Copyright 2003 by The American Institute of Architects (AIA)
Exclusively published and distributed by Architectural Computer Services, Inc. (ARCOM) for the AIA

SECTION 05210 - STEEL JOISTS

GENERAL COMMENTS

The Steel Joist Institute (SJI), an industry association of steel joist and joist girder manufacturers, has developed and published a number of standards, specifications, and technical guidelines for the design and specification of its products.

These technical publications form the basis of this Section. Publications include Standard Specifications, Load Tables and Weight Tables for Steel Joists and Joist Girders (hereafter, Specifications) and a series of technical digests, which are listed in the "References" Article in these Evaluations.

Individual manufacturers may produce joists that vary in depth or length from those listed in the standard tables in SJI's Specifications. Verify the availability of such joists with manufacturers.

PERFORMANCE REQUIREMENTS

Load tables in SJI's Specifications are based on simply supported steel joists carrying uniformly distributed gravity loads. Weight tables are based on simply supported joist girders sustaining equally spaced concentrated loads at panel points. Nonuniform, unequal, or special loading conditions invalidate the tables, except for KCS-type K-series steel joists.

If the Drawings are fully detailed and indicate types, locations, spacings, anchorages, and designations of steel joists and joist girders, the "Performance Requirements" Article in Part 1 of the Section Text is usually not required; the design professional has completed the design.

If loads depart from uniformly distributed conditions, or if simply supported spans do not apply, the "Performance Requirements" Article may be required. Because design professionals lack information on detailed structural properties of joists, they usually delegate responsibility for the design of these joists to joist manufacturers. To resist special loads, the joist must be custom designed by a qualified structural engineer retained by the joist manufacturer. The Section Text defines these joists as special joists.

Joists have a high strength-to-weight ratio, and their use can result in structures that weigh less than comparable structures using structural steel alone. Joist stiffness can be a concern, particularly under some live loads where the relative flexibility of joists may affect the selection of roof systems or floor construction. Coordinate joist design and selection with roofing or flooring materials sensitive to deflection or vibration. SJI has published data to determine the vibration characteristics of steel joist and concrete-floor assemblies.

A performance-loading test of K-series joists is described in "Recommended Code of Standard Practice for Steel Joist and Joist Girders" in SJI's Specifications. The Section Text does not include an in-place load test. When a structural assessment determines that the load-carrying capacity of a completed structure or portion of a structure may be deficient, model building codes usually mandate in-place load-testing procedures.

If preconstruction load-testing procedures are required, include requirements in the "Quality Assurance" Article in Part 1 of the Section Text.

MATERIALS

Steel joists and joist girders may be fabricated from hot-rolled or cold-formed steel. The choice of steel type is usually left to the manufacturer, subject to complying with minimum strength requirements. SJI's Specifications requires that hot-rolled or cold-formed steel comply with one of a number of ASTM standards.

JOIST TYPES

SJI has developed standard specifications for four joist categories: K-, LH-, and DLH-series steel joists; and joist girders. These trusslike products are fabricated to each manufacturer's standard web configuration and top- and bottom-chord construction. Joist girders, open-web K-series steel joists, and LH-series long-span steel joists are designed for supporting floors and roof decks. The use of DLH-series long-span steel joists is limited to supporting roof decks.

The Section Text uses the generic term joists to include steel joists and joist girders. The joist category or subcategory is identified when necessary. The term underslung is used in SJI literature to describe joists configured for top-chord bearing. Similarly, joists with "square ends" are for bottom-chord bearing.

Individual manufacturers may offer nonstandard steel joists and joist girders as well as standard joists that comply with SJI's Specifications. In these cases, the manufacturer's design tabulations would be consulted in place of standard SJI specifications.

Open-web K-series steel joists are underslung open-web units fabricated with parallel chords. Although the other three joist categories have open-web configurations, only K-series joists have the words "open web" in their descriptions. Depths of open-web K-series joists range from 8 to 30 inches (203 to 762 mm) for maximum spans of 36 to 60 feet (11 to 18.3 m), respectively.

Unlike other joist types, the bottom chords of K-series steel joists may be fabricated with either steel angles or rods. Steel joists with steel-angle chords are inherently stronger than those fabricated from steel rods and provide greater resistance to deforming forces. Most K-series steel joists are made with steel angles as the bottom chord, but SJI's Specifications does not prohibit the use of steel rods. The Section Text requires top and bottom chords to be fabricated from steel angles.

For short simple spans, usually less than 96 inches (2400 mm), SJI recognizes K-series joist substitutes. Joist substitutes may be configured as single channel, back-to-back channel, or boxed angles 2-1/2 inches (64 mm) deep. Individual SJI members may also depict joist substitutes in cantilever conditions; refer to manufacturers' literature for span and loading limitations.

KCS-type joists have been identified in SJI's Specifications as a subcategory of the K-series joist. KCS-type steel joists have been designed to support a range of nonuniform and concentrated loads as well as uniform loads. Depths of these joists range from 10 to 30 inches (254 to 762 mm). Rather than listing maximum spans and loads, SJI's Specifications lists the moment and shear capacity and gross moment of inertia for each joist.

LH-series long-span steel joists are open-web units fabricated either underslung or square ended with top chords parallel or pitched one or two ways. Depths of these joists range from 18 to 48 inches (457 to 1219 mm) for maximum spans of 36 to 96 feet (11 to 29.3 m), respectively.

DLH-series deep long-span steel joists are open-web units fabricated either underslung or square ended with top chords parallel or pitched one or two ways. Depths of these joists range from 52 to 72 inches (1321 to 1829 mm) for maximum spans of 104 to 144 feet (31.7 to 43.9 m), respectively.

Joist girders are open-web steel units used as primary framing members fabricated with either underslung or square ends and extensions for laterally bracing the bottom chord if required. Designed as simply supported trusses to sustain equally spaced concentrated loads applied through steel joists, depths of joist girders range from 20 to 72 inches (508 to 1829 mm) for maximum spans of 20 to 60 feet (6.1 to 18.3 m), respectively.

JOIST EXTENSIONS

SJI recognizes a number of joist-extension conditions where cantilevering of the joist ends is required. These conditions include full-depth steel joist cantilevers, top-chord extensions, and extended ends.

Top-chord extensions and extended ends are conditions classified by SJI for open-web K-series joists. For uniform loading, published load tables are available for each condition. Type S top-chord extension has only the top chords extended. Type R extended ends maintain the full 2-1/2-inch (64-mm) bearing depth the length of the extension. Extended ends of other steel joists and joist girders require special design and are usually arranged according to the manufacturer's standard configuration. If particular configurations are required, consult manufacturers.

Ceiling extensions, either extended bottom chords or a loose unit for field attachment to the bottom chord, cantilever horizontally and close the gap between the bottom chord and adjacent walls. SJI's Specifications states that "ceiling extensions shall be furnished to support ceilings which are to be attached to the bottom of the joists. They are not furnished for the support of suspended ceilings." Ceiling extensions are considered unnecessary with suspended ceiling because hangers may be tied to any portion of the joist's web or top chord. Direct application of ceiling framing to joists without furring may lead to uneven ceilings because joist soffit elevations may vary.

END-BEARING DEPTHS

Bearing depths for underslung or top-bearing joists have been established by SJI as 2-1/2 inches (64 mm) for K series, 5 inches (127 mm) for LH series, 5 or 7-1/2 inches (127 or 191 mm) for DLH series, and 7-1/2 inches (191 mm) for joist girders.

A distinction should be made between the terms bearing depth and bearing length. Bearing depth is the vertical dimension above the bearing plate to the top of the joist. Bearing length, or bearing, is the extension or horizontal dimension of the joist in contact with the bearing plate.

CAMBER, PITCH, AND SLOPE

Steel joists and joist girders are fabricated with a positive camber, except for open-web K-series joists where camber is optional depending on the manufacturer. SJI's Specifications recommends a value for positive camber for K-series joists if camber is to be provided. Positive camber is the upward curvature measured at midlength of the top chord of the manufactured joist.

Many roofing systems and model building codes require a minimum roofing slope of 1/4 inch per 12 inches (1:48) or, with built-up coal-tar roofing systems, a maximum roofing slope that may not be exceeded. Besides using tapered roof insulation, measures to eliminate or reduce unwanted ponding of water on the roof include sloping joists to a low point or specifying joists with pitched top chords. Pitch may be one way where slope is in one direction or two ways where slope is in both directions.

Except for K-series joists that have top chords fabricated parallel or without pitch as standard, steel joists and joist girders may be fabricated with a top-chord pitch of 1/8 inch per 12 inches (1:96). This standard top-chord pitch will not be sufficient alone to meet the minimum 1/4 inch per 12 inches (1:48) slope requirement.

SJI standard load tables are valid for parallel-chord joists installed to a maximum slope of 1/2 inch per 12 inches (1:24). If the pitch of top chords exceeds 1/8 inch per 12 inches (1:96), standard load tables do not apply.

If the slope exceeds 1/4 inch per 12 inches (1:48), steel joists and joist girders may be provided with beveled ends or sloped shoes.

END SUPPORTS

SJI's Specifications requires that steel joists and joist girders bear on and be positively attached to steel bearing plates in concrete and masonry construction. Setting joists directly on concrete or masonry is not permitted. SJI's Specifications states that it is not the responsibility of the joist manufacturer to design, furnish, or install steel bearing plates. Nevertheless, recommendations for the location and critical minimum dimensions for steel bearing plates are stated for concrete and masonry construction to guide the design professional.

Steel bearing plates can be included in the Section Text of this Section or Division 5 Section "Metal Fabrications."

Open-web K-series joists require joist ends to extend not less than 4 inches (102 mm) over steel bearing plates embedded in concrete or masonry supports, and not less than 2-1/2 inches (64 mm) over structural-steel supports.

LH- and DLH-series steel joists and joist girders require underslung ends to extend a minimum of 6 inches (152 mm) over steel bearing plates embedded in concrete and masonry supports, and not less than 4 inches (102 mm) over structural-steel supports.

Joists with underslung ends, meeting over steel supports narrower than the sum of the minimum end-bearing lengths of each joist, require special ends. Positive attachment to steel supports is required by welding or bolting.

SURFACE PREPARATION

Steel components typically receive minimal surface preparation before shop priming during the standard joist manufacturing process. If finish painting or special coatings are needed in the completed building, more attention to surface preparation may be warranted.

SSPC: The Society for Protective Coatings (SSPC) has approved several specifications that describe alternative methods for preparing steel surfaces as a preliminary step before painting. Although not mentioned in SJI's Specifications, suitable preparation specifications are incorporated by referencing SSPC paint systems.

The open webs of joists are usually prepared by hand-tool cleaning (SSPC-SP 2) or power-tool cleaning (SSPC-SP 3). Blast cleaning of steel is not usually appropriate for joists. See the Evaluations in Division 5 Section "Structural Steel" and SSPC's Steel Structures Painting Manual, Systems and Specifications, Vol. 2, for further information.

The Section Text includes an option for surface preparation without priming if required, for example, if the primer is part of a paint system and is specified in Division 9.

PRIMERS

Primers approved by SJI are suitable for protecting joists from corrosion for a limited time during delivery, storage, and erection, and until further protected by other construction or coatings. Primers, however, do not provide significant corrosion resistance. They also do not withstand extended exposure to rain and weather, such as when joists are stored outdoors on the Project site.

Where steel joists do not require finish painting and normal humidity levels are maintained in-service, minor corrosion might be acceptable. Where finish painting is required, consider using a better-quality primer.

Where shop priming is not permitted, distinguish locations of primed and unprimed joists on the Drawings or in the Section Text. Shop priming is typically part of the production process during joist manufacture. Testing of the bond strength of sprayed fire-resistive materials (SFRM) to primed joists may be required to satisfy building code requirements. See the International Building Code, Section 1704.11.5.1, for an example where special inspections are required. Consider requiring the joist manufacturer to produce certification from SFRM manufacturers that the joist primer used has been satisfactorily tested for bond strength. Coordinate with bond strength testing in Division 7 Section "Sprayed Fire-Resistive Materials."

SJI's Specifications approves the following shop primers:

• SSPC-Paint 15



• A shop paint that complies with minimum performance requirements in SSPC-Paint 15

Specifying a proprietary primer may be preferred to eliminate all confusion. Carefully select the primer for compatibility with the finish coats. Some paint manufacturers offer "universal" steel primers suitable for almost any type of topcoat.

Surface preparation and priming can be specified in Division 9 painting and coating Sections.

FIRE-RESISTANCE RATINGS

Fire-resistance-rated, floor- and roof-ceiling assemblies using steel joists are described in Underwriters Laboratories' (UL) Fire Resistance Directory, Vol. 1, and in the publications of other rating bureaus. Fire-resistance-rated construction prescribes limits on the type, size, and spacing of steel joists; the method of fastening joists to supporting members; and the type of ceiling construction. SJI's Specifications includes a partial listing of UL design numbers for general installations. For direct-applied SFRM, rating bureaus require steel surfaces of joists to be clean and free of dirt, oil, and loose scale. There is usually no prohibition by rating bureaus on joist primers for compatibility; but this may not be true of building code requirements for bond strength. The use of metal lath or nonmetallic fabric mesh as an application aid may be optional with some rating bureau designs.

Consult authorities having jurisdiction to establish minimum requirements. Field testing of bond strength of SFRM to joists may be required for special inspections.

When K-series steel joists were introduced, there was a need to qualify them for use in the previously rated assemblies that were tested with the eliminated S-, J-, or H-series steel joists. SJI's Specifications presents substitution procedures for designing floor- and roof-ceiling assemblies.

INSTALLATION CONSIDERATIONS

End Connections: Joists must be field welded or bolted to embedded steel bearing plates in concrete or masonry construction, or be directly connected to steel supporting construction. Minimum welding and bolting-connection requirements are established by SJI's Specifications. Further design consideration is needed if nonuniform or uplift loading conditions are anticipated.

Bridging and Bracing: Permanently bracing joists to maintain stability and prevent overturning is accomplished by lines of bridging, where horizontal or diagonal members are attached to joists by bolting or welding. SJI's Specifications for the installation of bridging is explicit and varies according to joist type, chord size, and uplift forces. The minimum number of rows of bridging for K-series joists and the maximum spacing of bridging for LH- and DLH-series joists are also established.

If the Project design dictates alternate bridging requirements to SJI's Specifications, indicate such requirements on the Drawings. The bottom chords of joist girders typically require lateral bracing because they are erected without bridging. The top chord is considered braced by the steel joists bearing on it. Bottom-chord bracing is required to comply with SJI performance criteria and is standard with joist manufacturers.

Splicing: LH- and DLH-series joists and joist girders too long to be shipped in one piece may be transported in sections and field spliced according to the fabricator's design. High-strength bolts and steel splice plates are supplied by the joist manufacturer, and the joist is spliced before erection.

For more extensive information on steel joist erection, refer to SJI's Technical Digest #9, Handling and Erection of Steel Joists and Joist Girders.

REFERENCED STANDARDS

Publication dates represent the editions on which the current Section Text is based. Standards are revised periodically, which may occur before this Section is updated again.

American Welding Society

ASTM International

Master Painters Institute

Research Council on Structural Connections

SSPC: The Society for Protective Coatings

Steel Joist Institute

REFERENCES

The following publications are useful in specifying steel joists. Other references may be needed for design purposes.

Association Publications

Magazine Article

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