Overview of seismic provision changes in National Building Code of Canada 1990

Abstract

This paper highlights the changes of the seismic provisions in the 1990 edition of the National Building Code of Canada (NBCC) and provides the reasons and interpretations for these changes. The major changes include load factor for earthquake load, base shear formula, force modification factor in place of structural coefficient, story drift estimation, design and anchorage force for parts of portions of building, importance factor, foundation factor, and top concentrated force on structure. A comparison of the base shear calculated according to NBCC-1985 and NBCC-1990 is given to show that the base shears for most structural systems are similar. The major exceptions are the ductile flex-ural wall systems and the unreinforced masonry system. The base shear is reduced for the former system and increased for the latter system in NBCC-1990. Key words: earthquake, seismic design, code, lateral loading, overstrength.