Base isolation is arguably the most reliable method for providing enhanced protection of buildings against earthquake-induced actions, by virtue of a physical separation between the structure and the ground through elements/devices with controlled force capacity, significant lateral deformation capacity and (often) enhanced energy dissipation. Such a design solution has shown its effectiveness in protecting both structural and non-structural components, hence preserving their functionality even in the aftermath of a major seismic event. Despite lead rubber bearings being invented in New Zealand almost forty years ago, the Christchurch Women's hospital was the only isolated building in Christchurch when the Canterbury earthquake sequence struck in 2010/11. Furthermore, a reference code for designing base-isolated buildings in New Zealand is still missing. The absence of a design standard or at least of a consensus on design guidelines is a potential source for a lack of uniformity in terms of performance criteria and compliance design approaches. It may also limit more widespread use of the technology in New Zealand. The present paper provides an overview of the major international codes (American, Japanese and European) for the design of base-isolated buildings. The design performance requirements, the analysis procedures, the design review process and approval/quality control of devices outlined in each code are discussed and their respective pros and cons are compared through a design application on a benchmark building in New Zealand. The results gathered from this comparison are intended to set the basis for the development of guidelines specific for the New Zealand environment.
The effects of soil-foundation-structure interaction (SFSI) have been a topic of discussion amongst the structural and geotechnical community for many decades. The complexity of the mechanisms, as well as the need for inter-disciplinary knowledge of geotechnical and structural dynamics has plagued the advancement and the consequent inclusion of SFSI effects in design. A rigorous performance-based design methodology should not just consider the performance of the superstructure but the supporting foundation system as well. Case studies throughout history (eg. Kobe 1995, Kocaeli 1999 and Christchurch earthquakes 2010-2011) have demonstrated that a poor performance at the foundation level can result in a full demolition of the structure and, in general terms, that the extent of damage to, and repairability of, the building system as a whole, is given by the combination of the damage to the soil, foundation and superstructure. The lack of consideration of the modifying factors of SFSI and an absence of intuitive performance levels for controlling foundation and soil behaviour under seismic loads has resulted in inadequate designs for buildings sited on soft soil. For engineers to be satisfied that their designs meet the given performance levels they must first, understand how SFSI affects the overall system performance and secondly have tools available to adequately account for it in their design/assessment. This dissertation presents an integrated performance-based design procedure for buildingfoundation systems that considers all of the major mechanisms of SFSI. A new soil-foundation macro-element model was implemented into a nonlinear finite element software and validated against several experimental tests. The numerical model was used to provide insights in to the mechanisms of SFSI and statistical analysis on the results yielded simple expressions that allow the behaviour to be quantified. Particular attention was paid to the effects of shear force on the foundation response and the quantification of the rocking mode of response. The residual deformations of the superstructure and distribution of forces up the structure were also investigated. All of the major SFSI mechanisms are discussed in detail and targeted numerical studies are used to explain and demonstrate concepts. The design procedure was validated through the design and assessment of a series of concrete buildings that were designed to account for the effects of SFSI.
As part of a seismic retrofit scheme, surface bonded glass fiber-reinforced polymer (GFRP) fabric was applied to two unreinforced masonry (URM) buildings located in Christchurch, New Zealand. The unreinforced stone masonry of Christchurch Girls’ High School (GHS) and the unreinforced clay brick masonry Shirley Community Centre were retrofitted using surface bonded GFRP in 2007 and 2009, respectively. Much of the knowledge on the seismic performance of GFRP retrofitted URM was previously assimilated from laboratory-based experimental studies with controlled environments and loading schemes. The 2010/2011 Canterbury earthquake sequence provided a rare opportunity to evaluate the GFRP retrofit applied to two vintage URM buildings and to document its performance when subjected to actual design-level earthquake-induced shaking. Both GFRP retrofits were found to be successful in preserving architectural features within the buildings as well as maintaining the structural integrity of the URM walls. Successful seismic performance was based on comparisons made between the GFRP retrofitted GHS building and the adjacent nonretrofitted Boys’ High School building, as well as on a comparison between the GFRP retrofitted and nonretrofitted walls of the Shirley Community Centre building. Based on detailed postearthquake observations and investigations, the GFRP retrofitted URM walls in the subject buildings exhibited negligible to minor levels of damage without delamination, whereas significant damage was observed in comparable nonretrofitted URM walls. AM - Accepted Manuscript
