Nonlinear Response History Soil–Structure Interaction Studies on UCSF Health Helen Diller Hospital Building

Abstract

The ASCE/SEI 7‐16 standard contains prescriptive provisions for soil–structure interaction (SSI). However, SSI is rarely incorporated into nonlinear response history analyses, particularly in performance‐based seismic design. This paper examines the seismic response of the $4.3 billion University of California, San Francisco Health Helen Diller Hospital Building, explicitly considering SSI effects. The 258‐foot‐tall structure comprises 15 aboveground levels and two basement levels and is supported by a pile foundation system embedded in complex soil conditions. Due to its proximity to the San Andreas Fault, the design incorporates a series of viscous dampers within a structural steel special moment frame system to enhance seismic performance. This paper extends beyond the SSI requirements of the project. The study employs a parametric approach starting with a fixed‐base model as benchmark and then progressively refining the representation of the soil and massive foundation system with springs and dashpots. The study focuses on how the representation of SSI affects the design demands of the different elements in the foundation and basement, even when forces above ground remain mostly unaltered. Additionally, results demonstrate the important dynamic higher mode effects of a massive and large footprint pile foundation. The higher modes associated with SSI resulted in significant inertia forces of the basement and the foundation even for small lateral deformations. The response above ground indicates that while interstory drift remains largely unaffected, SSI significantly influences floor accelerations. Finally, the effect of different sources of energy dissipation associated with SSI such as the hysteretic behavior and the radiation damping of the pile foundations, the soil passive pressure of the retaining walls, as well as the friction between the soil and the slabs on grade are explicitly studied.