Implementation of an advanced bounding surface constitutive model in OpenSees

The dynamic behaviour of saturated coarse-grained soils has recently received wide attention because of its impact on the seismic performance of geotechnical and structural systems. This is due to the peculiarities of their cyclic response (e.g., liquefaction, ratcheting and volumetric-deviatoric coupling). Consequently, the seismic risk mitigation of the built environment requires efficient predictive models applicable in design and assessment. To this end, several constitutive models have been developed for a realistic description of the cyclic soil behaviour. From this perspective, this paper describes the implementation and testing of the bounding surface plasticity model developed by Papadimitriou and Bouckovalas (2002) in OpenSees as a means for advanced assessment of soil-structure systems. The implemented model includes essential features of the cyclic soil response. Moreover, a modified fabric tensor evolution equation is introduced for improving the response and numerical stability in boundary value problems, at the cost of an extra model constant. The workflow concerning the integration of the model into OpenSees is presented, followed by instructions about its use in boundary value problems. A comprehensive verification of the model response is discussed. The numerical simulations demonstrated the robustness of the implemented code in capturing soil behaviour from small to large strain levels.