Size effect and strain rate effect on seismic behavior of reinforced concrete beam‐column joints

Abstract

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...

Dynamic simulation of CFRP‐shear strengthening on existing square RC members under unequal lateral impact loading

“…Numerous studies and research have been devoted to exploring and knowing the strain rate on structural member responses. 48 Still, this research hotspot remains open to discussion for all research studies, particularly concerning the high-velocity impact. Detailed examinations on strength increment can be determined by dynamic increase factor (DIF) for compressive and tensile strength with a given strain rate as typically.…”

“…By examining the effect of strain rates under the influence of impact loads, concrete and steel have high sensitivity; therefore, it is critical to include the effect of concrete and steel strain in numerical simulation. Numerous studies and research have been devoted to exploring and knowing the strain rate on structural member responses 48 . Still, this research hotspot remains open to discussion for all research studies, particularly concerning the high‐velocity impact.…”

Numerical study on shear capacity of geometrically similar RC interior beam‐column joints

“…Moreover, available scientific data outline that the size effect is more significant for concrete specimens with obvious brittleness. [26][27][28][29][30] Jin et al 31 conducted an experiment on RC beam-column joints with different structural sizes, particularly large specimens (the maximum section size of largest joint is 900 Â 900 mm), and found that size effect on shear strength of joints with shear failure was significant.…”

“…These experiment results showed that when the structural size increased, the shear strength of joints decreased, namely the size of joint had a significant effect on the nominal shear strength. Moreover, available scientific data outline that the size effect is more significant for concrete specimens with obvious brittleness 26–30 . Jin et al 31 conducted an experiment on RC beam‐column joints with different structural sizes, particularly large specimens (the maximum section size of largest joint is 900 × 900 mm), and found that size effect on shear strength of joints with shear failure was significant.…”

Experimental, Theoretical and Numerical Research Progress on Dynamic Behaviors of RC Structural Members

“…The consistent research findings are concluded that as the loading rate increases, both the tensile strength and compressive strength of concrete, the yield strength and ultimate strength of reinforcement are magnified, and the elastic modulus and the strain corresponding to the compressive strength of concrete are also affected by the loading rate [2]. As for structural members consisting of RC materials, such as columns [3][4][5][6], beams [7][8][9][10][11][12][13][14], shear walls [15][16][17][18][19] and joints [20][21][22][23][24][25], changes in mechanical behaviors to different degrees are observed for specimens under various loading rates, namely the dynamic effect at the member level. Different failure patterns of RC structural members could be observed in seismic hazards, as shown in Figure 2.…”