AS 1170.4:2024 Explained: Earthquake Actions in Australia

Understanding AS 1170.4:2024

When designing buildings in Australia, structural engineers need to consider a range of actions that may affect the safety and performance of a structure. One of the important standards covering earthquake effects is AS 1170.4:2024 — Structural design actions, Part 4: Earthquake actions in Australia.

The standard provides requirements and procedures for determining earthquake actions and designing structures to withstand the effects of earthquakes.

Although Australia is generally considered to have lower seismic activity than many other parts of the world, earthquakes can still occur in different regions. For this reason, earthquake resistance remains an important consideration in structural design.

AS 1170.4:2024 provides an Australian framework for incorporating seismic actions into structural engineering design.

What Does AS 1170.4:2024 Cover?

AS 1170.4:2024 focuses on earthquake actions that need to be considered when designing structures in Australia.

The standard addresses key issues such as:

Seismic hazard
Earthquake design actions
Site conditions
Structural response
Building importance
Structural systems
Seismic design parameters
Earthquake-resistant structural design

The standard works as part of the broader AS 1170 series, which establishes requirements for structural design actions.

While AS 1170.4 focuses specifically on earthquake actions, it needs to be considered together with the structural design requirements applicable to the particular building.

Why Is Earthquake Design Important in Australia?

Australia is not usually associated with major earthquakes, but Australian buildings can still experience earthquake ground motion.

Earthquakes have occurred in several parts of Australia, and seismic risk can vary depending on location and geological conditions.

Even moderate earthquake activity can generate forces within a building.

These forces may affect:

Columns
Beams
Walls
Connections
Bracing systems
Foundations
Non-structural components

The objective of earthquake design is to ensure that buildings have an appropriate level of structural resistance and can respond to seismic actions without unacceptable damage or collapse.

The Main Principles Behind AS 1170.4

A useful way to understand AS 1170.4:2024 is to consider the relationship between several key factors.

Earthquake Hazard

The expected level of earthquake ground motion depends on the geographical location of the building.

Site Conditions

Ground conditions can influence how earthquake motion is transmitted to a structure.

Building Characteristics

The size, structural system, mass and dynamic characteristics of a building influence its response to earthquake loading.

Importance of the Structure

Different buildings may have different consequences associated with earthquake damage or failure. The design requirements therefore take building importance into consideration.

Structural Response

The building needs to be capable of transferring earthquake-induced forces through its structural system and ultimately into the foundations.

Seismic Design Parameters

One of the most important parts of earthquake-resistant design is determining the appropriate seismic design parameters for the project.

These parameters are influenced by factors such as:

Building location
Site conditions
Structural characteristics
Building importance
Design methodology

Engineers use the applicable parameters to determine the earthquake actions that need to be considered during structural analysis.

This is why seismic design cannot simply use the same earthquake load for every building in Australia.

Site Conditions and Earthquake Response

The ground beneath a building can have a significant influence on how seismic motion affects the structure.

Different soil conditions can respond differently to earthquake ground motion.

Important site considerations may include:

Rock
Stiff soil
Soft soil
Filled ground
Groundwater conditions
Geological characteristics

A building located on one type of ground may experience a different seismic response from an otherwise similar building located on another type of ground.

For this reason, understanding the site is an important part of earthquake-resistant structural design.

Structural Systems and Earthquake Resistance

A building’s structural system determines how earthquake forces are resisted and transferred.

Depending on the building, earthquake resistance may involve:

Moment-resisting frames
Braced frames
Shear walls
Reinforced concrete systems
Steel structural systems
Timber structural systems
Masonry systems
Combined structural systems

The selected system needs to provide an appropriate load path.

A simple concept is:

Earthquake Ground Motion → Structural Elements → Connections → Foundations → Ground

Every major component along this load path needs to be capable of transferring the relevant forces.

Importance of Structural Connections

Connections are particularly important in seismic design.

A structural member may have sufficient strength on its own, but the overall system can still perform poorly if its connections cannot transfer the required forces.

Depending on the structural system, engineers may need to consider:

Connection strength
Connection stiffness
Ductility
Anchorage
Bolted connections
Welded connections
Reinforcement detailing
Load transfer mechanisms

Good seismic design therefore involves more than simply increasing the size of beams and columns.

Ductility and Earthquake Design

Ductility is an important concept in earthquake-resistant design.

A ductile structure can undergo significant deformation while maintaining its load-carrying capacity.

This behaviour can be particularly important during a strong earthquake because the structure may need to absorb and dissipate energy through controlled deformation.

In practical terms, earthquake-resistant design aims to avoid sudden and brittle structural failure.

The structural system should have an appropriate combination of:

Strength
Stiffness
Stability
Ductility
Energy dissipation

The exact requirements depend on the structural system and applicable design provisions.

Building Importance and Seismic Design

Not every building has the same level of importance.

A residential building, emergency facility and critical infrastructure may have very different consequences if they become unavailable following an earthquake.

AS 1170.4 incorporates the importance of the structure into the earthquake design process.

This allows the design approach to reflect the intended function and significance of the building.

For projects with higher importance, seismic design considerations may therefore be more demanding.

Earthquake Loads and Structural Analysis

Earthquake actions are dynamic rather than simply static.

When an earthquake occurs, the ground moves and the building responds according to its mass, stiffness, strength and dynamic characteristics.

Engineers may need to consider:

Building mass
Natural period
Structural stiffness
Structural configuration
Seismic actions
Torsional response
Vertical and horizontal load paths
Structural irregularities

Depending on the building and design requirements, different analytical approaches may be appropriate.

For relatively simple structures, a simplified analysis method may be suitable.

More complex buildings may require more detailed structural analysis.

Structural Irregularities

Building configuration can have a major influence on earthquake response.

Irregular buildings may behave differently from simple, symmetrical structures.

Examples of potential irregularities include:

Significant changes in floor stiffness
Uneven distribution of mass
Discontinuous structural elements
Large openings
Setbacks
Asymmetrical layouts
Irregular vertical configurations

These characteristics can result in more complicated structural behaviour during an earthquake.

For this reason, engineers should consider the overall structural configuration rather than analysing individual members in isolation.

Foundations and Earthquake Actions

Earthquake resistance does not stop at the superstructure.

The seismic load path must continue into the foundation system and the supporting ground.

Foundation design may need to consider:

Horizontal forces
Overturning
Uplift
Sliding
Bearing capacity
Anchorage
Soil-structure interaction

The appropriate foundation solution depends on the building structure and site conditions.

This is particularly important for structures with significant lateral loads or overturning effects.

AS 1170.4:2024 and Other Australian Standards

AS 1170.4:2024 should not be treated as an isolated document.

Structural design in Australia normally involves a combination of standards and regulatory requirements.

Depending on the project, engineers may need to consider standards covering:

General structural design actions
Concrete structures
Steel structures
Timber structures
Masonry structures
Foundations
Geotechnical conditions
Building regulations

AS 1170.4 provides the earthquake action component, while the relevant material and structural standards provide additional requirements for designing the actual structural elements.

Common Mistakes in Earthquake Design

Several common mistakes can reduce the effectiveness of seismic design.

Using the Wrong Site Information

Incorrect assumptions about site conditions can result in inappropriate seismic design parameters.

Ignoring Structural Irregularities

A building that looks simple in plan may still have irregularities that affect its seismic response.

Focusing Only on Member Strength

Earthquake performance depends on the behaviour of the entire structural system, including connections and load paths.

Neglecting Non-Structural Components

Architectural and building services components can also be affected by earthquake movement.

Treating Seismic Design as an Afterthought

Earthquake resistance should be considered early in the design process rather than added after the main structural system has already been developed.

AS 1170.4:2024 Design Checklist

Before finalising an earthquake-resistant structural design, engineers may need to review the following:

Design Item	Key Question
Building location	What seismic hazard applies to the site?
Site conditions	What are the relevant ground characteristics?
Building importance	What importance category applies?
Structural system	How will earthquake forces be resisted?
Load path	Can seismic forces be transferred continuously to the foundation?
Connections	Are connections capable of transferring the required actions?
Ductility	Can the structure undergo the required deformation?
Irregularity	Are there significant structural irregularities?
Foundations	Can the foundation resist the resulting actions?
Detailing	Are structural details consistent with the seismic design approach?

Frequently Asked Questions

What is AS 1170.4:2024?

AS 1170.4:2024 is an Australian Standard dealing with earthquake actions for structural design in Australia.

Is earthquake design required in Australia?

Earthquake design requirements depend on the building, location, applicable regulations and structural design requirements. Australia does experience earthquakes, so seismic actions may need to be considered for relevant structures.

What is the purpose of AS 1170.4?

The purpose is to provide a framework for determining and applying earthquake actions in structural design.

Does AS 1170.4 apply to concrete buildings?

It can be relevant to concrete buildings, but the design of the concrete structural elements also needs to comply with the applicable concrete design requirements.

Does AS 1170.4 apply to steel buildings?

Yes, earthquake actions can be relevant to steel structures. The seismic actions determined under AS 1170.4 need to be incorporated into the structural design together with the applicable steel design requirements.

Does AS 1170.4 apply to residential buildings?

The applicability depends on the building type, scope and applicable regulatory requirements. Residential projects may need to consider earthquake actions where required by the relevant design provisions.

Why is ductility important?

Ductility allows structural systems to undergo controlled deformation and dissipate energy without sudden loss of load-carrying capacity.

Is a stronger building automatically a better earthquake-resistant building?

Not necessarily. Earthquake performance depends on a combination of strength, stiffness, ductility, configuration, connections and overall structural behaviour.

Practical Guide for Building Designers

When starting a project that may require seismic design, it is useful to consider earthquake actions at an early stage.

A practical workflow is:

1. Identify the building location

Determine the relevant seismic conditions for the project site.

2. Establish site conditions

Obtain appropriate geotechnical and site information.

3. Determine the applicable design parameters

Use the relevant provisions of AS 1170.4:2024 to establish the earthquake actions applicable to the project.

4. Select the structural system

Choose a structural system capable of resisting the expected actions.

5. Establish the load path

Ensure that earthquake forces can be transferred from the structure through the foundations and into the ground.

6. Design structural elements and connections

Check beams, columns, walls, braces, diaphragms, connections and foundations as an integrated system.

7. Review detailing and constructability

Ensure that the final design can be constructed correctly and consistently with the engineering requirements.

Final Thoughts

AS 1170.4:2024 is an important reference for understanding earthquake actions in Australian structural design.

Effective seismic design requires more than calculating a single earthquake load. Engineers need to consider the interaction between site conditions, building importance, structural configuration, stiffness, strength, ductility, connections and foundations.

The key principle is simple:

Design the building as a complete structural system, not as a collection of individual components.

By considering earthquake actions early in the design process and coordinating AS 1170.4:2024 with the relevant structural and material standards, engineers and building professionals can develop structures that are better prepared to respond to seismic events.

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AS 1170.4:2024