Investigation of the effect of a bar's inadequate embedded length on the P-M interaction curve of reinforced concrete columns with rectangular sections

Authors: SEYED SHAKER HASHEMI, MOHAMMAD VAGHEFI

Abstract: In this research, the effects of embedded length and pull-out force on the seismic behavior of a reinforced concrete (RC) column were investigated. Separate degrees of freedom were used for the steel and concrete parts in the nonlinear modeling of the RC elements in order to consider the bond-slip effect. The analytical method was assessed through the comparison of experimental and analytical results. The effect of the bar's slippage on the axial force-bending moment (P-M) interaction curve of the RC column was calculated by nonlinear modeling of pull-out behavior. The P-M interaction curves for a variety of columns with different embedded bar lengths in the footing were calculated and compared. In most recommendations and instructions for the capacity of RC columns, it is assumed that the embedded length of the longitudinal bars in the joints is sufficient and slippage will not occur. However, in this research, the effect of reduction of the embedded length on the P-M interaction curve of RC columns was evaluated, and, in the end, a modification strategy was proposed for the curve suggested by the American Concrete Institute. The results show that as long as the embedded length is sufficient, responses do not differ significantly. By reducing the embedded length, much of the effect of the bar's pull-out on the P-M interaction curve occurs in terms of pure bending or low axial forces. By increasing the percentage of longitudinal bars, the capacity reduction increases due to the pull-out effect.

Keywords: Bar's pull-out, Embedded length, P-M interaction curve, Reinforced concrete column, Seismic analysis

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