Innovative Seismic Protection Concepts

It has been several decades since the realization of the earthquake engineering community that the increase of strength of a structural system does not necessarily enhance safety. This led to the development of new design principles and performance-based design. Less attention has been paid to the soil-structure system as a whole. In fact, current design practice attempts to avoid full mobilization of foundation bearing capacity. However, neglecting such phenomena prohibits exploitation of strongly nonlinear energy dissipation mechanisms in defense of the superstructure.

We have been investigating the mechanisms governing seismic soil–structure interaction (SSI), with emphasis on the rocking response of shallow foundations. As part of the ERC-funded DARE research project, a new design philosophy termed “rocking isolation” has emerged, exploiting soil “failure” to protect the superstructure (external pageJ28). By intentionally under-designing the foundation, this acts as a “fuse” and the plastic hinge is “invited” into the foundation soil. In this way, the soil yields progressively while the structure remains undamaged; the ductility capacity of the entire system is significantly increased. The price to pay is reflected in residual settlements (and rotations) that need to be accounted for in design.

Conventional design vs. rocking isolation.

Starting with the development and validation of numerical models (external pageJ35) and dimensional analysis (external pageJ43), combining numerical and physical modelling we have been investigating the efficiency of rocking isolation for a variety of structures, ranging from simple bridge piers and SDOF systems (external pageJ40, external pageJ45, external pageJ56, external pageJ63, external pageJ75) to frames (external pageJ36, external pageJ39, external pageJ41, external pageJ50, external pageJ61, external pageJ70) and complete bridge–foundation–abutment–soil systems (external pageJ74). We quantified the role of scale effects by testing the same rocking foundations in 1g and in a centrifuge (external pageJ57), and investigated shallow soil improvement through 1g (external pageJ44, external pageJ64) and centrifuge model testing (external pageJ62), demonstrating its effectiveness in reducing residual settlements. Our experimental work is included in the ForCy (external pageJ92) and ForDy (external pageJ93) databases, which are the result of international collaboration led by Prof. Bruce Kutter (UC Davis).

Buildings in Adapazari after the 1999 Kocaeli earthquake: pancake collapse of buildings on stiffer soil (left) vs. accidental mobilization of foundation bearing capacity leading to excessive settlement (middle) or rotation (right), but no collapse

To facilitate application of rocking isolation in engineering practice, we have devoted significant effort in developing simplified analysis techniques, accounting for fully inelastic soil response and geometric nonlinearities (external pageJ52, external pageJ53). Our recent work has focused on the robustness of such simplified analysis techniques (external pageJ99). Employing stochastic methods, we have shown that the developed simplified methods are not biased and can therefore be used to estimate probabilities of exceedance of a certain threshold of foundation rotation.

Shaking table testing proof of concept: conventional design vs. rocking isolation (as shown in the 59th Rankine Lecture by Prof. George Gazetas).

Selected recent publications

Sieber M., Klar S., Vassiliou, M. F. & Anastasopoulos I. (2020). “Robustness of simplified analysis methods for rocking structures on compliant soil”, Earthquake Engineering and Structural Dynamics, 1-18 (external pageJ99)

Agalianos A., Psychari A., Vassiliou M. F., Stojadinovic B. & Anastasopoulos I. (2017). “Comparative assessment of two rocking isolation techniques for a motorway overpass bridge”, Frontiers in Built Environment, 3(47) (external pageJ74).

Loli M., Knappet J.A., Brown, M. J., Anastasopoulos I. & Gazetas G. (2014). “Centrifuge modeling of rocking-isolated inelastic RC bridge piers”, Earthquake Engineering and Structural Dynamics, 43: 2341-2359 (external pageJ56)