What are the current standards and guidelines for foundation dynamics and soil-structure interaction?

1 Why SSI matters

SSI can have significant effects on the natural frequencies, damping, mode shapes, and displacements of structures and foundations. Depending on the soil and structure properties, SSI can either increase or decrease the dynamic response of the system. For example, SSI can reduce the seismic demand on a structure by increasing its natural period and damping, or it can amplify the response by creating resonance or soil liquefaction. Therefore, ignoring SSI can lead to either overdesign or underdesign of foundations and structures, resulting in higher costs, lower performance, or even failure.

3 What are the standards and guidelines

Various standards and guidelines offer recommendations for foundation dynamics and SSI analysis and design, such as ASCE 7-16, FEMA P-1050, NIST GCR 12-917-21, ASCE/SEI 41-17, and ACI 318-19. ASCE 7-16 specifies the minimum design loads for different types of structures, including seismic loads, while FEMA P-1050 provides guidance on seismic design of structures with SSI considerations. NIST GCR 12-917-21 offers a comprehensive overview of SSI theory, methods, and applications for building structures. ASCE/SEI 41-17 provides criteria and procedures for the seismic evaluation and retrofit of existing buildings with SSI effects. Lastly, ACI 318-19 includes provisions for SSI effects in the design and construction of reinforced concrete structures.

4 How to apply SSI analysis

The application of SSI analysis is dependent on the type, size, and location of the structure and foundation, as well as the level of risk and performance desired. Generally, SSI analysis is more applicable for large or heavy structures such as nuclear power plants, dams, or high-rise buildings; flexible or slender structures like bridges, towers, or long-span structures; and sites located on soft or liquefiable soils like alluvial or coastal sites that are subject to high-intensity or long-duration dynamic loads from near-fault earthquakes, wind gusts, or blast waves. In these cases, SSI analysis can provide more precise and realistic results than assuming fixed-base or simplified soil models and can help optimize the design while minimizing the costs and risks of failure.

5 What are the challenges and opportunities

SSI analysis comes with both challenges and opportunities. Challenges include the uncertainty and variability of soil properties and behavior under dynamic loading, the complexity of soil-structure systems and their interactions, the lack of data and experience for some types of structures, and the trade-off between accuracy and efficiency. Opportunities include the development of new methods and technologies for SSI analysis, such as artificial intelligence, machine learning, big data, cloud computing, or smart sensors; the integration and collaboration of different disciplines and stakeholders; and the enhancement and dissemination of knowledge and best practices for SSI analysis.