Computational Framework for Decision-Oriented Reinforced Concrete Column Simulation Capabilities

New computational tools are implemented into the open-source Finite Element platform OpenSees and proposed within the lumped-plasticity framework to simulate the lateral load-deformation response of reinforced concrete members up to complete loss of lateral and axial strength. The proposed computational tools implement new features that enhance the simulation fidelity of reinforced concrete members subjected to severe ground motions. The new classes added to the existing OpenSees library include:(i)Uniaxial material model with decoupled axial/shear/flexure degrees-of-freedom (DOFs): The new material model was proposed to improve the cyclic behavior response of concrete members under seismic excitation. It employs a cubic spline function to simulate the gradual changes of stiffness observed in the unloading-reloading behavior of concrete members under seismic loading. It takes a different approach to simulate cyclic behavior from existing models, by utilizing an energy dissipation term as the central parameter to adjust the level of pinching in a response. The model replicates the amount of cyclic energy dissipation specified by the user, regardless of other parameters. The model is equipped with deformation and energy-based damage functions that can realistically capture stiffness and strength damage in concrete members, even under non-symmetric cyclic loading. The proposed model is applicable for simulating the lateral shear or flexure behaviors of reinforced concrete members, such as columns, beams, walls, and joints. The model is implemented in the open-source simulation platform OpenSees as the CyclicReinforcedConcrete model.(ii)Calibrated coupled multi-axial material model, with nonlinear behavior in shear/flexure DOFs, coupled to a multi-axial zero-length element: The material model and element are intended for use within a two-dimensional framework and are aimed at capturing the lateral cyclic behavior of non-retrofitted and retrofitted reinforced concrete columns subjected to seismic motions, up to complete loss of lateral strength. The material model incorporates all the functionalities of the CyclicReinforcedConcrete for lateral DOFs and includes the following new features. The material model was calibrated using a newly compiled database of 689 cyclic column tests and only requires the input of column geometric and material properties to define envelope and cyclic behaviors, including identifying the appropriate strength-degradation modes, and the rate of strength loss due to cyclic loading. The proposed multi-axial material model houses several capacity models to capture salient lateral strength-degradation modes including flexure, shear, flexure-shear, splice, and flexure-splice modes. It accounts for coupling between axial/shear/flexure actions to automatically select the governing strength-degradation mode and adjust the limit surfaces during analyses. In addition to non-retrofitted columns, it is able to simulate the behavior of columns retrofitted by FRP and steel jacketing. The coupled multi-axial material and element were implemented in the open-source simulation platform OpenSees as CMAC2D and CMAZ2D respectively.(iii)Manual multi-axial material model, with non-linear behavior in shear/flexure DOFs, coupled to CMAZ2D element: The proposed material model and element are intended for use within a two-dimensional framework. In addition to employing all the functionalities that exist in the CyclicReinforcedConcrete to define the cyclic behavior in lateral DOFs, it utilizes generic multi-linear axial/flexure and axial/shear strength curves defined by up to 10 points by users. In this fashion, the material model is capable of generically implementing coupling behavior on yield and peak strengths, and can be used for a wide range of concrete members. The multi-axial material is implemented in the open-source simulation platform OpenSees as CMAM2D.(iv)Multi-axial material model, with non-linear behavior in all axial/shear/flexure DOFs, coupled to the CMAZ2D element: The proposed multi-axial material model incorporates all the features that exist in CMAC2D for lateral DOFs and adopts Limit-State capacity model to define the behavior response in axial DOF. The material model is intended to simulate the seismic behavior of concrete columns up to complete axial collapse. The multi-axial material is implemented in the open-source simulation platform OpenSees as CMACA2D.