SR404 Seismic effects of structural irregularity of light timber-framed buildings (August 2018)
- Valid from
- Information provider
- BRANZ Limited
- Angela Liu and Roger Shelton
- Information type
- Study report
The majority of residential buildings in New Zealand are low-rise light timber-framed (LTF) buildings, and their gravity load and lateral load-resisting systems are universally plasterboard-sheathed walls. Construction of residential LTF buildings in New Zealand largely follows a prescriptive standard - NZS 3604:2011 Timber-framed buildings - which specifies not only the seismic demand but also the seismic bracing provisions.
Earthquake damage observed in the 2010/11 Canterbury earthquake sequence demonstrated that simple regular LTF houses performed well while irregular houses often had significant damage that was uneconomical to repair. This suggested that the irregularity of LTF buildings was an important factor responsible for the exacerbated earthquake damage. The objectives of this study were to quantify seismic effects of permissible irregularities of single-storey buildings in NZS 3604:2011 and to provide sceintific evidence for elaborating irregularity limits in NZS 3604:2011.
To study the seismic effects of permissible plan irregularities from NZS 3604:2011 on LTF buildings, six case study buildings with different permissible bracing irregularities were seismically designed to NZS 3604:2011. Three-dimensional non-linear push-over analyses were conducted of these model buildings where LTF walls an ceiling diaphragms were modelled using the models developed in the project.
The study revealed that permissible irregular bracing arrangements in NZS 3604:2011 could amplify lateral deflections by 500% compared with regular counterparts. The consequence is that irregular LTF buildings within the scope of NZS 3604:2011 could be unacceptably flexible in earthquakes, implying the need for tightening the irregularity limits in NZS 3604:2011.