801 Market Street
San Francisco, California
An award-winning structure-within-a-structure facilitates the transformation of a 350,000 gsf historic office building into a flagship store and luxury hotel.
We teamed with Gensler and Plant Construction Company to renovate and reprogram the historic Pacific Union Building for two very different uses: the Old Navy flagship store on the lower five stories and the luxury Palomar Hotel on the upper five. Creating an open space suitable for retail necessitated the removal of eighty-six percent of the existing concrete columns and all floor framing below the fifth floor, while keeping the upper half of the building intact. This restructuring required an unconventional approach in which architect, engineer, contractor, and cost estimator collaborated in an iterative design process prior to completion of lease negotiations. To proceed, the team had to determine the project costs reliably in pre-design and reconcile them with the project value.
The engineering solution, building a new steel building within the existing concrete framework, allowed construction and demolition to occur without traditional and costly shoring. New steel work was erected within the original framing and new transfer trusses were added at the fourth story. The new framing was preloaded by means of an elaborate transfer sequence to remove load from existing framing. With the transfer completed, the lower columns were demolished. When the demolition contractor finally cut the existing concrete columns with a circular saw, the columns neither settled nor pinched the blade, indicating that the integral preloading and transfer tuning had successfully integrated the engineering within the construction sequence.
The existing grid layout was altered to accommodate new programmatic needs, while the brittle and aging building was provided with a structural system capable of resisting large earthquakes. The new exposed trusses and steel framework in the popular retail space are a monument to engineering innovation and collaborative design.
Executed as Steven Tipping and Associates
2000 American Institute of Steel Construction Engineering Awards of Excellence, National Winner
1999 NCSEA Excellence in Structural Engineering, Best Structure Award
1998 SEAOC Excellence in Structural Engineering, Award of Excellence
1998 SEAONC Excellence in Structural Engineering, H.J. Brunnier Award for Excellence in Design