Description

The New Zealand standard used for non-specific design of houses specifies that wall bracing ratings for bracing elements are determined using the BRANZ P21 test method. This prescribes the test procedure under which isolated walls are racked and how the results are used to evaluate the wall bracing ratings. Building designers then ensure that the sum of the earthquake or wind bracing demand, as stipulated in the standard, does not exceed the sum of the bracing resistances of house walls. To do this they, use manufacturers' published data giving wall bracing strengths.

The P21 test measures the ability of a wall to transmit a racking load from a wall top plate to its bottom plate. The bracing ratings derived implicitly assume that the load can transfer into the top plate and subsequently be carried from the bottom plate to the ground. By using theory and test results, this report attempts to determine a suitable upper limit wall bracing strength to ensure these assumptions are met. It calls on phase 2 of this project (see BRANZ Study Report SR163) for test results on a large room for load transfer from a single-storey superstructure to a piled foundation below and phase 3 of this project (see BRANZ Study Report 164) for test results on a large room for load transfer between upper and lower floors with typical NZS 3604 New Zealand house construction.