Ishihara Lecture Soil-Foundation-Structure Systems beyond Conventional Seismic Failure Thresholds

A new paradigm has now emerged in performance-based seismic design of soil foundation structure systems. Instead of imposing strict safety limits on forces and moments transmitted from the foundation onto the soil (aiming at avoiding pseudo-static failure), the new dynamic approach "invites" the creation of two simultaneous "failure" mechanisms: substantial foundation uplifting and ultimate-bearing-capacity slippage, while ensuring that peak and residual deformations are acceptable. The paper shows that allowing the foundation to work at such extreme conditions not only may not lead to system collapse, but it would help protect (save) the structure from seismic damage. A potential price to pay: residual settlement and rotation, which could be abated with a number of foundation and soil improvements. Numerical studies and experiments demonstrate that the consequences of such daring foundation design would likely be quite beneficial to bridge piers and building frames. It is shown that system collapse could be avoided even under seismic shaking far beyond the design ground motion.