Design Formula for Rehabilitated Angle Steel Member Using Carbon Fiber Reinforced Plastic Plates

Transcription

1 Dsign Formula for Rhabilitatd Angl Stl Mmbr Using Carbon Fibr Rinforcd Plastic Plats Hiroyuki TAMAI Nagasaki Univrsity, Faculty of Enginring, Nagasaki, Japan Ako HATTORI & Yoshiyuki OZAWA & Tokuji HAITANI Toray Construction Company, Tokyo, Japan Takao TAKAMATSU Hiroshima Institut of Tchnology, Faculty of Enginring, Hiroshima, Japan SUMMARY: Aging and dtrioration of xisting stl structurs ncssitats th dvlopmnt of simpl and fficint rhabilitation tchniqus. Th authors hav dvlopd a tnsil forc strngthning mthod using bondd carbon fibr rinforcd plastic (CFRP) plat to nhanc th livs of xisting buildings. This papr rports th rsults of comprssiv loading tsts on an angl stl brac bfor and aftr rhabilitation using bondd CFRP plats. Ths rsults show nhancd comprssiv forc carrying capacity and dformation capacity as follows. 1) Although buckling tsts showd nhancd flxural rigidity, thr was no incrmnt of axial stiffnss. ) An lastic buckling formula using th xprimntal flxural rigidity from a thr-point bnding tst, gav a consrvativ valuation of load carrying capacity. 3) Taking into count th contribution of CFRP up to th lastic limit strain of th stl mmbr, its load carrying capacity could b valuatd from th formula of th Dsign Standard for Stl Structurs of AIJ. Kywords: Carbon fibr rinforcd plastic plat, Angl stl mmbr, Bonding, Buckling 1. INTRODUCTION A Stl Towr to transmit th powr was dsignd by a standard basd on allowabl strss concpt. A stl towr which transmits a ncssary outsid powr supply to cool a nuclar ractor had collapsd du to grat Tohoku arthquak in th first Tokyo Elctric Fukushima Nuclar Powr Plant. It is vry important to kp a function of powr supply aliv during and aftr svr arthquak ground motion. Fujii t al.(fujii, 004) was pointd out that th highr axial forc acts on tall stl towr undr svr arthquak such as Hyogokn-Nanbu arthquak than undr strong wind of 40 m/s avragd spd. That is bcaus th natural priod of tall stl towr accordd in prdominant priod of bas ground and damping ratio of tall stl towr is lss than 1.0 %. To kp a function of th towr during and aftr arthquak, main column mmbr such as stl angl mmbr must b strngthnd against th comprssiv forc. Th authors hav dvlopd a tnsil forc strngthning mthod using bondd carbon fibr rinforcd plastic (CFRP) plat to nhanc th livs of xisting buildings. Aging and dtrioration of xisting stl structurs ncssitats th dvlopmnt of simpl and fficint rhabilitation tchniqus. To nhanc th strngth and plastic dformation capacity of stl structural mmbrs, a rhabilitation tchniqu is rquird for comprssiv forc strngthning as wll as for tnsil forc strngthning. Ordinary fibr rinforcmnt is usd for tnsil forc strngthning. To dmonstrat th applicability of comprssiv forc strngthning using bondd CFRP plats for stl structurs, monotonically axial load tsts wr prformd on angl stl mmbrs with bondd CFRP plats. It was thus vrifid that th comprssiv load carrying capacity of mmbrs with bondd CFRP plats is 1.9~3.0 tims highr than thos without plats. Evn if th angl mmbr buckls undr axial load, thr is no concntration of plastic dformation around th kinkd portion (Tamai t al, 005, 006). Buckling tsts wr prformd on full-scal angl stl mmbrs of a transmission stl towr as an application xampl (Tamai t al, 008).

2 180 Practical rinforcmnt dsign for this towr rquird a dsign formula for asily valuating th ffct of bondd CFRP plats. Hnc, concntrically axial loadd tsts wr prformd on rhabilitatd angl stl mmbrs with various ffctiv lngths. A strut strngth curv xprssing th rlation btwn slndrnss ratio and buckling strngth was thus drivd. W also proposd a simpl dsign formula for th rinforcmnt ffct of bondd CFRP.. DESIGN FORMULA FOR STRENGTHENING BY BONDED CFRP PLATES.1. Comprssion stl angl mmbr bonding CFRP plats A comprssion stl angl mmbr with bondd CFRP is shown in Figur 1(a), and th adhsion mthod is shown in Figur 1(b). Th tst spcimns wr angl stl mmbrs with carbon fibr plastic plat (CFRP) bondd to thir outr surfacs. Two typs of CFRP plats wr usd: TL (high tnacity typ carbon fibr, thicknss=mm) and ML (middl modulus typ carbon fibr, thicknss=mm). Th mchanical proprtis of ths matrials ar shown in Tabls 1(a),(b). Th CFRP and adhsiv hardnd tst mthod was basd on th Japan Industrial Standard K7073, K703. Young's moduli for th CFRP plats wr 169kN/mm (TL) and 96kN/mm (ML), which ar almost th sam as or gratr than thos of th stl plat. Th tnsil strngths of th CFRP plats wr 3085N/mm (TL) and 169N/mm (ML), which ar 5-7 tims of that of stl. Th longation of TL was 1.5% and that of ML was 0.71%. Both th CFRP plats brok suddnly at maximum load. Th ML CFRP plat brok into small pics and th TL CFRP plat xhibitd axial taring. A srratd fractur surfac of th fibr was obsrvd in th CFRP plats (TL and ML). Construction by bonding CFRP plats dos not nd a strong scaffold bcaus CFRP plats ar light and asy bond to th mmbrs. L-50x50x CFRP P L-00x180x8 L - 50x50x ,600 CFRP Unit : mm (a) Tst Spcimns CFRP(ML) t=mm nd Layr 1 st Outr 800, 1,600-0 mm (b) Bonding Mthod Figurs 1(a),(b). Comprssion angl stl mmbr bonding CFRP plats Tabls 1(a),(b). Mchanical proprtis of matrials Young's Mudulus (a) CFRP and Stl Yild Strss Tnsil Strngth Elongation kn/mm N/mm N/mm % CFRP (TL) CFRP (ML) Stl Young's Mudulus Bnding Strngth (b) Adhsiv Comprssiv Strngth Tnsil Strngth Tnsil and Shar Strngth Impact Strngth kn/mm N/mm N/mm N/mm N/mm kj/m JIS K708 JIS K703 JIS K708 JIS K7113 JIS K6850 JIS K7111

3 .. Dsign formula for strngthning by bonding CFRP plats In this sction, w propos a strngth curv for rhabilitatd angl stl mmbrs using bondd CFRP plats. Th assumptions ar: 1) Comprssion strss is normalizd by th ara of th stl mmbr. ) Yild strss for th composit mmbr taks into account th CFRP contribution of axial load rsistanc up to stl yild. W imitat th strut curv of th dsign standard for stl structurs, (AIJ, 005), and adopt th assumptions abov. Strut strngths σ of th rhabilitatd stl angl with bondd CFRP plats ar: For λ >Λ α σ y σ = (1.a) λ Λ For λ Λ λ σ 1 (1 α) = σ y (1.b) Λ whr, n σ sy E ci, Aci, + σ sy As π Es i= 1 Es Λ =, λ =, σ y = (.a-c) α σ i A y α: Exprimntal constant prscribd in non-lastic rgion. λ, Λ, σ y, i : Slndrnss ratio, lastic limit slndrnss ratio, quivalnt yild strss, quivalnt, radius of gyration of composit mmbr : Effctiv lngth EAσ : Young s modulus, sctional ara, yild strss of stl angl,, s s sy n: Numbr of ply of CFRP plat EI : Flxural rigidity of composit mmbr ( ) b Th flxural rigidity of a composit mmbr was calculatd assuming that th sctional plat normal rmains prpndicular to th cntroid aftr dformation. This assumption is th so calld Eulr-Brnoulli's hypothsis. s Figur. Concntrically axial loading tst machin

4 PL-00x180x P D.T.50mm 180 δv W.S.G εc εc1 εc3 εl1 εl3 εl Figurs 3(a),(b). Masurmnt systm 3. CONCENTRICALLY AXIAL LOADED TEST 3.1. Tst spcimn and tst stup εc4 15 εl4 δh D.T.300mm δ a D.T.50mm,δ b δ v l/4 l/ l D.T. : Displacmnt transducr W.S.G. : Wir strain gag Unit: mm (a) Location of D.T. and W.S.G. Tabls (a),(b). List of tst spcimns (b) Strngthnd Spcimns (a) Unstrngthnd Spcimns Thicknss of adhsiv Spcimn λ 1st Layr nd Layr Spcimn λ mm - mm mm mm - L50-08C L50-08N L50-07C L50-07N L50-06C L50-06N L50-05C L50-05N L50-04C L50-04N L50-03C L50-03N Avrag 1.3 i = 9.61 mm, Λ = 103 i = 15.1 mm, Λ = 78 σy=318n/mm σy=554n/mm A tst spcimn is shown in Figur 1 (a). As shown, it is an L-50x50x4 angl stl mmbr with plis of ML CFRP plat bondd to its outr surfac and rctangular stl plats (PL-00x180x8) wldd to its nds. Th adhsion mthod is shown in Figur 1(b). Th surfac mill scal was rmovd with a grinding machin, and th surfac was thn polishd with glass papr (#100). Th adhsion agnt was poxy rsin hardnd at room tmpratur. Spcimns with lngths of 800, 1000, 1170, 1300, 1500, 1600mm wr tstd, so as to vary th slndrnss ratio. Unstrngthnd spcimns wr also tstd as rfrncs, making a total of twlv spcimns. Tabls (a),(b) show (a) unstrngthnd spcimns and (b) strngthnd spcimns, quivalnt slndrnss ratio, λ, thicknss of adhsiv layr t 1, t. Th mchanical proprtis of th matrials, i.., th angl stl, CFRP, and hardnd adhsiv, ar shown in Tabls 1(a) ~(c). Th tst apparatus, a concntrically axial loading machin, is shown in Figur. Th loading program was monotonic until failur was dtctd. δh l/ (b) Schmatic Illustration of masurd valus l

5 3.. Masurmnt mthod Th axial load, P, was masurd from a load cll in th uppr joint. Cntral dflction in th wak-axis dirction, δ, and shrinkags of nd tabs, h δ a, δ wr masurd by 300mm and 50mm strok b displacmnt transducrs. Axial dirction strains at th cntral sction ( ε c1, εc, εc3, ε ) wr masurd c4 by wir strain gags attachd as shown in Figur 3(a). Th shrinkag of spcimn, δ, was calculatd v from shrinkags of th nd tabs, δ, δ, as: a b δ a + δb δv = (3) Th masurd variabls ar illustratd in Figur 3(b). 4. TEST RESULTS AND DISCUSSIONS 4.1. Tst rsults Th rsults ar shown in Figurs 4~6, Tabls 3, 4, and Photograph 1. Figur 4 shows th rlations btwn slndrnss ratio, λ, and flxural rigidity from maximum buckling loads normalizd by flxural rigidity of stl mmbr, ( ) ( / s s ) EI E I. a Figur 5 compars th comprssion strngth, σ, obtaind from prsnt formula Eqns.(1.a), (1,b) with xprimntal rsults. Symbols, show th xprimntal rsults. Th rigid lin and dashd lin dnot th dsign formula curvs. Tabls 3(a),(b) shows ffctiv lngth,, maximum load, P, max quivalnt slndrnss ratio, λ, comprssion strngth from xprimntal rsult, σ, ratio of σ to quivalnt yild strss, ( σ/ σ y), flxural rigidity from xprimntal comprssion strngth, ( EI ) a, ratio of ( EI ) a to calculatd flxural rigidity, (( EI ) / ( EI ) a b), Eulr's buckling strngth, σ, and ratio of σ to σ. Equivalnt flxural rigidity for (a) unstrngthnd spcimns and (b) strngthnd spcimns ar drivd from: ( EI ) a Pmax = π From th xprimntal rsults for spcimns with various slndrnss ratios, λ, th quivalnt flxural rigidity ( EI ) a for longr spcimns (largr slndrnss ratios) is constant as calculatd ( EI ) b. For th shortr spcimns, th quivalnt flxural rigidity ( EI ) a bcoms smallr, and w can idntify th slndrnss ratio limit for th non-lastic rgion from th ( EI ) a vs. λ rlation. Figurs 6(a),(b),(c) show (a) th axial load normalizd by full plastic axial forc of stl angl δ / δ rlations, ( PP / sy ) vs. axial shrinkag normalizd by lastic limit shrinkag of stl angl ( v sy) (b) th ( PP / sy ) vs. cntral dflction toward wak-axis dirction normalizd by ffctiv lngth, ( δh / ), rlation and (c) th ( PP / sy ) vs. axial strain of cntral sction, ( ε c1, εc, εc3, ε ) rlations. c4 Photograph 1 shows th spcimns aftr tsts (a) long typ (L50-07C) spcimns, (b) short typ (L50-08C) spcimns. In Figur 6(a), th assumd initial stiffnss and on without CFRP ar drawn for rfrnc. Tabl 4 compars th maximum axial loads bfor and aftr strngthning. (4)

6 L , l = mm Exp. with CFRP.50 (E I) a / E s I s λ =Λ α=0.6 Dsign Formula 0.50 Exp. without CFRP λ =Λ, α= λ Figur 4. Rlations btwn slndrnss ratio and flxural rigidity from axial strngth 600 L , l = mm 500 Eqn.(1.b) Dsign Curv with CFRP σ (N/mm ) Exp. with CFRP 0.6 σ y Dsign Curv without CFRP 0.6 σ sy Exp. without CFRP Eqn.(1.a) λ Figur 5. Comparison of comprssiv strngth with formula and xprimnt P sy =13.8kN P sy =13.8kN µ P sy =13.8kN P / P sy Initial Stiffnss without CFRP Exprimntal Assumd Initial Stiffnss 0. L50x50x4, L50-06C l=1170mm P / P sy Exprimntal L50x50x4, L50-06C l=1170mm δ v / δ sy δ h / l ε (μ) (a) P/P sy vs. δ v /δ sy rlration (b) P/P sy vs. δ h / rlration (c) P/P sy vs. ε c rlration P / P sy Figurs 6(a),(b),(c). Tst rsults for L50-06C spcimn ε c1 εc1 εc ε c3 εc4 ε c ε c4 CFRP Stl εc3 0. L50x50x4, L50-06C l=1170mm

7 Edg kink Kink at Cntr (a) Rlativly longr spcimn (L50-07C) (b) Rlativly shortr spcimn (L50-08C) Photographs 1(a),(b). Failur pattrn aftr tsts Tabls 3(a),(b). Tst rsults (a) Unstrngthnd Spcimns Exp. Exp. Cal. Nam Pmax λ σ σ/σy (EI)a (EI)a/(EI)b σ Exp./Cal. mm kn - N/mm - kn m - N/mm - L50-08N L50-07N L50-06N L50-05N L50-04N L50-03N σy=318n/mm (EI)b=7.37kN m (b) Strngthnd Spcimns Exp. Exp. Cal. Nam Pmax λ σ σ/σy (EI)a (EI)a/(EI)b σ Exp./Cal. mm kn - N/mm - kn m - N/mm - L50-08C L50-07C L50-06C L50-05C L50-04C L50-03C σy=554n/mm (EI)b=18.kN m

8 Tabl 4. Effct of strngthning by bonding CFRP plats Effct of Nam Pmax Nam Pmax Strngthning mm kn kn L50-08C L50-08N L50-07C L50-07N L50-06C L50-06N L50-05C 16.3 L50-05N L50-04C 85. L50-04N L50-03C 77.7 L50-03N Discussion From th tst rsults, w can dtrmin th following: Axial rigidity From Figur 4 and Figur 6(a), w can s that th flxural rigidity is incrasd by th bondd CFRP plats, and hnc th buckling strngth is incrasd. Howvr, th axial rigidity is almost th sam bfor and aftr bonding CFRP plats xcpt in th initial small loading rang. This is bcaus th larg dflction at th cntral sction rducs th axial stiffnss, and th dg of th CFRP dos not transfr axial load. Hnc, th axial forc rsistanc of th CFRP plats rquirs larg shar dformation of th adhsiv layr. Applicability of strut strngth dsign curv undr lastic rgion From Tabl 3(b) and Figur 4, w can s that for quivalnt slndrnss ratios largr than 78, th flxural rigidity obtaind from th xprimnt is largr than obtaind from th formula. Hnc, Eulr's thory can b adoptd in th lastic rang for a composit mmbr. From Figur 5 and Figurs 6(a),(b),(c), w can s that for quivalnt slndrnss ratios smallr than 78, th strngthnd spcimn (for instanc L50-06C spcimn) has 1. tims highr maximum strngth than th fully plastic axial forc of th stl angl. Th strain of th CFRP (ML) plat whn buckling occurrd rachd th plastic strain of stl (=100μ). Hnc, th quivalnt yild strss obtaind from th formula taks into account th CFRP plat s axial rsistanc whn its strain rachs stl-yild strain. Th prsntd dsign formula of Eqns. (1.a) and (1.b) accuratly prdict strut strngth of rhabilitatd stl angl with bondd CFRP plats. Failur pattrn From Photographs 1(a),(b), w can s that, xcpt for th short spcimns (for instanc, L50-08C spcimn), all spcimns buckld at thir cntrs in th wak-axis dirction. In L50-08C spcimn, local buckling was obsrvd at th nd of th stl angl. For short mmbrs, adhsion is rquird ovr thir full lngths. 5. CONCLUSION This papr has rportd th rsults of comprssiv loading tsts on an angl stl mmbr bfor and aftr rhabilitation using bondd CFRP plats. Th rsults showd nhancd comprssiv forc carrying capacity and dformation capacity as follows.

9 1) Although buckling tsts showd nhancd flxural rigidity, thr was no incrmnt of axial stiffnss. ) An lastic buckling formula using th xprimntal flxural rigidity from a calculation, gav a consrvativ valuation of load carrying capacity. 3) Taking into account th contribution of CFRP up to th lastic limit strain of th stl mmbr, its load carrying capacity could b obtaind from th formula of Dsign Standard for Stl Structurs of AIJ. 4) Th CFRP must b bondd ovr th full lngth of th angl mmbr. AKCNOWLEDGEMENT W would lik to thank T. Hayakawa from Toray Co. LTD. and N. Wakahara and A. Kubota from Konishi Co. LTD. for thir coopration in conducting th xprimnts. W would also lik to acknowldg th kind support providd by Toray Co. LTD. and Konishi Co. LTD. through thir donation of th FRP and adhsiv usd in this study. REFERENCES Fujii., K. t al.: Comparison of sismic and wind rsistanc prformanc on stl towr structurs, Summaris of JSCE 004 annual mting, pp Watanab, T., Ishida, K., Hayashi, K., Yamaguchi, T., Ikda, S.,:(00): Sismic rtrofit of stl pirs with carbon fibr shts, Journal of Structural Enginring, Vol.48A, pp (in Japans). El Damatty, A.A., Abushagur, M., Youssrf, M.A.,:(003): Exprimntal and analytical invstigation of stl bams rhabilitatd using GFRP shts, Stl and Composit Structurs, Vol.3, No.6, pp Tamai, H., Takamatsu, T., Sumida, A., Haitani, T., Hattori, A.,:(003), Enhancmnt of usag lif on stl buildings using continuous fibr plats, Bulltin of Hiroshima Institut of Tchnology, Vol.38.,pp (in Japans). Tamai, H., Takamatsu, T., Sumida, A., Haitani, T., Hattori, A.,:(004): Lif prolongation of stl building using continuous fibr plats, Proc. of th nd Intrnational Confrnc on Stl and Composit Structur, CDROM, Tamai,H., Takamatsu,T., Sakuraba,M., Haitani,T., Hattori,A.,:(005): Comprssiv forc rhabilitation of angl stl brac using Carbon Fibr Rinforcd plastic plat, Journal of Constructional stl,vol.13, pp (in Japans) Sakuraba,M., Tamai,H., Takamatsu,T., Haitani,T.,(006): Hattori,A.: Cyclic loading tst on rhabilitatd angl stl brac using Carbon fibr rinforcd plastic plat, Journal of Constructional stl, Vol.14, pp , (in Japans) Tamai,H., Takamatsu,T., Ozawa,Y., Hattori,A.,(008) :Buckling tst on full -scal angl stl brac with bonding CERP plats, Journal of Constructional stl, Vol.16, pp , (in Japans)