CROSS Safety Report
Sliding glass door - two-part subhead failure
This report is over 2 years old
Called to inspect the failure of a glazed sliding door system a correspondent noted that the system comprised a two-part subhead, which includes a removable bead that relies on a bearing of only a few millimetres.
This report highlights the need to check that fixings for glazed panels are capable of withstanding design loads, and that the fixings provide adequate bearing to accommodate building movements.
Key Learning Outcomes
For structural and civil engineers:
Need to understand the effects of any building movement that might affect fixings of glass panels and doors
Check that fixings for glass panels have been designed by the manufacturer to withstand design loads and have adequate bearing surfaces
For glazing designers:
Check that certificates state that methods of fixing glazing suites to supporting structures have been designed to withstand design loads
Need to understand the effects of any building movement and how this might affect fixings of glass panels and doors
Ensure adequate bearing surfaces within subheads and other connections supporting glazed panels and doors
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A correspondent received a report regarding the failure of a glazed sliding door system. Upon inspection it was noted that the system comprised a two-part subhead, which included a removable bead. They note that this type of system is gaining popularity in Australia for its ease of installation. The removable bead relies on mere millimetres of bearing in the hook-type arrangement seen in Figure 1.
Lack of understanding of building movement
In the report the correspondent received, the contractor had riveted the removable bead to the glazing suite (Figure 2). This then only required a small amount of building movement to dislodge the bead from the subhead, resulting in the glazing suite pushing into the building. The correspondent believes there is an apparent lack of understanding of allowances for building movement within some areas of the glazing industry.
Check glazing certificate for ability of fixings to withstand design loads
Similarly, the correspondent considers there is a gap in the industry where the fixings of the glazing suites to the structure are often not engineered or certified. The glazing suite itself may be certified to the glazing code, but the fixings/attachment between the glazing and the rest of the building are often overlooked – particularly on small to medium sized projects. Thus certifiers should ensure that the glazing designer’s certificate states that the fixing methods of the glazing suites to the supporting structure have been designed to withstand design loads.
The correspondent recommends that engineers should examine these two-part subhead systems and be convinced of their suitability. They suggest that a fixing between the two parts of the subhead be made after installation, to prevent dislodgement of the bead during its lifespan (Figure 3).
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Expert Panel Comments
An Expert Panel comment on the reports we receive. They use their experience to help you understand what can be learned from the reports. If you would like to know more, please visit the CROSS-AUS Expert Panel page.
As the correspondent has stated, there is a lack of understanding of building movement by many building practitioners, including engineers, architects, builders, and sub-trades such as the example given here. All structures deflect under load; concrete structures will continue to deflect over the long term; tall buildings will have significant shortening; and buildings move with changes in the environment (heating and cooling; wetting and drying).
Our attention has been drawn to another movement related incident, in this case in high-rise buildings where the movement of the building under wind has been transmitted to the steel-framed internal partitions resulting in very high noise levels in the apartments up to 70 dB.
Building design and movement report
Therefore, it is important that the design of glazing, curtain walls, internal partitions and similar attachments, makes allowance for the expected movements, both short and long term. To ensure this happens, the structural engineer should provide a building design and movement report for all buildings where significant movement is expected. Tolerances in construction must also be considered where small margins can affect safety-critical components.
Further guidance from overseas
The Centre for Window & Cladding Technology (CWCT) in the UK is a leading information provider and trainer in the field of building envelopes and glazing. Although there is no direct equivalent in Australia, the Australian Glass and Window Association (AGWA) does provide some industry guides.