Journal of the Korea Concrete Institute Vol. 23, No. 3, pp. 393~400, June, 2011 GGGGG DOI 10.4334/JKCI.2011.23.3.393 x RC { sƒ y y 1) *Á½ 1) Á 2) 1) y w œw 2) w œw Bond Strength Evaluation of RC Beams on the Rib Shape of Reinforcing Bars Geon-Ho Hong, 1) * Jin-Ah Kim, 1) G and Oan-Chul Choi 2) 1) Dept. of Architectural Engineering, Hoseo University, Asan 336-795, Korea 2) Dept. of Architectural Engineering, Soongsil University, Seoul 121-791, Korea ABSTRACT The needs for high strength structural materials have recently increased, because construction and cost efficiencies are demandey the costumers. But, the use of high strength reinforcing bars requires longer development and splice lengths compared to normal strength bars. This restriction may cause reduction in construction efficiency and require more complicated details. The purpose of this paper is to evaluate the bond strength on the rib shape of reinforcing bars to decrease development and splice lengths of high strength reinforcements. Total of 5 simple beam specimens were tested, and the main test variable was a rib shape of reinforcing bars. Test data was analyzed in the viewpoint of bond strength, load-deflection relationship, and crack pattern. Test results indicated that the bond strength of high relative rib area reinforcing bars increased up to 11% compared to normal strength reinforcements. And the improved rib shape reinforcements, which were formed with high and low height rib, increased the bond strength up to 23% even though the relative rib area was same as the high relative rib area reinforcements. Serviceability performances such as deflection number of cracking, and maximum crack width were similar in all specimens, so it is safe to conclude that the improved rib shape reinforcements can be applied to the structural members. Keywords : rib shape, relative rib area, bond strength, lap splice, crack 1. y š, œ š y ƒ š. p, š gj p œ œ w k, w t w w w w. ù ü gj p» w w ƒ ƒw ¼ ƒ ƒw œ., SD400 SD500 w 25%, 42%¾ e ¼ ƒ ƒw. w w ¼ x ƒœ gj p k w œ w k w. 1-3) w w w» w 1990 Darwin 4) *Corresponding author E-mail : honggh@hoseo.edu Received March 24, 2011, Revised May 12, 2011, Accepted May 13, 2011 201X by Korea Concrete Institute ƒ k w x mw ƒ ƒw ƒ ƒw ¼» x 16% k w. ù ƒ w ƒ gj p q q ƒ w ƒ w ƒ ùkû. ƒ q w» w, š ³ z û y w, ƒ yww w w» w x. 5)» k x yƒ e z w xk w w. 2.» ¼ ü gj p ³ w w y ƒ w, w T w y 393
w w., w v w T A s f y w w, txw (1) ùký. u u A A s f y (1)», A π txw, T (2) w. T = u u π (2) (2) w u u 1977 Orangun 6)» l z w z w (3) w. 3C 50 A tr f yt u u = 1.2 + ------ + ---------- + ---------------- f ( : psi) (3) l s 500sd c b, A tr f yt / 500s 3 ww. 1979 Jirsa w 7), v Ì, š w 62 xw k ¼ w. ¼ w f y, gj p» f ck txwš, ü ¼ 8) d y g wš. w, w e»k, e, s w, gj p w» w š w (4) tx. = 0.9 d f b y ---------- f ck αβγλ --------------------- 300mm c + K tr ---------------»,, α e e, β s, λ gj p, γ j», c l gj p t ¾ 1/2, K tr z w., (c + K tr )/ 2.5, q ƒ ù yw w. wr, 1996 Darwin 4) š w R r w, (5). T ---------- [ 63 ( c m + 0.5 ) + 2130A b ] 0.1 c M = ----- + 0.9 f c 1/4 NA tr 66 + 2226( t r )( t d ) ---------- + n ( : psi)», c M c m w v Ì d v Ì y 1/2 w ƒ ƒ j w, t r z c m (4) (5) 9.6R r + 0.28, t d j» z š w 0.72 +0.28, R r. ¼ w ùkü» w 66 wš N / s, f s f y w yw (6). ---- 1/4 f s /f c 2130ω = ---------------------------------------- 80.2 c ω + K tr ------------------------ ( : psi) (6)», ω v Ì w (0.1c M / c m +0.9) 1.25, c c m +0.5, K tr (35.3t r t d A tr )/sn w, (c + K tr 4 ww. ACI 408 z9) Darwin d wš, e, s gj p w š w (7) ¼ y g wš, (7) w 0.10~0.14¾ w. ---- x w ¼ y w w Fig. 1. ü š w š» ACI 408 z ¼ ƒ ¼ ùkù, ƒw (c + K tr w w ¼ ƒ ƒw ùkû. 3.1 x z 1/4 f s /f c 1900ω = -------------------------------------- αβr ( : psi) (7) 72 cω + K tr -------------------- 3. x z š û yww y w Fig. 1 Development length in accordance with bar diameters 394 w gj pwz 23«3y (2011)
Table 1 Details of specimen Specimen h r (mm) s r (mm) R r CV 1.6 18.0 0.088 HR 2.4 18.0 0.133 WA 3.2 36.0 1.6 36.0 0.133 WB 3.6 36.0 1.6 36.0 0.144 WC 4.2 36.0 1.6 36.0 0.161 f ck Tension bar f y 24 500 Tension bar (mm 2 ) 2-D25 (1,013 mm 2 ) Compression bar f y 400 Compression bar (mm 2 ) 2-D13 (253 mm 2 ) Stirrup Splice length (mm) D10@100 400 (16 )» w» x šw 2,4,5) ¼ x w z x (R r ) x w. 5 x w, ƒ x l Table 1. x x» x CV, 0.133¾ ƒ k HR š, w w š û yww WA, š û yww ƒ g 0.144, 0.161¾ ƒ k WB WC txw. Darwin 4) w w, (8). h r, s r w. R r Bearing ----------------------- area π( 2r + h r )h r = ----------- = ----------------------------- Shearing area 2π( r + h r )s r CV w HR (8) 1.5, x WA, WB, WC ƒƒ 2, 2.25, 2.625 w û CV w w. ƒ x Fig. 2. ¼ x Fig. 3 x 300 400 mm, ¼ 4,000 mm w, CV w ¼ w e 1,000 mm ƒœw w. Table 1 x z w gj p» 24 MPa, SD500 25 mm, SD400 13 mm w. w, x q w» w SD400 10 mm w, e ü z w w» w 5 w. ¼ w q w 16 400 mm, v Ì 2 50 mm zw. Fig. 2 Rib shapes of reinforcing bars Fig. 3 Specimen detairawing (unit: mm) (unit: mm) x RC { sƒ 395
3.2 x gj p w Table 2. gj p œ KS F 2403 gj p x œ, x z x w, s³ CV 23.4 MPa, ù 21.6 MPa ùkû. x xr(ks B 0801) ³ 2y xr» xr» x w. xw mw ü w,,» Table 3, w 0.2% off-set w w. 520 MPa w w š, x ƒœw 3 r s³ 533 MPa w w v w ƒ 13 MPa d ù 0.56% w ùkü. 3.3 x x» PC T w. š û ƒ yw x» d mw ƒœ w w. x š gj p k w» x d w» w x ó 4, w 3 w 2 6 w. x gj p k z 1» z»» w, 28 z x x x w. 3.4 x x ³ q xk y w» w Fig. 4 gj p k w Table 2 Mix proportion of concrete f ck W /C (%) S / a (%) Table 3 Properties of reinforcement Reinforcement Yield load (kn) Yield strength Unit weight (kg/m 3 ) W C S G (25 mm) AD 24 49.4 48.5 162 328 900 974 1.64 Tensile strength Elastic modulus Elongation (%) CV 241 520 670 224,000 30.0 bar #1 264 540 650 185,000 22.0 bar #2 259 530 650 184,000 23.0 bar #3 262 530 650 190,000 20.0 Fig. 4 Test set-up x ew w ƒw. ¼ 2.5 1,000 mm w, ó ƒ q 4 w 300 kn w. w, w sƒw» w x w w LVDT ew d w, x gj p x d w» w gj p x ¼ d 2, d 1 w. x ³ q w» w t w w z, w ³ j»» w q ƒ ¾ x w. 4.1 w 4. x e w x w x Table 4. t q w x q ƒ w w. m w CV x w HR 6%, WA WC ƒƒ 19%, 17% ü ƒw. WB x 2% ü ƒ w, x 2 v ̃ y w» w q ƒ. x l m ƒ w ü w, HR WA x w š û yww ƒ w. WA WC x r, ƒ j ƒw x ü j yƒ ùkù,»»wš 4) 0.15 š û yww j z» w sƒ. wr, ƒ x x ü gj p» ³ wš (4) AIC 408 z wš (7) w w Table 4 396 w gj pwz 23«3y (2011)
Table 4 Test results analysis Specimen f ck R r Test Theoretical value Ratio Failure load (1) (kn) KCI (2) (kn) ACI 408 (3) (kn) (1)/(2) (1)/(3) CV 23.4 0.088 88.81 58.29 83.22 1.52 1.07 HR 21.6 0.133 94.55 56.12 87.50 1.68 1.08 WA 21.6 0.133 105.42 56.12 87.50 1.88 1.20 WB 21.6 0.144 90.18 56.12 87.50 1.61 1.03 WC 21.6 0.161 104.29 56.12 87.50 1.86 1.19 w.» w x q w ¼ x w ¼ w f s w z, w ey w w. t ùkù ü gj p» š w w» x w ü sƒw ùkû, x ü x 152~188% ü ùkû. ACI 408 z š w CV x k x ü j sƒ ù, (c + K tr 4 ww ³ WA, WB, WC x ü w sƒ. x WA WC x ü w ³ k w sƒ ù, HR x WA x x w w. 4.2 ƒ x x d q w w mw y w z, w Table 5. w, CV x gj p ƒ w gj p w wš z w» w f ck ù y k z, CV x w w., WA x xk z 23% ƒw ùkû. WA x w ƒ k HR x 11% ƒ ùkü, 0.161¾ ƒ k WC x WA x w 21% ƒ ù kü. wr, ü gj p» w ( (4)), Orangun( (3)), Darwin( (6)) ACI 408 z ( (7)) l w x w, Table 5 ùkù ü» x x CV 70% ùkü, Orangun 9% ùkþ. ù x w z w w ü w 2.1, Orangun w 1.4 ùkü. š w Darwin ACI 408 z x w, x HR ƒƒ 5%, 17% w x ùkü. ACI 408 z š w w». wr, Darwin l š û yww x WA, WC x w, ƒƒ 17%, 16% ƒ ƒw ùkü. x w eš q. wr, x ü 100 mm w w (c + K tr w z ƒ wš. x (c + K tr y A tr f yt /500s w w w w Fig. 5. w x zw ùkü y wš q, (c + K tr y Table 5 Bond strength analysis Specimen Bond strength Bond stress Comparison KCI 8) Orangun 6) Darwin 4) ACI 408 9) τ/ f (kn) ck with CV (kn) (kn) (kn) (kn) CV 184.77 5.88 1.22 1.00 108.94 170.09 177.35 159.17 HR 196.71 6.26 1.35 1.11 105.66 163.39 187.59 168.09 WA 219.25 6.98 1.50 1.23 105.66 163.39 187.59 168.09 WB 187.62 5.98 1.29 1.06 105.66 163.39 187.59 168.09 WC 216.68 6.90 1.48 1.21 105.66 163.39 187.59 168.09 x RC { sƒ 397
Fig. 5 Bond strength comparison between theoretical value and test result according to influence of (c + K tr A tr f yt /500s w w w ƒ x w, q ww» w (c + K tr w w y g w q. p, ü» w š» w w j ùkü. ww ü» Orangun w k w ù, w š w š ƒ ƒ w» w q. w, z ƒ š Darwin ACI 408 z x y w w w» w v w q. 4.3 w - xk y sƒ w x w x w - w Fig. 6. x ww Fig. 6(a) r, ³ w»» x ƒ w ƒ š ù, ³ z ƒ CV x ƒ ƒ š z W HR x ùkû. wr Fig. 6(b) l š û ƒ yw WA, WB WC x Fig. 6 Load-deflection curve w ü w w - š ù kü, ƒ w w HR x ³ z WA x w ùkû., Fig. 6(c) w» w»» ƒw ù, ³ w 20 kn w z l»»ƒ HR 3.55 kn/mm, WA 4.28 kn/mm WA»»ƒ 21% ƒw ü, w 20 mm w ùkù. w x ü w. 4.4 ³ q x q Fig. 7 398 w gj pwz 23«3y (2011)
Fig. 7 Crack pattern w» w x { ³ w z x e q ƒ w. ³ xy Fig. 8 ùkü,» ³ w z ³ ƒ ƒw q p 6~8 ³. CV, WB, WC x 60~70 kn w w ¾ ³ ƒ ƒw x ùkü, HR WA x 40 kn w w ³ k w 6 ³. w ƒ ³ s xy Fig. 8(b) Table 6. ùkù x ³ s xy w q Table 6 Crack width analysis Specimen Load (kn) CV HR WA WB WC Crack number (EA) Test (1) Crack width (mm) Cal. (2) Ratio to CV (1) / (2) 40 6 0.20 0.10 1.00 2.00 60 7 0.35 0.20 1.00 1.75 80 8 0.45 0.30 1.00 1.50 40 6 0.20 0.10 1.00 2.00 60 6 0.30 0.20 0.86 1.50 80 6 0.60 0.30 1.33 2.00 40 5 0.13 0.10 0.65 1.30 60 6 0.35 0.20 1.00 1.75 80 6 0.50 0.30 1.11 1.67 40 5 0.10 0.10 0.50 1.00 60 6 0.30 0.20 0.86 1.50 80 8 0.40 0.30 1.14 1.33 40 6 0.15 0.10 0.75 1.50 60 8 0.35 0.20 1.00 1.75 80 8 0.50 0.30 1.43 1.67, 60 kn w w x x CV x w 86~100% ³ s ù küš, 80 kn w 111~143% ³ s ùkü. š w x ³ x m w q. wr, x d ³ s ü gj p» ³ s 10) w Table 6. ü» wš ³ s CEB-FIP ³ s w ³ wš, (9). ω k = ε cs l s, max ( ε sm ε cm ) (9) Fig. 8 Number of cracks and crack width», l s,max gj p ñ w ¼, ε sm l s,max ü s³ x, ε cm l s,max ü s³ gj p x, ε cs w gj p x ùkü. (8) z ƒ» x ³ s w, x CV HR 1.5~2, WA 1.3~1.75 ùkû. x (8) j ùkù (8) e ³ s w x ³ s d w». 5. x w x x RC { sƒ 399
w e x w l w. 1) ƒ ƒ m 11% w ùkü, š û yww 23% ƒ w. wr š û yww w w w ùkû. 2) ü» wš ¼ x w w x dw, ACI 408 z w ù, š û ƒ yw x z w w. 3) ³ ³ s r, xk m w ùkü. mw» x w w (09F07),. š x 1. ½, ½,, ½ û, š (SD500) y w, gj p wz, 15«, 2y, 2003, pp. 86~89. 2. y y,,, y», š w x, gj pwz, 17«, 3y, 2005, pp. 375~384. 3. y y,, x w x k w, gj p wz, 16«, 4y, 2004, pp. 95~99. 4. Darwin, D., Zuo, J., Tholen, M. L., and K.ldun, E., Development Length Criteria for Conventional and High Relative Rib Area Reinforcing Bars, ACI Structural Journal, Vol. 93, No. 3, 1996, pp. 347~358. 5. ½», x x, w w, w, 2007, pp. 1~13. 6. Orangun, C. O., Jirsa, J. O., and Breen, J. E., A Reevaluation of Test Data on Development Length and Splices, ACI Journal, 1977, pp. 114~122. 7. Jirsa, J. O., Lutz, L. A., and Gergely, P., Rational for Suggested Development, Splice and Standard Hook Provisions for Deformed Bars in Tension, Concrete Int., Vol. 1, No. 7, 1979, pp. 47~61. 8. w gj pwz, gj p» w,», 2007, pp. 205~209. 9. ACI Committee 408, Splice and Development Length of High Relative Rib Area Reinforcing Bars in Tension and Commentary, American Concrete Institute, ACI Manual of Concrete Practice, 2008, pp. 408.3-1~408.3-3. 10. w gj pwz, gj p» w,», 2007, pp. 495~503. y š, œ š y ƒ š. ù š w ¼ ƒ ƒw œ w š w. š ¼ j» w x yƒ e z w w.» sww x w 5 x x w xw, ƒ x e q w w. x, w - ³ w,» Á w. x ƒ ƒ m 11% w ù kü, ƒ š û yww 23% ƒ ùkü. w,, ³ ³ s r, xk m w ùkü x j ƒ. w : x,,, e, ³ 400 w gj pwz 23«3y (2011)