Steel Bar joist are an economical alternative to using standard beams for roof framing.
There are three major types of steel bar joists; Short Span, Long Span, and Joist Girders.
Some advantages that joists have over other types of roof and floor framing
Reduced dead load means savings in columns and foundations.
Increased bay sizes with little increase in cost, means fewer columns which allows for better flexibility in floor plans and room arrangements.
Maximum ceiling height is possible since the open webs of the joists allow for installation of mechanical systems within the webs.
Short Span Bar Joists
Spans from 8 ft. up to 60 ft., joist depths from 8 in. up to 30in., depending on load conditions.
Another type of Short Span joists are sometimes called "CS" series joists. These joists are designed to support a concentrated load as well as a distributed load. These joists are ideal when roof top mechanical units are to be installed.
Long Span Bar Joists
Spans from 25 ft. up to 144 ft., joist depths from 18 in. up to 72in., depending on load conditions.
Another type of Long Span joists are sometimes calles "SLH" series joists. This joist type has a double pitched top chord, with a minimum pitch of 1/4 in. per foot. Spans range from 111 ft. up to 240 ft., with joist depth from 80 in. up to 120 in.
Used as primary framing members between columns, usually to support bar joists for the bays. Spans up to 100 ft. are available, girder depth varies with loading condition, but a general rule is 1 inch of depth for every foot of span.
Steel roof and floor decks have several advantages over traditional decking systems:
Light weight and high strength-to-weight ratio allows for greater spans which menas that the number of supporting members can be reduced.
If installed according to manufacturers recommendations, decks can provide lateral diaphragm actions, reducing or eliminating the need for structural bracing.
Since steel is incombustible, fire ratings of up to 3 hours can be achived with proper construction.
Steel decking can be divided into three major categories: composite, non-composite, and roof.
Composite Deck - Used as a form for the concrete floor, ribs in the vertical webs cause the concrete, deck and supporting structure to act as one unit.
Non-Composite Deck - Used strictly as a form for the concrete floor.
Roof Deck - Used as an underlayment for the roofing system.