Following the Canterbury earthquakes, BRANZ carried out research funded by EQC to develop design guidance to mitigate damage to light timber frame (LTF) buildings. Read the abstract from the report: Design Guidance of Specific Seismic Bracing Systems in Light Timber-framed Residential Buildings and download the full report below.

In the Canterbury earthquakes, residential houses of mainly light timber-framed (LTF) construction achieved the Life Safety requirement, as required by the New Zealand Building Code. However, the earthquake damage was often significant. A survey of hundred houses in the aftermath of the earthquakes by BRANZ revealed that the mixed use of conventional plasterboard wall bracing elements with specifically designed bracing systems significantly exacerbated the seismic damage to the LTF residential houses. This was most likely caused by deformation incompatibilities between specifically designed bracing systems and the plasterboard walls. 

A BRANZ structural research funded by EQC was undertaken to develop design guidance to mitigate, through better designing and detailing, the earthquake damage to LTF residential buildings when the buildings include a mixture of specifically designed bracing elements and plasterboard wall bracing elements. 

In this guidance, the expected seismic performance level of LTF residential buildings constructed to NZS3604 was assessed, based on available seismic rating test results of plasterboard walls. The seismic performance requirement for specifically designed bracing elements in mainly NZS 3604 buildings was established as 1%, in terms of storey drift at ultimate limit state. Subsequently, a step-by-step design procedure for specifically designed bracing elements is developed and presented.

Download the report