Thermodynamic-Based Macroelement Approach for Dynamic Analysis of Soil-Structure Systems

Nonlinear dynamic analysis is becoming a routinary approach for assessing the seismic performance of structures, especially in the case of soil-structure systems with marked nonlinear features or in earthquake prone regions. In these cases, the conventional substructure approach, based on linearity, loses its effectiveness. On the other hand, a fully coupled modelling cannot be considered as a suitable analysis method for extensive studies or in standard design. A compromise is therefore proposed: an approach with macroelements simulating the combined frequency- and amplitude-dependent response of geotechnical systems in the time-domain analysis of structures, preserving a limited computational effort. The thermodynamic inertial macroelements (TIMs) describe the multiaxial force-displacement relationships of the geotechnical systems, such as bridge abutments, shallow, deep and caisson foundations. These models are implemented in Open-Sees as a new class of multiaxial materials, that can be assigned to a modified ZeroLength finite element with fully coupled translational-rotational response. The constitutive responses are completely defined by two potential functions having a straightforward calibration. The application of the TIM approach is presented with reference to some soil-structure systems exhibiting highly nonlinear responses, showing the comparison with the results of fully coupled numerical representations developed in OpenSees.