Immediate Occupancy Seismic Upgrade of an Operating High-Tech Manufacturing Facility

A design example is presented to illustrate the creative solutions implemented to achieve Immediate Occupancy (IO) performance for a voluntary seismic rehabilitation of a high-tech manufacturing facility, which is required to remain fully operational during construction. The owner desired to design for Immediate Occupancy performance per ASCE 41 for several reasons including risks associated with the use of hazardous chemicals and the crippling cost of a production shutdown. In addition to the challenge of retrofitting an operational manufacturing facility, the myriad of building utilities located throughout and around the building made locating strengthening elements a major challenge, and led to unusual and unique design features. The facility is located in the Silicon Valley, less than two miles from the Hayward Fault. The building is split level, with a two-story portion that is 45,000 square feet in plan, and a one-story portion that is 91,000 square feet. The entire ground floor of the building is occupied by operating clean rooms. The original lateral system of the building consists of exterior tilt-up concrete panel shear walls and steel concentrically braced frames with wood-framed roofs. A seismic evaluation concluded that the building did not satisfy IO acceptance criteria. The rehab design required careful consideration of the owner's objectives to upgrade the building while minimizing costs and providing continued operations. The upgrade utilizes exterior steel frame and concrete shear wall buttresses in conjunction with buckling restrained braces and link elements to improve seismic performance without interrupting operations. The new exterior buttresses limit the drift demands to the existing braced frames and gravity columns, while the buckling restrained brace elements provide ductility and limit demands to buttress foundations and collectors. Design and analysis of the building followed the ASCE 41 procedures for linear static, linear dynamic, and nonlinear static analysis procedures. The analysis confirmed that the external buttresses efficiently enhance the building performance to achieve the owner's desired performance level while minimizing impacts to the operating clean room.