The structural reliability performance requirements of NCC2025 offer opportunities to the suppliers of innovative building products and systems. This is a summary of the key points for the determination and use of structural reliability indices.
1. The purpose of including quantified structural reliability requirements within the mandatory Parts B1P1 and H1P1 of NCC 2025 is to achieve consistency and predictability for the structural reliability of structures covered by the NCC and achieve a “levelling of the playing field”, ensuring that competing products and systems are subject to the same requirements.
2. Although the approach may be useful for other structures (such as bridges), the mandatory application of the requirements applies only to buildings and other structures that are covered by the NCC.
3. Full compliance with a Deemed-to-Satisfy (DTS) Standard is considered to be compliance with the NCC.
4. Not all DTS Standards achieve the same structural reliability. Notwithstanding, it is likely that future Standards Australia DTS documents will, in time, more consistently reflect the mandatory requirements.
5. If a design is outside the scope of the DTS Standards, it must be treated as a performance solution, as defined and limited in the NCC.
6. The mandatory quantified structural reliability requirements currently reflect a consensus amongst the participants in the ABCB consultation process. As the engineering profession becomes more familiar with the use of the mandatory requirements, it is possible that the stringency may be adjusted … but that is a long way in the future.
7. Only a small proportion of practicing structural engineers will routinely need to refer to the NCC performance requirements. Rather, the majority of designs will be determined using DTS Standards.
8. The people most likely to routinely use the NCC performance requirements are regulators, Standards writers, the developers of new or innovative products and systems that are outside the scope of the DTS Standards, and the engineers choosing to use such products.
9. The basic premise of structural reliability is that when abnormally high actions (resulting from loads) coincide in a structure with abnormally low resistances (e.g. strengths), a structural failure can occur.
10. It is assumed that both the actions and resistances are log-normally distributed. While the actual distributions may differ, the assumption is reasonable in the region where the actions and resistances overlap.
11. A structural reliability index (β) is calculated using the equation given in the NCC.
12. The method of determining the means and coefficients of variation for the common actions is given in the NCC.
13. In addition to achieving a specified level of structural reliability, design must also achieve any serviceability requirements (e.g. deflection and crack limitations
