Standards Australia / Standards New Zealand · Published 2002

AS/NZS 1170.0:2002 (R2016)

Structural Design Actions — General Principles

AS/NZS 1170.0:2002 (Reconfirmed 2016) sets out the general principles for structural design and the basis of design used by all parts of the AS 1170 series. It defines design action combinations for ultimate limit state (ULS) and serviceability limit state (SLS), specifies importance levels (IL1 to IL4), the annual probability of exceedance values that flow through to wind and earthquake actions, and the partial factors for permanent and imposed actions. The standard establishes the framework that downstream parts (AS 1170.1 imposed actions, AS 1170.2 wind, AS 1170.3 snow and ice, AS 1170.4 earthquake) reference for action combinations and importance-level mapping. AS 1170.0 also sets out the requirement for structural robustness, the design situations engineers must consider (persistent, transient, accidental), serviceability limits including deflection and vibration response, and the concept of consequential structures requiring elevated design probabilities. It is the deemed-to-satisfy basis for structural action combinations under National Construction Code (NCC) Volume One, and the controlling reference for any structural calculation that combines multiple loads. The 2002 edition with 2016 reconfirmation remains current as of 2026; a draft revision (AS/NZS 1170.0:202x) has progressed through public comment but is not yet published.

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TRSC Engineering Interpretation

AS 1170.0 is the standard engineers most often reference incorrectly. It is short, easy to skim and easy to misapply. Three application points matter for existing-asset assessment. First, the load combinations in Section 4 are not a buffet from which the most convenient combination can be selected. The ULS combination 1.2G + 1.5Q is not a default; G + ψ_c·Q is the SLS combination, G + Wu is a wind ULS combination, G + ψ_c·Q + Eu is the earthquake ULS combination, and 0.9G + Wu is the wind uplift case. Existing-asset capacity assessment must demonstrate adequacy under the controlling ULS combination, not just the gravity case. Cyclone-prone existing assets routinely have wind controlling, particularly for facade elements, parapets, balcony balustrades, and roof connections. The Q1 Tower post-Cyclone Albert assessment used the AS 1170.0 wind ULS combination with an AS 1170.2 derived design wind speed to verify residual capacity of damaged building maintenance unit (BMU) rail systems before re-deploying access equipment. Second, AS 1170.0 importance levels (IL1 through IL4) drive the annual probability of exceedance used in downstream parts. IL2 (standard occupancy) corresponds to 1/500 ULS for wind and earthquake; IL3 (large public assembly, schools, important commercial) corresponds to 1/1000; IL4 (post-disaster, hospitals over 50 beds, emergency services, water and power infrastructure) corresponds to 1/2500. Selecting the wrong importance level changes the design action by a factor of 1.4 to 2.0 — enough to determine whether an existing asset is compliant. Importance level selection is owner and use-driven, not a standard default; TRSC confirms importance level in writing with the asset owner before any decision-controlling calculation. Third, the standard requires designers to consider robustness — that a structure should not sustain disproportionate damage from a single local failure. For existing-asset assessment, this is rarely codified explicitly, but it underpins our risk-classification approach: a Make Safe recommendation on an element with high consequence of failure and reasonable likelihood reflects the AS 1170.0 robustness intent. We routinely apply ψ_l (long-term imposed action factor) of 0.4 for office space, 0.6 for residential and retail, and 1.0 for storage — values that materially change SLS checks on long-span existing slabs. Serviceability deflection limits (Span/250 to Span/500 depending on use and finish sensitivity) are applied to measured deflections from our investigation reports to determine whether observed slab sag at 12 Creek Street, Marina Mirage and 140 William Street represents structural distress or acceptable in-service performance. AS 1170.0 also defines the accidental design situation — an under-used framework that supports assessment of post-disaster residual capacity against reduced action factors, which we apply on a case-by-case basis with documented engineering justification.

Form 15 RPEQ Certification Implications

Every Form 15 RPEQ Structural Adequacy Certificate that TRSC issues references AS/NZS 1170.0:2002 in the design basis statement, because the certification is conditional on the structure meeting the action combinations and importance level prescribed by this standard. The Form 15 declaration cannot be issued on the basis of dead-load-only verification or single-action checks; it must demonstrate adequacy under the controlling ULS combination defined in AS 1170.0 Section 4, with the importance level documented and agreed in writing with the asset owner. For existing-asset Form 15 certifications, TRSC's investigation file retains the AS 1170.0 combination calculation, the basis for importance-level selection, and the engineering justification for any reduced action factor (for example accidental design situation, planned demolition window, restricted-occupancy assumption). The Form 15 cannot stand alone — it must be supported by documentation showing which combination governed and how the calculated capacity exceeds the design action under that combination, retained in the investigation file for regulatory or legal review.

Frequently Asked Questions

Engineering questions about AS/NZS 1170.0:2002 (R2016)

Which AS 1170.0 importance level applies to a typical commercial building?
Most ordinary commercial buildings — offices, retail premises, hotels and standard residential — fall into Importance Level 2 (IL2), corresponding to a 1/500 annual probability of exceedance for wind and earthquake actions in standard southern-Australian locations. IL3 applies to buildings with large public assembly (more than approximately 300 occupants), schools, hospitals up to 50 beds, large commercial structures, and structures whose loss would cause significant economic or social disruption. IL4 applies to post-disaster facilities — hospitals over 50 beds, emergency services centres, water and power infrastructure essential to community function. The importance-level decision must be made before downstream loading parts are applied, because changing IL changes the design wind and earthquake actions by factors of 1.4 to 2.0. TRSC confirms IL in writing with the asset owner during scoping, and any deviation from IL2 is documented with the engineering basis.
How does AS 1170.0 handle existing-building load combinations?
AS 1170.0 itself does not have a separate existing-building provision — the standard applies the same load combinations to existing structures as to new construction. For existing-asset assessment, TRSC applies the standard ULS and SLS combinations from Section 4, with the design actions calibrated to actual occupancy and use rather than worst-case office or retail defaults. Where an asset is on a defined demolition pathway or has documented restricted occupancy, the engineering basis can support a reduced action — for example, applying the Accidental design situation factor or using a reduced ψ value reflecting agreed occupancy controls. Any reduction below the standard combination requires written engineering justification, owner sign-off, and is retained in the investigation file. The Form 15 always references the specific combination used and the basis on which it was selected.
Why does AS 1170.0 robustness apply to existing structures?
Section 6 of AS 1170.0 requires that structures be designed and constructed to avoid disproportionate collapse from local failure. For existing structures, this principle is rarely explicit in deemed-to-satisfy provisions, but it underpins how engineers think about the consequence of localised deterioration. A corroded reinforcement bar in a cantilever slab edge, a weakened tie connection in a heritage masonry wall, or a damaged column in a transfer-truss bay can each produce disproportionate consequence if they fail. TRSC's risk-classification matrix (consequence × likelihood, per AS/NZS ISO 31000) is the engineering tool we use to apply AS 1170.0 robustness in existing-asset practice — elements with high consequence are prioritised for intervention regardless of whether a single-element capacity check shows adequate margin. This was the framework used to triage the BMU rail damage at Q1 Tower.
What is the status of the AS 1170.0 revision?
A draft AS/NZS 1170.0 revision (AS/NZS 1170.0:202x) has progressed through public comment but is not published as of 2026. The revision targets clarification of action combinations, alignment with international practice (Eurocode 0), and updated importance-level definitions for post-disaster facilities. TRSC monitors the Standards Australia public review process for material changes, particularly to importance-level mapping and serviceability deflection limits, and tracks any provisional adoption pathways. Until the revised edition is published, AS/NZS 1170.0:2002 (Reconfirmed 2016) remains the controlling reference, and all TRSC Form 15 certifications cite the 2002 edition explicitly in the design-basis statement.
Relevant Services
Structural Investigation
Remediation Design
Certification
Sources & Further Reading