AS1170.4 Section 8 prescribes the earthquake-action requirements for parts and components of a building — including services, equipment, and architectural elements. This guide walks through importance levels, subsoil class, design horizontal force, and the exemption thresholds that determine when restraint is required.
What is AS1170.4 Section 8?
AS1170.4 is the Australian Standard for structural design actions — earthquake actions in Australia. Section 8 of the standard specifically prescribes the earthquake-action requirements for parts and components of a building — the services, equipment, fixtures, and architectural elements that must remain attached to the structure during a design earthquake event.
For MEP-F and architectural installers, Section 8 is the clause that determines whether seismic restraint is required, what level of restraint is required, and what the design horizontal force is on every restrained component.
The three inputs that drive the design
- Importance Level (IL). The building's importance level (IL2, IL3, IL4) sets the probability of exceedance used for design. Hospitals and post-disaster facilities are IL4; most commercial buildings are IL2.
- Subsoil class. Site-specific soil class (Ae through Ee) amplifies or attenuates ground motion. Soft soil sites attract more force.
- Component amplification + height factor. Where the component sits within the building (ground floor vs roof), and what type of component it is, applies an amplification factor on top of the base acceleration.
The design horizontal force
Section 8.1 prescribes the design horizontal force as a function of the component weight, the design acceleration coefficient, the component amplification factor, the height factor, and a performance factor. The calculation is deterministic once the inputs are fixed — the skill is in fixing the inputs correctly, which requires the project-specific site hazard data.
Exemptions and thresholds
Section 8 provides exemption thresholds — components below a given weight, or in low-importance buildings in low-hazard zones, may not require specific restraint. The exemption table is the first working an engineering review performs, because a correctly-exempted component never needs to enter the scope.
Documentation deliverables
A compliant Section 8 package for a typical MEP-F scope includes: a cover calculation sheet with the inputs used, a restraint schedule linking component types to assembly numbers, coordinated CAD layouts for each service discipline, and an installation verification checklist for the on-site sign-off.
Regional equivalents
- New Zealand: NZS 1170.5 — broadly equivalent, higher hazard factors nationally.
- United States: ASCE 7-22 Chapter 13 — similar structure, different input parameters (IP, SDS).
- Canada: National Building Code of Canada — incorporates similar component-level rules.