Seismic Restraint and Inter-Storey Drift Design for Australian Curtain Wall and Window Systems

Australia is sometimes perceived as a low-seismicity country, but significant earthquakes have occurred in Victoria, Newcastle, Kalgoorlie and offshore south-west Western Australia. The National Construction Code Volume One Section B references AS/NZS 1170.4 for structural design actions in earthquakes, and modern Australian commercial buildings, hospitals, schools and infrastructure projects must demonstrate compliance. For facades, the seismic challenge is twofold: the curtain wall and window system must resist earthquake loads without glass fallout or structural failure, and it must accommodate the inter-storey drift that occurs between adjacent floors during a seismic event. MEICHEN Windows & Doors supplies aluminium facade systems engineered for Australian seismic conditions, and this article explains the design principles, Australian regulatory framework and detailing required for safe seismic performance.

Why Seismic Design Matters for Australian Facades

Seismic events in Australia are less frequent than in Japan, New Zealand or California, but they are not rare. The 1989 Newcastle earthquake (M5.6), the 2021 Melbourne earthquake (M5.9) and the 2012 Moe earthquake (M5.4) all caused damage to buildings within their affected areas. Modern Australian buildings are designed for earthquake loads using the hazard map in AS/NZS 1170.4, which specifies a probability of exceedance of 1 in 500 for the ultimate limit state and 1 in 25 for the serviceability limit state.

Glass and facade failures have been observed in past Australian earthquakes. Common failure modes include:

Glass fallout. Annealed or heat-strengthened glass dislodged from frames due to inter-storey drift.
Frame buckling. Aluminium mullions buckled under seismic loads when not properly braced.
Sill and header failure. Connections between curtain wall and floor slab pulled out or sheared.
Sealant tearing. Rigid sealants tore under cyclic movement, allowing water ingress after the event.
Falling debris. Loose cladding panels and glass fell to the ground, endangering pedestrians.

These failures are preventable with proper seismic design of the facade system. MEICHEN engineers curtain wall, window and door systems to meet Australian seismic requirements and provides documentation to demonstrate compliance.

The Australian Regulatory Framework

Australian seismic design is governed by a layered regulatory framework:

NCC Volume One Section B. References AS/NZS 1170.4 for structural design actions in earthquakes.
AS/NZS 1170.4:2007. Sets out earthquake actions, including the hazard map for Australia, site factors, importance levels and structural design procedures.
AS 1288:2021. Sets glass selection and installation requirements that influence seismic glass design.
AS 2047:2014. Covers window performance, but does not specifically address seismic design. Seismic performance is typically assessed separately by the structural engineer.
AS/NZS 1170.0. General structural design principles including robustness and load combinations.

Importance levels in AS/NZS 1170.4 range from 1 (low consequence for loss of human life) to 4 (essential facilities such as hospitals). Most commercial buildings fall within Importance Level 2, while schools, hospitals and emergency facilities fall within Importance Level 3 or 4, requiring more stringent seismic design.

Seismic Loads on Facade Systems

During an earthquake, a facade experiences both inertial loads from its own mass and drift imposed by the building structure. The two effects must be addressed separately:

Inertial loads. The facade mass is accelerated by ground motion, generating forces proportional to mass and acceleration. Aluminium facade systems are relatively light, so inertial loads are typically small compared with structural elements, but connections must transfer the load to the building structure.
Inter-storey drift. Adjacent floors of the building move relative to each other during an earthquake. The facade must accommodate this movement without distress. Drift is expressed as a percentage of storey height and can exceed 1% for some structural systems.

A facade designed for gravity and wind loads alone may fail under seismic loads if connections are too rigid or if drift accommodation is insufficient. MEICHEN engineers facade connections to balance strength (for inertial loads) with flexibility (for drift).

Connection Detailing for Seismic Performance

Connection design is the most important aspect of seismic facade design. MEICHEN uses several detailing strategies depending on the building structure and facade system:

Slotted connections. Vertical mullions are connected to the floor slab with slotted brackets that allow vertical movement but restrain horizontal movement. This permits the facade to slide up or down with floor deflection without buckling.
Drift connections. At each floor, the facade is connected to the slab in a way that allows the facade to move horizontally with the floor below while remaining anchored against vertical loads. This accommodates inter-storey drift.
Knee braces. In stiff facade systems, knee braces or kicker brackets transfer lateral loads from the facade to the slab while allowing vertical movement.
Sacrificial connections. Some connections are designed to yield or fail in a controlled manner under extreme events, preventing catastrophic facade collapse.
Rigid connections. In small panels or stiff facade systems, rigid connections may be acceptable where drift accommodation is provided elsewhere.

MEICHEN provides connection details for each project, including bracket dimensions, fastener specifications and allowable loads. The structural engineer reviews and approves the connections before fabrication.

Glass Selection for Seismic Conditions

Glass selection is critical to prevent fallout during earthquakes. AS 1288 sets minimum requirements for safety glass, but seismic design often demands higher performance:

Laminated glass. Two or more plies bonded with a structural interlayer. If the glass cracks, fragments adhere to the interlayer, preventing fallout. Laminated glass is the standard choice for seismic applications.
Heat-strengthened laminated. Combines the strength of heat-strengthened glass with the safety of a laminated interlayer. Often used in seismic areas where wind and seismic loads both apply.
Toughened laminated. Maximum strength with safety interlayer. Used in high-rise and high-importance buildings.
Annealed glass. Not recommended for seismic applications due to the risk of large sharp fragments falling from the facade.

MEICHEN engineers specify laminated or heat-strengthened laminated glass for seismic projects, with interlayer thickness and glass make-up determined by the structural analysis.

Inter-Storey Drift Accommodation

Inter-storey drift is the relative horizontal displacement of adjacent floors during an earthquake. For a typical commercial building, drift may reach 30–60 mm at the floor level during a design earthquake. The facade must absorb this movement without damage:

Stack joint design. The horizontal joint between adjacent floors of the facade (typically 15–25 mm wide) must accommodate the expected drift. A standard stack joint with compressible backer rod and weather sealant can typically accommodate 5–10 mm of movement, which is adequate for many low-rise buildings.
Larger stack joints. For high-rise buildings with larger drift, wider stack joints with engineered movement joints (such as pre-compressed foam tapes or rubber gaskets) are used.
Mechanical movement joints. In extreme cases, mechanical joints designed for ±50 mm of movement may be required.
Vertical mullion design. The vertical mullion must be sized to allow movement at the stack joint without buckling or pulling out of its connections.

MEICHEN engineers facade stack joints to match the structural engineer’s drift analysis, including the contribution of thermal expansion and contraction.

Testing and Verification

Seismic performance of facade systems can be verified by testing or analysis:

Component testing. Individual connections are tested under simulated seismic loads to verify strength and drift capacity.
Mock-up testing. A full-scale facade mock-up can be tested under cyclic loading to simulate seismic events.
Analysis. Finite element analysis of the facade system, supported by connection test data, is often sufficient for design verification.
Post-earthquake inspection protocols. Building owners should have documented inspection protocols for facades following seismic events, including checks for cracked glass, displaced connections and torn sealants.

MEICHEN can coordinate seismic mock-up testing at accredited laboratories for projects that require physical verification. Test reports are provided to the structural engineer for inclusion in the building’s compliance documentation.

Coordination with the Structural Engineer

Seismic facade design requires close coordination between the structural engineer and the facade engineer. MEICHEN’s technical team works with project structural engineers from the early design stage to:

Confirm the design drift and acceleration levels
Develop connection details that balance strength and flexibility
Specify glass make-up that meets both wind and seismic requirements
Coordinate stack joint design with inter-storey drift allowances
Provide connection loads and fastener specifications for the structural engineer’s review
Document the design assumptions in the project calculations

This collaborative approach avoids coordination errors and ensures the facade performs as designed in a seismic event.

Specification Checklist for Seismic Facade Design

Item	Specifiable detail	MEICHEN reference
Importance level	1, 2, 3 or 4 per AS/NZS 1170.4	Project-specific
Design inter-storey drift	±20 to ±50 mm typical	From structural engineer
Glass type	Laminated or heat-strengthened laminated	AS 1288 compliant options
Connection type	Slotted, drift, knee brace or sacrificial	Engineered for each project
Stack joint width	15–50 mm depending on drift	Per structural analysis
Stack joint sealant	Pre-compressed foam or engineered rubber gasket	Tested for movement range
Mock-up testing	Full-scale under cyclic load for critical projects	Available on request
Verification	Analysis with connection tests	Reports provided

This checklist supports project teams in aligning facade specification with the structural engineer’s seismic design.

Case Study: Hospital Seismic Upgrade in Newcastle

A 1970s hospital in Newcastle required a seismic upgrade to Importance Level 4 under updated AS/NZS 1170.4 hazard values. The original single-glazed aluminium windows did not meet the new seismic requirements. MEICHEN supplied a replacement facade system consisting of heat-strengthened laminated glass, mullions with slotted connections, and engineered stack joints designed for ±40 mm of inter-storey drift.

The new facade was installed floor by floor to maintain hospital operations. Mock-up testing confirmed that the system accommodated the design drift without glass distress or sealant failure. The completed facade met the Importance Level 4 seismic performance requirements and allowed the hospital to continue essential operations.

Frequently Asked Questions

Does seismic design apply to all Australian buildings?

All buildings in Australia must be designed for earthquake loads under AS/NZS 1170.4, although the magnitude of the design event varies with location and importance level. Even single-storey houses in low-hazard areas require basic seismic considerations such as tying walls to the roof and floor structure.

What is inter-storey drift, and how is it measured?

Inter-storey drift is the relative horizontal displacement between adjacent floors during an earthquake. It is expressed in millimetres or as a percentage of storey height. The structural engineer calculates drift based on the building’s structural system, mass and the design earthquake.

Is laminated glass required for seismic design?

Laminated glass is strongly recommended and required by many structural engineers for seismic applications because it prevents glass fallout. MEICHEN engineers specify laminated or heat-strengthened laminated glass for seismic projects.

How are facade connections tested for seismic performance?

Connection testing involves applying simulated seismic loads—cyclic in-plane and out-of-plane forces—to a representative connection assembly in a laboratory. MEICHEN coordinates testing at NATA-accredited laboratories when project requirements demand physical verification.

Can existing facades be retrofitted for seismic compliance?

Yes. Common retrofit measures include replacing single glazing with laminated glass, adding drift connections at each floor, installing stronger mullion-to-slab brackets, and upgrading sealants to accommodate movement. MEICHEN’s technical team can advise on retrofit options for heritage and existing buildings.

Conclusion

Seismic design is an essential element of Australian facade engineering, even in regions of lower perceived seismicity. Proper seismic design prevents glass fallout, frame failure and life-safety hazards during earthquakes while maintaining weather sealing and structural integrity under normal service. MEICHEN’s aluminium curtain wall, window and door systems are engineered for Australian seismic requirements, with the connection detailing, glass specification and project coordination needed for safe, compliant facades. By engaging the facade engineer early in the design process, project teams can deliver facades that meet the highest standards of safety and performance.