Research Finds Strap Bracing Superior to K-Bracing

Wall frame with integrated 150mm strap bracing being tested with a hydraulic jack mounted to the top left corner.

The bracing of cold-formed steel (CFS) assemblies is critical to their performance. A proper bracing application provides lateral strength to the assembly and helps to prevent it from buckling under horizontal load.

What’s the right way to go?

The wrong way is to layer multiple bracing types, one on top of another. Some builders think such bracing redundancy has a cumulative lateral strengthening effect. But this is not true. Applying strap bracing, K-bracing and bracing boards together on the same wall prevents each bracing type from yielding its maximum lateral strength capacity, because each type has different ductility properties.

So, if a builder should use just one bracing type in his CFS-framed assembly, which is the clear favorite?

A research report, “Review of Strapping vs. K-Bracing,” from Scottsdale Construction Systems, Brisbane, Australia, shows that strap bracing, versus K-bracing, provides superior bracing capacity performance.

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Strapping v. K-bracing

“Review of Strapping vs. K-Bracing,” authored by structural engineers, Thanuja Ranawaka and Dushan Alahakone of Scottsdale Construction Systems, concludes that strap bracing is superior to K-bracing.

The engineers studied three bracing systems:

1. 0.75 – 30mm strap bracing using G550 steel
2. 0.95 – 150mm strap bracing using G550 steel
3. 450mm K-bracing using G550 steel

Each bracing type was tested separately using a 2.4m x 2.4m CFS-framed wall featuring G550-C90_37_0.75 studs. The researchers also tested various rivet and TEK screw combinations.

A hydraulic jack was mounted to the top corner of the frame to simulate lateral loading of the wall. The force applied was incrementally increased for each brace until structural failure occurred. Structural failure was determined both visually and by using a force meter.

Thanuja Ranawaka, structural engineer at Scottsdale Construction Systems, conducted the bracing tests.

And the winner is …

150mm strap bracing.

• The 150mm strap bracing failed a lateral loading force of 15.3 kN
• The 450mm K-bracing yielded to a much lower lateral loading force of 2.4 kN, at which point structural integrity was compromised

In tests, K-bracing (left) buckled under less lateral load force than did the strap bracing.

The 450mm K-bracing deflection sustained at the 2.4 kN load was measured to be 100mm. This greatly exceeded the deflection induced through the strap bracing.

Interestingly, the 150mm strap bracing connection face was not compromised under the loading tests. Rather, the lower wall member sustained the damage.

Ranawaka and Alahakone write that if the wall had been framed with 0.95mm CFS steel studs, as opposed to 0.75mm studs, the load capacity of the 150mm strap bracing would have had even better results.

“As shown in the data collected through experimentation of Strap bracing and K-Bracing, it was evident that Strap bracing is the most suitable bracing method in comparison to K-Bracing,” say the authors in “Review of Strapping vs. K-bracing.”

Thus, 150mm strap bracing provides greater bracing capacity performance over K-bracing.

The calculations featured in “Review of Strapping vs. K-Bracing” were conducted in accordance with Section 8 of Australian/New Zealand Standard 4600:2018. The basic premises and conclusions of the report, however, are applicable to the North American building market.

The information presented here is for illustrative purposes only. SFIA accepts no responsibility for the accuracy or completeness of the information or for loss or damage caused by any use thereof.