James Malley
Group Director & Senior Principal
Degenkolb Engineers, San Francisco

The 25th anniversary of the 1994 Northridge, California Earthquake highlighted the potential vulnerability of older tall steel-framed buildings to large earthquakes. A series of 2018 articles in the New York Times focused on buildings of this type in San Francisco, citing results reported in the “Haywired” Scenario reports published by the US Geological Survey (Detweiler et al, 2018). These articles caused building owners and tenants to request detailed seismic evaluations of a number of buildings.

The City of San Francisco recently commissioned the Applied Technology Council to perform a “San Francisco Tall Buildings Study” to consider the impact of earthquakes on tall buildings in the City. This study developed recommendations to address building code requirements, policies and practices for the design of new buildings, assessment and retrofit of existing buildings and post-earthquake inspection and response to promote the earthquake resilience of San Francisco. A number of cities in Southern California also have enacted seismic evaluation and retrofit ordinances that will include consideration of tall building performance.

Requirements are in place in these cities and the plan is being developed for San Francisco. The structural design and detailing of buildings evolved due to changes in construction technology, architectural considerations, engineering design techniques, and analysis software. Evaluation of the results showed that while it is not possible to draw broad conclusions about the seismic performance of tall steel framed buildings, detailed evaluations allow comparison between different seismic performance features. This type of information will be important to building owners and jurisdictions in determining the potential need for seismic upgrade of this important class of existing buildings.