Comparison of New Zealand standards used for seismic design of concrete buildings

Abstract

Major changes have occurred over the last six decades in New Zealand design codes for seismic resistance of structures. This paper describes the changes in the required design strengths, stiffness levels and capacity design provisions with particular reference to buildings where the lateral force resistance is provided by reinforced concrete moment resisting frames. It is shown that simple comparisons of response spectra and limiting inter-storey drifts can give misleading conclusions regarding relative strength and stiffness requirements unless allowance is made for many other interacting factors. To illustrate this, minimum design requirements defined in codes (or standards) over the last six decades are compared with the corresponding 2009 design requirements for regular buildings in which the lateral force resistance is provided by moment resisting frames. The approach that is described can be applied to other forms of structure. The paper is intended to provide background information for engineers planning to assess the need for seismic retrofit of existing buildings and to show the different factors which should to be considered in assessing existing structures against current design criteria.

Seismic performance of reinforced concrete buildings in the 22 February Christchurch (Lyttelton) earthquake

“…A ductility µ of 4 is assumed to be consistent with the NZS4203:1976 and the NZS1900:1965 assumptions. Detailed retrospective comparisons of New Zealand loading standards have been published by Davenport [14] and Fenwick and MacRae [21].…”

Experimental and parametric investigation of effects of built‐in staircases on the dynamics of RC buildings

“…This can be achieved if the shear hinges can sustain the displacements resulting from plastic hinge formation in the beams. The maximum elongation sustained in a plastic hinge before failure is of the order of 0.035h b where h b is the depth of the beam . Considering the common case of two hinges forming in beams that run in a direction along the staircase axes, the maximum deformation that can occur is 0.07h b .…”

Development of New Zealand seismic bridge standards

“…The development of detailing requirements focuses on foundation design, inter-span linkages and seat lengths at supports. A discussion regarding the reinforcement detailing of concrete piers is also outlined to highlight major shifts in bridge design philosophy, but this discussion is intentionally kept brief as the historical changes in seismic detailing of reinforced concrete have been thoroughly described by Fenwick and MacRae [9].…”

“…It should be noted that when comparing Era 2 and Era 3 bridges to current practice, the flexural capacities determined using working stress design will cause the section to yield at between 1.3 to 1.5 times higher loading than the design base shear. Further information with regards to comparing section capacities designed using working stress to current practice can be found in Fenwick and MacRae [9].…”

“…Early standards used the gross section, while subsequent standards used a percentage of the moment of inertia of the concrete section to account for cracked section behaviour. Fenwick and MacRae [9] computed shifts in fundamental period for historical concrete standards used during the design eras defined here. After adjusting these shifted periods to only account for column cracking, the adjusted periods were used to adjust the calculated base shear ratios calculated in Table 10.…”