The mechanical behavior of reinforced concrete (RC) beam-column joints with different sizes under cyclic loads at varying rates was investigated, aiming at attaining a better understanding of the size effect and strain rate effect on RC beam-column joints. First, a 2D mesoscale numerical model was established and verified by existing experimental results. Second, numerical tests regarding seismic performances of RC beam-column joints were carried out. A total of four structural sizes and five strain rates were taken into consideration. The damage patterns, hysteretic curves, skeleton curves, the displacement ductility, the stiffness degradation, and the shear deformation of joints under different working conditions were analyzed. Finally, the size effect and strain rate effect on shear resistance and shear failure mechanism of joints were discussed. In addition, a semitheoretical formula considering structural sizes and strain rates for shear strength calculation was proposed and verified by available experimental data.mesoscale simulation, RC joints, shear strength, size effect, strain rate effect Abbreviations: _ ε, the strain rate, s À1 ; _ ε 0 , the static strain rate, s À1 ; σ t , the tensile stress of concrete, MPa; d t , the tensile damage factor; E 0 , the initial stiffness, N/mm; ε t , the tensile strain of concrete; e ε pl t , the plastic tensile strain of concrete; σ c , the compressive stress of concrete, MPa; d c , the compressive damage factor; ε c , the compressive strain of concrete; e ε pl c , the plastic compressive strain of concrete; f c,imp,k , the compressive strength of concrete under high strain rate, MPa; f cm , the compressive strength of concrete under quasi-static state, MPa; _ ε c , the strain rate under compression, s À1 ; _ ε c0 , the strain rate under compression at quasi-static state, s À1 ; f ct,imp,k , the tensile strength of concrete under high strain rate, MPa; f ctm , the tensile strength of concrete under quasi-static state, MPa; _ ε ct , the strain rate under tension, s À1 ; _ ε ct0 , the strain rate under tension at quasi-static state, s À1 ; f ys , the yielding strength of steel bar under static strain rate, MPa; f yd , the yielding strength of steel bar under dynamic strain rate, MPa; f us , the ultimate strength of steel bar under static strain, MPa; f ud , the ultimate strength of steel bar under dynamic strain rate, MPa; ε y , the yield strain of steel bar; PSD, the displacement amplitude when the specimen yields, mm; T max , the loading time corresponding to PSD, s; V , the loading speed, mm/s; μ, the ductility coefficient; Δ u , the ultimate displacement of joints, mm; Δ y , the yield displacement of joints, mm; K i , the secant stiffness of joints, kN/mm; P i , the peak load of loading cycle, N; Δ i , the displacement corresponding to P i , mm; γ, the shear strain of joint; γ b , the joint shear strain at beam side; γ c , the joint shear strain at column side; h b , the joint height, mm; h c , the joint width, mm; Δ I , Δ II , the lengths of two diagonals in the jo...

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