New Thinking

The City as a System

Impacts to surrounding structures — other buildings, lifelines and utilities — are inevitable with the collapse of closely-spaced tall buildings, so the urban core must be viewed in its complex totality as a system.  This shift in thinking presents challenges for design and for risk analysis.

Probabilistic Nature of the Problem

Some earthquake damage and loss models can be based upon solid statistics from many past earthquakes. The issue of tall building collapse in the urban core is not so well constrained by historical experience. We must rely on our knowledge of physics, on computer models, on expert opinion and on judgment, and perhaps some tests. Initial studies suggest that the life-safety and economic consequences of tall building collapse may be very large [Graf, Lee & Eguchi, 2014].  Research needed to answer these questions should be given high priority. 

It is essential to address these issues within a probabilistic framework. The exact nature of the ground shaking and other hazards for any future earthquake are uncertain, and the response of any building to extreme earthquake shaking is subject to large variability. Interactions between buildings in earthquakes are also very difficult to predict, from pounding of adjacent structures to the collapse of a tall building on its neighbor. We cannot expect deterministic single answers to these complex issues, but probabilistic risk techniques (e.g., Taylor, 2013; Lee, 2014) can provide reasonable and realistic predictions that will allow us to draw reliable answers and take prudent actions to improve the seismic resiliency of our urban cores, in locations where tall buildings are subject to extreme earthquakes.

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