CROSS Safety Report
Failure of large aluminium composite panel
This report highlights the importance of correctly designed fixings and anchoring systems for cladding panels to buildings to minimize the risk of failure.
It discusses how the failure in this case might have been avoided if there had been an adequate facade inspection regime in place.
Key Learning Outcomes
For structural and civil engineers:
Remember that fixings and anchoring systems are generally the critical parts of all cladding design and require appropriate investigation of the possible modes of failure
All fasteners into concrete should comply with AS5216 - Design of post-installed and cast-in fastenings in concrete
Being exposed to the weather, cladding requires consideration of durability of materials and the corrosion potential with dissimilar metals
When designing cladding and other elements for wind pay attention to the possible dynamic effects under low wind speeds
For building owners and managers:
Be aware that all elements of cladding present a significant risk to the public and require correct design and installation by qualified experienced practitioners
Consider having a regular inspection and maintenance program performed and documented by a competent engineer who has experience with the form of construction
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An aluminium composite panel (approximately 3m tall by 1m wide) fell from the façade of a multi-storey building into a high traffic pedestrian area. Many witnessed the incident and fortunately nobody was hit by the panel. The reporter was involved in the subsequent investigation, including the condition of the remaining aluminium composite clad elevations. The facade comprised aluminium composite cladding panels, screw-fixed to aluminium framing which in turn was connected back to the primary concrete structure behind.
Investigation of cladding
An inspection of the exposed framing found large holes had been cut into the mullions in certain locations with packers behind the mullion. Given the arrangement of the holes and packers it was expected that structural concrete anchors would be fixed at these holes between the back of the mullion to the structure behind. However generally there were no anchors found at these holes and instead, what appeared to be restraining the framing to the structure were brackets (approximately 1mm thick), which, according to the reporter, were undersized and fixed back to the concrete structure with (non-structural) hammered-in fixings.
The investigation concluded that these were not an appropriate anchorage system for structural purposes. In one instance it was noted that there had been a complete shear failure of a mullion-to-transom bracket which utilised metal of a similar thickness (approximately 1mm thick).
The investigation concluded that these were not an appropriate anchorage system for structural purposes
The investigation also revealed several screws across the rest of the aluminium composite clad façade to be loose or missing. A similar situation had been found during an earlier maintenance inspection when all loose screws were reportedly re-tightened into position by a rope access contractor. This suggests that many of the screws had significantly loosened, and dislodged in some cases, since that time. This loosening is suspected to be attributed to the inadequately fixed support framing allowing the framing to vibrate under low winds. The investigation concluded that the failed panel likely had several fixings unscrew due to this vibrating effect, resulting in the panel becoming partially dislodged from its position and then tearing through the final fixing when the panel fell from the building.
As the investigation had revealed several screws across the rest of the façade to be loose or missing, it was concluded that there was significant risk of further panels falling from the building. Subsequently the aluminium composite cladding panels and framing were removed from the facades.
Maintenance of facades
Although there was an inherent flaw with the construction of the facade, the reporter believes this incident could have been prevented by an adequate facade condition assessment regime. The previous facade maintenance inspections were undertaken by rope-access contractors, with no engineer supervision or review. As such, the earlier observations of extensive loose screws were not diagnosed correctly, leading to failure of the panel.
The reporter believes this incident could have been prevented by an adequate facade condition assessment regime
Additionally, the design and installation of such panels by the relevant designers and contractors (and the incident itself) have the potential to be the subject of investigations by regulatory authorities and result in a variety of legal proceedings.
Expert Panel Comments
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While this report is about the failure of screw-fixed aluminium composite panels, it highlights a general issue with cladding that in many cases it has been regarded as non-structural and therefore not given adequate attention to quality of engineering design and construction. In such cases the design and detailing of the connections have often been left to the installer with little or no structural engineering input.
When the consequences of failure are considered, all elements of building facades require correct engineering design, with clear documentation, good standards of installation, and an on-going maintenance regime.
All elements of building facades require correct engineering design, with clear documentation, good standards of installation, and an on-going maintenance regime
Cladding panels are typically exposed to the extremes of weather and due attention must be paid to durability of materials, and details such as the use of dissimilar metals.
When designing for wind, the report notes the importance of considering the dynamic effects under low wind speeds and this is particularly important when relatively lightweight elements are being used. Allowance for movement between elements is always an important consideration and in this case the type of fixings used were found to be inadequate.
There have been other examples of issues with the installation of aluminium composite panels. In one case, aluminium composite soffit lining panels were fixed with proprietary very high bond double-sided adhesive tape. Although this tape may be an accepted form of fixing for this type of panel, it is very dependent on the quality of on-site installation. In this instance a panel fell from the soffit onto a public concourse and re-fixing of all panels, this time with mechanical fastenings, was subsequently undertaken.
Fasteners into concrete should comply with AS5216: 2018 - Design of post-installed and cast-in fastenings in concrete.
Maintenance (or the lack thereof) is a recurring theme in CROSS reports (e.g., refer to report 878) and is too often neglected by building owners. The maintenance of facades is particularly important, being exposed to all the elements and by introducing a regular maintenance program carried out and documented by a competent experienced engineer and/or suitably qualified and experienced person, not only will safety be enhanced, but significant future remediation costs may also be avoided.
The maintenance of facades is particularly important, being exposed to all the elements
There have been numerous reports of fixing and anchor failures made to CROSS over the years and these can be found on the website www.cross-safety.org. As with many such cases the example here demonstrates progressive collapse in that an initial failure leads to overloading on adjacent fixings resulting in an unzipping effect.
Refer to CROSS reports IDs 7, 11, 340, 461 and 498 linked below to see parallel situations.
Report ID 7: Cladding fixed to stainless steel
Report ID 11: Stud framing with self-tapping screws
Report ID 340: Nuts falling from tension glazing system
Report ID 461: Metal cladding panels blowing in the wind
Report ID 498: Cladding panel blown off
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