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Steel Designers' Manual - 6th Edition (2003)
5.2.2 Structural types
Space frames 179
Space frames are classified as single-, double- or multi-layered structures, which
may be flat, resulting in grid structures, or may be curved in one or two directions,
forming barrel vaults and dome structures. Grid structures can be further categorized
into lattice and space grids in which the members may run in two, three or
four principal directions. In double-layer lattice grids the top and bottom grids are
identical, with the top layer positioned directly over the bottom layer. Double-layer
space grids are usually formed from pyramidal units with triangular or square bases
resulting in either identical parallel top and bottom grids offset horizontally to
each other, or parallel top and bottom grids each with a different configuration
interconnected at the node points by inclined web members to form a regular stable
structure.
Single-layer grids are primarily subject to flexural moments, whereas the members
in double- and triple-layer grids are almost entirely subject to axial tensile or compressive
forces. These characteristics of single-, double- and triple-layer grids
determine to a very large extent their structural performance. Single-layer grids,
developing high flexural stresses, are suitable for clear spans up to 15 m while
double-layer grids have proved to be economical for clear spans in excess of 100 m.
The main types of double-layer grids in common use are shown in Fig. 5.12.
Skeletal space frames curved in one direction forming single- or double-layer
barrel vaults also provide elegant structures capable of covering large clear spans.
Single-layer vaults are suitable for column-free spans of up to 40 m, which may be
substantially increased by incorporating selected areas of double-layer structure
forming stiffening rings. Double-layer barrel vaults are normally capable of clear
spans in excess of 120 m. Figure 5.13 shows the main types of bracing used for singlelayer
barrel vaults.
Dome structures present a particularly efficient and graceful way of providing
cover to large areas. Single-layer steel domes have been constructed from tubular
members with spans in excess of 50 m while double-layer dome structures have been
constructed with clear spans slightly greater than 200 m. Skeletal dome structures
can be classified into several categories depending on the orientation and position
of the principal members. The four most popular types usually constructed in steel
are ribbed domes, Schwedler domes, three-way grid domes and parallel lamella
domes.
Ribbed domes, as the name suggests, are formed from a number of identical rib
members, which follow the meridian line of the dome and span from the foundations
up to the top of the structure. The individual rib members may be of tubular
lattice construction and are usually interconnected at the crown of the dome using
a small diameter ring beam.
The Schwedler dome is also formed from a series of meridional ribs but, unlike
the ribbed dome, these members are interconnected along their length by a series
of horizontal rings. In order to resist unsymmetric loads the structure is braced by
diagonal members positioned on the surface of the dome bisecting each trapezium
formed by the meridional ribs and horizontal rings.