## Diamonds and diagonals

Fig. 72a: The four corner columns with intersecting linear members function in a similar way to Suchov's mast.

Toyo Ito: Mediothek, Sendai (J), 2001

Fig. 72a: The four corner columns with intersecting linear members function in a similar way to Suchov's mast.

Toyo Ito: Mediothek, Sendai (J), 2001

Herzog & de Meuron: Prada store, Tokyo (J), 2003

Herzog & de Meuron: Prada store, Tokyo (J), 2003

The bracing diagonal is frequently an addition, an unavoidable solution inserted to complete the structural concept in those designs where bracing components such as rigid service cores and shear walls are lacking. But when used as a primary structural element they are very popular, as recent examples show - whether as a bundle of apparently random, raking columns ("pickup-sticks" effect), or integrated into a regular lattice. In such cases the fascination is due to the fact that the vertical and horizontal loads can be accommodated with a single structure of linear members seemingly without any hierarchy, but equally because the network takes on an ornamental quality.

Fig. 72b: The corner columns house the stairs.

Toyo Ito: Mediothek, Sendai (J), 2001

Early examples of non-orthogonal lattice structures are the towers of Vladimir Suchov, which originated out of a search for a form of water-tower construction that would save materials. A comparison between Suchov's radio mast in Moscow (1919-22) and the Eiffel Tower in Paris (1889) supplies impressive proof of the potential savings of a tower constructed exclusively of angle and channel sections. Whereas the Eiffel Tower is 305 m high and weighs 8850 tonnes, the radio mast is 350 m high and weighs just 2200 tonnes!

The hyperbolic form employed is based on two cylinders with straight members whose top and bottom rings are "rotated" in opposite directions to create a rhombus-shaped lattice structure. The intersections were riveted together and horizontal rings were attached inside to increase the stiffness, which resulted in the triangular look of the lattice.

A contemporary example that borrows the ideas of Suchov can be seen in Toyo Ito's Mediothek in Sendai (2001), where the four corner towers are constructed according to similar principles.

Fig. 74: Glazed barrel-vault roof based on triangular lattice

Norman Forster: Faculty of Law, Cambridge (GB), 1995

Fig. 74: Glazed barrel-vault roof based on triangular lattice

Norman Forster: Faculty of Law, Cambridge (GB), 1995

Whereas the loadbearing members in the structures of Suchov and Ito adhere to a clear hierarchy, the diagonal and horizontal members of the barrel-vault roof to Norman Foster's Faculty of Law in Cambridge (spanning nearly 40 m) appear to be equals. The construction employs circular hollow sections with a diameter of 160 mm, with alternate ones braced together in pairs. It is interesting to note that the glazing is positioned a few centimetres in front of the I oadbearing structure. Was this done merely to enable Foster to feature this membrane, or was there a more practical reason - the fact that the circular sections are unsuitable for fixing the glazing directly?

There is no such separation at the Prada Store in Tokyo by Herzog & de Meuron (2003). In this building the glazing is fixed directly to the lattice structure, which together with the three internal cores carries the vertical loads. This is an impressive demonstration of the structural potential of welding (at the nodes of the horizontal rhombuses); for the loading is considerably higher than with vertical rhombuses and therefore calls for rigid corner joints.

Fig. 75: Linear members consisting of two channels in a spiral form create a hyperbola.

Fig. 75: Linear members consisting of two channels in a spiral form create a hyperbola.