Experimental research, as well as analysis of buildings and bridges damaged in earthquakes shows that in reinforced concrete columns longitudinal reinforcement often buckles under seismic loads. The onset of phenomena, the numerical modelling and effect of phenomena on the ductility of reinforced concrete columns are the focus of this thesis. We have summarized a portion of the current research efforts in the field. Then we have described numerical models for nonlinear analysis of reinforced concrete columns and material models which are used to describe buckling of longitudinal reinforcement.
From a wider database of experimental data we have selected a group of specimens that shows signs of buckling. Experimentally observed ultimate displacements of selected specimens were determined from hysteretic responses that were included in the database. We have conducted nonlinear
analysis to predict ultimate displacements of specimens, with or without buckling. Calculated ultimate displacements were compared with experimentally observed. For one specimen we have calculated hysteretic response using different finite elements available in OpenSees.
We have gathered that the buckling of longitudinal reinforcement has little influence on columns that have unsupported length to bar diameter ratio smaller than 6 and have adequate diameter of transverse reinforcement. Although existing numerical models can describe lower resistance of the reinforcing bar in compression, they still have problems predicting displacements of the whole column. For better modelling of reinforced concrete columns models that take into account the interaction between confined concrete core and longitudinal reinforcement should be developed.