Kaikoura earthquake challenges met by steel construction

March 2018

Recently published research confirmed that most structural steel buildings performed well; however, several recommendations in the report will further improve steel construction performance in severe earthquake events. Photo: HERA.

The magnitude 7.8 Kaikoura earthquake struck the North-Eastern region of the South Island on 14 November 2016. It was the largest earthquake in New Zealand since 1855, involving the rupture of over six faults with a rupture zone extending 200km – the closest point to Wellington was only 60km away.

The ground shaking resulted in between 80,000 and 100,000 landslides which blocked the coastal road and rail route to Kaikoura. There were also two fatalities attributed to this event.

Post-Kaikoura earthquake, little was mentioned about systemic failures in steel construction. HERA’s General Manager Structural Systems Dr Stephen Hicks said that while this gave them confidence that most structures performed well, they wanted to make sure, so took the opportunity to commission research to pinpoint any weaknesses in New Zealand’s steel constructions.

The recently published research confirmed there were no serious problems; however, several recommendations in the report will further improve steel construction performance in severe earthquake events.

Lack of information

According to the report, following the quake no site-specific information was obtained to determine if any structural steel buildings were subject to seismic demands in excess of design levels. “As there was no immediate significant damage observable no disaster event was declared for Wellington. This meant there was no official government-run investigation.

“This coupled with reluctance from parties associated with damaged steel buildings to reveal insights due to commercial sensitivity and legal liability, left us quite in the dark around how steel performed.

“However, as the level of demand was in excess of the ultimate limit state (ULS) force-based elastic design level for many buildings, damage was expected.”

Best known are the significant failures of concrete framed buildings with pre-cast floor systems in Wellington, leading to some early decisions to demolish buildings such as Statistics House, with many more currently on the investigation list.

New Zealand is a country prone to earthquakes. That’s why at HERA, we believe understanding how our industry’s structures truly perform in these types of events is key if we’re to continue keeping our communities safe during seismic activity.”

HERA commissioned Tangent Consultant Structural Engineer Alistair Fussell to assist with research. This consisted of field observations and data collected from building officials, structural engineers, steel fabricators, academics and a literature review of media, technical publications and websites.

The study found that structural steel buildings in the Wellington region performed well during the earthquake, with one notable exception – the Queensgate cinema and car parking complex in Lower Hutt.

Additionally, four examples of damage to steel buildings were noted, one being the vulnerability of gusset plate connections to a sway mode of behaviour.

“What continues to ring true is the importance of following established procedures and avoiding the use of details with known poor seismic performance – such as eccentric cleats in compression of seismic resisting systems.

“One of our key recommendations coming from this investigation is to consider the feasibility of a confidential industry reporting mechanism for design and construction problems – similar to the SCOSS/CROSS initiative in the UK to facilitate learning from such incidents.

“Recommendations have also been made to prepare practice notes for design engineers to promote good detailing practice with respect to tension only braces.

“There’s also a need to consider out-of-plan actions when designing gusset plate connections in seismic-load-resisting braced frames. Further research is suggested as there’s currently no recognised procedure in New Zealand that appropriately accounts for this mode of failure.

“However, our research confirms that steel construction in the Kaikoura earthquake performed equally to that positively documented in the Royal Commission Reports for the Christchurch earthquakes.

“But, as an industry we can’t rest on our laurels. We have to address the pinpointed areas for improvement – including educating and learning about best design practice.

“We also ask those involved in remedying steel construction building failures to let us know of any further issues which our research may have overlooked.”

Contact

Dr Stephen Hicks - stephen.hicks@hera.org.nz.

HERA Report No.R4-150:2017 - the seismic performance of structural steel buildings in the 2016 Kaikoura Earthquake is downloadable from the HERA website.