Journal of Southeast U niversity (English Edition ) V ol .25,N o .4,pp.506-512D ec .2009 ISSN 1003—7985
Se is m i c strengthen i n g of re i n forced concrete colu mn s damaged
by rebar corrosi on usi n g co m b i n ed CFRP and steel j acket
L i J inbo G ong J inx in
(S tate Key L aboratory of C oastal and O ffshore Engineering,D alian U niversity of Technology,D alian 116024,C hina )
Abstract:In order to study the effectiveness of com bined carbon
fiber 2reinforced polym er (CFRP )sheets and steel jacket in
strengthening the seis m ic perfor m ance of corrosion 2dam aged reinforced concrete (RC )colum ns,t w elve reinforced concrete colum ns are tested under com bined lateral cyclic disp lacem ent excursions and constant axial load .The variables studied in this p rogram include effects of corrosion degree of the rebars,level of axial load,the am ount of CFRP sheets and steel jacket .The results indicate that the com bined CFRP and steel jacket retrofit 2ting technique is effective in i m p roving load 2carrying,ductility and energy absor p tion capacity of the colum ns .Compared w ith the corrosion 2dam aged RC colum n,the lateral load and the ductility factor of m any strengthened colum ns increase m ore than 90%and 100%,respectively .The for m ulae for the calculation of the yielding load,the m axi m um lateral load and the disp lacem ent ductility factor of the strengthened colum ns under com bined constant axial load and cyclically increasing lateral loading are developed .The test results are also compared w ith the results obtained from the p roposed for m ulae .A good agreem ent bet w een calculated values and experi m ental results is observed .Key words:reinforced concrete colum n;seis m ic perfor m ance;corrosion;retrofitting;steel jacket ;fiber 2reinforced polym er (FRP );ductility
Rece i ved 2009201206.
B i ograph i es:L i J inbo (1981—),m ale,doctor ;G ong J inxin (correspond 2ing author ),m ale,doctor,p rofessor,gong -jx .vi p @eyou .com.
Founda ti on item :The Program for Changjiang Scholars and Innovative
Research Team in U niversity of M inistry of Education of C hina (N o .IRT 0518).
C it a ti on:L i J inbo,Gong J inxin .Seis m ic strengthening of reinforced con 2crete colum ns dam aged by rebar corrosion using com bined CFRP and steel jacket[J ].Journal of Southeast U niversity (English Edition ),2009,25(4):506-512.
M
any existing reinforced concrete (RC )structures dam 2aged by corrosi on may have inadequate seis m ic resist 2ance due to the l oss of the reinforcing steel cross 2sectional ar 2ea as well as the loss of bond along the steel 2concrete inter 2face .A s a result,many of these structures suffer extensive structural damage and even collap se when subjected to a
strong gr ound moti on [1-4]
.Therefore,it is necessary to clarify the influence of rebar corr osion and strengthen the damaged column in order t o upgrade the seis m ic perfor mance of dam 2aged structures .
There are considerable research efforts being directed at de 2vel op ing and app lying retr ofit strategies to upgrade the seis mic perfor mance of deficient structures .Externally bonded fiber 2reinforced poly mers (FRP ),as a p r o mising rehabilitation sys 2tem t o upgrade da maged RC colu mns,have been exa mined in
much of the literature [4-5]
.The researches have p r oved the a 2bility of the FRP syste m t o i mp r ove the ductility and energy abs or p ti on capacity of corr oded RC colu mns,but the FRP sys 2tem cannot significantly i mp r ove the strength of the corr oded
RC colu mn .Steel jacketing,as a conventional strengthening technique,can i mp r ove the bending strength,the shear capac 2ity,the stiffness,the ductility and the axial l oad carrying ca 2
pacity of strengthened ele ments [6-7]
,but the strengthening technique is not suitable for strengthening the corr oded RC colu mn because the steel jacket may be da maged by marine envir on ments and deicing salts .
A lthough a variety of strengthening methods are used t o strengthen the damaged column,currently no attemp ts have been made t o strengthen the corroded RC column with com 2bined CFRP sheets and steel jacketing .Thus,a study is made in this p rogram in order to make full use of the advanta 2ges of the t wo kinds of materials in i mp r oving the seis m ic per 2for mance of the RC column .
1 Experi m ental Program
111 Speci m en details
T welve RC colu mns are constructed and tested under co m 2bined axial load and reversed cyclic lateral dis p lace ment ex 2cursi ons .As sho wn in Fig 11,the original colu mns have a clear height of 1500mm with a cr oss secti on of 200mm ×200mm.Four 142mm dia meter bars are used as longitudinal rein 2forcement,stirrup s of 82mm dia meter bars are s paced at every 100mm and have 135°hooks at the ends .Three 150mm ×150mm ×150mm cubes are cast al ong with the s peci mens,and the 282day mean cube co mp ressive strength is 4418MPa .The other details of the s peci mens are sho wn in Fig 11.The black region in which the length is 500mm in Fig 11(c )is the region wrapped with CFRP sheets .The repair p r ocedure of the s peci 2mens in Fig 11(c )consists of bonding steel jacketing first and
then wrapp ing CFRP sheets .
112 Accelerated steel corr osi on test
The external current method is used t o induce corr osi on in
the columns after a 28d curing [8]
,as shown in Fig 12.The s peci mens are p laced in a water tank containing 315%salt
s olution .A reinforcement cage of each s peci men is used as the anode and corrosi on resistant p lates i mmersed in the bank are used as the cathode .The current and the voltage in each column are measured periodically .To achieve the same level of corr osion in all colu mns,the current in each column is tuned s o that areas under the current 2ti me p l ots for s peci mens are si m ilar .Tab 11gives the weight l oss of the rebars corre 2s ponding t o different corrosi on degrees .The appearances of the colu mns at the end of the accelerated corr osion p r ocess are given in Fig 13.
A t the ter m ination of the corr osion p r ocess,l ongitudinal s p litting cracks are running parallel t o the steel reinforcing bars for all corr oded s peci mens .I n addition to the cracks,many red 2black corr osion p r oducts,which are concentrated on or c lose to the corr osion cracks,are observed leaching out of the cracks .This phenomenon i m p lies that rendering
F i g 11
G eom etrical size of the strengthened colum n (unit:mm )
the structural behavi ors of the RC column have been dam 2aged due to seri ous rust stains and concrete deterioration
.
F i g 12 Experi m ental device of the accelerated corrosion of rebars by the electrochem ical m
ethod
F i g 13 C olum ns after rebar corrosion Tab 11 C onfiguration of speci m ens
Speci m ens
Corrosion loss ratio /%A xial
load /kN S trengthening m ethods
RA 0
0420Sound speci m en
RBJ 12119156180S teel jacket +1layer of C FRP
sheet
RB 219117300U nstrengthened RBJ 2216150300S teel jacket
RBJ 22118180300S teel jacket +1layer of C FRP sheet
RBJ 22217120300S teel jacket +2layers of C FRP sheets RBJ 22316189300S teel jacket +1layer of C FRP
sheet RB 316180420U nstrengthened
RBJ 32116170420S teel jacket +1layer of C FRP
sheet
RC 211149300U nstrengthened RCJ 229190300S teel jacket
RCJ 221
9130300
S teel jacket +1layer of C FRP
sheet
113 S trengthening p rocess
Eight of the corroded speci m ens described above are strengthened w hen the speci m ens reach the destined corro 2sion ratio .The repair p rocess consists of rem oving deterio 2
rated concrete,cleaning the corroded reinforcing steel,casting repair m aterial,and strengthening the colum ns w ith different retrofitting m ethods .The repair m aterial is a nor 2m al strength concrete w ith a 282day com p ressive strength of 3217M Pa .Tw o strengthening techniques are used and Tab 11gives the details .It is noticed that,for the speci 2m ens strengthened w ith com bined CFRP sheets and steel jacket,the steel jacket is bonded w ith epoxy resin first and then epoxy based m ortar is app lied as screed 2coat before w rapp ing the CFRP sheets .
The steel jacket,w hich is used for strengthening the cor 2roded speci m ens,consists of four steel angles .The cross 2section of steel angle in speci m en RBJ 223is 30mm ×30mm ×3mm ,but that in other speci m ens is 40mm ×40mm ×4mm.Four steel angles are w elded by batten p lates w ith a cross 2section of 30mm ×3mm and by a space of 150mm.The m echanical characteristics of the steel rebars,steel angle and batten p lates are given in Tabs .2and 3.
Tab 12 M echanical p roperties of steel rebars
Elem ent
B ar diam eter/mm
Y ield stress /M Pa
U lti m ate stress /M Pa
L ongitudinal reinforcem ent 14384177604187S tirrups
8
326195
510170
Tab 13 M echanical p roperties of steel angle
E lem ent
C ross 2section
Yield stress /M Pa
U lti m ate stress /M Pa
S teel jacket 140mm ×40mm ×4mm
35045813S teel jacket 230mm ×30mm ×3mm 3381546115B atten p late
30mm ×3mm
53313
66617
For the speci m ens strengthened w ith com bined CFRP
sheets and steel jacket,the corners of each colum n are rounded to a radius of 20mm and CFRP sheets are w rapped around the w hole test region in a peripheral direction w ith a 200mm overlap.It is noticed that,excep t for the speci m en
7
05Seis m ic strengthening of reinf orced concrete colu mns da maged by rebar corr osi on using combined CFRP and ??
RBJ 222w rapped w ith t w o layers of CFRP sheets,all the other speci m ens have only one layer of CFRP sheet .Tab 14gives the m aterial p roperties of the CFRP sheet .
Tab 14 M aterial p roperties of C FR P
Sheet thickness /
mm
Tensile strength /GPa
Tensile m odulus /GPa
Tensile elongation /%
011113164621516119
114 Test setup
Fig 14show s the loading fram e and part of the instrum en 2
tation used for the lateral load tests .The top and bottom of each colum n are fixed by the test fram e using the bolts and a ball socket bearing is p laced under the bottom of the col 2um n.A xial load,given in Tab 11,is first app lied using hy 2draulic loading equipm ent and rem ains constant during the testing p rocess to si m ulate the dead load on the colum n .The reversed cyclic lateral load is then app lied through t w o one 2w ay hydraulic jacks and m easured by t w o load cells at 2tached to the hydraulic jacks .The disp lacem ent control m ode is used to app ly the p redeter m ined disp lacem ent his 2tory,w hich m eans that the speci m en is subjected to a dis 2p lacem ent of Δ1=1mm for the first cycle follow ed by
three cycles,each of 2
Δ1,4Δ1,6Δ1,?,until the colum n fails,as show n in Fig 15
.
F i g 14 Test setup for colum n
testing
F i g 15 L ateral disp lacem ent history
2 Test R esults
Three control speci m ens (RB 2,RB 3and RC 2),w hich
have different corrosion levels,are tested to failure w ithout any strengthening to establish the behavior against w hich the perfor m ance of the strengthened speci m ens can be eval 2uated .S ince they have si m ilar failure m echanism s,speci 2m en RB 3is selected as a rep resentative sam p le .Speci m en RB 3has four longitudinal corrosion cracks due to rebar cor 2
rosion before loading and the longitudinal cracks continue to develop as the lateral load increases .This is follow ed by the appearance of flexural cracks at the interval w ithin 300
mm from the stub interface,during the second cycle (δm ax
=2Δ1).From the third cycle (δm ax =4Δ1)onw ard,all the cracks continue to grow and lead to initiation of spalling of the concrete near the colum n 2stub interface .D uring the last cycles,the concrete cover falls off com p letely .From this observation on the speci m en after failure,it is concluded that the falling off of the concrete cover is caused by the corrosion of the rebar,w hich reduces the bond bet w een the concrete cover and the core .
Speci m ens RBJ 22and RCJ 22are strengthened w ith steel jacketing only,so speci m en RBJ 22is selected as a rep re 2sentative sam p le .The behavior of speci m en RBJ 22is char 2acterized by stable hysteretic hoops in both directions of loading due to confinem ent of the steel jacket .The m axi 2m um load is 265179kN and the corresponding disp lace 2
m ent is 8mm.From the ninth cycle (δm ax =16
Δ1)onw ard,the connection bet w een steel angle and batten p late near the colum n 2stub interface is rup tured and results in considerable degradation of flexural strength of the colum n .
O ther speci m ens excep t RA 0,strengthened w ith com 2bined CFRP sheets and steel jacket show si m ilar behavior .Hence speci m en RBJ 321is chosen as a rep resentative sam 2p le .The speci m en RBJ 321exhibits m ore stable behavior than the colum ns strengthened only w ith steel jacketing due to the confinem ent of com bined CFRP sheets and the steel jacket .There is a distinct yield p lateau follow ed by a grad 2ual hardening up to a m axi m um load,follow ed by gradual softening after the m axi m um load .D uring the 11th cycle (δm ax =20
Δ1),the rup ture of the steel angle near the loca 2tion of the colum n 2stub interface occurs and results in rap id degradation of the flexural strength of the colum n,and the test is ter m inated .
Fig 16gives the view s of failure of som e speci m ens and Fig 17gives the lateral load against disp lacem ent curves for som e speci m ens .Tab 15summ arizes the results of the cy 2clic tests .P y and Δy are the yield load and corresponding disp lacem ent,respectively .P m ax is the m axi m um app lied lateral load and Δm ax is the corresponding disp lacem ent
.P u is the failure load,w hich is defined as 85%of the m axi 2m um lateral load P m ax ,and Δu is the corresponding failure disp lacem ent .μΔis the disp lacem ent ductility factor,calcu 2lated by Δu /Δy ,E end is the total cum ulative dissipated ener 2gy
.
Fi g 16 V ie w s of failure of the speci m ens .(a )RBJ 22;(b )RBJ 321
8
05L i J inbo,and Gong J inxin
Tab 15 L ist of the test results
Speci m en P y /kN
Δy /mm
P m ax /kN
Δm ax /mm
P u /kN
Δu /mm
μΔ
E end /(kN ?m )
RA 0
16016621101901876110162124715031605123RBJ 1212231712145253160816021515618140715179170RB 215311011901641916130140117618031584144RBJ 222201212175265179811722519218102615578170RBJ 22126516821733161459195268198191907129116198RBJ 2222531142145291117141452471492615010180221124RBJ 22317214321052341314125199116221711110878189RB 313512011601731203110147122417421963173RBJ 32126215731003341681216428414719176615881192RC 2135142216016718081101421631212341708159RCJ 22230158316027916210133237168221906136104187RCJ 221
2721143100
32016412128
27215419149
6147
117.
00
F i g 17 L oad against disp lacem ent curves for all speci m ens .(a )RB 2;(b )RB J 22;(c )RB J 221;(d )RB J 222
3 D iscussion
311 L ateral load 2disp lacem ent response
D uctility factors and lateral loads are t w o of the m ost
comm on param eters used for the seism ic evaluation of structural com ponents .In Fig 18,the envelopes of the later 2al load 2disp lacem ent response of all test speci m ens are com 2pared w ith rebar corrosion,CFRP layers,axial load level and steel jackets on the ductility factors and lateral loads of the speci m ens .
F i g 18 L ateral force 2disp lacem ent response envelopes
It can be seen from Fig 18that,the enhancem ent in dis 2p lacem ent ductility factors is found to be larger for speci 2m ens RBJ 22and RBJ 221,w hich are tested w ith larger cor 2
rosion degrees,than the corresponding enhancem ents for speci m ens RCJ 22and RCJ 221,w hich are tested w ith low er corrosion degrees .The reason for this behavior is that,al 2though the steel jacket or com bined CFRP and steel jacket reduces the bond degradation of the corroded rebars,but the speci m en RB 2exhibits poorer disp lacem ent ductility than speci m en RC 2due to the greater degree of corrosion . The effect of axial load on the cyclic behavior of the strengthened colum ns w ith com bined CFRP sheet and steel jacketing can also be evaluated in Fig 18.The enhancem ents in the m axi m um lateral load and the ductility factor are high 2er for speci m en RBJ 321,w hich is tested under a high axial load,w ith the m axi m um lateral load value and the ductility factor value increasing 9312%and 12213%,respectively,than those w ith corresponding values of control speci m en RB 3.Corresponding enhancem ents in the m axi m um lateral load value and the ductility factor value for speci m en RBJ 221are 9119%and 10316%,respectively,than for those of speci m en RB 2.This is because under low axial load,both the strengthened and control speci m ens are able to sustain a large num ber of cyclic excursions;the strength 2ened colum ns do so w ith gradual degradation of strength w hile the strength degradation in control colum ns is m ore se 2vere,but for the speci m ens tested under high axial load,the control speci m en undergoes rap id degradation of strength and
9
05Seis m ic strengthening of reinf orced concrete colu mns da maged by rebar corr osi on using combined CFRP and ??
fails m uch earlier than the strengthened speci m en.
Fig18also show s the effect of CFRP sheets on the ductili2 ty and lateral load of speci m ens.B y comparing the results of the speci m ens,it is evident that,strengthening of the col2 um ns w ith com bined CFRP and steel jacketing or steel jack2 eting results in m ore stable responses w ith larger strength and ductility.The i mp rovem ents are found to be m uch greater in the speci m ens strengthened w ith com bined CFRP and steel jacketing than in the speci m ens strengthened only w ith steel jacketing due to CFRP w raps.It is due to the confinem ent of concrete in the p lastic hinge regions.Confining the strength2 ened colum n using steel jacketing w ith one or t w o layers of FRP helped to delay the for m ation of internal sp litting cracks bet w een the corroded colum ns and the steel jacket,thus i m2 p roving the seism ic behavior of the strengthened colum ns. 312 Energy absorp tion capacities
Fig19show s the total cum ulative dissipated energies for the speci m ens.The total cum ulative dissipated energy is calculated from the sum of the energy absorbed in all cycles before the speci m ens failed .
F i g19 Total cum ulative energy absor p tion for all speci m ens
It can be seen from Fig19that,integration of the total hysteretic energy absorbed by the colum ns indicates that the retrofitted colum ns are capable of absorbing m ore energy than that of the corroded colum ns before the colum ns fail. It can also be seen that the CFRP confinem ent substantially i m p roves the energy absorp tion and dissipation capacities of the speci m ens strengthened w ith steel jacketing.Increasing the area of CFRP from zero to t w o layers results in a siza2 ble increase in the energy absorp tion capacity.
4 A nalytical S tudies
411 Yield force and the m axi m um lateral load calculations of the strengthened speci m ens
A ccording to the test results,the strengthened speci m ens fail in the flexural m ode.Thus,the yield force and the m axi m um lateral load are obtained from the flexural strength of the bottom section of the colum n.The tension reinforcem ent in the original colum n is considered by m ulti2 p lying the reduced factor of018.This is because the bond force bet w een the reinforcem ent and concrete is reduced due to the back2filled concrete cover.
The yield m om ent and yield load of the strengthened col2 um ns are calculated by
M
y
=018f y A s(1-p)(h0-a0)+015N h(1-n0)+k A a f ay h
(1)
P
y
=
M
y
H
(2)
w here M
y
is the yield m om ent of the strengthened colum ns;
P
y
is the yield load of the strengthened colum ns;f
y
is the
yield strength of the longitudinal bars;A
s
is the area of the longitudinal bars;h0is the effective dep th of the colum n; a0is the dep th of concrete cover;p is the corrosion ratio of
the longitudinal bars;N is the axial load;n
is the axial
load ratio;n
=N/(f
c
bh);k is the effectiveness factor of the steel jacket.For the colum n strengthened only w ith steel jacketing,k=017,for the colum n strengthened both w ith CFRP and steel jacket,k=018;A a is the area of ten2
sile steel angle;f
ay
is the yield strength of the tensile steel angle,and H is the shear span of the colum n.
A ccording to Ref.[9],the m axi m um lateral loads P
m ax of the colum ns are calculated by
P
m ax
=(1124-0115ρ-015n0)P y(3) w hereρis the tension steel ratio,ρ=ρ1+ρ2,ρ1is the ten2 sion longitudinal steel ratio andρ2is the tension steel angle ratio.
The com parison bet w een test values w ith calculated val2 ues of the yield loads and the m axi m um lateral loads of the strengthened colum ns are show n in Tab16.In Tab16,P y t
and P
m ax t
are the test values of the yield loads and the m axi2
m um lateral loads of the colum n,respectively;P
yc
and
P
m axc
are the calculated values of the yield loads and the m axi m um lateral loads of the colum n,2a215a22f121dd36a32d82a62 paring the test values w ith the calculated values of the yield loads and the m axi m um lateral loads,it can be seen that the test results of the yield loads and the m axi m um lateral loads of the strengthened colum ns agree w ell w ith the correspond2 ing calculated values.
Tab16 C om parison of yield load and m axi m um lateral load
Speci m en P yt/kN P yc/kN P yc/P yt P m axt/kN P m axc/kN P m axc/P m axt
RBJ12122317122916011032531602681751106
RB J2222012123216611062651792661081100
RBJ22126516825812501973161452901900192
RBJ22225311425910711022911172911821100
RBJ22317214319911011152341312241460196
RBJ32126215727919011073341683021950191
RCJ2223015823916011042791622691890197
RCJ22127211426311201973201642961390192
015L i J inbo,and Gong J inxin
412 D uctility factor calculations of the strengthened speci2 m ens
D uctility factor is one of the m ost comm on param eters used for the seism ic evaluation of structural com ponents.In order to evaluate the perfor m ance of the colum ns under the current research,the disp lacem ent ductility factorsμΔof the strengthened colum ns are used.B ased on the test results, the disp lacem ent ductility factorsμΔof the strengthened col2 um ns are calculated by
μΔ=
1+20αwλw
01045+111n0
(4)
w hereαw is a factor rep resenting the type of hoops,αw= 110for square hoops;λw is the equivalent transverse rein2 forcem ent index for the confinem ent from steel hoops, w rapped CFRP and steel jacketing,and it can be exp ressed asλw=ρw1αf1+ν2ρw2αf2+ν3ρw3αf3.Hereρw1,ρw2andρw3 are the volum e ratios of stirrups,CFRP and batten p late to the confined concrete,respectively;αf1,αf2andαf3are the ratios of the yield strength of stirrups,the tensile strength of CFRP and the yield strength of batten p late to the equiv2 alent com p ressive strength of concrete f
c
,respectively.ν2 andν3are the effective confinem ent factors of CFRP and batten p late,respectively.ν2=εcf/εcu,εcf is the average CFRP strain in the p lastic hinge zone of the colum n at the ulti m ate lateral disp lacem entΔu,andεcu is the rup ture strain of CFRP.ν3=εaf/εau,εaf is the average strain of batten p late in the p lastic hinge zone of the colum n at the ulti m ate lateral disp lacem entΔu andεau is the strain of batten p late corresponding to the yield strength of batten p late.B ased on the test results,ν2=0145,ν3=0135.
Tab17show s the com parison bet w een the test values w ith the calculated values of the disp lacem ent ductility factors of the strengthened colum ns.In Tab17,μΔt andμΔc are the test disp lacem ent ductility factors and calculated disp lacem ent ductility factors of the strengthened colum ns,respectively. Com pared the calculated values w ith the test values of the disp lacem ent ductility factors in Tab17,it can be seen that,excep t for the speci m ens RBJ121and RBJ221,all the other calculated results are w ithin a17%error band.This error band scope is allow able for calculating the disp lace2 m ent ductility factor of strengthened colum ns.Thus,the calculated results confir m the ability of the p roposed calcu2 lation m ethod to p redict the disp lacem ent ductility factor of strengthened colum ns.
Tab17 C om parison of disp lacem ent ductility factor
Speci m enμΔtμΔc μ
Δc
-μΔt
μΔ
t
/%
RBJ12171511110647 RB J22615551999 RBJ221712971655 RBJ22210180910017 RBJ22311108719129 RBJ3216158516914 RCJ22613651917 RBJ22161477157175 C onclusions
The effectiveness of strengthening dam aged RC colum ns using com bined CFRP sheets and steel jacketing to i m p rove the seism ic perfor m ance of RC colum ns has been exam ined in this paper.B ased on the research results,the follow ing conclusions are derived:
1)The technique of strengthening corroded RC colum ns w ith com bined CFRP sheets and steel jacketing or w ith steel jacketing alone is quite effective,w hich significantly in2 creases the strength,ductility and energy absorp tion and dissipation capacities of the strengthened colum n,but strengthening a corroded RC colum n w ith com bined CFRP sheets and steel jacketing is m ore effective than strengthe2 ning only w ith steel jacketing in i m p roving the strength, ductility and energy absorp tion and dissipation capacities.
2)The degree of corrosion has a considerable influence on the behavior of the strengthened colum ns.The strength2 ening effects of the speci m en w ith a greater degree of corro2 sion in the ductility is better than those w ith a low er degree of corrosion.
3)Com pared the speci m ens strengthened w ith steel jack2 eting only and those strengthened w ith com bined CFRP and steel jacketing,the CFRP sheet w raps significantly i m p rove the seism ic behavior of the strengthened colum ns.
4)H igh axial load results in considerable reduction in the ductility of the strengthened colum ns.The strengthening effect of the colum ns under low axial load is low er in duc2 tility than that of the colum ns under high axial load.
5)The yield force,the m axi m um lateral load and the dis2 p lacem ent ductility factor of the strengthened colum ns can be calculated by the p roposed for m ulae in this paper.A good agreem ent bet w een calculated values and experi m ental results is observed.
References
[1]Shi Q ingxuan,N iu D itao,Yan G uiyun.Experi m ental re2
search on hysteretic characteristics of corroded RC m em bers w ith flexural and com p ressive axial loads under repeated horizontal loading[J].Ea rthquake Engineering and Engi2 neering V ibra tion,2000,20(4):44-50.(in C hinese) [2]G ong J inxin,Zhong W eiqiu,Zhao G uofan.Experi m ental
study on low2cycle behavior of corroded reinforced concrete m em ber under eccentric com p ression[J].J ourna l of B uild2 ing S tructures,2004,25(5):92-104.(in C hinese) [3]N iu D itao,C hen X inxiao,W ang X uem in.Experi m ental
study on seism ic perfor m ance of corroded reinforced con2 crete m em bers w ith flexure and com p ression[J].B uilding S tructure,2004,34(10):36-38.(in C hinese)
[4]B elarbi A bdeldjelil,B ae Sang2W ook.A n experi m ental
study on the effect of environm ental exposures and corrosion on RC colum ns w ith FR P com posite jackets[J].C omposites Pa rt B:Engineering,2007,38(6):674-684.
[5]M aaddaw y T.B ehavior of corrosion2dam aged RC colum ns
w rapped w ith FR P under com bined flexural and axial load2 ing[J].C em ent and C oncrete C omposites,2008,30(6):
524-534.
[6]L u Y iyan,C hen S haoxiong,Zhao G uofan.A n experi m en2
tal study on the seism ic behavior of reinforced concrete col2 um n strengthened w ith bonded steel hoops and carbon fiber reinforced polym er sheet[J].C hina C ivil Engineering J our2 na l,2005,38(8):10-17.(in C hinese)
115
Seis m ic strengthening of reinf orced concrete colu mns da maged by rebar corr osi on using combined CFRP and??
[7]S heikh S A,Yau G.Seism ic behavior of concrete colum ns
confined w ith steel and fiber2reinforced polym ers[J].AC I S tructura l J ourna l,2002,99(1):72-80.
[8]Zhong W eiqiu,G ong J inxin.C ontrol m ethod for quick
electrochem ical corrosion experi m ent of rebars[J].B uilding Technique D evelopm ent,2002,29(4):28-29.(in C hi2
nese)
[9]W ang G uangyuan.P ractica l m ethods of op ti m um seism ic
design for engineering structures and system s[M].B eijing:
C hina A rchitecture&B uilding Press,2000:66-68.(in
C hinese)
碳纤维布与钢构套复合加固锈蚀钢筋混凝土柱抗震性能研究
李金波 贡金鑫
(大连理工大学海岸和近海工程国家重点实验室,大连116024)
摘要:为改善锈蚀钢筋混凝土柱的抗震性能,利用碳纤维布与角钢对锈蚀柱进行复合抗震加固.试验共对12根试件进行了低周反复加载试验,研究参量包括钢筋锈蚀程度、轴向荷载、碳纤维布层数和角钢用量.试验结果表明,利用碳纤维布和角钢复合加固锈蚀柱可以显著改善锈蚀柱的承载能力、延性和耗能能力.复合加固后,加固柱的强度和延性与锈蚀柱相比,可分别提高019倍和1倍以上.基于试验结果,提出了计算加固构件屈服荷载、最大荷载和位移延性系数的简化公式,计算结果与试验结果极为吻合.
关键词:钢筋混凝土柱;抗震性能;锈蚀;加固;钢构套;纤维布;延性
中图分类号:TU37511
215L i J inbo,and Gong J inxin
