Article Written by: Farhad Darani PhD CPEng

How the Prolam PLX Column helps architects and engineers achieve open-plan building designs while meeting bracing, stiffness, deflection and NZS 3604 design requirements. 

In modern light timber construction, architects and engineers are often balancing two competing goals: creating open, functional and flexible spaces while meeting demanding structural performance requirements. 

Large openings, cleaner interior layouts and better connection to natural light are highly desirable from an architectural perspective. At the same time, the structural system must deliver reliable bracing performance, manageable deflections and compliance with established design standards. 

The Prolam PLX Column has been developed to help resolve this tension. By combining the advantages of engineered timber with the stiffness and strength of steel, this composite glulam-steel bracing system offers a practical way to balance design goals with structural requirements. 

For project designed within the scope of NZS 3604, the primary New Zealand standard for light timber-framed buildings, the PLX Column provides a technically supported, builder-friendly bracing solution that can unlock more architectural possibilities. 

Composite glulam-steel bracing for open-plan designs

At its core, the Prolam PLX Column is a cantilever bracing column formed from a composite glulam-steel system. This hybrid arrangement increases both stiffness and strength compared with conventional timber-only elements, enabling designers to reduce the amount of bracing length required in a light timber-framed building. 

For architects, reduced bracing length can support larger window and door openings, along with more open-plan layouts. 

For engineers, it offers a system that fits into familiar residential timber design frameworks while still delivering enhanced lateral performance. 

This is especially valuable in projects where design intent calls for openness and natural light, but the structural layout would otherwise be constrained by bracing requirements. In these situations, the PLX Column can serve as a strategic component that supports both aesthetic ambition and technical performance. 

PLX Column and NZS 3604 bracing design

The PLX Column’s development has been aligned with NZS 3604 requirements and informed by P21 testing procedures. This means engineers working within standard timber-framed residential design can apply the product within a familiar compliance context. 

Importantly, the general NZS 3604 bracing design rules continue to apply to the bracing line that includes the PLX Column.  As a result, engineers can incorporate the system into their designs using available bracing design software that is compatible with NZS 3604 – making adoption more straightforward. 

Understanding PLX Column structural performance

The structural performance of the PLX Column is underpinned by P21 cyclic testing, which assesses wall behaviour under repeated lateral loading applied at the top of the wall. 

These tests are carried out through multiple displacement cycles, allowing the response of the system to be understood in terms of both load capacity and deformation capacity. From these results, bracing units can be interpreted for both earthquake and wind design cases. This is important because performance in these scenarios is not assessed by strength alone. 

Each case must satisfy two different design criteria:

Ultimate Limit State (ULS)

This relates to life-safety performance under severe loading, such as a major earthquake or wind event The structure must remain safe for occupants and the public. 

Serviceability Limit State (SLS)

This addresses deformation under more moderate events to ensure the building remains functional and comfortable in use. 

For engineers, this distinction is critical. A system may have adequate ULS capacity, but if its deformations are excessive under service loads, it can still create performance issues. 

Earthquake bracing, drift limits and design interpretation

Although the published PLX Column bracing units are based on P21 displacement limits, some engineers may prefer to design timber-framed houses for higher performance targets, particularly in seismic applications. This often means adopting a more conservative drift limit than the default P21 test interpretation allows.

The published earthquake bracing values for the PLX Column are derived using displacements equivalent to 1.5% drift based on P21 requirements. If the design engineer chooses a stricter target – for example, 1.0% drift – the published earthquake bracing units can be conservatively reduced using a proportional factor: 1.0/1.5 = 0.67.

This gives engineers a practical starting point when designing for reduced drift demands. 

For more refined reductions or project-specific interpretation, additional support can be sought from the Prolam engineering team. 

Wind bracing and serviceability deflection

In the case of wind bracing units, performance is governed by serviceability deflection. This means the column has sufficient capacity at ULS while deformation is limited under service wind conditions. 

For a 2.4m stud height, deflection is limited to 8mm for the NZS 3604 wind SLS case. 
Where engineers need to assess PLX Column SLS deflections for Specific Engineering Design (SED), loading scenarios or alternative performance criteria, lateral stiffness data may be available from Prolam’s technical team.

This flexibility is particularly relevant for engineers who want to move beyond minimum compliance and design with greater confidence around drift control and building behaviour. 

Technical documentation to support specification

Technical performance alone is not enough to make a structural product successful in the market. It must also be easy to understand, specify and communicate to builders, councils and project stakeholders. 
This is another area where the PLX Column system has been deliberately developed to add value. 
The product is supported by a comprehensive suite of technical documents, including:

• PLX Column Design Guide
• PLX Column Installation Guide
• Fixing and footing details for a range of applications

This documentation is intended to streamline the specification process and provide certainty during design and construction. 

Engineers and architects can work through the design guide, confirm the relevant structural requirements, and then select appropriate details to suit the project conditions. 

PLX Column design scope and application limits

As with any proprietary structural solution, correct specification depends on staying within the scope of the product application and supporting documentation. 

The Prolam PLX Column is intended for buildings that fall within the scope of NZS 3604. 

The system can only be specified for buildings with concrete slabs, where the slab supporting the column forms part of the overall foundation system. Additional concrete reinforcement may be required within a certain distance of the column base, as specified in the product documentation. 

Where the column is supported by an isolated slab or block wall, SED footing design should be carried out by a structural engineer. 

This is an important point for specifiers: the value of the system is best realised when it is used within the technical envelope for which it has been developed and documented. 

The PLX Column Design Guide also includes a Producer Statement from an independent CPEng engineer who played a key role in the development of the system. This adds credibility and confidence, but it remains essential to ensure the proposed use falls within the defined scope of that statement. If there is a possibility that a project sits outside that scope, advice should be sought from Prolam or an appropriately qualified structural engineer. 

Builder-friendly installation and fixing details

One of the practical strengths of the PLX Column system is that it has been developed with installation efficiency in mind. 

Too often, high-performing products struggle in the market because they are difficult to install, rely on uncommon components or introduce unnecessary site complexity. The PLX Column addresses this by focusing on a builder-friendly delivery and fixing strategy.

Roof and top fixings are based on widely used, off-the-shelf solutions available in New Zealand, helping reduce procurement and installation complexity. 

The column is delivered to site as a kitset with its specially designed base plate already attached, which saves time and improves consistency. The kitset also includes: 

• Post-installed anchors
• Washers
• Epoxy (Chemical Anchor)

To assist with installation accuracy and improve anchor edge distance, the base plate incorporates a drill guide that enables inclined holes to be drilled at the correct angle for inclined anchors. This is a considered design detail that supports both constructability and performance.

As with any anchoring system, correct installation remains critical. There is a pre-torque specified for installing the anchors, which is important and should not be missed as part of the installation process. 

The epoxy supplied as part of the package must be used in accordance with the manufacturer’s requirements, particular regarding hole preparation and application procedures. 

A smarter timber bracing option 

For engineers and architects working in light timber construction, the Prolam PLX Column offers a compelling combination of structural efficiency, design flexibility and practical usability. 

It allows teams to retain the benefits of timber bracing solutions in light timber-framed buildings, while achieving enhanced stiffness and strength through a composite glulam-steel system. 

The result is a solution that help reduce bracing length, support larger openings, and simplify the path from design to specification, building consent and construction.  

Backed by testing, documentation and practical technical support, the PLX Column is well positioned for projects that need more from their structural bracing elements without leaving behind familiar New Zealand design frameworks. 

For architects, it opens up spatial and visual possibilities. 

For engineers, it provides a tested and supportable solution that aligns with recognised design methodologies. 

For the wider project team, it offers a product designed not only for performance on paper, but for successful use in real buildings. 

How to specify the PLX Column 

The PLX Column can be specified using the Prolam Design Guide and general software or spreadsheets developed for 3604 bracing design. A guide for using GIB EzyBrace® for specifying PLX Column is included in the next section of this article.    

Prolam’s in-house engineering team can support architects, engineers and builders with technical guidance on PLX Column specification, design scope and project-specific applications. 

To learn more, download the PLX Column Design Guide or contact the Prolam team to discuss how the PLX Column could support your next timber-framed project. 

FAQs about PLX Column

What is a PLX Column?

The Prolam PLX Column is a composite glulam-steel bracing column designed for light timber-framed buildings. It combines the strength and stiffness of steel with engineered timber to help achieve larger openings and more open-plan designs.

When should a PLX Column be specified?

A PLX Column is typically specified when a project requires increased bracing performance while maintaining large window openings, open-plan spaces or architectural flexibility.

Can the PLX Column be used in NZS 3604 buildings?

Yes. The PLX Column has been developed for buildings that fall within the scope of NZS 3604 and can be incorporated into standard timber-framed residential designs.

How does the PLX Column improve building design flexibility?

By reducing the required bracing length, the PLX Column can enable larger openings, improved natural light and more flexible floor plans.

What are the advantages of a glulam-steel bracing system?

A composite glulam-steel system provides higher stiffness and strength than conventional timber-only bracing systems while remaining practical and builder-friendly.

How is the PLX Column specified?

The PLX Column can be specified using the Prolam Design Guide or EzyBrace bracing design software. Prolam's engineering team can also provide project-specific guidance.

Can I use the GIB EzyBrace® Bracing Software to specify the PLX Column?

The answer is yes! You can use the GIB EzyBrace® Bracing Software to specify the PLX Column, Prolam's compact, high-strength bracing solution for light timber-framed structures within the scope of NZS3604. It can easily be integrated into GIB EzyBrace Bracing software with standard sheet bracing products and Prolam PLX Portals.

Follow our step-by-step guide:

GIB EzyBrace® Bracing Software Guide

Unlike sheet bracing products, the bracing capacity of PLX Columns is only determined by height, not length. 

1.    Open GIB EzyBrace® Bracing Software 
2.    Open “Custom” page 

3.    Enter below details in relevant cell 

a.    Supplier = Prolam 
b.    System = PLXCH1-400100 or PLXCH1-450100 depending on bracing demand (refer to design guides for bracing capacities for each system)
c.    Min. Length = 1m
d.    Untick “Element Foundation Dependant” so full capacity is shown in calculations

4.    Use in bracing calculations 

a.    Use length of 1m to show correct bracing values 
b.    Stud height from 2.4 to 3.0m

Notes

-    Max stud height = 3m
-    PLX Columns only suitable for concrete slab
-    3604 bracing design only 

This guide only covers the bracing design for the PLX Column.