G Journal of the Korea Concrete Institute Vol. 20, No. 4, pp. 531~539, August, 2008 š x y w m š gj p { sƒ z 1) * 1) w w Evaluation of Flexural Strength for Normal and High Strength Concrete with Hooked Steel Fibers Young-Hun Oh 1) * 1) Dept. of Architecture, Konyang University, Nonsan 320-711, Korea ABSTRACT The purpose of this study is to investigate the mechanical properties of high strength concretes reinforced with hooked steel fiber. For this purpose, total 36 specimens whose variables are concrete compressive strength, steel fiber aspect ratio, and steel fiber volume contents, are made and tested. From the test results including previous research work, flexural performance of steel fiber reinforced high strength concrete is evaluated in terms of flexural strength and toughness index. Flexural behavior of steel fiber reinforced high strength concrete is enhanced with respect to the fiber volume content, the aspect ratio, and concrete compressive strength. More efforts are devoted to evaluate quantitatively between the flexural strength and the structural parameters such as the fiber volume content, the aspect ratio, and concrete compressive strength. Keywords : steel fiber concretes, flexural strength, toughness, fiber factor, energy dissipation capacity 1. gj p w ww, {w w ³ wš q p š. p gj pƒ š y w q w zw y š w. gj pƒ, ³ w p w y š. gj p w w p 1-6),, {, gj p, x, y gj p w p w w š w. 1,5,6) w m š gj p { sƒw» w x ww, w x» x ƒw gj p w { { p w. w» w { z sƒwš, w { wš w. *Corresponding author E-mail : youngoh@konyang.ac.kr Received May 19, 2008, Revised June 26, Accepted July 25, 2008 2008 by Korea Concrete Institute 2. x 2.1 x z x x gj p (30 50 MPa), x (62 72), y (1.0, 1.5 2.0 %) x w, KS F 2566 JSCE-SF4 ( gj p { x ) w ƒƒ 150 150 550 mm { x 3 w. gj p qk» w w, yw p,, n w 3 w n w 3 ywwš, w 5 ƒ yw w. y 2.0% ex w œ w w w. 2.2 x gj p msp p e 19 mm w ww. ü K S š x x Table 1 ùkù. x w 1,000 kn x» w 3 ƒ w š, d Fig. 1 ùkù d w. 531
Table 1 Properties of concrete and steel fiber W/C S/a Unit weight (kg/m 3 ) (MPa) (%) (%) W C S G 30 55 65 220 400 1020 560 50 40 69 220 468 1008 449 Steel fiber Hooked end Length Diameter l f (mm) d f (mm) l f /d f Tensile strength (MPa) 30.5 0.49 62 1,267 50.97 0.7 72 1,060 Fig. 1 Setup for flexural strength test 3.1 q xk 3. x x q xk y w x w ³ w w w ³ s j x ¾ mw ³ w ƒ q š. ù y w x» {³ e ³ y y w x w ùkû, x ü ³e s ƒ w w w w z d ³ s f» w m q. 3.2 w - š Fig. 2 x w - š w š.» {³ w» ¾ w - š»» y y w w ùkùš, y ƒw w ƒw y w. wr x 72 y w x w - š x 62 w w w z w w š. w x ³ ƒw, gj p ¼ ƒ ƒ w. ³ ƒ Fig. 2 Load-displacement curves for specimens x ƒ f ù œw q w. 4. gj p { p 4.1 { w x gj p, x y ƒ š x w gj p { p e w w» w 4» ( 2), û 3), National Taiwan Univ. 4), Dahan Institute of Technology ) ww { 5) x Table 2 w š. gj p x z» 532 w gj pwz 20«4y (2008)
Table 2 Flexural strength of specimens Research group Specimen size (mm) Author 150 150 550 Kwandong Univ. 2) 150 150 600 f c (MPa) V l f /d f F 1 f r Eq. (1) Eq. (2) f f 28 (%) (=V f l f / d f ) (test) Prediction Test/pred. Prediction Test/pred. 30 29.1 50 51.0 62 1.0 0.62 5.25 9.25 0.57 7.53 0.70 62 1.5 0.93 6.34 11.17 0.57 9.64 0.66 62 2.0 1.24 7.84 13.08 0.60 11.92 0.66 72 1.0 0.72 6.37 9.25 0.69 7.53 0.85 72 1.5 1.08 6.81 11.17 0.61 9.64 0.71 72 2.0 1.44 8.51 13.08 0.65 11.92 0.71 62 1.0 0.62 6.51 10.83 0.60 8.63 0.75 62 1.5 0.93 8.34 12.75 0.65 10.74 0.78 62 2.0 1.24 9.97 14.66 0.68 13.02 0.77 30 25.7 60 0.5 0.30 3.79 7.34 0.52 5.57 0.68 45 49.8 70 68.7 Chungnam Univ. 3) 150 150 550 100 100.7 Taiwan Univ. 4) 150 150 600 27 29.9 Dahan Institute of 150 150 530 90 95.0 Technology 5) 60 0.5 0.30 6.15 8.56 0.72 6.42 0.96 60 1.0 0.60 8.23 10.47 0.79 8.38 0.98 60 1.5 0.90 9.72 12.39 0.78 10.49 0.93 60 0.5 0.30 7.75 10.20 0.76 7.57 1.02 60 1.0 0.60 8.72 12.11 0.72 9.52 0.92 60 1.5 0.90 10.77 14.03 0.77 11.64 0.93 60 2.0 1.20 12.75 15.94 0.80 13.91 0.92 80 1.5 1.20 20.90 15.65 1.34 12.77 1.64 80 2.0 1.60 24.80 17.56 1.41 15.04 1.65 60 1.0 0.60 14.00 13.73 1.02 10.65 1.31 60 1.5 0.90 16.10 15.65 1.03 12.77 1.26 55 0.8 0.44 5.15 8.21 0.63 6.53 0.79 55 0.6 0.33 4.82 7.44 0.65 5.76 0.84 55 0.4 0.22 4.78 6.68 0.72 5.01 0.95 55 0.8 0.44 6.07 8.21 0.74 6.53 0.93 55 0.8 0.44 5.09 8.21 0.62 6.53 0.78 55 0.8 0.44 5.36 8.21 0.65 6.53 0.82 65 0.8 0.52 5.30 8.21 0.65 6.53 0.81 64 0.5 0.32 8.20 11.04 0.74 8.16 1.01 64 1.0 0.64 10.10 12.96 0.78 10.11 1.00 64 1.5 0.96 12.30 14.87 0.83 12.23 1.01 64 2.0 1.28 14.50 16.79 0.86 14.50 1.00 Mean - 0.74-0.90 STD - 0.19-0.24 C.O.V - 26% - 27% ƒ j» w. Fig. 3 Table 2 ùkù gj p, y (V f ), x (l f /d f ), (F 1 = V f l f / d f ) { e w š. gj p, y, x ƒ f { ƒw ùkû, w { (R) gj p, y, x, w ƒƒ 87.5%, 77.8%, 81.0%, 85.7% ùkû. gj p, y, x ƒƒ gj p { š w š q. 4.2» { sƒ Wafa 6) Ashour gj p { sƒ w» w x ww, ¼ 60 mm, 0.8 mm, w 260 MPa w» 100 MPa x 150 150 530 mm j» w. x y y (0%, 0.5%, 1.0%, 1.5% 2%), x k (1) { w. = 0.99 + 3.83V f» V f y (%). (1) š x y w m š gj p { sƒ 533
Fig. 3 Relationship between flexural strength and structural parameters Song 5) Hwang ¼ 35 mm, 0.55 mm š x w» 90 MPa x w. y 0%, 0.5%, 1.0%, 1.5%, 2% y g, x l (2) { w. 2 = 0.69 + 3.43V f + 0.32V f (1) (2) w x { w (2) Table 2 ùkù, w d x Fig. 4 š. Wafa Ashour w { Fig. 4(a) ùkù x w d s³ 0.74 ( 26%) { sƒw š. wr Fig. 4(b) ùkù Song Hwang x w s³ 0.90, 27% yw { d š. ù gj p { Fig. Fig. 4 Prediction of flexural strength using proposed equation by previous researcher 534 w gj pwz 20«4y (2008)
3 gj p y x y w q. gj p { w w š w w v ƒ š q. 4.3 d sƒ» { y sƒw» w d sƒw. (3) w w š, ƒƒ d w s³ Fig. 4(c) Fig. 4(d) š. Error (%) Wafa Ashour { s³ 37.9% ùküš, Fig 4(c) d d š y w. w Song Hwang { s³ 15.3% ùkü yw d š d d ƒ.» { d y y w w sƒw, y w k w { w v. 5. š w { p sƒ 5.1 { sƒ = -------------------------------------- 100 V predicted V test V test { gj p x ƒ { y q w t w - š sƒw w. Table 2 ùkù x JSCE-SF4 { w 28 x w { Table 3 š. w r Table 3 ASTM C1018 w w { wì ùkù. JSCE w { gj p, y, x, j ùkùš, ASTM w s jš ùkû. Fig. 5 JSCE w { š. JSCE w { g j p, y, x, w ƒƒ 80.9%, 74.7%, 65.6%, 82.9% ùkû. (3) Table 3 Flexural toughness index of specimens Research group Author Kwandong Univ. 1) Chungnam Univ. 2) Taiwan Univ. 5) Specimen ( -l f -V f ) 5.2 { Flexural toughness index ASTM C 1018 JSCE- I 5 I 10 I 20 I 30 SF4 30-62-1.0 5.8 13.3 29.9 46.6 3.5 30-62-1.5 5.5 12.2 27.5 42.9 4.9 30-62-2.0 6.1 14.7 34.3 53.5 6.2 30-72-1.0 6.2 15.0 35.0 55.9 5.9 30-72-1.5 5.7 13.3 30.9 49.5 6.4 30-72-2.0 6.1 14.5 34.0 55.5 8.2 50-62-1.0 5.2 10.9 21.6 30.9 4.7 50-62-1.5 5.3 11.6 22.9 32.3 5.6 50-62-2.0 5.6 12.8 28.9 44.8 8.1 30-60-0.5 6.1 8.5-22.9 4.3 45-60-0.5 4.5 8.3-19.6 6.5 45-60-1.0 5.2 11.0-34.9 12.2 45-60-1.5 5.8 12.4-37.8 15.2 70-60-0.5 4.6 7.6-16.8 5.9 70-60-1.0 4.5 9.1-22.7 8.5 70-60-1.5 5.1 10.7-31.4 15.5 70-60-2.0 5.5 12.2-39.8 23.2 100-80-1.5 - - - - 12.5 100-80-2.0 - - - - 16.0 100-60-1.0 - - - - 7.7 100-60-1.5 - - - - 10.3 27-55-0.8 4.2 7.1 11.5 15.7 2.8 27-55-0.6 4.3 7.6 10.8 13.7 2.0 27-55-0.4 3.9 6.5 9.4 12.0 2.2 27-55-0.8 4.4 7.4 12.6 17.7 3.7 27-55-0.8 4.4 7.4 13.1 18.3 2.9 27-55-0.8 4.4 8.3 13.2 16.9 2.7 27-55-0.8 4.2 7.6 12.3 16.6 3.0 gj p gj p, y, x ƒ { e w q w» w Fig. 6 { gj p { 7) w w 0.63 { w sƒw. gj p w gj p { ƒ j ùkù, y w w { w» w., gj p, y { ƒ j ùkùš. gj p» wš,» y ƒƒ w ù w w z { sƒw. w s š x y w m š gj p { sƒ 535
Fig. 5 Flexural toughness index calculated by the JSCE-SF4 method ƒ Fig. 6(e) Fig. 6(h)¾ ùkù, gj p y w ƒ yw š. p gj p w (F 1 ) { 93.4% ùk üš. gj p { gj p w xk l š w z x w { z dw q. š y x w s ww gj p z w xk { sƒƒ ƒ w š w. 5.3 gj p { gj p { sƒw» w» w { w, sƒw ù d { dw ùkû. w (1) (2) ù kù { gj p w w š w» d x w š w. gj p { w dw v ƒ, w { F 1 z x l w»» w gj p { w. = 0.63 + 1.03F 1 (4)» F 1 = l f / d f V f š, V f = y (%), l f / d f = x (aspect ratio) ùkü. (4) w { d k Fig. 7 { x w š. w x w d s³ 0.93, 12% yw d š. ù Fig. 7(b) d lƒ d sw y w. d { w v ƒ, d dw 25% (4) 0.75 g { w. = 0.63 + 0.75F 1 (5) w š gj p { dw Fig. 8 š., (5) gj p { y d yw dw ùkû. { x s³ 1.07, 13% dw š. w sƒw s³ 9% d { dw. Table 4 {» w { d l sƒw y t w š. (5) gj p { w gj p, y x (5) 536 w gj pwz 20«4y (2008)
Fig. 6 Increasement of flexural strength with various structural parameters w š w xk, y d { yw dw š q w. 6. š x w š gj p { sƒw» w x m ww,. 1) gj p { { j» gj p, y, x w w ùkùš, w z š w { p sƒw k w š q. 2) { { j» y e w gj p, y, j ùküš, š x y w m š gj p { sƒ 537
Fig. 7 Efficiency of the proposed Eq. (4) Fig. 8 Validation of the proposed Eq. (5) x z š. 3) y w { x { gj p w { w, w { gj p ùkü ƒ ƒ j ùkù š. gj p { w w sƒw w š q. 4) w { gj p w { ƒw gj p gj p, y x w š w gj p w w w xk. { s³ 1.07, 13%, s ³ 9% { dw š,» { y d š. = 0.63 + 0.75F 1 (MPa) 2006 w w w (KRF-2004-202-D00697) Table 4 Comparison between flexural strength prediction methods Investigator Mean S. D. Median py g ( ) x w,. š x C.O.V. (%) Mean error (%) Wafa and Ashour 6) 0.74 0.19 0.74 26 37.9 Song and Hwang 5) 0.90 0.24 0.93 27 15.3 Proposed Eq.(5) 1.07 0.14 1.03 13 9.0 1. xy, y, y š w SFRC x p, gj pwz, 16«, 6y, 2004, pp.759~766. 2. x, ½, š gj p p {, w wz, 24«, 2y, 2004, pp.455~458. 3.,, š gj p w p» x p w x, wm wz, 26«, 2Ay, 2006, pp.401~409. 4. Jeng, F., Lin, M. L., and Yuan, S. C., Performance of Toughness Indices for Steel Fiber Reinforced Shotcrete, Tunnelling and Underground Space Technology, Vol. 17, 2002, pp.69~82. 538 w gj pwz 20«4y (2008)
5. Song, P. S. and Hwang, S., Mechanical Properties of High- Strength Steel Fiber-Reinforced Concrete, Construction and Building Materials, Vol.18, 2004, pp.669~673. 6. Wafa, F. F. and Ashour, S. A., Mechanical Properties of High-Strength Fiber Reinforced Concrete, ACI Materials Journal, Vol. 89, No. 5, 1992, pp.449~455. 7. ACI Committee 318, Building Code Requirements for Reinforced Concrete, American Concrete Institute, 2002, 443 pp. š gj p { { sƒw» w x ww, w x» x ƒw š gj p { p w. š gj p { p sƒw, w p gj p, y x, w w q.» w { z sƒw, gj p { gj p, y x, w š w sƒw w š q. y { w w { w. w : gj p, {,,, š x y w m š gj p { sƒ 539