CROSS Safety Report
Modifications to balustrades in a shopping centre
This report is over 2 years old
Overview
A reporter raises concerns about balustrades on a balcony at an existing shopping centre which they feel may not be adequate for their purpose.
Key Learning Outcomes
For civil and structural design engineers:
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Glazing design is often carried out by a specialist contractor. If the glazing is to withstand crowd loading this requirement should be conveyed to the contractor
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Where specialist systems are used, it is beneficial to have a close working relationship with the supplier from the earliest opportunity to ensure design requirements are met
Full Report
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A reporter was asked by a fabricator about balustrades on a balcony at an existing shopping centre. A previous contractor had repaired the balustrade and replaced glass infill panels, but additional work was needed. The reporter was concerned that the balustrades would not stand up to the currently required loadings.
The reporter knows that the glass which has been used for infilling is laminated and not toughened. They believe the balcony could present a serious risk as the section sizes do not appear to be adequate.
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Feedback
I have noted some anomalies within this report that may need to be addressed; principally the differentiating between 'toughened' and 'laminated' glass, which is not very clear. These are not strictly speaking two different types of glass, as it is possible to have laminated toughened glass. One is a single monolithic sheet while the other is a series of sheets of glass of any type stuck together using an interlayer, typically PVB but can also be ionoplast or EVA. Additionally the installation of laminated glass in balustrades is preferable than a single sheet of toughened as in their post failure condition they tend to remain within their supporting frame. A single sheet of toughened however will shatter into small cubes that initially form fist sized clumps until they impact onto a solid object. It may have also been prudent to cite the CIRIA guide to glazing at height in the report as it discusses balustrades at length as well as BS 6180: 2011, which is the code of practice for barriers in buildings.
Expert Panel Comments
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Weakness in balustrades can be highly dangerous since the prime loading, and indeed the only loading, is from crowds and hence a failure could well result in severe injury. Laminated glass is generally accepted as suitable for resisting barrier loadings and its mode of failure is tolerable in that it cracks but does not create shards, always provided of course that the pane as a whole is retained in its supports.
In changing from one type of material to another, replacing toughened with laminated glass for example, careful consideration needs to be given to the whole system including thickness of glass and support types. Barriers in shopping centres can be subject to severe crowd loading, and so need to be designed and installed appropriately.
CROSS report 61 which discussed balustrades in public buildings stressed the importance of having properly designed and constructed balustrades, particularly in buildings to which the public have access. In the case of a modification such as is described here it may be appropriate to discuss the works with the local authority. Information on this specialist field may be found from the Glass and Glazing Federation and in BS 6262-4:2005, Glazing for buildings.