A modified multi-yield-surface plasticity model: Sequential closest point projection method

This paper presents a modified multi-yield-surface (MMYS) plasticity model employing a 'sequential closest point projection' method that is consistent with the discretization of the backbone curve of a multi-yield-surface (MYS) model. Compared with existing MYS models, the newly developed MMYS model eliminates the main sources of numerical errors caused by inconsistencies between the model and discretized backbone curve, which significantly improves the numerical stability and convergence rate of the Newton-Raphson (N-R) iterative process at a structural level. Furthermore, tangent operators consistent with the integration algorithm are derived, preserving the quadratic rate of convergence in the N-R process. The MMYS model has been implemented in OpenSees, an open system for earthquake engineering simulation, and verified by two application examples. The N-R process is more stable and generally converges faster when using the MMYS model rather than a MYS model. The advantages of the MMYS model become more remarkable when the tolerance used in convergence criterion is tightened, the external pushover force or seismic excitation is increased, or the time/load step size is enlarged, regardless of the number of yield surfaces used in the models. This study enhances the capacity of the existing MYS model that is widely used in geotechnical or soil-structure interaction (SSI) problems.