Summarizes the developments and changes to the seismic design provisions of the National Building Code of Canada (NBCC 1990) since its 1977 edition and discusses the changes to the seismic design provisions of the Canadian Standards Association Standard, Design of Concrete Structures for Buildings (CAN3-A23.3). The paper outlines the philosophy of seismic-resistant design of the Canadian code and discusses the changes to the zoning maps, static design procedures, and the introduction of the force modification factors. The paper also deals with the changes to the Canadian reinforced concrete code and especially with the section on ductile walls, changes to load combination factors, and the explicit links between the concrete code sections containing the detailing requirements and the NBCC sections on determination of the design seismic forces.

To survive a major earthquake, current practice requires seismic resistant frames to be designed to be ductile. To achieve the required level of ductility in multistory frames, the majority of the potential plastic hinge zones are located in the beams. The inelastic rotation, which may develop in these zones, arises predominately from the tensile yielding of the reinforcement. The associated compressive strains are small and, as a consequence, elongation occurs. Test results show that elongation on the order of two to four percent of the member depth develop in plastic hinge zones of beams subjected to cyclic loading before strength degradation occurs. The factors influencing elongation are reviewed in this paper. The results of a time history analysis, in which elongation effects are modeled, shows that this action, which is neglected in current design practice, has important implications for the detailing of columns and the design of supports for precast components and external cladding.

Discusses aspects of the design of connections in reinforced concrete frame structures which often get overlooked. The need for careful assessment and detailing of slab-column connections in flat plate structures combined with walls is addressed. The way in which the strength and stiffness of spandrel beams can significantly alter the expected response of beam-column connections is illustrated by experimental results and observed seismic damage. Detailed analysis of beam-column joint regions using the modified compression field theory demonstrates behavioral features that have important design implications. The use of nonlinear finite element modelling of joint regions to design efficient, yet practical, retrofit measures is discussed. An alternate form of construction using ductile steel link beams to connect reinforced concrete walls is presented. The important design features for the connection of these beams to the walls are highlighted.

The method of transversely reinforcing columns and beam-to-column connections with bellows square steel tubes was devised to develop a construction method necessary to realize reinforced concrete frame highrise buildings which are easy to design and execute in zones where high earthquake resisting performance is required. To secure a ductile seismic behavior for columns subjected to heavy load, strong shear reinforcement and transverse reinforcement are necessary to prevent brittle failure, such as shear failure, bond split failure along the longitudinal bars, and failure of the compressed extreme fiber of concrete, or to change it into ductile failure. It was manifested by concentric compression tests of 1/4 scale columns, combined compression, bending and shear tests of 1/3 scale columns, seismic load tests of 1/3 scale and 1/4 scale beam-column subassemblages, and bond tests of main bars embedded in 1/4 scale columns that no dangerous collapse of the building is likely to occur even if shear forces of some of the columns and/or beam-to-column connections in the same story reach the loading capacity, because the mechanical behavior of the columns and beam-to-column connections is very ductile even when the webs of their tube yield in shear. Field execution tests of this structure have been conducted.

Describes design and construction aspects of precast concrete moment resisting frames for the lateral load resistance of multistory buildings. Discussion will concentrate on the particular aspects of the framing system of a 13-story building constructed in Wellington, New Zealand. The building is octagonal in plan with a perimeter lateral load-resisting frame consisting of two-story high precast reinforced concrete elements. Each element includes a column plus two levels of beam stubs. In-situ concrete midspan beam splices and grouted steel sleeve column reinforcing bar splices form the joints between individual units. The paper also briefly presents other similar precast systems used for multistory buildings. A review of laboratory testing recently completed is given which confirms the good structural performance of the framing systems described.