THE PARTIAL COLLAPSE of precast concrete floors in Statistics House in Wellington during the 2016 Kaikōura earthquake sparked serious concerns about the seismic performance of precast floors.
Investigation into performance of building
In response, the Ministry of Business, Innovation and Employment (MBIE) commissioned an investigation into the performance of the building.
In December 2016, a letter from MBIE to Wellington City Council highlighted early observations from these investigations. It emphasised the need for systematic and careful engineering inspections of buildings of a similar construction to Statistics House.
Council launched assessment programme
As a result, Wellington City Council created the Targeted Assessment Programme. The focus of this programme was to address public safety issues by confirming the structural integrity of multi-storey buildings that had experienced significant shaking in the earthquake.
The Targeted Assessment Programme included about 80 buildings containing similar structural characteristics to Statistics House. The summary report of the programme, released in May 2017, highlighted the need for urgent research into seismic assessments and developing retrofit guidance for existing buildings with precast floors.
Challenges for assessment and retrofit
Concrete buildings represent over 80% of existing commercial buildings in New Zealand cities, and most have precast floors.
Assessing the likely performance of precast floors in an earthquake is a challenge because there are many unanswered questions about the potential failure mechanisms when seismic actions are transferred across the building structure.
Engineers will also need guidance on retrofit approaches to address vulnerable buildings.
Research led to national programme
In response to the urgent research call on precast floor construction, especially after the Kaikōura earthquake, a BRANZ project investigating the seismic performance of buildings with precast floors was initiated in April 2018.
This project became a catalyst for a national research programme on seismic issues relating to precast floors. The programme, called ReCast, started in July 2018 and is a 3-year workstream led by Professor Ken Elwood.
Research includes two components:
- Real-world investigations including interpretation of post-earthquake observations, case studies of damaged buildings, in situ floor tests and in situ damage investigations.
- Lab-based investigations including computer simulations and tests at the component and system levels.
Revised guideline expected
The expected output of the programme is a revised guideline for seismic assessment and retrofit of buildings with precast floors. Research updates will be through seminars organised by relevant technical societies.
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