage reduction in the mechanical properties for 1% loss of cross-section area of steel reinforcement.
To meet this aim, pitting corrosion has been simulated by mechanically removing a portion of the cross section form 10mm, steel reinforcement. The reduction factors in terms of yield stress, ultimate stress, module of elasticity and elongation have been estimated from monotonic tensile tests. The relevant deterioration models have been developed based on the experimental results, and have been used for section-level analysis of a reinforced concrete bridge pier. The results of section-level analysis show degradation in moment-curvature and force-displacement of the corroded RC bridge pier due to pitting corrosion.
1 INTRODUCTION
There are a number of causes of corrosion in reinforced concrete (RC) structures including: chloride-induced, carbonation-induced, bacterial-induced and stray current-induced corrosion. Chloride-induced corrosion is generally the most common cause for corroding of RC structures. Chloride-induced corrosion is an electrochemical process that degrades reinforced concrete (RC) structures. While RC structures in pristine condition can be expected to satisfy the code requirement of a given era corrosion of reinforcing steel will degrade the seismic capacity of the structure over time. Therefore, old corroded RC structures become vulnerable to future earthquakes. Past studies have reported some corroded RC bridge in New Zealand (Bruce and Land Transport 2008, Pank 2009, Rogers, Al-Ani et al. 2013). Figure 1 shows examples of real corroded bridge in New Zealand (Rogers, Al-Ani et al. 2013).
There are two corrosion configuration named general corrosion and pitting (or localized) corrosion. Figure 2 shows configuration of pitting and general corrosion simulated by accelerated corrosion technique.
According to the literature, there are a number of studies on general corrosion, while few investigations have been carried out on pitting corrosion. Pitting corrosion significantly decreases cross-section area of steel bars and affects the service life of RC structures. It is worth to note that, diameter size of bar affects pit depth. Increasing diameter of reinforcing steel raises pit depth (Stewart
and Al-Hreinforce
Figure 1.corrosion
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ifferent technrine environartificial mem process th
m, have theorpitting corro
no experimened pitting coh a cylindricof methods
g current eletly used (Caselerated methting corrosiogeneral and p
gure 3. Accele
paper, the e
8, Stewart 20so does caus
rroded bridgsion tendons
Corrosion co
niques are utnment (naturthods to sim
hat is not fearetically moosion (Stewantal study onrrosion by rcal shank (Chave been
ectricity namstro, Veleva hods. It shouon is not pospitting corros
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009). Pitting e reduction i
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onfiguration:
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med galvanoset al. 1997,
uld be stated sible using asion.
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ing corrosio
2
g corrosion nin effective m
New Zealand; ms.
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rrode steel reon. Machinene environmused for res
ng corrosionHowever, acccal simulatedpart of steelari et al. 200rode RC strustatic methoYuan, Ji et that with exc
accelerated c
p, left: Galva
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not only decrmechanical p
Right: corro
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einforcementd and accelent corrosioearch progra
n as a part oording to th
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corrosion, be
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reases cross-properties of
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machined, acosion techninatural corroudies, to sim
hat is very swledge of theonly approacng hemisphecelerated corers in salt wchamber me
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climate cham
ate stress, m
a of steel rcement.
; Left:
ccelerated iques are
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2 EXPE
Corrosioaccuratepitting crepresenwere cutmedium machine
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To take distance 2008, St
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uses up to 10%dium and seves of steel resection level-curvature mbehaviour of
ERIMENTA
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. Left: geomed for tensile t
into conside(3 pits in to
tewart 2009)
ifferent pit simm and 5mm percentagcorrosion, thd 5mm pit d
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AL METHO
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ed through ed steel bars hical cutter. Aal pitting correver pitting than 35% rede deterioratiodeveloped bae pier to invresults show
MULATE PIT
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TTING COR
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and depth ples of lengthm and 5mm on 10mm de
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5. In the reseusing machi3%, 26.5% atages are 0.1caused by eaorrosion. Ac
not affect Maslehuddin
monotonic tulated by me
d simulated ptake several yave been simucross-sectionf reduction inensile test reeffect of pit
orrosion has
RROSION
e technique wFigure 4 shoare two ma
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earch, three inery operatand 39% res4%, 0.97% ch pit divide
ccording to tmechanical
et al. 1994).
tensile tests.echanically rpit is an acyears. Three
mulated. In thn area is consn the four me
esults. Then ttting corrosioa critical im
which can bows the geoain geometry300mm gaugorrespondingl reinforcem
s; Right: steel
a pit at evertewart and A
different dimtions. The aspectively. Aand 1.73% f
ed by mass othe literaturel properties
To meet removing ccelerated
different is regard,
sidered as echanical they have on on the mpact on
be used to ometry of y factors
ge length) g to low, ent using
l bar
ry 10mm Al-Harthy
mensions, associated Assuming for 2mm,
of 100mm e, general
of steel
The relat
The max
Where, band A1 a
3 TENS
Monotoneffects ofor each controllewas incrfor measused to d
F
tionship betw2 1ximum corro
( )b, dc and D0
and A2 are est
2 sin2 sinSILE TEST
nic tensile teof pitting corr
level of corred rate of disreased to 2msuring the strdevelop the r
Figure 5. The
ween pit dep
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are pit widthtimated as fo
TS
ests have beerosion on merosion, 12 tesplacement. m per minutrain, force anrelevant dete
e sizes of pits
th and pit wi
own in the Ah, pit depth anollows: en carried ouechanical pests have beenThe rate of
te in plastic rnd displacemrioration mo
Figure 6. Mo
4
on the surfac
idth have bee
A-A cross sec √√nd diameter
ut on the nonerformance on performeddisplacemen
region. An exment. Figure odels.
onotonic tens
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n-corroded af 10mm defoin total. The
nt in elastic rxtensometer 6 shows the
sile test setup
deformed bar
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re 1) can be c
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and corrodedormed bars ge tests have bregion was 1has been settest setup. T
p
rs
calculated as
ment respecti
d bars to comgrade 300. Thbeen carried 1mm per mint up betweenThe results h
(1)
s follows:
(2)ively,
(3) (4)(5)(6)mpare the hree tests out using nute, and n two pits have been
4 RESU
The effeseen thapits’ geonot affeccorroded
Sp
Non cor
Figure 7.
5 DEVE
Several dof corroCairns, Pgeneral presentedeterioraresults. reinforce
Wher
of corrosThe equa
ULTS
ective stress at pitting corometry and thct inherent md bars.
Ta
pecimen
rroded (N.C)
PL1
PL2
PL3
. Stress-strain
ELOPING D
deteriorationded memberPlizzari et acorrosion hd in the literation modelsThe equati
ement that ha1re, cβ : mech
sion in the teation 7 is ind
0
50
100
150
200
250
300
350
400
450
0
Str
ess
(MP
a)
strain curvesrrosion altershe associated
mechanical p
able 1. pitting
Pit width (m
0
3.92
7.33
8.66
n curves of 10
DETERIOR
n models basrs or materia
al. 2005, Leehas been adrature have s in the literaon 7 showas been used
hanical prop
erm of reducdependent fr
0.00 0.
PL2
PL3
s of monotons effective md cross sectioroperties rein
g geometry an
mm) Pit de
0mm deform
RATION M
sed on matheals degrade e and Cho 2
dapted for ea wide variaature have b
ws the gened for both gen
erties of cor
tion percentarom type of c
05 0.10
PL
PL1
5
nic tensile temechanical pon loss percenforcing stee
nd percent of
epth (mm) C
0
2
4
5
med steel reinf
ODELS
ematical relatdue to corro
2009, Oyadoestimating thation indicatieen presente
eral form oneral and pitt
rroded bars,
age of mass, corrosion, an
0 0.15
Strain
L3 PL2
ests have beeproperties of entage. It shoel. It alters e
f cross-section
Corroded area
0
5.75
20.8
30.7
forcement of
tionships shoosion exist io, Kanakubohe reductioning the needed based on of deterioratting corrosio
α : relevant
and β : mecnd the mecha
0.20
n
Non corroded
2 PL1
en presented the steel ba
ould be stateeffective mec
n loss of samp
a (mm2) C
various degr
owing how min the literato et al. 2011n factors. Md for further linear regresion models
on:
reduction fa
chanical propanical proper
0.25
d (N.C)
N.C
in figure 7. ar. Table 1 sed that corroschanical prop
ples
Cross section l
0
7.3
26.5
39
ree of pitting
mechanical pture (Morina1). However,Moreover, th
studies. Thession of expe for corrod
actors, corrQperties of sorties of corro
0.30
It can be hows the sion does perties of
oss (%)
corrosion
properties aga 1996, , usually,
he results e existing erimental ded steel
(7)
: amount
und bars. oded bars
6
can be calculated by given relevant parameters. Figures 8 and 9 show deteriorated modulus of elasticity, elongation, yield stress and ultimate stress for different amount of cross section reduction. Assuming linear regression, reduction factors for each of these properties have been calculated using equation 7 as 0.65, 2.78, 1.19 and 0.81 respectively. The results indicate that further studies are needed to estimate the reduction factors of mechanical properties of reinforcing steel, and linear regression presented by past studies is not suitable in case of pitting corrosion. While all reduction factors have been estimated based on linear regression in the literature, the results show that with exception of ultimate stress and modulus of elasticity, the linear regression are not suitable methods basically for variation of reduction factors for different amount of corrosion. The reduction in elongation, for example, for up to 7.3% corrosion in much higher than that for corrosion between 7.3% and 26.5%, and the reduction for corrosion greater than 26.5% is relatively low. The results indicate further investigation to estimate reduction factors based dependent on amount of corrosion.
Figure 8. Relationship between corrosion and reduction in left: module of elasticity, right: elongation
Figure 9. Relationship between corrosion and reduction in left: yield stress, right: ultimate stress
6 CROSS SECTION ANALYSIS OF A CORRODED RC BRIDGE PIER
Cross-section analysis is a quite common numerical method to evaluate the key structural parameters for the seismic performance R.C. members. Recently research studies incorporated degradation models for concrete and steel which allows to predict the long term seismic performance of RC bridge piers (Palermo and Pampanin 2008, Ghosh and Padgett 2010, Biondini, Camnasio et al. 2013). Corrosion is usually modelled by decreasing cross-section area of steel reinforcement and causing reduction in effective mechanical properties of steel reinforcements which leads to reduction in the seismic capacity. The moment-curvature and force-displacement relationship have been utilized to
0
0.2
0.4
0.6
0.8
1
1.2
0 20 40 60
Ec/
E
Cross-section reduction (%)
Reduction in modulus of Elasticity
0
0.2
0.4
0.6
0.8
1
1.2
0 20 40 60
εc/ε
Cross-section reduction (%)
Reduction in elongation
0
0.2
0.4
0.6
0.8
1
1.2
0 20 40 60
fyc/
fy
Cross-section reduction (%)
Reduction in yield stress
0
0.2
0.4
0.6
0.8
1
1.2
0 20 40 60
fuc/
fu
Cross-section reduction (%)
Reduction in ultimate stress
evaluate The crosintent is terms ofThe redimplemeinvestiga“Long-teCanterbuplain rein
In this siand liveconcretemoment section aby 14.3%respectiv100mm 1.73% ryielding the ultim
Figure 10different
Force-di(Paulay differentin lateraductility26.5% anis 0.14%11%, 71steel strashow few
the effects ss-section co to evaluate
f strength anduction in thented in CUation and moerm seismicury. To achinforcing stee
imple case se loads of dee and steel. T
capacity anarea due to p%, 25% andvely. The redlength of ste
respectively. curvature h
mate curvatur
0. Right: detat percent loss
isplacement and Priestle
t amount of al load carryiy. The resultsnd 39% loss
%, 0.97% an% and 93%
ain, curvaturw small pits
of corrosiononsidered is a
how pittingnd stiffness ahe mechanic
UMBIA (Moore tests and c performaneve the objeel and reinfo
tudy, a 100 Keck. Figure The moment-nd corresponpitting corrosd 36% for piduction in creel bar, the The corresp
as not changre.
ails of cross-sof cross secti
relationship ey 1992). Figcross-sectioning capacitys show base s of cross secnd 1.73% res
respectivelyre and lateralsignificantly
n on seismicat the bottom
g corrosion aand more imcal propertieontejo 2007)numerical ace of corro
ectives of thercing steel gr
KN vertical 10 shows d-curvature rending curvation. The resuitting corrosiross-section equivalent pponding curvged, this mea
section of the ion area of st
has been angure 11 shown loss due to and in elonshear capac
ction area resspectively. Ty. The effectl displacemey reduce the d
7
c performancm of the bridalters the ov
mportantly dues obtained ). Authors a
analyses are noded bridge e project, 10
grade 500 wil
load has beedetails of theelationship isture have beults show thaion decreasinareas is just
percentage ofvature has bans that the
bridge pier; teel reinforce
nalysed usingws force-dispo pitting corrngation leadicity has beenspectively. T
The correspots of pitting ent of the briductility whi
ce of a corrodge piers whverall seismicuctility (straiby experim
acknowledgeneeded. Ther
pier” is in0mm, 16mm ll be examine
en applied one cross sectis shown in theen decreaseat bending mng 7.3%, 26t in the locatf general cor
been decreascurvature du
Left: Momenements in the
g the model placement rerosion. The ping to decrean decreased bThe equivaleonding reduccorrosion ondge pier are ich impact se
oded bridge phere plastic hc performann, sectional
mental tests ie that this irefore, a rese
n progress aand 25mm
ed.
n the bridge on and mechhe left side. ed basically
moment capac6.5% and 39tion of pits. rrosion are aed by 19%,
uctility drops
nt- curvaturebridge pier
presented byelationship opitting corrosase of conseby 21%, 75%nt reduction ction in dispn ductility inshown in th
eismic perfor
pier (Montejhinge is formnce of bridge
and structurin the sectiois just a preearch prograat the Univdeformed an
pier to simuchanical propAs expectedfor decreasi
city has been9% cross-sec
Having a pias 0.14%, 0. 66% and 9s exactly the
e relationship
y Paulay andof the bridgesion causes r
equence disp% and 58% f by general c
placement dun terms of rehe table 2. Thrmance of br
jo 2007). ming. The e piers in ral level). on 5 are eliminary m named
versity of nd 10mm
ulate dead perties of d bending ing cross n reduced ction area it in each .97% and 92%. The e same as
p for
d Pristley e pier for reduction
placement for 7.3%, corrosion uctility is einforcing he results ridges.
Figure 11reinforce
Tab
Corrosion
Corrosionlevel
N.C
PL1
PL2
PL3
7 CON
The effeout of 1corrosionof elastipropertieresults h25mm rebar size column bbeen sum
1. Pb
2. Tn
3. Td
1. Lateral forements in the
ble 2. Ductili
n characteristi
n Loss of cross
section (%
0
7.3
26.5
39
NCLUSIONS
ects of pitting12 samples hn. Three leveicity, elongaes have been
have been preeinforcing stcan be neg
bridge pier fmmarized as
Pitting corrobe taken into
The reductionegative imp
The experimductility. Th
rce-displaceme bridge pier
ity of the D1
cs Steel bar
f
%)
fy
(MPa)
374
294
218
199
S
g corrosion hhas been simels of pitting
ation, yield sn developedesented in thteel. Howeveglected. Finafor the levelsfollows:
osion causes o considerati
on in elongatpact of pittin
mental resulthis is very im
ment relations
10 reinforcin
r Bridge
M
(KN.m)
280
240
215
178
have been invmulated with
g corrosion hastress and u
d and brieflyhis paper neeer, it is expeally, momens of pitting c
reduction inon in the des
tion is the grg corrosion o
ts show thatmportant bec
8
ship for diffe
ng steel and corrosion
e pier
F
(KN)
98 1
79 4
73 1
53 1
vestigated byh mechanicaave been sim
ultimate stresy presented ied to be revisected that fornt-curvature corrosion hav
n mechanicalsign of RC st
reatest amonon ductility,
t even a vecause corros
erent percent
the bridge p
Ductility
με
μφ
13.5 26
4.5 21
1.78 9
1.08 2
y testing 12 ally induced
mulated. The ss. Deteriorain this papersed based onr the same pand force-dive been carr
l properties otructures exp
ng all mechansince the yie
ery small pitsion process
loss of cross
pier for diff
y
μD
μ
14.6
13 0
4.3 0
1.05 0
specimens. Pd defects wh
results showation modelsr. Authors a
n experimentapercent of coisplacement ied out and t
of steel reinfposed to corr
nical propertelding curvat
t causes signusually star
section area
ferent amou
Reduction in
μcε/με μc
φ/μ
1 1
0.333 0.81
0.131 0.34
0.08 0.07
Pitting corrohich represenw reduction ins for the meacknowledgeal tests on 16
orrosion, the analyses of the main res
forcement throsion.
ties indicatinture does not
gnificant redurts with a nu
of steel
nt of
n ductility
μφ μcD/μD
1
1 0.89
46 0.294
77 0.072
sion on 9 nt pitting n module echanical e that the 6mm and effect of
f a single sults have
at should
ng critical t change.
uction in umber of
9
small pits.
4. Pitting corrosion decreases both bending moment and associated curvature indicating decreasing in seismic capacity of corroded RC bridge piers.
5. Pitting corrosion also decreases load carrying capacity and displacement ductility confirming corroded bridge pier are more vulnerable in seismic events.
6. Further investigations are needed to develop deterioration models for pitting corrosion, and linear regression, presented by past studies for general and pitting corrosion, probably is not suitable in case of pitting corrosion.
8 ACKNOWLEDGEMENTS
The research program was supported by the Natural Hazards Research Platform (NHRP) project named “Advanced Bridge Construction and Design for New Zealand (ABCD – NZ Bridges)”, 2011-2015. We gratefully acknowledge the support from NHRP. The authors also acknowledge Mr. Kevin Stobbs at the laboratory of mechanical engineering and Mr. Timothy Perigo at the laboratory of structures.
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