A seismic isolation approach offered almost “for free”

A seismic isolation approach offered almost “for free”

by

Grid Engineers Research Group

“It takes a Nobel Prize-winner, the physicist Hannes Alfven, to so phlegmatically stigmatize our hoped-for vision of an earth where “no acts of God can be permitted and everything happens according to the blueprints”
Even if such a place may ever arise, neither our past nor our contemporary experience, provide evidence of such a utopia reaching us soon. On the contrary, society has repetitively witnessed natural disasters so unprecedented in nature and intensity that have therefore been termed “Black Swan Events”.

With an official death toll of 230,000 the Haiti earthquake of 12 January 2010 serves as the most recent dramatic reminder: as highly improbable as it may be, a physically possible large-scale failure can occur sooner or later anywhere in the world bringing immense economic loss. But when they occur in developing countries they are invariably followed by humanitarian calamities of demonic dimensions. A plethora of major events worldwide confirm this reality: the 1976 Tangshan (China) earthquake and the 2004 Sumatra earthquake and tsunami disaster were accountable for the loss of 240,000 human lives each; the death toll of the 2005 Pakistan earthquake rose to 80,000; the 1970 great Peruvian earthquake killed 70,000 people; the 1990 Western Iran quake claimed 50,000 lives and left over 400,000 homeless. Although the list is merely indicative, the population of victims is, unfortunately, still rising whenever such events take place.

This observation has led many to interpret this kind of tragedies less as the results of geophysical extremes and more as functions of a (mis-aligned) social order (Hewitt, 1983[1]) which correlates disaster proneness with societal and economic fragility. Bilham (2010)[2] most illustratively describes collapsed buildings in Haiti as already doomed during their construction –a metaphor to demonstrate the construction quality characteristic of several disaster-prone regions.

Motivated by this appalling reality, our research aims to propose an unconventional earthquake engineering design strategy in hope of easing the consequences of Black Swan earthquakes. As it is apparent that totally risk-free design for all structures in earthquake-prone areas constitutes an unrealistic scenario, this research will focus on the development of an inexpensive technique for the design or retrofitting of critical clusters of structures such as hospitals, water treatment plants, power generation units and lifelines. The Survival of these clusters will not wipe out the catastrophe due to collapse of houses. But if operable immediately after the earthquake, such facilities can enable an unequivocally more efficient treatment of the humanitarian crisis following the event and thus a plummet in the population of victims. Understandably, building or rehabilitating the facilities in accord with modern seismic code provisions would definitely be a great part of the solution; but such a resource-demanding one that renders the idea totally prohibitive for developing countries.

Thus, the main idea governing our research –which has partially been formed during our involvement in the DARE research project–calls for a complete deviation from the current practice. A range of innovative foundation design schemes are envisaged, which will be inherently resilient themselves: they will not aim to resist the excessive loading but rather shield the facility from the consequences of extreme shaking or earthquake-induced soil displacements. To this end, a number of “mainstream” principles would be either revisited or totally abandoned:

  • Instead of being strictly prohibited, “failure” at the soil-foundation interface will be invited. For the structures to be examined, soil yielding may in fact be considered as the only ‘reliable’ energy dissipation mechanism.
  • Foundation detachment from soil due to extreme load eccentricity will be promoted as it can act as a “fuse” mechanism impeding inertia loading transmission to the –usually weak- superstructure.
  • Fail-safe adaptive systems will be proposed which will are expected to demonstrate superior response as the level of imposed displacement increases by exhibiting over-strength or hardening[3]

In essence, the main concept proposed, refers to the development of a seismic isolation approach offered almost “for free” by simply exploiting a natural energy dissipation mechanism; as such it is by-and-large worth examining.

[1] Hewitt, K., Ed. (1983) “Interpretation of Calamity: from the viewpoint of human ecology”, Boston, Allen

[2] Bilham R. (2010) “Lessons from the Haiti Earthquake”, Nature, 463, 878-879

[3] “Although both terms have been borrowed from soil mechanics terminology, they are herein used to describe the response of the foundation system rather than soil itself.