As a leading international software and machine manufacturer in the light gauge steel framing sector, Scottsdale Construction Systems was approached by one of their clients, Australian Framing Solutions (AFS), to investigate the most efficient way of improving lateral bracing options in steel building design.
Dr. Thanuja Ranawaka, Scottsdale’s, Australian based Engineering Consultant designed the testing parameters, closely liaising with the AFS team to:
- Develop a sound testing plan
- Decide the testing model and analysis to be undertaken
- Develop practical testing scenarios
- Report on the results and findings, communicate these to the wider Scottsdale network of global fabricators
Bracing is considered one of the most important elements of LGS frame and building design, adding strength and stability, particularly where there are seismic and wind loads to consider. Builders typically use a combination of K-bracings, strap bracings, and bracing boards to increase performance. However, a common myth is that by using all of these types of bracings together, you will get increased loadings/performance.
That myth was part of understanding the first question the research team set to answer:
Can we get the cumulated capacity by using a combination of bracing techniques together? And the answers was, No. Due to the different ductility levels of different bracings, they do not work together. So, while one bracing is giving its full capacity, the second bracing doesn’t act properly. Unfortunately, some builders are using all the different bracing types together when the bracing requirements are higher, thus wasting time, money, and resources.
The second question addressed by the research team was what to do when the bracing requirement is higher, but you do not have enough walls to install them?
Most builders use K-bracing as it can be installed in a narrow wall area like 450mm. Do we actually get the required capacity from them? Or, can we get reasonable capacity when compared to the labor and material cost? The answer was, no. The ductility of K-bracing is very high. It can deflect considerably with a 1 kN load. So, K-bracing capacity is almost non-comparable to the low cost and capacity of strap bracing. Summary, K-bracing is not a recommended solution in this instance.
Next, the Scottsdale team reviewed the analysis process to determine the best possible bracing options using data from other international regions, particularly the United States. Indications were that there are more efficient methods of improving structures by restraining the lateral loads other than using K bracing. The first step was to prepare documentation for a series of tests to determine the most efficient type of bracing for K Brace, 30mm (1.2inch) strap brace, 150mm (5.9inch) strap brace and plywood.
These tests were again conducted by Scottsdale own, Dr Thanuja Ranawaka and third party engineers, Eiger Engineering.
Scottsdale selected to use 150mm (5.9in) straps as cross bracing since it is often readily available as offcuts from onsite steel coil. We discussed this method with different consulting engineers and, their opinion was not initially not overly positive. So tests were conducted to prove that 150mm (5.9in) strap bracing can carry a significant amount of load. The testing team fabricated 2.4m by 2.4m (7.9ft x 7.9ft) walls with C90_37_0.75 (3.55in x 1.45in x @22ga) wall studs. The result showed that 150 mm (5.9in) strap bracing could carry 15 kN horizontal load, and neither the strap or the connection failed, wall members, however, did. This is also indicated that with thicker gauge material i.e. 0.95 mm (@18 ga), the load capacity could be higher.
The Key Finding
After thorough testing and analysis, Scottsdale can recommend that a 150mm strap brace provided a significant amount of capacity (15 kN) compared to standard K-bracing (1 kN) or most other traditional bracing methods. The outcome and testing was considered successful for Australian Framing Solutions, who implemented the findings into their day to day manufacturing and assemble operations. By using strap bracing as outlined, costs are significantly reduced as offcuts and left material can provide the straps (bracing).