Multi-axial computational model for simulating the seismic behavior of concrete columns including axial collapse

This paper describes a coupled multi -axial material model that can capture the interaction between axial/shear/ flexure and simulate the lateral cyclic response of non -retrofitted and retrofitted concrete columns under seismic loads up to complete loss of lateral and axial strength. The new material model is intended for use within twodimensional lumped -plasticity framework and implemented in the open -source simulation software OpenSees as CMACA2D. The material model was calibrated using a newly compiled database of 719 cyclic and monotonic pushover column tests and only requires the input of column geometric and material properties. It includes several capacity models to capture all the salient lateral and axial strength -degradations including flexure, shear, flexure -shear, splice, up to complete axial collapse. These capacity models for each axial/shear/flexure degree -offreedom (DOF) depend on the boundary conditions and applied demands in its own and other DOFs and constantly change during the analysis so the governing strength -degradation mode is not known a priori of the analysis. The material model employs an energy dissipation term to define the cyclic behavior response and to adjust the strength damage rate observed in test data. Finally, the performance of the proposed computational tools is compared with results from shake table tests.