Award of Excellence: Strengthening Category
Seismic Retrofit of McKinley Tower
Submitted by QuakeWrap, Inc.
Schneider & Associates Structural Engineers, Inc.
The McKinley Tower apartments, a historic landmark in downtown Anchorage, is a 14-story reinforced concrete structure constructed in 1951-52. Several features make this project unique:
- The building was subjected to the March 1964, 9.2 magnitude “Good Friday” Earthquake (strongest tremor in North America to date);
- The building was the tallest in town and suffered significant damage from this earthquake;
- Conventional retrofit measures began in the early 1980s to comply with current design code requirements, but were later suspended due to the very high costs involved, leaving the building vacant for approximately 20 years;
- An innovative fiber-reinforced polymer (FRP) retrofit design was implemented based on the seismic demands of the partially retrofitted building;
- The FRP retrofit design allowed for the elimination of interior shearwalls, maximizing interior space use; and
- A total of 55,000 square ft (5110 square meters) of FRP fabric was installed in 11 weeks allowing for a quick reopening of the historic landmark.
The FRP retrofit involved wrapping all columns to increase their compressive strength and ductility, transforming conventional bearing walls into shearwalls, and shear reinforcement of coupling beams and boundary element generation in existing shearwalls. It also involved shear and flexural reinforcement of cantilever beams and flexural reinforcement of roof slab for heavy equipment installation.
This project showcases applications of FRP technology to retrofit projects of damaged buildings in severe seismic hazard areas. Lightweight FRPs do not increase the dead weight to the building, minimizing foundation retrofit requirements and additional seismic force demands, making it an economical alternative. Also, the ease of installation minimizes construction time, making it an attractive alternative for tight-schedule projects.