STRUCTURAL DESIGN FOR ARCHITECTURE

Steel structures

Fig. 3.60 The bundled-tube system. In this system,

closely-spaced columns on the perimeter of the building

act in conjunction with rows of closely-spaced columns

which cross the interior. These provide additional shear

connections between the windward and leeward walls and

reduce the phenomenon of shear lag.

(Figs 3.61 and 3.62). Multi-cable systems have

the advantage that the cables can be stressed

against each other (prestressed) which further

restricts the amount of movement which can

occur in response to variations in load. The

higher the level of prestress the more rigid

does the structure become.

Although a cable structure will always take

up the form-active shape^14 of the loads which

act on it, this does not mean that the designer

has no control over its shape, because differ-

ent geometries can be produced by altering the

97

14 See Appendix 1 for an explanation of the term 'form-

active'.

Fig. 3.59 The tube-in-tube system. In this system closely-
spaced columns on the perimeter of the building act
compositely with the core to resist horizontal load.

and cable structures must be designed so that

drastic changes in shape, such as might occur

due to a complete reversal of load under the

action of high wind suction, must be

prevented. A number of techniques are used to

achieve this. Most are based on the use of two

sets of cables, which are arranged so that the

structure can resist forces from all directions