Considerations for Seismic Soil-Structure Interaction (SSI) Modeling
At the Rocscience International Conference 2025 held in Sydney, Australia earlier this month, Dr. Youssef Hashash delivered a keynote speech titled "Advances in Nonlinear Seismic Structure-Fluid-Soil Interaction Modeling.”
This keynote touched upon many topics surrounding capturing the complexities of Soil-Structure Interaction (SSI), essential for seismic assessments required for infrastructure projects. Dr. Hashash started his presentation by outlining some foundational considerations for SSI modeling, which are crucial for infrastructure resilience in earthquake-prone areas.
1. Site Characterization
Dr. Hashash stated: "A thorough site investigation is "paramount" because "no amount of computational power can compensate for poor site data."
2. Seismic Hazard and Ground Motion Parameters
Selecting appropriate ground motions is a specialized task, as it is "a major issue to find motions that are representative of your design cases."
3. Soil Constitutive Models
Selecting an appropriate soil model is critical for reliably representing soil behavior under seismic loading and “each soil model has its pros and cons.”
4. Structural Modeling
Dr. Hashash advocates for using a "software platform that will allow you to equally represent with a similar fidelity of both the soil and the structure." Instead of representing the soil with simplified springs or the structure with pendulums, true soil-structure interaction modeling requires a comprehensive approach that accounts for both components' behavior.
5. Soil-Structure Interface Conditions
Carefully modeling the contact interface between the structure and the soil is essential. As "not all contacts that are implemented in finite element codes are good. They have to be dealt with carefully and with prudence," the contact formulation must account for potential slippage and other interface behaviors, as it significantly impacts force transmission and overall system response.
6. 2D and 3D Modeling and Meshing
Representing complex SSI systems in 2D or 3D models requires robust meshing tools. The ability to "import the geometry, clean up the geometry, and repair the geometry" is crucial for creating reliable models. Dr. Hashash also notes, "it's a tremendous challenge" to develop these meshes, and AI-powered tools that can automate mesh generation are the future.
If you weren’t able to attend RIC2025, you can now watch Dr. Hashash’s entire Keynote Lecture on the Rocscience YouTube channel.