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In order to evaluate the influence of freeze–thaw action on the durability of concrete structures, this paper presentedan experimental study to investigate the effects of freezing–thawing cycles and concrete strength on the bond behavior between steel bars and concrete confined with stirrups. Through freeze–thaw cycles and center pullouttests, the...
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Context 1
... ft,0 is the splitting tensile strength before freeze-thaw, MPa; ft,N is the splitting tensile strength after N cycles of freeze-thaw, MPa; and k1 represents the coefficient of strength reduction, with k1 = 0.452 for C20 series and k1 = 0.426 for C40 series obtained by regression of the test data. The variation of bond strength with freeze-thaw cycles is shown in Figure 7. It can be seen that the bond strength of the C20 and C40 series specimens increased at first and then decreased with the increase in freeze-thaw cycles. ...
Context 2
... f t,0 is the splitting tensile strength before freeze-thaw, MPa; f t,N is the splitting tensile strength after N cycles of freeze-thaw, MPa; and k 1 represents the coefficient of strength reduction, with k 1 = 0.452 for C20 series and k 1 = 0.426 for C40 series obtained by regression of the test data. The variation of bond strength with freeze-thaw cycles is shown in Figure 7. It can be seen that the bond strength of the C20 and C40 series specimens increased at first and then decreased with the increase in freeze-thaw cycles. ...
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Citations
... Overall, the bond-slip curve is composed of the ascending and descending parts. The elastic stage, the softening stripping stage, and the complete stripping stage are the important stages for these curves [52][53][54][55][56]. Referring to a two-stage model, which included the ascending stage and descending stage, that was adopted to simulate the bond-slip relationship of steel bars in concrete confined with stirrups under freeze-thaw cycles [57]. The bond-slip relationship can be expressed using the equations in Table 4, in which A and B are constants determined by the test results, A = 0.8 and B = 3, which are obtained through nonlinear curve fitting in this study for all groups of specimens. ...
The bond performance of CFRP to concrete plays a vital role in CFRP strengthening on concrete structures. In this paper, an experimental study was carried out to investigate the bond performance of CFRP to concrete with a convex-circular arc interface. The main factors were the curvature of the concrete surface and the bond length and the layers of the CFRP laminate. Based on the experimental results, the failure mode of the bond specimens, the variation of the bond capacity, the CFRP strain, and the bond–slip constitutive model are analyzed. The results showed that most of the specimens failed to peel off the interface concrete, and the bond capacity tended to increase with the increase in bond length when the bond length was within an effective value. When the interface curvature increased to 1/0.8 m, the bond capacity tended to increase due to the CFRP exerting a certain pressure on the concrete surface. The prediction formula of the bond capacity between the CFRP and concrete is proposed considering the influence of the interface curvature. The bond–slip curves are given out based on the finite differential analysis of the strain distribution of CFRP laminates. The accuracy and applicability of the proposed model are verified with a comparison to the test results and other existing models.
Present studies show that steel fibres can improve the bond of steel bar in steel fibre reinforced concrete (SFRC) with a correlation to the fibre factor and the fibre distribution uniformity. As a foundation of high-flowability SFRC working together with 400 MPa grade hot-rolled ribbed (HRB400) steel bar in reinforced structures, the bond between them was evaluated through a series of pull-out testing on 48 specimens with a central arranged steel bar. The bond behaviours of steel bar were estimated with a constant bond length of 5d (d is the diameter of steel bar) embedded in high-flowability SFRC, the main research parameters included the ingot mill steel fibres with a fibre volume fraction varied from 0.8 to 2.0%, the strength grade C40 and C50 of SFRC or referenced conventional concrete, and the diameter of steel bars varied from 14 to 20 mm. Results showed that the high-flowability SFRC compacted with a slight vibration is beneficial to improve the bond failure pattern since steel fibres effectively eliminate the crack appeared on the SFRC blocks during the pulling out of steel bar, leading to all specimens failed with the steel bar pull out of SFRC blocks. The bond strength was dominant by the SFRC strength, and obviously strengthened with the increase of fibre volume fraction, while the peak-slip was slightly influenced by the diameter of steel bar. By conducting analyses of test data, equations for calculating the bond strength and the peak-slip are proposed accounting for the effect of steel fibres. Then the predicting method for the anchorage length is suggested linking with different design codes for concrete structures. Compared with test results of this study, a little shorter anchorage length of steel bar in SFRC is obtained from the specification of Chinese code JGJ/T46, which should be noticed to ensure a rational anchorage of ribbed steel bar in SFRC with ingot mill steel fibres.
