"The Bowls Project"—A Prototype for Full Scale Testing As an Alternate Approval Process for Small Scale Base-Isolated Structures

The Bowls Project in San Francisco, California was synthesis of music, history, architecture, and engineering inspired by ancient Babylonian clay bowls. The structure is a base-isolated pair of intersecting masonry domes using the Mediterranean system of tile-vaulting. Construction of the domes as an unreinforced masonry structure would not be permitted by the San Francisco Department of Building Inspection if not for an alternate means of compliance through a base-isolated design. The typical ASCE 7-05 approval process for base-isolated structures is expensive and time-consuming — the review cost alone would have exceeded the entire budget for this small project. The Department of Building Inspections recognized the seismic protection that base-isolation would provide to the domes and agreed to permit the design using full scale testing of the completed structure to validate design properties of the isolation system. This not only made the project feasible, it allowed the schedule to move from conception to completion in only 2 months. The isolators use a Ball-N-Cone design by Worksafe Technologies. Upon completion of the masonry dome construction on the isolated plinth, the structure was pulled to maximum displacement and released in a series of "snap back" tests in orthogonal directions. The plinth and the top of the dome were monitored with accelerometers to capture the acceleration time history in free vibration. The data was used to confirm the maximum acceleration of the plinth, the damping ratio, fundamental period, and hysteretic behavior of the isolation system. This method to verify isolation system properties satisfies the intent of ASCE 7-05 by providing engineers with the design properties and surpasses the intent by providing these properties under actual load conditions. Future applications could provide artists, architects, and engineers the ability to build innovative, efficient structures in high seismic areas with the assurance that structure performs as intended.