Concrete buildings recently constructed in New Zealand with “low-damage” systems have been proven capable of withstanding earthquakes of even greater intensity than those that struck Christchurch and Kaikoura.
These are the findings of research led by QuakeCoRE, and involving the University of Auckland, University of Canterbury and China’s Tongji University (in Shanghai), which entailed testing a two-storey precast concrete building on one of the world’s largest and most flexible shaking tables.
Utilising the shaking table, which is located within the International Joint Research Laboratory of Earthquake Engineering (ILEE) facilities at Tongji University, the ten-metre by six-metre by eight-metre high building was subjected to about 40 different tests.
Commencing at low intensity and gradually increasing, these tests aimed to replicate a variety of forces that accurately characterise different types of earthquakes experienced in New Zealand, ranging from typical 25-year to 2,500-year return periods. These included sudden, intense earthquakes as potentially generated by the Wellington fault line, and long-duration subduction earthquakes as potentially generated by a rupture of the Hikurangi fault off the East Coast of New Zealand.
Emphasising the testing equipment’s size has enabled the building to be evaluated as an integrated whole rather than via testing of its individual components. University of Auckland senior lecturer in civil and environmental engineering and project leader Dr Rick Henry describes the project as “the most exciting” in his career to date.
“It’s the largest and most complex test I’ve completed, on a much larger scale than we would ever be able to achieve in New Zealand,” he says.
“Tests of this scale are extremely valuable. The data you can gather from a large-scale test and what you can subsequently learn from it, is correspondingly immense.”
Dr Henry says the low-damage technology systems tested in the project represent designs that have already been implemented in New Zealand – albeit there are so far only about ten to 15 buildings in total.
“The main objective was to prove that what has already been implemented will achieve the desired performance. This is primarily focused at the building system level – i.e., do all the components work as intended when connected together in a real building?”
“The research should provide engineers with greater confidence in the new low-damage technology systems used in concrete buildings and allow them to be certain that the performance objectives can be met – both the minimum required by the New Zealand Building Code and enhanced objectives to maintain use of the building and minimise repair required.”
“It is important for engineers to introduce such systems as alternatives when discussing options with clients, particularly those who have a long-term interest. With increased implementation in both Wellington and Christchurch, these low-damage systems are becoming more common rather than being considered novel or one-off.”
Drawn further on certain aspects of low-damage design, Dr Henry confirms some system elements will require specific maintenance plans.
“In general, buildings are more frequently relying on devices and gadgets that may need to be checked to ensure they are still operational. However, this is not unique to the systems we tested and applied to all types of new building systems.”
While noting the focus of the research was on the structural system and so did not consider other aspects of the Building Code relating to durability or fire, Dr Henry nonetheless adds that “given such buildings have already been built there is evidence that all requirements can be satisfactorily met.”
According to the research team, no similar tests to those undertaken in this project have previously been conducted on New Zealand construction methods. Thus, they observe, it has not always been possible to determine in the past if a design would perform as expected when considering the entire building system.
Furthermore, the research work is understood to have raised Chinese interest in New Zealand construction practice and seismic design methods – such as using post-tensioned precast concrete walls.
Having completed the testing phase of the project this January, Dr Henry says the team is now in the throes of analysing the test data to prepare reports and papers on the findings and provide recommendations.
“The test has been a great way to showcase how such systems can be successfully implemented. The next step for us is to work to refine the guidance available to engineers to ensure they have the right tools and expertise to be confident when implementing the designs.”
An industry advisory group with practitioners from leading engineering consultancies have provided valuable input to the test objectives and building design of the project.
Dr Henry was supported on this project by Tongji University’s co-Principal Investigator Ying Zhou, along with QuakeCoRE researchers Geoff Rodgers (University of Canterbury) and Ken Elwood (University of Auckland) serving as Associate Investigators, and with University of Auckland’s Yiqiu Lu having co-ordinated and supervised the building construction and testing at Tongji University.
QuakeCoRE, ILEE and the Ministry of Business, Innovation and Employment (MBIE) have collectively provided about $500,000 in funding to the project.
ILEE and QuakeCoRE commenced a partnership in 2016, which has provided New Zealand researchers with the opportunity to access some of the world’s largest and most sophisticated earthquake engineering testing facilities.
Taken from Concrete magazine.