Assessment of soil-structure interaction practice based on synthesized results from Lotung experiment - earthquake response

On the assumption that the foundation can be appropriately modeled, it would be difficult to distinguish between the computational capabilities of the SASSI, CLASSI and SUPERALUSH/CLASSI methods of SSI analysis. Given the appropriate model, all three methodologies would produce very similar valid results. However, both CLASSI (Bechtel) and Soil-Spring methods should be used cautiously within their known limitations. The use of FLUSH should be limited to essentially 2D problems. More than the computational methods, the differences in the seismic response results obtained are due to the modeling of the soil-structure system and the characterization of the input motions. A number of insights have been obtained with respect to the validity of SSI analysis methodologies for earthquake response. Among these are the following: vertical wave propagation assumption in performing SSI is adequate to describe the wave field; equivalent linear analysis of soil response for SSI analysis, such as performed by the SHAKE code, provides acceptable results; a significant but non-permanent degradation of soil modulus occurs during earthquakes; the development of soil stiffness degradation and damping curves as a function of strain, based on geophysical and laboratory tests, requires improvement to reduce variability and uncertainty; backfill stiffness plays an important role in determining impedance functions and possibly input motions; scattering of ground motion due to embedment is an important element in performing SSI analysis. (author)