Defining What San Francisco Needs From Its Seismic Mitigation PoliciesFebruary 1, 2009
When a major earthquake strikes the Bay Area, we will face thousands of casualties, hundreds of thousands of displaced households, and losses in the hundreds of billions of dollars. Recovery will take years.
This paper addresses one aspect of the broader policy problem related to making San Francisco resilient in the face of a disaster: the standards we use for deciding when a structure is "safe enough." Our building code embodies hundreds of judgment calls about how strong structures should be, but the public and the policy makers generally have no idea what these standards mean, what the outcomes will be from the black box of engineering decisions.
The truth is that when we choose our engineering standards we really are choosing to define how many deaths, how many building demolitions, and how long a recovery time we will have for various levels of earthquakes. Currently, the City of San Francisco has no adopted performance objectives for determining these factors. As a result,
- Design and construction requirements for new construction still focus mostly on preventing the loss of life and in most cases ignore the question of building damage and post-earthquake usability.
- Little is being done to rehabilitate older existing structures, which constitute the majority of buildings and which were built without earthquake-resistant features now required.
- There is no consistent approach to providing, maintaining, and restoring lifeline systems that are needed to support economic recovery.
The overall impact and cost of a disaster is strongly influenced by how long it takes to recover. The time needed to recover depends on the level of damage sustained by buildings, the availability of utilities, and how quickly communities can re-establish usable housing and livable environments.
This paper provides a new framework for improving San Francisco's resilience through seismic mitigation policies. Our goals are to:
- define the concept of "resilience" in the context of disaster planning,
- establish performance goals for the "expected" earthquake that supports our definition of resilience,
- define transparent performance measures that help us reach our performance goals; and
- suggest next steps for San Francisco's new buildings, existing buildings and lifelines.