AS 1170 is the multi-part Australian Standard defining the loads (design actions) that structures must be designed to resist: permanent, imposed, wind, snow, and earthquake actions.
It is the starting point for almost every structural design in Australia, feeding into AS 3600 (concrete), AS 4100 (steel), AS 1720 (timber), and other material standards.
The AS 1170 Suite
| Part | Title | Covers |
|---|---|---|
| AS 1170.0 | General principles | Load combinations, limit states, importance levels |
| AS 1170.1 | Permanent, imposed and other actions | Dead loads, live loads |
| AS 1170.2 | Wind actions | Regional wind speeds, terrain, dynamic response |
| AS 1170.3 | Snow and ice actions | Ground snow load, roof shape factors |
| AS 1170.4 | Earthquake actions | Seismic hazard, site classification, response spectra |
Importance Levels
Structures are assigned an Importance Level (1–4) based on consequence of failure, which sets the annual probability of exceedance used to derive design loads.
| Importance Level | Example | Annual Exceedance (ULS, wind) |
|---|---|---|
| 1 | Low consequence (minor structures) | 1:100 |
| 2 | Normal structures (most buildings) | 1:500 – 1:1000 |
| 3 | High consequence (large crowds) | 1:1000 – 1:2000 |
| 4 | Essential post-disaster facilities | 1:2000 – 1:2500 |
Load Combinations (AS 1170.0)
Ultimate limit state, typical combinations:
$$ 1.35G $$ $$ 1.2G + 1.5Q $$ $$ 1.2G + W_u + \psi_c Q $$ $$ 0.9G + W_u $$ $$ G + E_u + \psi_c Q $$Where $G$ = permanent action, $Q$ = imposed action, $W_u$ = ultimate wind action, $E_u$ = ultimate earthquake action, $\psi_c$ = combination factor for imposed loads.
Imposed Actions (AS 1170.1)
| Occupancy | Uniformly Distributed Load |
|---|---|
| Residential (self-contained) | 1.5 kPa |
| Offices | 3.0 kPa |
| Retail | 4.0–5.0 kPa |
| Car parks (light vehicles) | 2.5 kPa |
| Storage areas | 2.4 kPa per metre height (min 5 kPa) |
Wind Actions (AS 1170.2)
$$ V_{des,\theta} = V_R M_d (M_{z,cat} M_s M_t) $$Where:
- $V_R$ = regional wind speed for return period $R$
- $M_d$ = wind directional multiplier
- $M_{z,cat}$ = terrain/height multiplier
- $M_s$ = shielding multiplier
- $M_t$ = topographic multiplier
Design wind pressure:
$$ p = 0.5 \rho_{air} V_{des,\theta}^2 C_{fig} C_{dyn} $$Wind Regions in Australia
| Region | Description |
|---|---|
| A | Non-cyclonic (most of southern/inland Australia) |
| B | Non-cyclonic, higher wind speed (e.g. parts of NSW/VIC coast) |
| C | Cyclonic |
| D | Severe cyclonic (NW Australia) |
Earthquake Actions (AS 1170.4)
Australia is a low-to-moderate seismicity region, but AS 1170.4 still applies to most structures above a minimum size/importance threshold.
$$ E_u = k_p Z C_h(T) S_p / \mu I $$ *(simplified static analysis form)*Where $Z$ = hazard factor (site-specific, varies ~0.03–0.22g across Australia), $S_p$ = structural performance factor, $\mu$ = structural ductility factor.
Practical Notes
- Importance Level drives almost every downstream load: confirm it with the building classification and consequence of failure before any load calculation begins.
- Wind is the dominant lateral load for most low-rise Australian structures; earthquake governs more often for taller, stiffer buildings in some regions.
- Combination factors ($\psi_c$, $\psi_l$, $\psi_s$) are frequently missed in manual calculations: check AS 1170.0 Table 4.1 rather than assuming full imposed load applies alongside wind or earthquake.