The 14th November Kaikoura earthquake was a sequence of ruptures with a combined magnitude of 7.8 on the Richter scale, and struck 15 kilometres north-east of Culverden, 95 km from Christchurch.
Whilst the rupture started at the epicentre, the earthquake progressed northwards, travelling at a speed of 2 km per second, over a distance of up to 200 km.
The complexity of the earthquake was such that the largest amount of energy released did not occur at the epicentre, but rather 100 km to the north near Seddon with a strong impact particularly in the Wellington region. From engineers’ feedback, HERA understands that the earthquake load was well above the serviceability limit state and, therefore, design conditions were applied, with expected damage to building structures.
According to public reports on damage experienced, around 60 buildings are affected, particularly medium-rise buildings in Wellington. We also know that damage to the Lower Hutt Queensgate car park and cinema complex, which employed steel construction elements, was one of the structures to be taken down immediately because of severe damage and the fear of collapse in aftershocks. It will require close investigation to determine the damage and whether this is expected for this level of earthquake severity.
However, feedback received so far indicates damage to the largest proportion of multi-storey structures appears to be confined to reinforced concrete structures. At this early stage, however, we do not know how steel structures have performed in general, and we have no specific feedback on the performance of more modern designs such as those using the sliding hinge joint and EBFs, or low damage technologies such as rocking frames.
In the interest in learning lessons from the event, HERA is intending to develop a report describing the performance of steel structures. We cannot do this alone without significant input from engineers and building owners and therefore, this article serves as a call for feedback and observations.
You can make a contribution, so please contact the GM of HERA’s Structural Systems Dr Stephen Hicks.