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Steel Designers' Manual - 6th Edition (2003)
30.2 Open-grid flooring
Orthotropic decks 913
Open-grid proprietary systems are often the economical solution for industrial
flooring and walkways, particularly where ventilation or light must be available
through the flooring. They are generally available in spans up to 2.0 metres, but can
be supplied to span 4.0 metres. The design allows spanning in one direction only.
Stair treads are also available. (See Fig. 30.2.)
Open-grid systems are usually manufactured in grade S275 steel, with painted or
galvanized finish. Aluminium and stainless steel types are also available. Loadcarrying
capacities and fixing details are readily available from suppliers’ catalogues.
Open-grid flooring is manufactured in accordance with BS 4592: Industrial type
metal flooring, walkways and stair treads. It has the following relevant parts:
BS 4592: Part 1: 1995, Specification for open bar gratings
BS 4592: Part 2: 1987, Specification for expanded metal grating panels
BS 4592: Part 3: 1987, Specification for cold formed planks.
30.3 Orthotropic decks
Orthotropic decks first came into regular use for long-span bridges in the 1950s.
They replaced the earlier battle deck system where steel plates were supported on
an independent grillage of steel plates.
In the orthotropic system a stiffened plate deck is integral with the support
members which together form the primary members of the bridge. A typical
orthotropic bridge system is shown in Fig. 30.3.
All steel orthotropic decks are used when the dead weight of the bridge must be
reduced to a minimum. They are therefore ideally suited to long-span bridges with
single spans exceeding 120 metres, and are usually incorporated in suspension and
cable-stayed bridges. Other applications are for bridges with moving or lifting spans.
It should be noted that for short-span bridges, steel/concrete composite decks
are generally more economic than orthotropic decks. A composite deck of depth
250 mm will be three to four times the mass of an orthotropic deck but may be only
one-third of the cost.
A typical orthotropic deck consists of a 12–15 mm deck plate stiffened with longitudinal
stringers about 300 mm wide at 600 mm centres, intersecting with deeper
transverse cross girders. Stringers are of the closed or open type.
Closed stringers
Closed, torsionally stiff, stringers are formed as a ‘trough’ and are rolled or pressed
from plate of 6–10 mm thickness.They provide the lightest overall weight, since they