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AUS-5 Sliding glass door - two-part subhead failure
Report ID: 818
Report Overview
Called to inspect the failure of a glazed sliding door system a correspondent noted that the system is comprised of a two-part subhead, which includes a removable bead that relies on mere millimetres of bearing.
Report Content
A correspondent received a report regarding the failure of a glazed sliding door system. Upon inspection it was noted that the system is comprised of a two-part subhead, which includes 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 3a.
In the report the correspondent received, the contractor had riveted the removable bead to the glazing suite (Figure 3b). 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.
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 3b).
Comments
Images
Fig. 3a General arrangement
Fig. 3b As installed
Fig. 3c Suggested fixing
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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.
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.
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.