STUDY ON EFFECTIVE PRESTRESS OF RC BEAM STRENGTHENING WITH PRESTRESSED FRP

Transcription

1 Aia-Paifi Conferene on FRP in Struture (APFIS 27) S.T. Smith (ed) 27 International Intitute for FRP in Contrution STUDY ON FFCTIV PRSTRSS OF RC BAM STRNGTHNING WITH PRSTRSSD FRP X.Y. Guo, P.Y. Huang and G.M. Pan College of Traffi and Communiation, South China Univerity of Tehnology, Guangzhou, 5164, China ABSTRACT The appliation of bonded arbon fibre reinfored polymer (FRP) laminate to the expoed fae of onrete member provide an effiient, light-weight, non-orroive alternative to other rehabilitative method. The method of uing pretreed CFRP for trengthening truture i effiient with the advantage of external pretre. Thi par dedue the formula of the effetive pretre on FRP trengthened RC beam. It how the effetive pretre inreaed with the higher pretre level applied. An exrimental program i the polyarbonate retangle beam are trengthened with externally bonded pretreed arbon fiber laminate(cfl), a new ty CFRP material invented by Huang i-yan team. Another exriment i CFL get pretre through indiret method by ompreing RC beam. The reult from two tet how that the theory analyi of effetive pretree on the CFL aorded with theory analyi. KYWORDS FRP, CFL, trengthening, effetive pretre;. INTRODUCTION The fibre reinfored polymer(frp) laminate have been uefully applied to trengthen truture in ivil engineering throughout the world. It provide effiient, light-weight, non-orroive, onvenient alternative to other rehabilitative method. Now the tehnology uing FRP laminate for trengthening i paive, whih ha many problem inluding the tenile trength of FRP laminate han t ued ompletely and the raking load and the maximum load have a little improvement. In order to overome thee problem, an innovative area of thi work that i emerging i the ue of pretreed laminate for trengthening truture. Thi ialized appliation ombine the benefit of paive bonded FRP laminate ytem with the advantage with external pretreing. By applying a pretre to the laminate, the material may be ued more effiiently ine a greater portion of it tenile apaity i engaged. Many reearher(e.g.andra HP et al. 1999;l-Haha R et al. 23 ;Garden HN et al. 1998)have began the theory and exrimental tudy on pretreed FRP laminate trengthening tehnique, uh a the ytem of bonding pretreed FRP laminate, the mehanial prortie of trengthened member. Triantafillou&Dekovi teted the pretre when the member trengthened with pretreing arbon fiber heet (CFS) detroyed and provided the half exriential formula to ompute the rmiible pretre. R.J.Quantrill&L.C.Hollaway teted virtual pretre and pretre lot on the two kind of RC beam trengthened with pretreed FRP, from whih the valuable exrimental date are obtained. It i neeary to et up a formula to ompute pretre on RC beam trengthened with pretreed FRP laminate for reognizing the regular of tre ditribution and etablihing the reliable ytem to apply pretre. Thi par dedue the formula of the effetive pretre on FRP trengthened RC beam. It how the effetive pretre inreaed with the higher pretre level applied. xternal pretreing arbon fiber laminate(cfl), a new ty CFRP material invented by Huang i-yan team(e.g. Guo xin-yan et al.23; Huang i-yan et al.22), bonded to the bottom of polyarbonate retangle beam. The tre ditribution of polyarbonate retangle beam are obtained by photoelati exriment. Another tet i CFL get pretre through indiret method by ompreing RC beam. MTHOD OF SOLUTION Applying a fore F to the FRP laminate, and then bonding the pretreed FRP laminate to the bottom of RC beam with ro-etion. When the epoxy adheive i fully ured, the fore F i releaed. Aume the RC beam 373

2 trengthened with pretreed FRP laminate i in elati phae after releae of initial applied fore F,the ditribution tree of etion are hown in Figure.1. Figure1 Stre ditribution on etion of RC beam quation (1)(2) are obtained from the tati balane relation Af + bxdx + Α + Α = 1 bxdx (1) h t 2 2 Af + ( 1 ) Α ( 1 ) = 2 bx dx h a 1 bx dx h a A (2) h where i tenile tre of FRP laminate after releaing fore F, alled a effetive pretre. and tree of retively. and are tree on tenile onrete and ompreive onrete. A and A are etional area of tenile ribbed bar and ompreive ribbed bar. Af i etional area of FRP laminate. t i the thikne of FRP laminate, definition of the other ymbol are hown in Figure2. Baed on balane equation and ditortion orrepond ondition, we obtain the effetive pretre bh 1+ β 1+ β = [ (1 β ) + α A (1 a) α A ( β a)] A 2 h h f where = = β, α = /, i the elati modulu of teel bar, Thi par only onider the pretre redued by onrete elati hortening of the beam. derement, i tenile tre of FRP laminate. i the elati modulu of onrete. (3) l i pretre l = (4) There are elati hortening deformation when onrete i under the pretre. Baed on the theory of deformation harmony, we obtain Δ ε = Δ (5) ε where Δε i train inrement of FRP laminate after releae the fore, Δ i train inrement of onrete. From formula (3) ~(5), there i relation between effetive pretre ε and tenile tre of FRP laminate h α A 1+ β α A 1+ β = /{1 + tλ /[ (1 β) + (1 a) ( β a)]} (6) 2 b h b h where λ = f, i the equivalent modulu of onrete and teel bar. PHOTOLASTIC XPRIMNTS Prortie of Material Photoelati exriment were arried out to validate the theory of effetive pretre. Carbon fiber laminate(cfl)i one ort of the FRP ued to trengthen beam,whih not only have the advantage of arbon fiber heet and arbon fiber plate, but alo have the prortie of low prie, onvenient ontrution and timely weave on the ize of trengthened member. The mehanial prortie of CFL are hown in table.1.they have been uefully applied to trengthen bridge in ivil engineering. The adheive ued in tet are epoxy, whih i multi-funtional and high-rformane trutural adheive with A and B omponent.. Mix evenly aording to APFIS

3 volume ratio when uing. The effetive temrature of adheive are -3~+1 and the hear trength of adheive i 14MPa(Aluminum/Aluminum). The elati modulu of polyarbonate i 1.895GPa. Table1. Mehanial prortie of CFL Number Thikne Strength Modulu of elatiity (mm) (MPa) (GPa) CFL Group Frature treth ratio (%) In order to tet the mehanial tranfer prortie of adheive (epoxy)before the tet, one beam wa divided into two piee. Bonded two piee together and teted under three- point bending, the photoelati exriment how that iohromati of the beam(hown in Figure2.) are ame a the whole polyarbonate beam(hown in Figure3.). The tet reveal the adheive ha good mehanial prortie of tranferring. The elati modulu of polyarbonate i 1.895GPa Figure 2.Iohromati of bonded Polyarbonate beam in three-point bending tet Figure 3. Iohromati of a whole Polyarbonate beam in three-point bending tet Pretreing CFL Preteed CFL an improve effiieny greatly. The tep of photoelati exriment are hown a bellow. Firt, the eletrial reitane train gauge were bonded to the CFL on the fae oppoite the bonding urfae, whih i ued to meaure applied pretre level. The extenion fore wa applied by lamp loated on the end of the CFL. Cleaning the CFL bonding urfae and polyarbonate beam by alohol, and then bonding CFL on polyarbonate beam. After a week, exreent CFL were ut and the tenion fore wa releaed when the adheive and beam bonded together. At the ame time the train on the CFL are reorded. The polyarbonate beam trengthened with pretreing CFL are hown a Figure 4. Pretreing three CFL, whih tre train are 98 MPa, 153 MPa and 2379 MPa. The three CFL were bonded to No.1, No.2 and No.3 polyarbonate beam retively. Figure 4. Polyarbonate beam reinfored by pretreed CFL Figure 5. Iohromati pattern of the polyarbonate Beam with CFL pretre APFIS

4 Tet Reult The three polyarbonate beam trengthened with different level of pretreed CFL were put in photoelati intrument. Iohromati pattern of the polyarbonate beam reinfored by pretreed CFL i hown in Figure 5. The iohromati pattern how the zero tri in the near middle of the height and the tenile i le than ompre area. The pae of iohromati pattern in the middle are ame and parallel. The tre ditribution along the height i loe to linear and ame a the flexural beam. Baed on the formula(6),the effetive pretre of CFL are alulated. Compared with the effetive pretre of alulated and exrimental value, the differene are hown in Figure 6. The level of applied pretre are expreed by rent ratio of tenile pretree and trength f. alulating value 7 exr i ment al val ue %% / f / f Figure 6. Calulating and exrimental value of effetive pretre TSTS OF RC BAMS RINFORCD BY PRSTRSSD CFL Pretreing CFL The ize of reinfored onrete beam i 18mm 1mm 2mm and the pan length i 16mm.Shear link in the beam onited of two eparated R4 link joined together to ahieve a uffiient area of teel to eliminate hear failure in the beam. And the beam wa reinfored internally with two R5 tenile bar o that different level of beam dutility ould be enouraged. The elati modulu and trength apability of teel bar i 24GPa and 333MPa retive. The prortie of CFL lited on table 1 are ame a photoelati tet. The method of applying pretre i teel line outide. The anhorage and lamp are devied for retangle RC beam (imen). Tenile teel line outide beam by jak until to applied level.the mehanial model of offet ompre i hown a Figure 7. Burnihing and leaning the urfae of ompreion, then the CFL wa bonded to the urfae. The eletrial reitane train gauge were bonded to the CFL. The teel line wa releaed when bonded fully. Then CFL get pretre indiretly. P P Figure 7. Mehanial model of offet ompre Reult CFL get pretre through the indiret method. Compared with the effetive pretre of alulating and exrimental value, the differene are hown in Figure 8. APFIS

5 Figure 8.how that the exrimental reult i onitent with alulated value. But the numerial value are little lower than the exrimental value, for only onidering the elati hortening of the beam intead of the other two fator, The majority of thi lot i to be attributable to elati hortening of the beam, and the other two fator of frition and FRP laminate reep are ignored. Theory and exriment how the relationhip between the effetive pretre and the initial applied tre. It an be onluded that the higher-level initial applied tre, the greater amount of effetive pretre. Further, the effetive pretre ha relation with the elati modulu of beam and inreae with the high elati modulu. Alo, the thinner of the CFL, the more effetive pretre get. alulating value exrimental value 25 2 / f % / f % CONCLUSIONS Thi par dedue the formula of the effetive pretre of FRP. The theory wa tetified by two exriment. The method of pretreing CFL are different. One i tenioning CFL diretly, the other i CFL get pretre through indiret method by ompreing RC beam. The reult from two tet how that the theory analyi of effetive pretree on the CFL aorded with theory analyi, but the exrimental value of indiret method are little lower than average exrimental data. The reaon i indiret method have two tep, whih will aue more error. ACKNOWLDGMNTS The author gratefully aknowledge the finanial upport provided by the Natural Siene Fund Projet of China (Projet No:127247) and Siene Fund Projet of Guang dong Provine (Projet No: 2856). RFRNCS Figure 8. Calulating and exrimental value of effetive pretre Andra, H.P., Sandner, D. and Maier, M. (1999). Strengthening of reinfored onrete truture by pretreed or non-pretreed externally bonded arbon fiber reinfored polymer (CFRP) trip, Proeeding of the International Conferene on Sialit Tehnique and Material for Conrete Contrution, 7: Char, M.S., Saadatmaneh, H. and hani, M.R. (1994) Conrete girder externally pretreed with ompoite plate, PCI Journal, 39(3), l-haha, R., Wight, R.G. and Green, M.F. (23). Innovative ytem for pretreing fiber-reinfored polymer heet, ACI Strutural Journal, 1(3), I-Haha, R., Wight, R.G. and Green, M.F. (21). Pretreed fiber-reinfored polymer laminate for trengthening truture, Prog. Strut. ngng Mater, 3, Garden, H.N. and Hollaway, L.C. (1998), An exrimental tudy of the failure mode of reinfored onrete beam trengthened with pretreed arbon ompoite plate, Compoite Part B, 29B, Guo, X.Y., Huang, P.Y. and Zheng, X.H. (23). Mehanial analyi of RC beam trengthened with pretreed FRP, Journal of South China Univerity of Tehnology:Natural Siene dition, 31 (7), Huang, P.Y., Zhou, X.P. and Zhao, C. (22). Some key mehanial on FRP heet applied in ivil engineering, Journal of South China Univerity of Tehnology (Natural Siene dition), 3(11), Triantafillou, T.C., Dekovi, N. and Deuring, M. (1992). Strengthening of onrete truture with pretreed fiber reinfored plati heet, ACI Strutural Journal, 89, APFIS

6 Wight, R.G., Green, M.F. and rki, M.A. (21). Pretreed FRP heet for pottrengthening reinfored onrete beam, Journal of Compoite for Contrution, ASC, 5(4), Wight, R.G., l-haha, R. and rki, M.A. (23) Pretreed and non-pretreed CFRP heet trengthening: damaged ontinuou reinfored onrete beam, International Journal of Material & Produt Tehnology, 19(1-2), APFIS