Atria - Type of Cladding - Steel Structures.

Atria generally require transparent or translucent forms of cladding. Glazing is a traditional solution but is relatively heavy. If the space beneath is heated the thermal performance may dictate double-glazing, which is both heavy and  costly. Other forms of cladding such as ETFE foil cushions can offer a lightweight, thermally  efficient and cost-effective alternative to glazing.

Glazing systems may be framed or unframed.The allowable spans of the systems vary.The relationship between the layout of the primary structure and the cladding system will determine whether there is a need for a secondary system of support.

It is important to consider this relationship at concept stage to achieve the minimum  of elegantly arranged members. The following dimensions provide guidance:

• Planar glazing – spans in either direction around 2m
• Framed systems – spans 4–6m by 2m
• ETFE foil cushions – spans 6–8m in either direction.

Manufacturers should be consulted for more precise information.

Framing systems are generally made from aluminium extrusions, and therefore have thermal expansion and contraction characteristics which differ from steelwork.

This needs to be considered in the detailing of the connectivity between the two elements.

Tolerance between cladding and supporting steel framework also needs careful consideration. The accuracy with which steelwork can be fabricated and erected is generally lower than that of the cladding system. This incompatibility should also be accounted for in the detailing of connections.

Deflections of the atrium structure under loads can have significant bearing on the cladding system. Some glazing systems require a minimum slope to ensure their water tightness. The deflected shape of the supporting structure must satisfy these requirements under all relevant loading conditions. This may require the structure to incorporate a precamber from the theoretical final geometry.The cladding system must also be capable of accommodating any differential movements of the sup- porting structure.

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