CIVIL ENGINEERING 365 ALL ABOUT CIVIL ENGINEERING



AbstractThis study presents a numerical model to evaluate the flexural behavior of concrete beams reinforced with hybrid fiber-reinforced polymer (FRP) and steel bars. The bond–slip action between the reinforcing bars and the surrounding concrete was considered. The cracking load, yielding load, ultimate flexural capacity, strain development, moment–curvature relationship, and midspan deflection were predicted using the proposed numerical model. The model was compared with the experimental results available in the literature and the theoretical results from the design codes. The equations from the design codes underestimated the cracking load by 7%–9%. The averages of numerical yielding moments without and with a bond were 0.96 and 0.97, respectively. The predicted yielding moment considering the bond behavior was approximate to that of neglecting bond. The predicted ultimate flexural capacity without a bond was 3% higher than the test result, whereas the predicted result with the bond was 1% lower than the experimental result. Both design codes underestimated the mid-span deflection under service loads for hybrid-RC beams. The postyielding deflection and deflection behaviors at the service load level were captured well by the proposed model. A parametric study investigated the effects of the reinforcement arrangement. Beams [with a glass FRP (GFRP) reinforcement ratio of 2.06%] with reinforcements placed in one layer presented the highest ultimate capacity, 19.6% and 14.0% higher than those of GFRP bars placed at the outer and inner layers, respectively. Beams with GFRP bars placed in the outer layer showed the highest deformability index when the GFRP reinforcement ratio was less than 1.75%.Practical ApplicationsThis study presents a reliable model to simulate the flexural behavior of concrete beams reinforced with hybrid fiber-reinforced polymer (FRP) and steel bars. The bond–slip action was considered in the model. ACI 318-19 and CAN/CSA A23.3-19 underestimated the cracking load by 7% and 9%, respectively. In addition to the tensile strength of the concrete and the geometry of the section, the layout of the reinforcement was considered in the proposed model, thus achieving a more accurate prediction of the cracking load. The model without bond stress overestimated the ultimate flexural capacity of compression-controlled members and underestimated the ultimate capacity of tension-controlled members. Both ACI 318-19 and ACI 440.1R-15 underestimated the midspan deflection under service loads for hybrid-RC beams. The strain in FRP bars was highly related to the effective reinforcement ratio based on the strength transform (Lau’s equation) for hybrid-RC beams. For a designed strain limit for the FRP bars, the required effective reinforcement ratio for beams can be obtained from Fig. 9(b). Beams with reinforcements placed in one layer exhibited the highest ultimate capacity.



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