The Tallest Modular Tower Design Using a Performance Based Approach

When completed in 2019, 2044 Franklin St. in Oakland, CA, will be the tallest structure in the U.S. utilizing prefabricated prefinished volumetric construction (PPVC) as an alternative to conventional construction methods. A vertically integrated team of AEC professionals in collaboration with manufacturing experts designed a modular system suitable for a mixed-use tower of this size. The structural engineering team developed a unique structural system comprising a steel plate shear wall (SPSW) core supplemented with buckling restrained brace (BRB) outriggers to provide a ductile response to severe West Coast earthquakes. This structural system not only complied with the architectural and rentable space requirements, but also helped to maximize off-site construction and to minimize the on-site labor work. The use of performance based design in conjunction with full-scale testing of some of the critical structural components helped to establish a compatible lateral story drift ratio of up to 2.75% at MCE level for the modular gravity space frame. The primary energy dissipation mechanism is envisioned to be a combination of steel plate shear wall post-buckling tension field action and BRB yielding. The proposed structural system translated to substantial material savings up to 30% and improved the construction speed by 6 months compared to conventional structural systems and construction methods.