Directing Low-Damage Seismic Design with Building Functionality

Abstract

The upcoming New Zealand Low-Damage Seismic Design (LDSD) guidance information, currently in preparation, is widely anticipated to provide a reference point for aligning low-damage seismic performance targets. A key aspect of this guidance is neutrality in associating performance targets with different lateral force-resisting systems (LFRS) being considered for a given structure. Identified design targets are equally intended for differing structural systems, meaning that structural engineers can attempt to better align the LFRS with the building function or architecture, rather than be forced into particular structural formats. Not all lateral systems will be capable of providing efficient low-damage seismic performance as fixed-based structures, but they may well be suitable as the superstructure to a base isolated system, thereby making this an appealing option to open up more general coordination aspects i.e. better building utility. Designing for post-event functional recovery is a reference point that can be used to better inform LDSD via greater prioritization of building functionality preferences, rather than fitting function around a low-damage structure. Using two base isolated buildings, designed and built over the past five years in central Christchurch, a brief discussion is presented around key inputs and outcomes that led to similar LDSD targets producing entirely different LFRS that best suited the day-to-day building functionality and assisted post-event functionality. While the designs were completed ahead of recently published NZ guidelines, performance targets closely aligned with both the LDSD guidance draft, and the design process reflected many of the key requirements in the NZSEE Base Isolation Design Guidelines.