ASSESSMENT OF STRENGTHENING EFFECT ON RC BEAMS WITH UHP-SHCC

Transcription

1 - Tehnial Paper - ASSESSMENT OF STRENGTHENING EFFECT ON RC BEAMS WITH UHP-SHCC Ahmed KAMAL *1, Minoru KUNIEDA *2, Naohi UEDA *3 and Hikaru NAKAMURA *4 ABSTRACT Ultra High Performane Strain Hardening Cementitiou Compoite (UHP-SHCC) i a new train hardening ompoite with outtanding mehanial and protetive performane. In thi tud, UHP-SHCC wa applied to RC beam a a tenile trengthening material, and the beam were teted under four-point bending etup. It wa larified that trengthening b UHP-SHCC ignifiantl ontributed to inreaing the load arring apait. And tre-train relation obtained from the tenile tet an well imulate the repone of the trengthened beam. Keword: UHP-SHCC, trengthening effet, load arring apait, deformation apait 1. INTRODUCTION In the lat deade, fiber reinfored ementitiou ompoite with higher dutilit uh a Strain Hardening Cementitiou Compoite (SHCC) have been developed. Thee new kind of material are ver effetive in tranferring the tre aro a rak, and alo provide multiple raking and train hardening behavior in tenion. Several reearhe have been arried out uing SHCC a a trutural material intead of the ordinar onrete. For example, Kanda et al.[1] applied SHCC to the prodution of hear reitant trutural element. Fukuama et al. [2] teted SHCC element under eimi loading. An appliation on trengthening or repairing uing SHCC i one of the attrative one. For example, Horii et al.[4], Li[5], and Li et al.[6] tried to appl SHCC to repair or retrofit of onrete truture, and onfirmed the effet of the dutilit of repair material on the trutural performane. Shin et al. [7] alo invetigated the trengthening effet of dutile fiber reinfored ementitiou ompoite (DFRCC) that wa applied to plain onrete beam. Mot reearhe on trengthening uing SHCC revealed that load arring apait of SHCC itelf provided additional load arring apait to trengthened truture. Kunieda et al. [8] developed Ultra High Performane Strain Hardening Cementitiou Compoite (UHP-SHCC) with ultra high trength and train hardening in tenion. Epeiall, tenile trength of UHP-SHCC i ignifiantl larger (twie or more) than that of ordinar SHCC. So, UHP-SHCC might be one of the effetive material for trengthening of onrete truture. In thi paper, the trengthening effet of RC beam with UHP-SHCC in tenion ide wa aeed through four-point bending tet. The reult were ompared with beam trengthened b ordinar reinfored onrete (RC). In addition, anali to predit -urvature relation wa arried out and ompared with the experimental reult. 2. EXPERIMENTAL PROGRAMS 2.1 Material (1) Ordinar onrete for ubtrate beam Table 1 how the mix proportion of the onrete ued for ubtrate beam. Water to ement ratio wa B onduting ompreive tet on 6 lindrial peimen with the ize of ø100x, the averaged ompreive trength at the age of 28da, whih wa the date on ating of trengthening laer, wa 22.7MPa. The ompreive trength of the onrete at the age of 56da, whih wa the date on loading tet of trengthened beam, wa 24MPa. (2) Strengthening material UHP-SHCC wa ued a a trengthening material in thi tud. Table 1 how the mix proportion of UHP-SHCC. Water to binder ratio (W/B) wa Low heat Portland ement (denit: 3.14g/m 3 ) wa ued, and 15% of the ement ontent wa ubtituted for a ilia fume (denit: 2.2g/m 3 ). The quartz and (le than 0.5mm in diameter, denit: 2.68g/m 3 ) wa ued a the fine aggregate. High trength polethlene (PE) fiber wa hoen for UHP-SHCC and the fiber volume in the mix wa 1.5%. The diameter and length of the PE fiber were 0.012mm and 6mm, repetivel. Superplatiizer wa ued to enhane the workabilit of the matrixe. Uniaxial tenile tet were onduted b uing 6 dumbbell-haped peimen (teted ro etion: 10x30mm) for UHP-SHCC. Fig.1 illutrate the tre-train relationhip for the tenile tet. The averaged tenile trength and train at the tenile *1 Dotoral tudent, Department of Civil Engineering, Nagoa Univerit, JCI Member *2 Aoiate Profeor, Department of Civil Engineering, Nagoa Univerit, Dr. E., JCI Member *3 Aitant Profeor, Department of Civil Engineering, Nagoa Univerit, JCI Member *4 Profeor, Department of Civil Engineering, Nagoa Univerit, Dr. E., JCI Member

2 Strengthening laer Table 2 Tpe of trengthening laer Thikne t= (mm) Reinforement Reinforement ratio in trengthening laer (%) No. of teted beam Non. (ontrol beam) UHP-SHCC D10 (SD295A) Reinfored onrete 70 3 D10 (SD295A) D13 (SD295A) Fig.1 Stre-train urve of UHP-SHCC in uniaxial tenile tet trength of the UHP-SHCC at the age of 28da were 10.5MPa and 1.7%, repetivel. For ompreive propertie, 5 lindrial peimen having the ize of ø50x100mm were teted at the age of 28da. The averaged ompreive trength wa 86.7MPa. For omparion, ordinar reinfored onrete wa plaed a a trengthening material. Table 1 how the mix proportion of the onrete ued for the trengthening laer. The averaged ompreive trength of the onrete at the age of 28da, whih wa the date on loading tet of trengthening beam, wa 20.6MPa. Two or three rebar were plaed in the RC trengthening laer. D10 (SD295A, f=362n/mm 2 ) and D13 (SD295A, f=362n/mm 2 ) were ued. 2.2 Speimen and tet etup Fourteen reinfored onrete (RC) beam with length of 1800mm and ro etion of 150 x were prepared uing ubtrate onrete hown in Table 1. Two rebar of D10 (SD295A, f=362n/mm 2 ) were ued a reinforement of eah beam. Stirrup of D6 (SD295) were ued in the hear pan at the interval of 90mm, a hown in Fig. 2. After the ating of onrete, the peimen were demoulded at the age of 2da, and the bottom urfae of the beam, whih wa the interfae between the trengthening laer and the ubtrate, wa wahed out uing a retarder to obtain a roughed urfae. Then the peimen were overed with wet towel for 28da in a ontant temperature room (20C ). After 28da, trengthening laer were plaed at the bottom ide of the ubtrate beam. Six beam were trengthened uing UHP-SHCC with the thikne of 30, 50, and 70mm (two beam for eah ae). And ix beam were trengthened uing reinfored onrete with different reinforement ratio. Table 2 how the tpe, dimenion, reinforement and reinforement ratio in trengthening laer, and the number of teted peimen for eah ae. In addition to thee peimen with trengthening, two ubtrate beam were teted a ontrol beam. The trengthened beam were demoulded at the age of 2da after ating of trengthening laer. The peimen were overed again with wet towel for 26da additionall. At the age of 28da after ating of trengthening laer, loading tet were arried out b mean of a four-point bending. In all tet, the length of the and hear pan were 600mm and 450mm, repetivel, a hown in Fig.2. Diplaement at loading point and mid point, and load were meaured b diplaement tranduer (troke: 50mm, 150 mm Table 1 Mix proportion of UHP-SHCC, ubtrate and trengthening onrete Unit ontent (kg/m 3 ) Water/ Material Fiber Binder* Silia Chemial Superplatiizer Water Cement Sand Coare agg. ontent fume admixture (6mm) UHP-SHCC Subtrate & trengthening onrete * Binder mean ement + ilia fume 150 mm 150 mm Diplaement tranduer 600 mm D6@90mm 90 2 D10 70 Beam trengthened b RC t Beam trengthened b UHP-SHCC Control beam 1500 mm 1800 mm Strengthening laer Fig.2 Reinforement detail of trengthened beam and tet etup.

3 enitivit: 0.005mm) and load-ell (apait: 294kN, enitivit: 98N), repetivel. The urvature of the pan wa determined b omputing the meaured defletion at loading and mid point. The loading tet wa terminated when ompreive failure of onrete on the top urfae of the peimen wa viuall reognized or udden drop in the load wa oberved. 3. EXPERIMENTAL RESULTS 3.1 Moment-urvature relation Fig.3 and 4 how the -urvature urve of the beam trengthened b UHP-SHCC and RC. Table 3 tabulate obtained value on firt raking, ielding, maximum and urvature at maximum. The relation between the amount of trengthening material (i.e. thikne of UHP-SHCC and reinforement ratio in RC) and maximum are ummarized in Fig. 5 and 6, repetivel. In ae of uing UHP-SHCC a a trengthening laer, the load arring apait and initial tiffne of the trengthened beam were inreaed with inreaing of the thikne of UHP-SHCC. After the loalization of frature on UHP-SHCC wa oberved, the beame equal to that of the ontrol beam, a hown in Fig Crak pattern Fig.7 how the rak pattern of beam with UHP-SHCC (thikne: 30mm) and RC (A: 1.36%), repetivel. In the peimen with RC, rak in the trengthening laer (RC) propagated to the ubtrate ontinuoul, and the number of rak in the trengthening laer (RC) wa almot the ame a that of ubtrate. For the beam with UHP-SHCC, ditributed fine rak were oberved, and the number of rak in UHP-SHCC wa dramatiall inreaed omparing to the peimen trengthened b RC. No delamination at the interfae between UHP-SHCC laer and the ubtrate wa oberved. Table 3 Firt raking, ielding, maximum, and urvature at maximum Strengthening ae Firt Craking Yielding Maximum Curvature at max. (10-3 /mm) Non. (ontrol beam) t=30mm UHP-SHCC t=50mm t=70mm Reinfored onrete (t=70mm) Reinforement 2 D D D Fig.3 Moment-urvature urve of trengthened beam uing UHP-SHCC Fig.5 Effet of UHP-SHCC thikne on maximum Fig.4 Moment-urvature urve of trengthened beam uing RC Fig.6 Effet of reinforement ratio within RC maximum

4 Table 4 Comparion between the hear apait of ontrol peimen and the maximum experimental of UHP-SHCC peimen Shear apait of the ontrol beam Maximum experimental of UHP-SHCC peimen t=30mm t=50mm t=70mm Fig.7 Crak pattern obtained in UHP-SHCC laer ompared with that of RC laer 3.3 Deformation apait and loation of loalized frature of UHP-SHCC A hown in Fig.3 and 4, the deformation apait of the trengthened peimen that wa repreented b the urvature at maximum dereaed b inreaing the amount of trengthening material, whih wa thikne of UHP-SHCC or reinforement ratio in RC. The relation between the amount of trengthening material (i.e. thikne of UHP-SHCC and reinforement ratio in RC) and urvature at maximum are ummarized in Fig.8 and 9, repetivel. For the peimen with RC trengthening laer, urvature at maximum wa governed b the ompreive failure of ubtrate onrete. However, the failure mode of the beam trengthened b UHP-SHCC depend on the frature of the UHP-SHCC itelf not on the ompreive failure of the ubtrate onrete. In addition, in the ae of uing maller thikne of UHP-SHCC (epeiall 30 and 50mm), tenile failure of UHP-SHCC wa obtained in the pan, a hown in Fig.10. In the ae of UHP-SHCC with thikne of 70mm, that wa the thiket laer in thi experiment, however, the loalization of frature of UHP-SHCC wa oberved within the hear pan not the pan, a hown in Fig.10. Table 4 deribe the omputed from the hear apait of the ontrol beam omparing to the maximum of the beam trengthened b UHP-SHCC. The hear apait wa alulated b the proedure peified in JSCE peifiation (Strutural Performane Verifiation) [9], and the obtained value omputed from the hear apait wa 20.07kN.m. A hown in Table 4, the maximum of the beam peimen trengthened b UHP-SHCC with the thikne of 70mm wa imilar to the omputed from the hear apait of the ontrol peimen. In fat, a diagonal rak within the hear pan wa opened widel, a hown in Fig.10. It eem that the diagonal rak within the hear pan initiated the loalization of frature on UHP-SHCC, before a tenile frature of UHP-SHCC within the pan. Fig.8 Effet of UHP-SHCC thikne on the deformation apait Fig.9 Effet of reinforement ratio within the RC on the deformation apait UHP-SHCC 30mm ae UHP-SHCC 70mm ae Fig.10 Effet of UHP-SHCC thikne on it failure mode

5 4. ANALYSIS TO PREDICT RESPONSE OF BEAM 4.1 Anali flow Moment-urvature anali wa arried out to predit -urvature relation for the beam trengthened b UHP-SHCC. The anali depended on the aumption that plane etion remain plane. Anali flow i a follow: The input data inlude the peimen ize, and tre train relationhip of the onrete, UHP-SHCC, and reinforement. Give the train at extreme ompreion fiber a the inrement parameter. Compute the tre orreponding to the train at eah fiber level (aording to tre-train relationhip of the material). Determine the depth of the neutral axi that aue the equilibrium. Compute the and urvature at equilibrium tage, and then repeat the ame proedure after giving new train inrement. The anali wa terminated if an of thee ae happened: ompreion failure of the ordinar onrete, or tenion failure of UHP-SHCC. 4.2 Material model About the tre-train relationhip of the material ued in anali: (1) UHP-SHCC: From the tre-train urve of UHP-SHCC in uniaxial tenile tet, uing the averaged firt raking tree and averaged maximum tenile trength and orreponding train, the averaged tre-train urve, hown in Fig.1, wa ued for the material repone of UHP-SHCC in tenion. (2) Ordinar onrete: Fig.11 illutrate the ompreive tre-train relationhip of the ordinar onrete for the ubtrate ued in the anali. The onrete tre value wa governed b Eq.1 up to train value equal to. The tre value after the train exeed i equal to 85% of ompreive trength of the onrete (f =24MPa). When the train value of onrete exeeded , the anali wa terminated. The material repone in tenion of the ordinar onrete wa negleted in the anali. k 1f ' 2 (1) k 1f ' where, : ompreion tre of onrete f : ompreive trength of onrete : ompreion train of onrete k f ' 0.85 (3) Reinforement: Fig.12 how tenile tre-train relationhip of the reinforement ued in the anali. Bilinear tre-train relationhip wa ued Stre k 1 f = 0.85x24 MPa Equation of the urved line k 1f ' 2 Strain Fig.11 Compreive tre-train urve of ordinar onrete ued in urvature anali Stre f =362MPa E 0.01E Strain f /E Fig.12 Tenile tre-train urve of the reinforement ued in urvature anali in the anali, a deribed in Fig.12 and Eq.2.. E f / E f 0.01 E.( f / E ) f / E (2) where, : tenile tre of reinforement E : Young modulu of reinforement : tenile train of reinforement f : ield trength of reinforement Fig.13 how a omparion between the -urvature urve obtained from the anali and experiment for the beam trengthened b UHP-SHCC. In ae of beam with UHP-SHCC having the thikne of 30mm, the anali howed that tenile failure of UHP-SHCC wa obtained before the ompreive failure of ubtrate onrete, and thi behavior wa well agreed with the experimental failure mehanim. In the ae of 50 and 70mm thikne, the anali howed that the ompreive failure in onrete wa ourred before the failure of UHP-SHCC. The omparion howed good agreement between experimental and analtial reult up to reinforement ielding point in all ae, a hown in Fig.13. For beam with 70mm thikne of UHP-SHCC, the differene between the analtial and experimental urve inreae rapidl after the ielding point. A mentioned before, a major diagonal rak in hear pan wa oberved in the experiment, and the rak might initiate the (hear) failure of UHP-SHCC, before tenile failure of UHP-SHCC itelf. Generall, the experimental reult of beam with UHP-SHCC an be roughl imulated b the

6 Yielding point Yielding point Yielding point (a): Thikne of 30mm (b): Thikne of 50mm (): Thikne of 70mm Fig.13 Comparion between analtial and experimental -urvature urve of beam trengthened b UHP-SHCC anali uing the above material repone, exept for the beam with UHP-SHCC having the thikne of 70mm. From thi anali and tud, it wa revealed that the material repone of UHP-SHCC obtained from the tenile tet an be ued to predit the repone of trengthened beam, exept for the deformation apait of beam with thiker UHP-SHCC (70mm in thi tud). 5. CONCLUSIONS In order to diu the trengthening effet of RC beam with UHP-SHCC, four-point bending tet were arried out, in addition to the anali to predit -urvature relation. The following onluion were obtained: (1) The load arring apait and initial tiffne of the trengthened beam were inreaed with inreaing of the thikne of UHP-SHCC. (2) For the beam with UHP-SHCC, ditributed fine rak were oberved, and the number of rak in UHP-SHCC wa dramatiall inreaed omparing to the peimen trengthened b RC. In addition, no delamination at the interfae between UHP-SHCC laer and the ubtrate wa oberved. (3) The failure mode of the beam trengthened b UHP-SHCC depend on the loalized frature of the UHP-SHCC itelf not on the ompreive failure of the ubtrate onrete. In the ae of uing maller thikne of UHP-SHCC (epeiall 30, and 50mm), tenile frature of UHP-SHCC wa obtained in the pan. (4) The loalized frature of UHP-SHCC wa oberved within the hear pan not the pan in the ae of UHP-SHCC with thikne of 70mm. It eem that the diagonal rak within the hear pan initiated the loalization of frature on UHP-SHCC, before a tenile frature of UHP-SHCC within the pan. (5) The experimental reult of beam with UHP-SHCC an be roughl imulated b the anali uing the material repone obtained from the tenile tet. ACKNOWLEDGEMENT Thi reearh wa finaniall upported b Servie Center of Port Engineering (SCOPE). The fiber were provided b Toobo Co., Ltd, and hemial admixture wa provided b Takemoto oil&fat Co., Ltd. The author would like to thank thoe upport. REFERENCES [1] T. Kanda, S. Watanabe, and V.C. Li: Appliation of Peudo Strain Hardening Cementitiou Compoite to Shear Reitant Strutural Element, Frature Mehani of Conrete Struture, FRAMCOS-3 Proeeding, pp , Ot [2] H. Fukuama, Y. Sato, V. C. Li, Y. Matuzaki, and H. Mihahi: Dutile Engineered Cementitiou Compoite Element for Seimi Strutural Appliation, 12 th WCEE Proeeding, [3] J. Zhang, C.K.Y. Leung, and Y. Cheung: Flexural performane of laered ECC-onrete ompoite beam, Journal of Compoite Siene and Tehnolog, Vol. 66, pp , [4] H. Horii, S. Matuoka, P. Kabele, S. Takeuhi, V.C. Li, and T. Kanda: On the Predition Method for the Strutural Performane of Repaired/Retrofitted Struture, Frature Mehani of Conrete Struture, FRAMCOS-3 Proeeding, pp , Ot [5] V.C. Li: ECC for Repair and Retrofit in Conrete Struture, Frature Mehani of Conrete Struture, FRAMCOS-3 Proeeding, pp , Ot [6] V.C. Li, H. Horii, P. Kabele, T. Kanda, and Y.M. Lim: Repair and Retrofit with Engineered Cementitiou Compoite, International Journal of Engineering Frature Mehani, Vol.65, No.2-3, pp , [7] S.K. Shin, J.J.H. Kim, Y.M. Lim: Invetigation of the trengthening effet of DFRCC applied to plain onrete beam, Journal of Cement & Conrete Compoite, Vol. 29, Iue 6, pp , [8] M. Kunieda, E. Denarié, E. Brühwiler, H. Nakamura: Challenge for Strain Hardening Cementitiou Compoite Deformabilit Veru Matrix Denit, Pro. of the fifth International RILEM Workhop on HPFRCC, pp.31-38, [9] Standard Speifiation for Conrete Struture, Strutural Performane Verifiation, JSCE Guideline for Conrete No.3, pp.76-78, 2002.