Comparison of Seismic Design Provisions for Steel Building Structures between U.S. and Japan

Abstract

This paper presents a study on the U.S. and Japanese seismic design provisionstipulated for moment resisting and braced steel frames. Width-to-thickness requirements, bracing length requirements, structural classification, seismic force reduction coefficients, and design seismic forces are compared, and differences and similarities are discussed. Unreduced seismic forces are relatively similar between the two countries but significant differences are present for the seismic force reduction coefficients that allow for the system ductility. Expected strength capacity of braced frames is estimated in consideration of seismic force reduction coefficients, strength carried by braces relative to frames, buckling and post-buckling strengths of braces. Japanese braced frames are generally stronger than the corresponding U.S. braced frames, with the difference most conspicuous for frames arranged with braces of medium lengths. A combination of larger design seismic forces and large seismic force reduction coefficiets enforced in the Japanese provisions are responsible for the difference.