STRUCTURAL DESIGN FOR ARCHITECTURE

Fig. 3.34 Fully three-dimensional two-way-spanning
space framework.

be given the rectangular or diagrid form
depending on the orientation of the elements
with respect to the principal span directions.
Space frameworks of both of the kinds
described above are highly statically indeter-
minate and this, together with the fact that
they are triangulated, allows very efficient use
of structural material. They are, however,
complicated to design and construct and are
therefore more expensive than the one-way-
spanning systems described above. Truly
three-dimensional frames are economically
competitive with conventional structures at
spans greater than 20 m; space frames which
consist of intersecting plane frames are used
mainly in the span range 15 m to 20 m.

Fig. 3.35 Plan and cross-sectional arrangements for

space frameworks.

Because space frames are two-way-spanning

systems, the most suitable overall plan-form is

a square in which the frame is supported

around its entire perimeter on regularly spaced

columns or walls (Figs 3.36 and 3.37). A square

plan-form with supports at the corners is

another common arrangement. The high degree

of statical indeterminacy allows an irregular

pattern of support to be used, however, if this

Fig. 3.36 Support arrangements

for space frameworks. Space frame-

works are normally supported either

by regularly spaced perimeter

columns around the entire perime-

ter or by a symmetrical arrangement

of columns or piers set back from

the perimeter. The two-way-

spanning capability of the space

frame allows, however, an irregular

pattern of support. This is

sometimes the reason for adopting

a space frame as the horizontal

structure in a building.

Steel structures

Double layer

Single layer Span up to 30 m

Span greater than 30 m

Diagrid

Orthogonal DepthSpan= 30(approx.)

Span

Depth

= 40 (approx.)

Lattice beams

Square space frames supported

around their perimeters by

columns and deep lattice beams

Central

quadrupal

column

81

Support around perimeter Minimal support