Ductile or Non-ductile, that is the Question

Spencer Nicholls School of Architecture, University of Auckland

New Zealand is currently grappling with the opportunities presented by a surge of interest in constructing medium rise commercial and apartment buildings in timber. NZ is earthquake- prone and for timber the anti seismic design demands do not readily combine with the other desirable requirements for acoustic isolation, vibration minimisation and fire control. This has meant that the majority of built projects have been designed in a manner to bypass the specific seismic design requirements of ductility.

A NZ- specific multi rise timber design manual has been under preparation for several years, with the purpose of bringing together all the research efforts and results relevant to timber construction for up to 6 storeys. This effort has identified several areas where further work is desirable but contentious points in design, in particular have meant this document is still not published.

An area of confusion is over the need, or otherwise, for designing to ensure a ductile failure mode for the primary structure.

Much of the present timber construction is concentrated in the north island (especially Auckland and its environs) where EQ risk levels are low, wind loads are often more critical allowing the design and construction to follow ‘elastic’ design methods. This method does not demand a ductile approach and the methodology can be similar to other non- EQ prone environments like Australia or UK. Most of the current buildings being constructed are non- ductile and are designed following elastic methods.

Issue 3 Volume 9

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