The Keystone Hilton Garden Inn hotel in downtown Oakland, CA, currently under construction, will comprise the historic, Keystone building and a new adjacent 8-story building totaling approximately 135,000 square feet. The Keystone building was constructed in 1912 and is listed on the National Register of Historic Places. It was severely damaged in the 1989 Loma Prieta earthquake and has remained unoccupied since. The 7-story building is U-shaped in plan with a light well on one side and long solid wall on the other side, adjacent to another building that was demolished following the earthquake. The new eight-story hotel wing will be constructed on the site of the demolished building and tied integrally with the existing structure. The new building is L-shaped in plan with large floor plates and will be constructed of cast in-place concrete columns, post tensioned concrete flat plate slabs and shear walls. To maximize the number of guest rooms and first floor retail space, shear walls were strategically located around architectural elements, resulting in slender, coupled configurations. In order to reduce project costs, rather than providing an independent lateral force resisting system for each structure, the old and new structures were interconnected, each providing a portion of the lateral force resisting system for the other, and in the process, removing severe torsional irregularities that would have existed for either structure acting alone. This approach also permitted minimal impact on the historic fabric of the historic building while providing a lateral-force resisting system conforming to current code criteria. Since floor levels for the two structures did not align, interconnection of the two buildings presented an interesting challenge. This complex project was presented challenges associated with foundation design, as it sits adjacent to the Bay Area Rapid Transit District's underground railway station. District right of way regulations prohibit construction of foundations that will surcharge the station walls or roof. The final foundation design comprised a combination of a mat foundation in the existing building anchored by soil anchors and driven pre-cast concrete piles for the new structure.
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