What is a non-ductile column?
Non-ductile columns are concrete columns used as load-bearing support for some buildings three or more stories high designed between 1982-1995. Ductile refers to the capability of the column to move or withstand force without breaking.
In layman’s terms a non-ductile column is a stiff reinforced concrete column that does not perform as a column in a modern building would when shaken or twisted.
This can cause a problem in an earthquake when the columns do not move with, or to, the same level as the other elements in the building, meaning that they are at greater risk of failing in an uncontrolled manner.
Do non-ductile columns meet the building code?
Between 1982 and 1995 some buildings of three or more stories were designed with non-ductile columns which met the standard at the time. Today’s building code reflects what we have learnt through earthquake engineering research and such columns would not be designed in the same way today.
Many older buildings with non-ductile columns have been retrofitted to meet modern building standards. However, some have not.
The Council, working with MBIE, and building owners are seeking to understand how many buildings with non-ductile columns are in Wellington, their expected performance, how many have been retrofitted and how many have not.
What is the Non-Ductile Survey?
In 2012 MBIE did a desktop assessment to identify buildings that may potentially have non-ductile columns throughout New Zealand. Once confirmed, building owners carried out their own engineering assessment and were asked to voluntarily share this information to update the Council’s records.
Because there was no requirement for building owners to share their engineering assessments, the information that the Council received was inconsistent and adhoc, making it difficult to compare. To help streamline the information a survey was sent to the owners of buildings with non-ductile columns, which put the information into a consistent format.
The survey results are available at the link below. Also below is a copy of the survey that was sent out.
Do non-ductile columns need to be fixed?
There is currently no legislation in place that requires non-ductile columns to be retrofitted if they achieve 34% New Building Standard (NBS). Council recommends owners review the performance of their buildings and improve them where-ever it is appropriate and feasible to do so.
Buildings which are less than 34%NBS are earthquake-prone and are required to be strengthened.
Buildings which are 34%NBS or more are considered not earthquake-prone and there is no legislation which requires these buildings to be strengthened.
I think the building I’m in has non-ductile columns, what can I do?
Tenants should ask their building owners for their engineering reports. We encourage building owners to share this information with their tenants.
Results of the non-ductile survey (25KB PDF)
Need help?
Email: buildingresilience@wcc.govt.nz
Phone: 04 499 4444