Frame-Spine System with Force-Limiting Connections for Low-Damage Seismic-Resilient Buildings

A novel structural system is being investigated collaboratively – by an international team including three U.S. universities, two Japanese universities and two major experimental research labs – as a means to protect essential facilities, such as hospitals, where damage to the building and its contents and occupant injuries must be prevented and where continuity of operation is imperative during large earthquakes. The new system employs practical structural components, including (1) flexible steel moment frames, (2) stiff steel elastic spines and (3) force-limiting connections (FLC) that connect the frames to the spines, to economically control building response and prevent damaging levels of displacement and acceleration. The moment frames serve as the economical primary element of the system to resist a significant proportion of the lateral load, dissipate energy through controlled nonlinear response and provide persistent positive lateral stiffness. The spines distribute response evenly over the height of the building and prevent story mechanisms, and the FLCs reduce higher-mode effects and provide supplemental energy dissipation. The Frame-Spine-FLC System development is focusing on new construction, but it also has potential for use in seismic retrofit of deficient existing buildings. This paper provides an overview of the ongoing research project, including selected FLC cyclic test results and a description of the full-scale shake-table testing of a building with the Frame-Spine-FLC System, which represents a hospital facility and includes realistic nonstructural components and medical equipment.