Technical Advances and Remaining Challenges since Loma Prieta
Chris Poland SE, NAE
The 1989 Loma Prieta Earthquake caused damage throughout the Bay Area even though it was centered in a remote mountainous area about 60 miles south of San Francisco. While this magnitude 7.1 earthquake was considered a moderate size event, it represented an important case study into the impact of local geology and site soil conditions, the response of structures to strong shaking, the vulnerability of non-conforming construction, the need for coordinated emergency response and the challenges of recovery. Stanford University was greatly affected and provided a rich case study in repair, retrofit and setting seismic design criteria that would lead to a more resilient future. The seismic repair retrofit and restoration of such campus landmarks as the Memorial Church, the Art Museum, and the Mitchell Earth Science Building stand as examples of state-of-the-art engineering that have since led significant new techniques.
Every earthquake leads to advances in earthquake science and engineering. The rapid-fire occurrence of the 1989 Loma Prieta and 1994 Northridge Earthquakes stimulated widespread seismic hazard mapping, the expansion of the statewide network of strong motion recording stations, and the production of near real time shake maps and supporting data. The thousands of strong motion records gathered since the early 70’s has led to the ability to develop site specific strong motion records that account for local geologic and site conditions. Advanced research into the performance of new structural systems and historic materials, aided by the development of advanced computational methods has led to refined techniques for designing structures to perform in predictable ways. New rating systems are now available to communicate the expected performance to the public. All these advances come with significant uncertainty that must be understood and accounted for in their use.
In 1989, many earthquake professionals knew that the San Francisco Bay area was vulnerable to significant earthquake caused damage, social disruption, and economic chaos. According to a report by the National Academy of Sciences, government and business leaders expressed great surprise that professionals knew so much and so little was done. They called for a new communication program to close the knowledge gaps among researchers, practicing professionals, decision makers, and the public to mitigate the vulnerabilities in a prioritized and systematic way. While new public policies led to a massive retrofit program for California’s hospitals and freeway bridges, systematic mitigation of vulnerable structures has not happened.
This failure to communicate and achieve a systematic mitigation program is fundamentally due to a lack of a common message from the earthquake professional community and a serious disconnect between the consensus views of the professionals and the community decision makers on what levels of risk are acceptable. Design professionals focus on the building owner’s responsibility to provide adequate life safety. The social and economic systems of communities, on the other hand, need a critical mass of buildings and infrastructure systems to be usable, just in time, if they are to be resilient and recover.
Since 2007, various Community Resilience frameworks have been proposed and a few programs are being implemented in Oregon, San Francisco, and Los Angeles. The National Institute of Standards and Construction recently published a Community Resilience Planning Guide that outlines an orderly process that can be adapted to the unique needs of communities of all sizes. One of the keys to implementing a community resilience program is the development of functional recovery standards for buildings and infrastructure systems. It is an activity that is now on going and the success of which will depend on the ingenuity, persistence, and collaboration of structural engineers working in concert with all earthquake professionals and community leaders.
Chris Poland is an internationally recognized authority on earthquake engineering and champion of disaster resilience. His passion for vibrant, sustainable, and healthy communities drives his consulting engineering practice. He focuses on community resilience and the buildings and systems that contribute to it. Chris served as a Community Resilience Fellow in the National Institute of Standards and Technology (NIST) from 2014-2019 and was a member of the team of authors that developed the Community Resilience Planning Guide.
Chris is a member of the National Academy of Engineering (2009) and serves on a number of their study committees and boards. He is a Fellow of the American Council of Engineering Companies, the Structural Engineers Association of California and the American Society of Civil Engineers Structural Engineering Institute. He is also an honorary member of the Earthquake Engineering Research Institute and the Structural Engineers Association of California.
His structural engineering career spans over 45 years and includes hundreds of projects related to the design of new buildings, seismic analysis repair and strengthening of existing buildings, structural failure analysis, historic preservation, as well as the development of guidelines and standards that are used worldwide. He was a Senior Principal, Chairman and CEO of Degenkolb Engineers during his 40 years with the firm from 1974 through 2014.