Potential Problems in Design for Maximum Flexibility
A. J. Carr and M. Tabuchi
Appears on pages(s):
deflection; flexibility methods; loads (forces); shear properties; standards; stiffness; structural design; Design
The New Zealand Standard for design loadings for buildings (NZS4203) was revised in 1992 superseding the earlier standard NZS4203 (1984). Some of the most significant changes in the new code are a considerable increase in the allowable interstory drifts and a marked reduction in the seismic lateral forces for structures with longer natural periods. Designers may now be encouraged to design buildings to the maximum allowable drifts as the resulting buildings will attract smaller lateral loads. Reinforced concrete buildings designed with the new loadings code may be constrained by the minimum reinforcement requirements rather than strength requirement of the loadings code; as a result, they may have a different distribution of strength capacity from that assumed in the code design. Because of this, buildings designed using the capacity design principles may not have the strength distribution that the designer intended. The reasons for this problem are discussed in this paper and the effects of the irregular distribution of strength capacity are investigated using inelastic response analysis. It was found that the large reduction of the design lateral forces resulting from the large allowable interstory drifts may lead to the problem. The design lateral forces or the deflection limits defined in the new code, NZS4203 (1992), may need to be reconsidered.