Steel moment frames for earthquakes in United States and Japan

Steel moment frames are used for seismic design in the United States and Japan and are highly regarded structural systems, but severe damage to steel frames occurred during the 1994 Northridge and 1995 Hyogoken-Nanbu earthquakes. Examination of similarities and differences in the engineering research and practice for these frames in the two countries provides insight into this important seismic issue. A brief history of the engineering practice in both countries is provided, and current practice and design methods are summarized and compared. The evolution of structural systems and the details and practices employed in the two countries are described. Damage from past earthquakes is briefly reviewed. Welding processes and material behavior are also compared, because they influence the seismic behavior of these systems. Many U.S. engineers believe that Japanese buildings are much stiffer and stronger but less ductile than comparable U.S. buildings. It will be shown that this is not always the case. Significant differences in U.S. and Japanese design practices will be shown, but even greater similarities in our structures and design procedures will be noted. As a consequence, this paper should help engineers from both countries learn from one another.