Chch home quake resilience researched

A woman and her dog survey her quake-hit home in Christchurch. File photo / Brett Phibbs

Improving the resilience of homes which performed poorly in the Canterbury earthquakes is the subject of a new research project.

Engineering experts from research organisation Branz with support from EQC, will use computer modelling to assess the impact of simulated seismic action on modern homes with more complex configurations.

The research was prompted by the finding that less complex homes in Christchurch performed better in the quakes than those built beyond the limits of a more recent building standard, known as New Zealand Standard 3604.

Variation in the stiffness of bracing systems was common in less complex homes, especially in hillside houses or older houses which had been altered to make them more open plan, the researchers found.

They are planning on examining how the bracing systems of different stiffness interact during a seismic event.

Project leader Angela Liu, a member of the team which inspected residential properties for damage in Christchurch, said the team found many older buildings, pre the 3604 standard, such as light timber framed houses with small windows and smaller rooms, had performed better than many modern buildings with complex seismic resisting systems.

"The team observed more severe earthquake damage in homes which often had a mixture of different seismic resisting systems, either because of the presence of bigger rooms at one end of the dwelling or larger windows included on one side for a better view."

Under the current regulations, seismic design of buildings focussed on preserving life and residential houses performed very well in this regard, Ms Liu said.

However, as more people were wanting bigger spacing between bracing lines in order to have bigger rooms and windows, the spacing was becoming too large to comply with the 3604 standard, Ms Liu said.

The team also observed cracking in extensions, including at the junctions between pre-1978 suspended timber piles and modern concrete slab floors, and also with houses which had been built on different levels down hillsides.

"We are aiming to find better ways to improve the performance of these more complex houses," Ms Liu said.

"We will be looking at what the action is in individual areas and the computer model will allow us to adapt the bracing elements to ensure all the elements of bracing work together.

"That will enable us to provide guidance around areas where engineers need to pay more attention in future designs."

Branz is an independent and impartial research, testing, consulting and information company providing services and resource for the building industry.