Seismic Retrofit of a NonDuctile Concrete Building using Buckling Restrained Brace Frame (BRBF)

摘要

This paper describes the innovative use of a Buckling Restrained Brace Frame (BRBF) system in the seismic retrofit of an existing non-ductile concrete building in Southern California. The building, designed in the early 1960's and used as a medical office building, is approximately 148 feet by 158 feet in plan with seven stories above grade and three stories below grade. In addition there is a two-story penthouse above the main roof level. Typical floor and roof framing consists of a reinforced-concrete slab and beam system. The original lateral load resisting system of the building consisted of reinforced concrete floor and roof diaphragms that transfer seismic inertial loads to reinforced concrete shear walls. The existing concrete walls were poorly distributed making the building highly irregular in torsion. Although the building is located approximately 25 miles from the epicenter of the 1994 Northridge Earthquake, it suffered significant structural damage requiring extensive structural repair. A performance-based seismic evaluation was performed and from that a retrofit scheme was developed to achieve at a minimum the "Collapse Prevention" performance level of FEMA- 356. The design team was asked to develop a seismic retrofit scheme, which is cost effective, aesthetically acceptable, non-intrusive, and essentially allowed the building to remain open and operational throughout the construction. The retrofit solution developed using the BRBF system exceeded the expectations of the owner and received high praise from the city for improving the aesthetic appeal of the building and all at a cost significantly less than the owner's budget which was based on a conventional retrofit design developed by others. This paper will describe the analysis performed, the design of the BRBF retrofit scheme, and the logistics and challenges of the construction.