Structureenvelope relationship

Steel is often used in applications in which the relationship with the building envelope is important to the visual effect. There are five basic relationships between the enclosure of a building and the primary structure:

• structure located entirely inside the building envelope (Colour Plate 1)

• structure located in the plane of the building envelope (Colour Plate 12)

• internal structure continued outside the building envelope (Figures 1.1, 1.11 and Colour Plate 13)

• semi-independent external structure supporting external wall, glazing or roof (Colour Plate 13)

• structure located completely outside the building envelope (Figure 2.17 and Colour Plate 6).

At Bedfont Lakes, London, the beams and columns were located in the plane of the building envelope and used expressed connections, as illustrated in Colour Plate 12. Many 'tent-type' structures continue to support the structure through the building envelope, as was done at the Dynamic Earth Centre, Edinburgh, illustrated in Figure 1.5. The same concept was also used in the glazed cladding support to the Western Morning News building, Plymouth, illustrated in Colour Plate 13. An early example of a completely external structure is the Inmos factory in Newport, south Wales, shown in Figure 2.17.

Inmos Factory

2.17 Structure outside the building envelope, Inmos, Newport (architect: Richard Rogers Partnership)

2.18 Stratford Station showing use of repetitive curved frames (architect: Wilkinson Eyre)

Inmos Factory Wales

This relationship between the envelope and the primary structure brings with it other issues important to the building design, such as:

• expression of the connections

• foundation and holding down points

• security and access (for external structures)

• fire-safety strategy

• corrosion protection of the external elements

• 'cold-bridging' through the envelope

• secondary supports to the roofs and walls to complement the chosen structural solution.

The mixture of structural elements, including curved members, trusses, fabricated components, cables, cast and stainless steel elements, illustrates the variety of techniques that are achievable.

The repetition of the internal structure externally can also be used to great visual effect. The curved frame of Stratford Station in Figure 2.18 was extended outside the glazed façade to emphasise the structural solution. The tapered fabricated beams were curved with decreasing radius down to heavy cast steel footings. This same notion was first used in the Centre Pompidou, Paris, where the external framework replicates the internal structure.

Buildings can be extended later by using the external framework to connect into the structure of the extended building without having to remove the existing cladding. This is important in the operation of existing buildings, which would otherwise lead to disruption of internal activities.

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