Panels

Although cladding panels are sometimes fabricated from relatively light-weight materials like fibreglass, most are concrete. They represent a serious hazard should they fall from a building. They can also damage the primary structure if their fixings prevent interstorey drift. For these reasons designers separate panels from the structure and from one another unless the panels are strongly connected to the structure and designed to act as shear walls (see Fig. 5.12). Just as snake and fish scales remain attached to the body yet flex relative to each other when movement occurs, so must cladding panels allow a primary structural frame to move to-and-fro without offering any resistance. Fig. 11.7 shows two possibilities of connecting yet separating storey-height panels. One method is to hang a panel from the top and create a clear horizontal gap between it and the panel beneath. Alternatively, a panel is supported at its base with the gap to accommodate interstorey drift located at the top of the panel. In both cases, even though the structural frame behind undergoes interstorey drifts, the panels remain vertical and each moves with the floor that provides its gravity support. All four panel connections resist out-of-plane forces. Two on one level allow horizontal seismic movement and the others need to accommodate only small contractions and elongations from shrinkage and temperature variations. A common detail that allows movement yet resists out-of-plane forces consists of bolts passing through slotted holes in steelwork connected to the structure (Figs 11.8 and 11.9). Given that panels should never

Direction of movement

Direction of movement

▲ 11.10 Provision for horizontal movement where panels meet at a corner as shown in plan.

Bearing connection

Movement connection

▲ 11.12 Spandrel panel bearing and movement connection details for a steel frame (a) and a reinforced concrete frame (b).

▲ 11.12 Spandrel panel bearing and movement connection details for a steel frame (a) and a reinforced concrete frame (b).

▲ 11.11 One approach to isolating spandrel and column panels from the interstorey drifts of a structural frame.

fall from a building, even during a severe quake, slot lengths are calculated by the structural engineer and details are designed to be as ductile as possible. Attention also needs to be paid to panel movement at external corners (Fig. 11.10).

Many variations in panel arrangements and connections are possible for spandrel panels and column cover panels (Fig. 11.11). Detailing must accommodate the interstorey drift. Spandrel panels are usually attached to the structural frame by bearing connections that support the weight of the panel at the middle to top of the panels. Near the base of panels, flexible or ductile connections allow for movement in the plane of the panel. These connections are usually threaded steel bars that have minimal resistance to movement perpendicular to their lengths, yet can withstand out-of-plane forces (Fig. 11.12). This kind of connection combination allows the structural frame to drift independently of the panel. Since the panels are not a full storey-height, the movement allowance need be less than for taller panels. Restraint against out-of-plane forces is shared by all four connections. The column cover-panels are attached to the columns using an identical approach except that the bearing connection is now near the bases of the panels. Horizontal gaps of between 10 mm to 20 mm between panels are usually sufficient to allow them to move freely relative to each other.

The diagrams are intended to illustrate the principles involved in the design of cladding panel connections. Other methods of connection are possible and will vary depending upon the components involved and the movement to be accommodated. In all cases appropriate architectural details need to be designed to addresses weather-tightness and other requirements of exterior movement joints.

Strip joint cover

- Flexible sealant Thin sheet

Building paper

Framing not fixed to column

Seismic separation

(a) Plan detail

(a) Plan detail

Flashing

Seismic separation

Flashing

(b) Vertical section detail

▲11.13 Separation details for thin sheet-cladding attached to a flexible structural frame.

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