Bracing for wind and earthquake
Wind pushes a building sideways, but can also cause uplift on roof claddings and open structures such as verandas and carports. The wind force on a building depends on wind speed (resulting in pressure) and building size. A larger building in an exposed location catches more wind and requires more bracing.
Earthquakes cause ground movement. Building foundations move with the ground, but the structure above ground lags behind causing potentially damaging sideways forces that must be resisted. The earthquake force on a building depends on the intensity of shaking and the weight of the building. The heavier the building, the more bracing that needs to be provided.
When GIB® bracing systems are correctly designed and installed, a building will resist wind and earthquake forces.
Designing to resist ‘serviceabilty’ and ‘ultimate’ events
A ‘serviceability’ event happens reasonably regularly and you can expect a building to survive this without any damage such as cracking or even minor annoyances like sticking doors and windows.
An ‘ultimate’ event has a small probability of occurring during a building’s life. Once every 500 years is the base assumption for houses designed in accordance with NZS3604:2011. In an ultimate event, the main objective is to keep occupants safe while some material damage and repairs must be expected.
All new houses must be designed to meet the requirements of NZS 3604:2011. These designs are a minimum and ensure adequate performance during exposure to serviceability and/or ultimate events.
Understanding the New Zealand Building Code
The New Zealand Building Code (NZBC) sets out the compliance requirements for new buildings. For most light timber framed homes, the requirements covered in New Zealand Standard NZS3604:2011 (which was recently updated) are deemed to comply with the NZBC. NZS3604:2011 specifies the wind and earthquake resistance required for a building. GIB EzyBrace® Systems 2011 are fully compliant with NZS 3604:2011.In addition, GIB EzyBrace® Systems 2011 and the associated software have been extensively tested and are independently appraised by BRANZ Appraisal 294 (2011).
Tested with the Canterbury Earthquakes
GIB® bracing systems performed very well during the Canterbury earthquakes which were sometimes up to two times the ‘ultimate’ level the building code requires them to be designed for. Although the severity of the earthquakes did cause some damage to wall linings, typically at sheet joints around window and door openings, this was expected. The fact that no lives were lost in houses due to collapse, is testament to our building code requirements and the outstanding performance of GIB® bracing systems.
Building Code Plus
Designing a building’s bracing resistance to a higher standard is a discretionary option that an owner may wish to consider. GIB EzyBrace® Systems 2011 software makes it easy to design higher bracing resistance. This is achieved by increasing the ‘annual probability of exceedence’ that relates to the likelihood of an event occurring. Homeowners should talk to their building professional to make sure the correct GIB® bracing system has been included in their homes design.