The caissons at 181 Fremont, the deepest of any condominium tower in San Francisco, burrow 260 feet below ground and are anchored into the bedrock. A five-story concrete basement is supported with 5 to 6 foot diameter concrete piles socketed into bedrock, controlling against total and differential settlement within the surrounding soil layers. Through ingenious engineering, the building’s foundation is able to “lift” itself slightly to create additional space for movement, and a set of safety elevators are designed to remain operational during any seismic activity.
The structural engineers at Arup had to think outside of the box, literally. They devised an ingenious high-strength steel exoskeleton structural system that behaves like a giant shock absorber whenever there is seismic activity underfoot. This design also allows for column-free interior floor plans, maximizing living space and minimizing sightline obstructions for the best views imaginable.
A series of viscous dampers allow for a completely elastic superstructure, with plumbing and electrical lines given enough flexibility to move without disruption. Taken in total, the building’s innovations have earned it a REDi Gold Rating, the latest resilience-based design guidelines that establish a new beyond-code benchmark for seismic construction.