The Cathedral Parish of Saint Eugene’s in Santa Rosa, California purchased an antique Baldacchino sculpture in early 2014 to serve as a backdrop for their altar. The 80,000 pound, 24-foot tall marble sculpture was previously located in a non-seismic zone, which made installation of the brittle structure, which had no positive connections between its 500 pieces, to resist seismic forces a considerable challenge. Other design challenges included limited access during construction and tight constraints for lateral movement of the structure. The Parish also requested that none of the structural modifications or retrofits be visible from the front of the sculpture, requiring creative solutions and careful coordination. ZFA was engaged to provide the structural engineering design to install the sculpture.
Preliminary analysis determined that a base isolation system was the best option to reduce the imposed seismic demands on the structure and limit the amount of intrusive retrofit work required. A unique trio of devices was used to isolate the structure, which included three friction sliders, two rubber bearings, and four viscous dampers. The isolation devices were specially designed for the project due to the unique size of the sculpture, which was too large to use components designed to isolate equipment, but too small to use components intended for buildings. ZFA worked closely with two different manufacturers on an iterative design solution that carefully tuned each of the components to the mass of the sculpture. Positive connections of the sculpture’s superstructure were designed with fiber reinforced polymer (FRP), thickened epoxy, and epoxy-grouted dowels. After a thorough third party peer review, the system and sculpture were approved for construction. The Baldacchino sculpture can now be seen on display in Saint Eugene’s Cathedral.