Bond-slip behavior of bundled steel/FRP bars and its implementation in high-fidelity FE modeling of reinforced concrete beams.

• Pull-out tests of bundled steel/FRP bars embedded in concrete were performed. • The influence of bond-slip effect of bundled bars in RC beams was investigated. • Equivalent bond-slip model of bundled steel/FRP bars was theoretically derived and validated. • High-fidelity FE model incorporating bond-slip effect by cohesive elements is developed. Due to the controllable bond performance and high-efficiency construction of bundled hybrid reinforcements, the seismic performance and accelerated construction of a precast concrete structure can be guaranteed. Eighteen pullout specimens of bundled deformed steel bars and basalt fiber reinforced polymer (BFRP) bars (single, double, three-bundle) were tested under monotonic loading. The peak bond strength decreased by 40.7% as the reinforcement bundles increased from one to three. The corresponding experimental investigations on five concrete beams reinforced by different types of bundled reinforcement showed that, compared to a beam with ordinary distributed reinforcement (control beam), the ultimate displacement of the beams with three bundles and six bundles increased by 60% and 90%, respectively. The load bearing capacity of the six-bundle beam was 9.6% larger than that of the control beam. A simplified bond-slip model based on the concept of equivalent bond area was proposed and showed good agreement with the test results. In addition, finite element analysis considering the bond-slip between the reinforcement and concrete was conducted to predict the load–deflection relationships of the new composite beam. A comparison of the analytical and experimental results showed that the analytical model could accurately predict the failure modes, load–deflection relationships and strain developments of bundled hybrid reinforced beams. [ABSTRACT FROM AUTHOR]