Low damage solutions for earthquake

Details of joint

New Zealand is a world leader in the development of earthquake resistant technologies for buildings. In the 1970s, our ductile design concept for buildings affected by severe earthquakes was adopted worldwide.

This concept is based on the fact that, while statistically severe earthquakes are very unlikely to occur during a building’s lifetime, they can be very damaging. The focus therefore was to design buildings that remain largely undamaged during moderate – but more frequent – earthquakes and to allow controlled damage in more severe events.

This is similar to how we design cars for accidents: damaging the body of the car but protecting the occupants as much as possible.

However the run of recent severe earthquakes since 2010 has “raised the bar” on this concept, giving earthquake engineers the strong incentive to design building systems that can withstand severe earthquakes without the need for repair or where damage is concentrated into components that can easily be replaced. These are called “low damage” structural systems.

Te Puni village frame with SHJs

One example is the Sliding Hinge Joint (SHJ). Used in Victoria University’s Hall of Residence, Te Puni Village, it was invented by Professor Charles Clifton of the University of Auckland’s Faculty of Engineering. During severe earthquake, the beams and columns which would normally remain rigid during the motion of a seismic event instead become flexible, allowing a column to rotate relative to beams – when the earthquake is over, the structure becomes rigid again.

The joint is installed in more than $4 billion worth of new buildings in New Zealand and has proved extremely effective: Te Puni Village has been struck by two severe earthquakes during which the joints slid as designed, then returned to their previous (and rigid) position.

Another innovation in building resilience is the eccentrically braced frame with bolted replaceable active links.

Traditionally, bolted replaceable links have been designed as part of the beams on either side, which in practice means cutting them out and replacing them after an earthquake event as was done in Christchurch after 2011 and is being done for one building in Wellington after 2016.

But a bolted replacement link option, where the active link is bolted into the structural system during initial fabrication, means that after the earthquake this can simply be unbolted and replaced with a new one, avoiding having to cut out and weld in a new link. This can be done during scheduled building maintenance. It has become a standard solution and is another New Zealand first, developed through a partnership between the University of Auckland, Steel Construction New Zealand (SCNZ) and the Heavy Engineering Research Association (HERA).

Other low damage structural steel systems which the University of Auckland has had a role in developing, along with University of Canterbury, SCNZ and HERA include:

  • Buckling restrained braced frames, in which the braces can stretch in tension and squash in compression in a severe earthquake
  • Central rocking braced frames.

In a country that has experienced severe earthquakes in recent times, it’s important that New Zealand’s leading earthquake engineers are also leading innovation in building design that will limit damage from earthquakes and make buildings less costly and easier to repair. 

Associate Professor G Charles Clifton is a member of the Department of Civil and Environmental Engineering, in the University of Auckland's Faculty of Engineering.

Article reproduced with permission from the National Business Review (NBR), Low Damage Solutions for Earthquake developed by the University of Auckland, published in their "Special Report: Investing in Property" on Friday 5 May 2017.