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
搜索“diyifanwen.net”或“第一范文网”即可找到本站免费阅读全部范文。收藏本站方便下次阅读，第一范文网，提供最新高等教育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_英文_全文阅读和word下载服务。
相关推荐：
醉歌离人