Pioneer Square Buildings
Seismic Renovations
Seattle, Washington

Seattle's Pioneer Square District is essentially the birthplace of the City. The district contains an abundance of historic buildings that were built on the tide flats of Elliott Bay or fill that was washed down from the adjacent hillsides to reclaim a portion of the Bay for the expanding City. The district was ravaged by fire in the late 1890's. While a number of structures survived the fire, others were rebuilt on their original foundations and remain today. The existing buildings are commonly 3 to 5 story, unreinforced masonry (URM) structures. Many survived the regions historic earthquakes in 1949 (M=7.1) and 1965 (M=6.5) only to be damaged during the recent Nisqually Earthquake of February 28, 2001. Mr. Grant, with PanGEO, has been involved in retrofitting many of these structures before and following the Nisqually Earthquake, including:
Developing seismic retrofit strategies for these buildings is challenging because as-built building and foundation plans are non-existent and the buildings are supported on a variety of foundations ranging from shallow and deep spread footings to timber piles. Another challenge in developing the appropriate level of retrofitting is determining the owners desired level of building performance and still maintaining life safety standards for the public. In these retrofit projects, the geotechnical studies typically involved determining subsurface conditions at the building site and exhuming a foundation of the building to confirm the type and condition of the foundation elements. The sites were evaluated for liquefaction potential or other mechanisms that might lead to a catastrophic collapse. Ground motions were developed for the sites, consistent with the performance objectives for the buildings and foundation schemes are devised to support the structural retrofitting elements, such as shear walls. The foundations for the new structural systems may range from reuse of the existing foundations to the installation of new foundation elements, such as micropiles. None of the structures that Mr. Grant had studied before the Nisqually Earthquake had experienced any significant damage from this earthquake.