Finite element microanalysis using fiber technique was carried out to study the buckling mechanism of reinforcing bars. It was found that reinforcing bars under inelastic axial compression exhibit lateral deformation defined as buckling due to the geometrical nonlinearity. Further investigation revealed that the postbuckling average compressive stress is less than the local stress corresponding to the same strain due primarily to the different stiffness for loading and unloading fibers in the laterally deformed section. It was clarified that the average compressive stress-strain relationship including the softening in the postbuckling range can be completely described in terms of the product of square root of yield strength and the slenderness ratio of the reinforcing bar. Moreover, a unique relationship between the average stress and average strain of reinforcing bars including the effect of buckling is established through various parametric analyses. The comparison of the analytical results and proposed model with some experimental results showed good agreement, thus verifying the reliability of the microanalysis and proposed computational model.
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