Final Report Summary - DARE (Soil Foundation Structure Systems Beyond Conventional Seismic Failure Thresholds: Application to New or Existing Structures and Monuments)
The "Ideas" Project with the acronym DARE, proposed, and developed, a double Paradigm shift in seismic geotechnical engineering.
First, contrary to the “Conventional Wisdom” that enforces engineers to use large “overstrength” and "safety" factors in the design of foundations against strong seismic shaking, DARE investigated and proved the possibility of turning such "wisdom" completely up-side-down. The resulting new design philosophy allows “below-ground” support systems to respond beyond certain thresholds that would conventionally imply failure and which are presently forbidden by Seismic Codes worldwide. Yet, such new "daring" design leads to safer, more robust, and more economic design. The list of "failure" thresholds that are exceeded includes: (a) separation and uplifting of shallow foundations from the soil; (b) mobilization of “bearing–capacity” failure mechanisms for shallow foundations; (c) sliding at the soil-foundation interface; (d) structural yielding of pile foundations, (e) interface sliding of caisson foundations.
A novel cost-effective seismic protection methodology was hence developed; “rocking isolation”; it was applied to structures founded on shallow or deeply embedded footings which are, deliberately, under-designed for their seismic capacity to be much lower than that of the corresponding column. When earthquake demand exceeds the foundation capacity, the latter momentarily " fails", but thus (surprisingly) limits the distress on the superstructure. The methodology, corroborated in a variety of experimental studies, was explored with a plethora of numerical simulations. Field observations in recent earthquakes provided qualitative support of the idea and supporting its reliability.
The second Paradigm shift stemmed from our numerical as well as experimental proof that foundation-structure systems can be designed to withstand ground failure due to a tectonic fault rupturing underneath, or to other forms of soil failure such as lateral spreading due to liquefaction and slope instability that impose large demands on the systems.