Buckling modeling of reinforcing bars with imperfections

Reinforced concrete columns in seismic zones are subjected to combined actions, resulting in axial loads in longitudinal reinforcing bars. Thus, knowing the bar’s response, especially when it is subjected to important axial compressive forces that might lead to buckling, is important. A bar buckling model based on concentrated plasticity and with the capability of introducing an initial imperfection is described. The initial imperfection is imposed by bending the bar with a transversely applied nonpermanent force. Additionally, a comprehensive study of the monotonic tensile response beyond the peak stress point and a simple cyclic rule, complete the physical approach of the model. Comparisons of the model with experimental results reveal that peak capacity (average axial stress) is well captured, as well as the post-peak response shape (average axial stress versus strain), with differences observed basically in the peak capacity for specimens with high bar imperfection-to-diameter ratio, and in the shape of the post-peak response for specimens with low bar length-to-diameter ratio.