Examples of cast nodes and arms

Castings using steel and other alloys may be used in a wide variety of applications in steel construction, many of which have opportunities for architectural expression, as follows:

The extended arms or 'gerberettes' of the Centre Pompidou provide the connections to the columns and tension ties. The shape of the 'gerberettes' is designed to resist combined shear and bearing forces and bending effects (see Figure 3.14). Ornamental details in fa├žades, as in the bronze supports used in Bracken House, London (Figure 11.5).

At the top or intermediate points of masts where cables connect, as used at L'Oreal, Paris (Figure 11.6).

The nodes of tension-tie systems, particularly where a number of ties meet. In this case, the castings are designed to transfer the multiple forces smoothly (Figure 11.7).

Connections between columns and beams, as at Bedfont Lakes near London. The use of castings is a relatively under-used method of connection in regular frames, and is generally used only in exposed applications, as in Figure 11.8 and Colour Plate 12. Brackets or other attachments to members.

An SCI guide covers the design and use of castings. In summary, a steel casting may be preferable to other alternative forms of connection or fabrications when:

cost is not a major constraint, and where the casting or node is visually important relatively large numbers of components are required and the cost of welding stiffeners and other details would otherwise be excessive curved or softer shapes are required, e.g. saddles to column ends the design includes complicated tubular connections with incoming members at different angles (see following section) the design of the steelwork requires considerable fabrication work (steel castings can usually be made with sufficient dimensional accuracy to reduce or eliminate machining costs) the design uses highly tapered sections that cannot be readily fabricated high toughness and/or fatigue strength are important the connections are subject to high forces where large welds would otherwise be required.

11.9 Stainless steel cast legs at the Ludwig Erhard Haus, Berlin (architect: Nicholas Grimshaw & Partners)

The form and profile of the casting can reflect the structural action and forces within the connection or, alternatively, it can be designed to suit a given architectural motif or shape. The shape of the casting between the steel columns and beams in Figure 11.8 reflects the reduction of the column sizes at the floor level.

The shapes available for castings are generally only limited by the practicalities of pattern making and casting. Due to the bespoke nature of each type of casting, it is more difficult for the costs to be assessed accurately at the design stage. However, the maximum degree of economy is likely to be achieved if the casting use is repeated many times. The maximum size of an individual casting is limited only by the capacity of the foundry, and can extend to several tonnes.

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