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Failure behavior of strain hardening cementitious composites for shear strengthening RC member
Construction and Building Materials 78 (2015) 470–473
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Failure behavior of strain hardening cementitious composites for shear strengthening RC member Yongxing Zhang a,b, Shu Bai c, Qingbin Zhang d, Haibo xie d, Xueming Zhang e,⇑ a
School of Civil Engineering, Nanjing Forestry University, No. 159 Longpan Road, Nanjing 210037, China Department of Civil Engineering, Nagoya University, Chikusa-ku, Nagoya 464-8603, Japan c Hunan Provincial Communications Planning Survey & Design Institute, Changsha 410008, China d School of Civil Engineering, Changsha University of Science & Technology, No. 960, Wanjiali South Road, Changsha 410004, China e School of Civil Engineering, Central South University, No. 22 South Shaoshan Road, Changsha 410075, China b
h i g h l i g h t s SHCC has obvious advantage for shear strengthening RC member. The carried shear load of strengthened RC member was significantly increased. Shear load on SHCC layer was contributed by both matrix and fiber. Shear load on SHCC layer was assumed as sum of that carried by matrix and fiber.
a r t i c l e
i n f o
Article history: Received 7 August 2014 Received in revised form 16 December 2014 Accepted 4 January 2015 Available online 23 January 2015 Keywords: Shear failure behavior SHCC strengthening layer Crack pattern Shear load carrying capacity
a b s t r a c t This paper presented a experimental investigation into the advantage of RC member with shear strengthening using strain hardening cementitious composites (SHCC), focused on the crack pattern of SHCC strengthening layer and its obvious advantage for increasing the shear load carrying capacity of the strengthened RC member. Especially, the shear failed SHCC member was also adopted to reflect the reduced multiple fine crack distribution in SHCC strengthening layer. Moreover, the contributions of matrix and reinforcing fiber for shear load carrying capacity of SHCC strengthening layer were also calibrated respectively, and the shear load carrying capacity of SHCC strengthening layer was assumed as the sum of load carried by matrix and reinforcing fiber. This work provided experimental foundations for RC member with shear strengthening using SHCC. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction Strain hardening cementitious composite (SHCC) was an attractive material used for strengthening RC member, due to its obvious advantages in terms of excellent mechanical and physical properties, such as large strain capacity in uniaxial tensile behavior, as well as permeability and compatible thermal expansion [1–4]. Several investigations on the advantages of SHCC strengthening reinforced concrete (RC) structures have been carried out, such as enhanced ductility of SHCC on the structural performance [5–9] and mechanical advantages of an interface crack trapping mechanism within SHCC/concrete composites [10]. However, the
⇑ Corresponding author. E-mail address: [email protected] (X. Zhang). http://dx.doi.org/10.1016/j.conbuildmat.2015.01.037 0950-0618/Ó 2015 Elsevier Ltd. All rights reserved.
ductility of SHCC was reduced while it was used for strengthening reinforced concrete (RC) member by the effect of crack within the RC member [3,11,12], since multiple fine cracks of SHCC in uniaxial tensile behavior were distributed evenly, but those of SHCC used for strengthening RC member were limited in a ranged area adjacent to crack within RC member. Especially, there were seldom researches on behavior of SHCC used for shear strengthening RC member, and the performance of SHCC used for shear strengthening RC member was not understood clearly until now, even though some researches on shear behavior of SHCC members had been carried out [13,14]. Thus, the characteristics of SHCC layer for shear strengthening RC member was experimentally investigated in this paper, and the contributions of matrix and reinforcing fiber for shear load carrying capacity of SHCC strengthening layer were also calibrated respectively.
471
Y. Zhang et al. / Construction and Building Materials 78 (2015) 470–473 2. Experimental program 2.1. Material used 2.1.1. SHCC The mix proportions of SHCC used in the experiment is demonstrated in Table 1. Fig. 1 shows the uniaxial tensile stress–strain curves and ultimate crack pattern of SHCC, obtained from uniaxial tensile test with dumbbell-shaped specimens, the cross section of which was 13 30 mm2. The strain was defined as elongation rate in measurement length of 100 mm. All specimens exhibited significant strain hardening behavior until ultimate tensile strength (point B1 or B2), since multiple fine cracks occurred and propagated while stress reached initial tensile strength with initial cracking (point A). Thereafter, tensile stress decreased due to localization of some multiple fine cracks. Moreover, the 28-day compressive strength and Young’s modulus of SHCC were 91 MPa and 29 GPa.
Fig. 1. Result obtained from uniaxial tensile test.
2.1.2. Reinforcements and concrete As mentioned above, the deformed bar with diameter of 25 mm was used in SHCC member, with Young’s modulus and yield strength of 200 GPa and 1050 MPa, respectively. Besides, the deformed bar with diameter of 10 mm was used in RC member, with Young’s modulus and yield strength of 200 GPa and 345 MPa, respectively. Moreover, the compressive strength and Young’s modulus of concrete were 27 MPa and 23.5 GPa, respectively.
2.2. Specimen characteristics Fig. 2 shows the geometries of RC member with shear strengthening using SHCC, the shear span length to effective depth ratio of which were equaled to 3. Three RC beams with length of 1200 mm and cross section of 100 200 mm2 were prepared, two of which were strengthened by SHCC with thicknesses of 5 mm and 10 mm (named as SHCC-5 and SHCC-10), respectively, the left one was considered as control beam (named as SHCC-0). Two deformed bars with diameter of 10 mm were arranged as longitudinal bar, and no web reinforcement was arranged in RC members. Both side surfaces of RC beams, which were the interface between RC member and SHCC strengthening layer, were washed out using a retarder to obtain roughed surfaces. Thereafter, SHCC strengthening layers were casted at both sides of RC beams. Moreover, the crack pattern of a shear failed SHCC member was presented in this study, the geometry of which was shown in Fig. 3, including effective depth d, width t, shear span length a. The shear span length to effective depth ratio of the specimen was also 3, and member width was 100 mm. Especially, one deformed rebar with diameter of 25 mm was arranged as longitudinal bar for ensuring the SHCC member was failed in shear, and no web reinforcement was arranged in the member.
2.3. Setup All the tested specimens were loaded under three-point bending setup, as shown in Fig. 4. In the experiment, displacements at loading points, support point and mid-point (point A in Figs. 2 and 3) were measured by displacement transducers, and load (point B in Figs. 2 and 3) was measured by load-cell. The range of load cell was about 300 kN with the sensitivity of 0.1 kN, and that of displacement transducer was 25 mm with the sensitivity of 0.002 mm. Under the condition of displacement larger than that value, the displacement transducer was required to be adjusted during test. The loading test was terminated when sudden drop in the load was observed.
3. Experimental result
Fig. 2. Geometry of strengthened RC members.
Fig. 3. Geometry of SHCC members.
Fig. 6 demonstrates the ultimate crack distribution of the shear failed SHCC member. It could be obviously seen there were many multiple fine cracks in diagonal shear direction of the SHCC member, and it was finally failed in shear due to localization of some multiple fine cracks. 3.2. RC member with shear strengthening using SHCC 3.2.1. Crack pattern Fig. 7 demonstrates the ultimate crack distribution of cases SHCC-0 (RC member), SHCC-5 and SHCC-10, respectively. Compared with the observed multiple fine cracks in diagonal shear direction of aforementioned shear-failed SHCC member as shown in Fig. 6, those in diagonal shear direction of SHCC strengthening layer were obviously decreased, which meant the ductility of SHCC strengthening layer was also reduced while it was used for shear strengthening RC member, similar with that of SHCC used for flexural strengthening RC member [3,11,12]. Moreover, the localized crack in SHCC strengthening layer of case SHCC-5 was similar with that of case SHCC-10, as shown in Fig. 8.
3.1. Shear failed SHCC member Fig. 5 shows the experimental shear load–displacement curves of SHCC member, in which linear curves was up to peak shear load and almost sudden failure occurred thereafter, probably due to smooth fracture surface of SHCC member. The maximum shear load was 210 kN.
3.2.2. Load carrying capacity Fig. 9 shows the experimental shear load–displacement curves of RC member with shear strengthening using SHCC. It could be clearly seen the shear load carrying capacity of strengthened RC member was significantly increased with the increasing thickness of SHCC strengthening layers. Moreover, the carried shear load
Table 1 Mix proportions of SHCC. Water/bindera
0.22 a
Unit content (kg/m3) Water
Cement
Silica fume
Fine sand
PE fiber
Expansion agent
Super-plasticizer
Air reducing agent
338.5
1267.9
230.8
153.9
14.6
40.0
15.4
0.06
Binder means cement + silica fume.
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Y. Zhang et al. / Construction and Building Materials 78 (2015) 470–473
Fig. 4. Setup.
250
Load (kN)
200 150 100 50 0
2
4 6 Displacement (mm)
8
10
Fig. 5. Load–displacement curves.
(a)
Fig. 6. Ultimate crack distribution. of SHCC strengthening layer showed linear relationship with thickness of SHCC strengthening layer, which might be caused by similar shear stress transfer behavior on localized crack surface of SHCC strengthening layer for cases SHCC-5 and SHCC-10, contributed by both contact stress and fiber bridging stress on crack surface of SHCC strengthening layer.
(b) Fig. 7. Crack patterns of tested members. (a) SHCC-5 and SHCC-10. (b) SHCC-0.
3.2.3. Verification of shear load carried by SHCC strengthening layer The shear load carried by SHCC strengthening layer was contributed by both contact stress and fiber bridging stress on crack surface of SHCC strengthening layer, which was thus assumed as the sum of shear load carried by matrix and reinforcing fiber of SHCC strengthening layer herein, represented by Eq. (1):
Vy ¼ Vc þ Vf
ð1Þ
where, Vy was the shear capacity, Vc was the shear load carried by matrix, and Vf was the shear load carried by reinforcing fiber. Moreover, Vc and Vf could be calculated by Eqs. (2) and (3), respectively [15]:
V c ¼ 0:18
qffiffiffiffi 0 fc t d
V f ¼ ðf v = tan bu Þ t z fc0
ð2Þ ð3Þ
where, was compressive strength of SHCC, t and d were width and effective depth of SHCC layer, z was the distance from location of compressive stress resultant to centroid of tensile steel, may generally be taken as d/1.15, bu was angle of the diagonal crack surface to the member axis.
Fig. 8. Positions of localized cracks.
Fig. 10 demonstrates the experimental and calculated shear loads of SHCC strengthening layer in cases SHCC-5 and SHCC-10, which also confirmed the linear increasing of SHCC strengthening layer carried shear load with the increasing thickness of SHCC strengthening layer. Moreover, the calculated shear loads of SHCC strengthening layer were similar with those obtained from experiment. Therefore, the shear load carried by SHCC strengthening layer thus could be assumed as the sum of shear load carried by matrix and reinforcing fiber of SHCC strengthening layer respectively, governed by the factors shown in above-mentioned Eqs. (2) and (3).
Y. Zhang et al. / Construction and Building Materials 78 (2015) 470–473
473
(2) The shear load carrying capacity of strengthened RC member was significantly increased with the increasing thickness of SHCC strengthening layers, and the carried load of SHCC strengthening layer showed linear relationship with thickness of SHCC strengthening layer, caused by similar shear stress transfer behavior on localized crack surface of SHCC strengthening layer, contributed by both contact stress and fiber bridging stress on crack surface of SHCC strengthening layer. Moreover, the shear load carrying capacity of SHCC strengthening layer could be assumed as the sum of shear load carried by fiber and matrix, respectively.
Acknowledgements Fig. 9. Shear load–displacement curve.
The author would like to acknowledge the support from National Natural Science Foundation of China (No. 51408124 and 51378505), Natural Science Foundation of Jiangsu Province (No. BK20140629), and a projected funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions. References
Fig. 10. Experimental and calculated shear loads on SHCC layer.
4. Conclusions In this paper, the experimental investigation of RC member with shear strengthening using SHCC was carried out, and the shear load carrying capacity of SHCC strengthening layer was calibrated. (1) The ductility of SHCC strengthening layer was significantly reduced while it was used for shear strengthening RC member, accompanied with the occurrence of seldom multiple fine cracks in diagonal shear direction of SHCC strengthening layer, quite different from the behavior of shear failed SHCC member with many multiple fine cracks in diagonal shear direction. The cracking behavior of shear failed SHCC member also illustrated the multi-cracking process was due to fiber bridging effect and contact effect in crack surface.
[1] Li VC, Horikoshi T, Ogawa A, Torigoe S, Saito T. Micromechanics-based durability study of polyvinyl alcohol-engineered cementitious composite (PVA-ECC). ACI Mater J 2004;101(1):242–8. [2] Kunieda M, Rokugo K. Recent progress of HPFRCC in Japan-required performance and applications. J Adv Concr Technol 2006;4(3):19–33. [3] Kamal A, Kunieda M, Ueda N, Nakamura H. Evaluation of crack elongation performance of a repair material with strain hardening behavior. J Cem Concr Compos 2008;30(10):863–71. [4] Li HD, Xu SL, Leung CKY. Tensile and flexural properties of ultra high toughness cemontious composite. J. Wuhan Univer. Technol. (Mater. Sci.) 2009;24(4):677–83. [5] Horii H, Matsuoka S, Kabele P, Takeuchi S, Li VC, Kanda T. On the prediction method for the structural performance of repaired/retrofitted structures. Fracture Mechanics of Concrete Structures. In: Proceedings FraMCoS-3 1998, p. 1739–50. [6] Li VC, Horii H, Kabele P, Kanda T, Lim YM. Repair and retrofit with engineered cementitious composites. J. Eng. Fract. Mech. 2000;65(3):317–34. [7] Shin SK, Kim JJH, Lim YM. Investigation of the strengthening effect of DFRCC applied to plain concrete beams. J Cem Concr Compos 2007;29(6):465–73. [8] Martinola G, Meda A, Plizzari GA, Rinaldi Z. Strengthening and repair of RC beams with fiber reinforced concrete. J Cem Concr Compos 2010;32(9):731–9. [9] Zhang YX. Simplified evaluation method on the behavior of RC member strengthened by SHCC in flexural failure. Eng Fract Mech 2014;121– 122:11–27. [10] Lim YM, Li VC. Durable repair of aged infrastructures using trapping mechanism of engineered cementitious composites. J Cem Concr Compos 1997;19(4):373–85. [11] Hussein M, Kunieda M, Nakamura H. Strength and ductility of RC beams strengthened with steel-reinforced strain hardening cementitious composites. J Cem Concr Compos 2012;34(9):1061–6. [12] Zhang YX. Zero-span tensile model for evaluating cracking behaviour of SHCC for RC flexural strengthening. Mag Concr Res 2013;65(24):1486–93. [13] Kanakubo T, Shimizu K, Nagai S, Kanda T. Shear transmission on crack surface of ECC. Fracture mechanics of concrete structures. In: Proceedings FraMCoS-7 2010, p. 1623–30. [14] Suryanto E, Nagai K, Maekawa K. Modeling and analysis of shear-critical ECC members with anisotropic stress and strain fields. J Adv Concr Technol 2010;8(2):239–58. [15] Japan Society of Civil Engineers. Recommendations for design and construction of high performance fiber reinforced cement composite with multiple fine cracks (HPFRCC), Concrete engineering series 82, 2008.
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Failure behavior of strain hardening cementitious composites for shear strengthening RC member Yongxing Zhang a,b, Shu Bai c, Qingbin Zhang d, Haibo xie d, Xueming Zhang e,⇑ a
School of Civil Engineering, Nanjing Forestry University, No. 159 Longpan Road, Nanjing 210037, China Department of Civil Engineering, Nagoya University, Chikusa-ku, Nagoya 464-8603, Japan c Hunan Provincial Communications Planning Survey & Design Institute, Changsha 410008, China d School of Civil Engineering, Changsha University of Science & Technology, No. 960, Wanjiali South Road, Changsha 410004, China e School of Civil Engineering, Central South University, No. 22 South Shaoshan Road, Changsha 410075, China b
h i g h l i g h t s SHCC has obvious advantage for shear strengthening RC member. The carried shear load of strengthened RC member was significantly increased. Shear load on SHCC layer was contributed by both matrix and fiber. Shear load on SHCC layer was assumed as sum of that carried by matrix and fiber.
a r t i c l e
i n f o
Article history: Received 7 August 2014 Received in revised form 16 December 2014 Accepted 4 January 2015 Available online 23 January 2015 Keywords: Shear failure behavior SHCC strengthening layer Crack pattern Shear load carrying capacity
a b s t r a c t This paper presented a experimental investigation into the advantage of RC member with shear strengthening using strain hardening cementitious composites (SHCC), focused on the crack pattern of SHCC strengthening layer and its obvious advantage for increasing the shear load carrying capacity of the strengthened RC member. Especially, the shear failed SHCC member was also adopted to reflect the reduced multiple fine crack distribution in SHCC strengthening layer. Moreover, the contributions of matrix and reinforcing fiber for shear load carrying capacity of SHCC strengthening layer were also calibrated respectively, and the shear load carrying capacity of SHCC strengthening layer was assumed as the sum of load carried by matrix and reinforcing fiber. This work provided experimental foundations for RC member with shear strengthening using SHCC. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction Strain hardening cementitious composite (SHCC) was an attractive material used for strengthening RC member, due to its obvious advantages in terms of excellent mechanical and physical properties, such as large strain capacity in uniaxial tensile behavior, as well as permeability and compatible thermal expansion [1–4]. Several investigations on the advantages of SHCC strengthening reinforced concrete (RC) structures have been carried out, such as enhanced ductility of SHCC on the structural performance [5–9] and mechanical advantages of an interface crack trapping mechanism within SHCC/concrete composites [10]. However, the
⇑ Corresponding author. E-mail address: [email protected] (X. Zhang). http://dx.doi.org/10.1016/j.conbuildmat.2015.01.037 0950-0618/Ó 2015 Elsevier Ltd. All rights reserved.
ductility of SHCC was reduced while it was used for strengthening reinforced concrete (RC) member by the effect of crack within the RC member [3,11,12], since multiple fine cracks of SHCC in uniaxial tensile behavior were distributed evenly, but those of SHCC used for strengthening RC member were limited in a ranged area adjacent to crack within RC member. Especially, there were seldom researches on behavior of SHCC used for shear strengthening RC member, and the performance of SHCC used for shear strengthening RC member was not understood clearly until now, even though some researches on shear behavior of SHCC members had been carried out [13,14]. Thus, the characteristics of SHCC layer for shear strengthening RC member was experimentally investigated in this paper, and the contributions of matrix and reinforcing fiber for shear load carrying capacity of SHCC strengthening layer were also calibrated respectively.
471
Y. Zhang et al. / Construction and Building Materials 78 (2015) 470–473 2. Experimental program 2.1. Material used 2.1.1. SHCC The mix proportions of SHCC used in the experiment is demonstrated in Table 1. Fig. 1 shows the uniaxial tensile stress–strain curves and ultimate crack pattern of SHCC, obtained from uniaxial tensile test with dumbbell-shaped specimens, the cross section of which was 13 30 mm2. The strain was defined as elongation rate in measurement length of 100 mm. All specimens exhibited significant strain hardening behavior until ultimate tensile strength (point B1 or B2), since multiple fine cracks occurred and propagated while stress reached initial tensile strength with initial cracking (point A). Thereafter, tensile stress decreased due to localization of some multiple fine cracks. Moreover, the 28-day compressive strength and Young’s modulus of SHCC were 91 MPa and 29 GPa.
Fig. 1. Result obtained from uniaxial tensile test.
2.1.2. Reinforcements and concrete As mentioned above, the deformed bar with diameter of 25 mm was used in SHCC member, with Young’s modulus and yield strength of 200 GPa and 1050 MPa, respectively. Besides, the deformed bar with diameter of 10 mm was used in RC member, with Young’s modulus and yield strength of 200 GPa and 345 MPa, respectively. Moreover, the compressive strength and Young’s modulus of concrete were 27 MPa and 23.5 GPa, respectively.
2.2. Specimen characteristics Fig. 2 shows the geometries of RC member with shear strengthening using SHCC, the shear span length to effective depth ratio of which were equaled to 3. Three RC beams with length of 1200 mm and cross section of 100 200 mm2 were prepared, two of which were strengthened by SHCC with thicknesses of 5 mm and 10 mm (named as SHCC-5 and SHCC-10), respectively, the left one was considered as control beam (named as SHCC-0). Two deformed bars with diameter of 10 mm were arranged as longitudinal bar, and no web reinforcement was arranged in RC members. Both side surfaces of RC beams, which were the interface between RC member and SHCC strengthening layer, were washed out using a retarder to obtain roughed surfaces. Thereafter, SHCC strengthening layers were casted at both sides of RC beams. Moreover, the crack pattern of a shear failed SHCC member was presented in this study, the geometry of which was shown in Fig. 3, including effective depth d, width t, shear span length a. The shear span length to effective depth ratio of the specimen was also 3, and member width was 100 mm. Especially, one deformed rebar with diameter of 25 mm was arranged as longitudinal bar for ensuring the SHCC member was failed in shear, and no web reinforcement was arranged in the member.
2.3. Setup All the tested specimens were loaded under three-point bending setup, as shown in Fig. 4. In the experiment, displacements at loading points, support point and mid-point (point A in Figs. 2 and 3) were measured by displacement transducers, and load (point B in Figs. 2 and 3) was measured by load-cell. The range of load cell was about 300 kN with the sensitivity of 0.1 kN, and that of displacement transducer was 25 mm with the sensitivity of 0.002 mm. Under the condition of displacement larger than that value, the displacement transducer was required to be adjusted during test. The loading test was terminated when sudden drop in the load was observed.
3. Experimental result
Fig. 2. Geometry of strengthened RC members.
Fig. 3. Geometry of SHCC members.
Fig. 6 demonstrates the ultimate crack distribution of the shear failed SHCC member. It could be obviously seen there were many multiple fine cracks in diagonal shear direction of the SHCC member, and it was finally failed in shear due to localization of some multiple fine cracks. 3.2. RC member with shear strengthening using SHCC 3.2.1. Crack pattern Fig. 7 demonstrates the ultimate crack distribution of cases SHCC-0 (RC member), SHCC-5 and SHCC-10, respectively. Compared with the observed multiple fine cracks in diagonal shear direction of aforementioned shear-failed SHCC member as shown in Fig. 6, those in diagonal shear direction of SHCC strengthening layer were obviously decreased, which meant the ductility of SHCC strengthening layer was also reduced while it was used for shear strengthening RC member, similar with that of SHCC used for flexural strengthening RC member [3,11,12]. Moreover, the localized crack in SHCC strengthening layer of case SHCC-5 was similar with that of case SHCC-10, as shown in Fig. 8.
3.1. Shear failed SHCC member Fig. 5 shows the experimental shear load–displacement curves of SHCC member, in which linear curves was up to peak shear load and almost sudden failure occurred thereafter, probably due to smooth fracture surface of SHCC member. The maximum shear load was 210 kN.
3.2.2. Load carrying capacity Fig. 9 shows the experimental shear load–displacement curves of RC member with shear strengthening using SHCC. It could be clearly seen the shear load carrying capacity of strengthened RC member was significantly increased with the increasing thickness of SHCC strengthening layers. Moreover, the carried shear load
Table 1 Mix proportions of SHCC. Water/bindera
0.22 a
Unit content (kg/m3) Water
Cement
Silica fume
Fine sand
PE fiber
Expansion agent
Super-plasticizer
Air reducing agent
338.5
1267.9
230.8
153.9
14.6
40.0
15.4
0.06
Binder means cement + silica fume.
472
Y. Zhang et al. / Construction and Building Materials 78 (2015) 470–473
Fig. 4. Setup.
250
Load (kN)
200 150 100 50 0
2
4 6 Displacement (mm)
8
10
Fig. 5. Load–displacement curves.
(a)
Fig. 6. Ultimate crack distribution. of SHCC strengthening layer showed linear relationship with thickness of SHCC strengthening layer, which might be caused by similar shear stress transfer behavior on localized crack surface of SHCC strengthening layer for cases SHCC-5 and SHCC-10, contributed by both contact stress and fiber bridging stress on crack surface of SHCC strengthening layer.
(b) Fig. 7. Crack patterns of tested members. (a) SHCC-5 and SHCC-10. (b) SHCC-0.
3.2.3. Verification of shear load carried by SHCC strengthening layer The shear load carried by SHCC strengthening layer was contributed by both contact stress and fiber bridging stress on crack surface of SHCC strengthening layer, which was thus assumed as the sum of shear load carried by matrix and reinforcing fiber of SHCC strengthening layer herein, represented by Eq. (1):
Vy ¼ Vc þ Vf
ð1Þ
where, Vy was the shear capacity, Vc was the shear load carried by matrix, and Vf was the shear load carried by reinforcing fiber. Moreover, Vc and Vf could be calculated by Eqs. (2) and (3), respectively [15]:
V c ¼ 0:18
qffiffiffiffi 0 fc t d
V f ¼ ðf v = tan bu Þ t z fc0
ð2Þ ð3Þ
where, was compressive strength of SHCC, t and d were width and effective depth of SHCC layer, z was the distance from location of compressive stress resultant to centroid of tensile steel, may generally be taken as d/1.15, bu was angle of the diagonal crack surface to the member axis.
Fig. 8. Positions of localized cracks.
Fig. 10 demonstrates the experimental and calculated shear loads of SHCC strengthening layer in cases SHCC-5 and SHCC-10, which also confirmed the linear increasing of SHCC strengthening layer carried shear load with the increasing thickness of SHCC strengthening layer. Moreover, the calculated shear loads of SHCC strengthening layer were similar with those obtained from experiment. Therefore, the shear load carried by SHCC strengthening layer thus could be assumed as the sum of shear load carried by matrix and reinforcing fiber of SHCC strengthening layer respectively, governed by the factors shown in above-mentioned Eqs. (2) and (3).
Y. Zhang et al. / Construction and Building Materials 78 (2015) 470–473
473
(2) The shear load carrying capacity of strengthened RC member was significantly increased with the increasing thickness of SHCC strengthening layers, and the carried load of SHCC strengthening layer showed linear relationship with thickness of SHCC strengthening layer, caused by similar shear stress transfer behavior on localized crack surface of SHCC strengthening layer, contributed by both contact stress and fiber bridging stress on crack surface of SHCC strengthening layer. Moreover, the shear load carrying capacity of SHCC strengthening layer could be assumed as the sum of shear load carried by fiber and matrix, respectively.
Acknowledgements Fig. 9. Shear load–displacement curve.
The author would like to acknowledge the support from National Natural Science Foundation of China (No. 51408124 and 51378505), Natural Science Foundation of Jiangsu Province (No. BK20140629), and a projected funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions. References
Fig. 10. Experimental and calculated shear loads on SHCC layer.
4. Conclusions In this paper, the experimental investigation of RC member with shear strengthening using SHCC was carried out, and the shear load carrying capacity of SHCC strengthening layer was calibrated. (1) The ductility of SHCC strengthening layer was significantly reduced while it was used for shear strengthening RC member, accompanied with the occurrence of seldom multiple fine cracks in diagonal shear direction of SHCC strengthening layer, quite different from the behavior of shear failed SHCC member with many multiple fine cracks in diagonal shear direction. The cracking behavior of shear failed SHCC member also illustrated the multi-cracking process was due to fiber bridging effect and contact effect in crack surface.
[1] Li VC, Horikoshi T, Ogawa A, Torigoe S, Saito T. Micromechanics-based durability study of polyvinyl alcohol-engineered cementitious composite (PVA-ECC). ACI Mater J 2004;101(1):242–8. [2] Kunieda M, Rokugo K. Recent progress of HPFRCC in Japan-required performance and applications. J Adv Concr Technol 2006;4(3):19–33. [3] Kamal A, Kunieda M, Ueda N, Nakamura H. Evaluation of crack elongation performance of a repair material with strain hardening behavior. J Cem Concr Compos 2008;30(10):863–71. [4] Li HD, Xu SL, Leung CKY. Tensile and flexural properties of ultra high toughness cemontious composite. J. Wuhan Univer. Technol. (Mater. Sci.) 2009;24(4):677–83. [5] Horii H, Matsuoka S, Kabele P, Takeuchi S, Li VC, Kanda T. On the prediction method for the structural performance of repaired/retrofitted structures. Fracture Mechanics of Concrete Structures. In: Proceedings FraMCoS-3 1998, p. 1739–50. [6] Li VC, Horii H, Kabele P, Kanda T, Lim YM. Repair and retrofit with engineered cementitious composites. J. Eng. Fract. Mech. 2000;65(3):317–34. [7] Shin SK, Kim JJH, Lim YM. Investigation of the strengthening effect of DFRCC applied to plain concrete beams. J Cem Concr Compos 2007;29(6):465–73. [8] Martinola G, Meda A, Plizzari GA, Rinaldi Z. Strengthening and repair of RC beams with fiber reinforced concrete. J Cem Concr Compos 2010;32(9):731–9. [9] Zhang YX. Simplified evaluation method on the behavior of RC member strengthened by SHCC in flexural failure. Eng Fract Mech 2014;121– 122:11–27. [10] Lim YM, Li VC. Durable repair of aged infrastructures using trapping mechanism of engineered cementitious composites. J Cem Concr Compos 1997;19(4):373–85. [11] Hussein M, Kunieda M, Nakamura H. Strength and ductility of RC beams strengthened with steel-reinforced strain hardening cementitious composites. J Cem Concr Compos 2012;34(9):1061–6. [12] Zhang YX. Zero-span tensile model for evaluating cracking behaviour of SHCC for RC flexural strengthening. Mag Concr Res 2013;65(24):1486–93. [13] Kanakubo T, Shimizu K, Nagai S, Kanda T. Shear transmission on crack surface of ECC. Fracture mechanics of concrete structures. In: Proceedings FraMCoS-7 2010, p. 1623–30. [14] Suryanto E, Nagai K, Maekawa K. Modeling and analysis of shear-critical ECC members with anisotropic stress and strain fields. J Adv Concr Technol 2010;8(2):239–58. [15] Japan Society of Civil Engineers. Recommendations for design and construction of high performance fiber reinforced cement composite with multiple fine cracks (HPFRCC), Concrete engineering series 82, 2008.