A newly proposed steel-framed system designed to allow buildings to sway with the motion of earthquakes and then return to their original positions may help avoid lasting damage to buildings in future earthquakes. The system is based on a ground-breaking study, led by researchers from Stanford University and the University of Illinois at Urbana-Champaign (UIUC), and was successfully tested on the world's largest shake table in Japan last summer.
Principal researchers include Gregory G. Deierlein, director of the John A. Blume Earthquake Engineering Center at Stanford; Jerome F. Hajjar, professor; and Narbey Khachaturian, faculty scholar in the Department of Civil and Environmental Engineering at UIUC. The research team also consisted of students and faculty from both universities and collaborative researchers from Japan.
The American Institute of Steel Construction contributed technical support and funding; Tefft Bridge and Iron, an AISC member, provided steel fabrication for the project; and Infra-Metals, an AISC member, donated a significant amount of materials and financial support for large-scale testing at UIUC.
The Controlled Rocking Frame system is designed with a self-centering steel structure and engineered with replaceable shock diffusers that absorb energy as the building moves laterally and vertically, shielding the rest of the framing from damage. According to an article published by the project team, tests have been very successful. When a two-thirds-scale model of a multi-story building was shaken on top of a 7.0-magnitude earthquake simulator, the only damage recorded in the frame was right where it was supposed to be―in the replaceable fuses.
"In moderate to large earthquakes, today's buildings can sustain significant damage throughout their structural framing systems," explained Hajjar. "While they are designed to accept this damage and not collapse, many structures are permanently damaged after such an event. In extreme cases, they may need to be condemned, even if they were designed to satisfy the building code."
The controlled rocking test results prove the worth of this pioneering performance-based seismic technology, which can make buildings more resilient in earthquake-prone communities, and keep them habitable after earthquakes happen. This project also shows the value and importance of international research collaboration and large-scale design method testing before actual earthquake events occur.
Headquartered in Chicago, AISC is a not-for-profit technical institute and trade association established in 1921 to serve the structural steel design community and construction industry.