Steel Joists Research Articles

Design of cold-formed compression web members with periodically varying section properties

In this paper, a design procedure for cold-formed channels periodically closed on their open face and utilized as joist web members is detailed. The design method for periodically closed sections is based on the representation of the cross-sectional properties using Fourier series introduced in Timoshenko quotients for the determination of the buckling loads about each of the three member axes. Once those loads are computed, they are used in the current framework of the North American Specification for the design of cold-formed structures with appropriate effective length coefficients. The proposed design methodology is compared with test results obtained from 36 stub column samples and 21 full-scale joist specimens, also presented in this paper.Key words: cold-formed struts, periodically varying cross sections, steel joists, flexural–torsional buckling, effective length coefficients.

Nucor Corp.

AbstractMetal Works (MIC: 11.3 SIC: 3312 NAIC: 331111)Nucor is engaged in the manufacture and sale of steel and steel products. Co.'s principal products from the steel mills segment are hot‐ and cold‐rolled steel, while its steel products segment produces steel joists and joist girders, steel deck, cold finished steel, steel fasteners, metal building systems and light gauge steel framing. Co.'s steel joists and hoist girders, and steel deck are sold to general contractors and fabricators domestically. Co.'s cold finished steel and steel fasteners are sold primarily to distributors and manufacturers, and hot‐rolled steel and cold‐rolled steel are sold primarily to steel service centers, fabricators and manufacturers throughout the U.S.

Flexural strength of cold-formed steel joists with reinforced web openings

The floor joists of cold-formed steel (CFS) structures often require large web openings. Reinforcement of such openings may mitigate the detrimental effects of such web openings. This paper is based on an experimental investigation that considered 203 mm deep (base thickness 1.89 mm) galvanized, lipped channel sections with circular, square, and rectangular openings and two associated reinforcement schemes (screw fastening of 31.8 mm × 1.1 mm thick bridging channel). Since the focus of this investigation was on the flexural strength of such joists, the test specimens were simply supported and were subjected to two equal point loads at equal distance from the supports. Two lipped channel sections were set face-to-face to form the test specimen assembly. Based on 11 sets of three identical flexural tests, it was determined that (i) the tension zones of the web with a large opening need not be reinforced, (ii) closely spaced screw fastening of reinforcements (bridging channel) is essential, and (iii) the reinforcements need to be fastened as close as possible to the compression edges of the opening to minimize local buckling of these edges. This paper demonstrates that it is possible to establish cost-effective reinforcement schemes for CFS sections with large web openings.Key words: cold-formed steel, joists, flexural strength, web openings, reinforcements, experimental.

Buckling Strength of Single Angle Compression Members in K-Series Joists

Single angle web members in open web steel joists are typically crimped to facilitate web placement and maintain a constant chord gap with varying web angle size. If the web members are not crimped force eccentricity will exist between the web member's area centroid and the vertical plane of symmetry for the joist. The analytical consequence of this eccentricity is that uncrimped single angle web members must be designed as eccentrically loaded columns. The resulting interaction design strength is significantly less than the concentric column analysis design strength used for crimped web members of identical cross section and slenderness. This study compares the measured and analytical strengths of like single angle L1x1x7/64 inch crimped and uncrimped web members in steel joists. Experimental results from 18 joist samples show that existing analytical assumptions associated with end fixity and beam-column interaction result in an overly conservative design methodology for both crimped and uncrimped web members.

Short- and long-term analyses of composite beams with partial interaction stiffened by a longitudinal plate

This paper presents a novel analytical formulation for the analysis of composite beams with partial shear interaction stiffened by a bolted longitudinal plate accounting for time effects, such as creep and shrinkage. The model is derived by means of the principle of virtual work using a displacement-based formulation. The particularity of this approach is that the partial interaction behaviour is assumed to exist between the top slab and the joist as well as between the joist and the bolted longitudinal stiffening plate, therefore leading to a three-layered structural representation. For this purpose, a novel finite element is derived and presented. Its accuracy is validated based on short-and long-term analyses for the particular cases of full shear interaction and partial shear interaction of two layers for which solutions in closed form are available in the literature. A parametric study is carried out considering different stiffening arrangements to investigate the influence on the short-and long-term behaviour of the composite beam of the shear connection stiffness between the concrete slab and the steel joist, the stiffness of the plate-to-beam connection, the properties of the longitudinal plate and the concrete properties. The values of the deflection obtained from the finite element simulations are compared against those calculated using the effective flexural rigidity in accordance with EC5 guidelines for the behaviour of elastic multi-layered beams with flexible connection and it is shown how the latter well predicts the structural response. The proposed numerical examples highlight the ease of use of the proposed approach in determining the effectiveness of different retrofitting solutions at service conditions.

Design parameters for impact sound insulation in lightweight wood and steel structures

One of the challenges in the acoustical design of multifamily wood and steel joist buildings is reducing low-frequency sounds from footfalls on both carpeted and isolated hard-surfaced floors. Theoretical calculations and field-testing experience indicate that low-frequency impact noise in lightweight structures is clearly audible, and that traditional isolation methods do not reduce low-frequency impact noise to inaudibility [Blazier and DuPree, J. Acoust. Soc. Am. 96, 1521–1532 (1994)]. We report numerous measurements performed on wood-frame assemblies in the United States using the tapping machine method as defined in ASTM E1007. The impact sound-pressure level was measured down to the 20-Hz third-octave band, instead of 100 Hz as described in the standards. Representative case studies will be presented showing the effect of changes in construction on occupant complaints. The results indicate that the unweighted level in the 50–80 Hz third-octave bands correlates much better with occupant reaction than any of the other metrics [LoVerde and Dong, J. Acoust. Soc. Am. 112, 2201 (2002); LoVerde and Dong, INCE Inter-Noise 2004 Proceedings, 167 (2004)]. Factors in the design of successful lightweight floor/ceiling assemblies, including structural design parameters, shall be presented along with corresponding acoustical performance and subjective reactions.

Distortional Buckling Tests on Cold-Formed Steel Beams

Failure in cold-formed steel beams is generally initiated by one of three instabilities: local, distortional, or lateral-torsional buckling. For cold-formed steel joists, purlins, or girts, when the compression flange is not restrained by attachment to sheathing or paneling, distortional buckling may be the predominant failure mode. Experimental results on cold-formed steel beams with unrestrained compression flanges are scarce. Therefore a series of distortional buckling tests on cold-formed steel C and Z sections in bending was conducted to establish the capacity in distortional buckling failures. Test details were selected to allow distortional buckling to form, but restrict lateral-torsional buckling to the extent possible. These distortional buckling tests also provide a direct comparison against the local buckling tests previously performed by the writers. As expected, large strength reductions are observed in the tested specimens when distortional buckling initiated the failure instead of local buckling. U.S., Canadian, and joint North American standards for design, which are known to primarily focus on local buckling, provided unconservative predictions of the observed strength. The Australian/New Zealand Standard and the direct strength method, which provide explicit methods for calculating the capacity in the distortional buckling mode, provided reasonably accurate and reliable predictions.

Bracing of Beams, Trusses, and Joist Girders Using Open Web Steel Joists

Designers typically use joists as a part of the lateral bracing for the compression flange of beams, or for the lateral bracing of the top chord of trusses and joist girders. Joists serve as the connection to the primary members to deliver the brace force to a diaphragm or horizontal bracing system. The attachment of the joist seat to the primary member is an important element of the bracing system. Traditionally joist seats have been attached to primary members (beams, trusses, and joist girders) by welding. The OSHA Steel Erection Standard, Part 1926.757 - Open Web Steel Joists states: (i) Except for steel joists that have been pre-assembled into panels, connections of individual steel joists to steel structures in bays of 40 ft (12.2 m) or more shall be fabricated to allow for field bolting during erection; (ii) These connections shall be field-bolted unless constructability does not allow. The purpose of this paper is to discuss possible alternatives to welding the joists to the primary members in order to provide bracing to the primary members.

Analytical Solutions for the Viscoelastic Response of Composite Beams Including Partial Interaction

This paper addresses the issue of the deformations that occur in composite steel-concrete beams caused by the quasi-viscoelastic effects of creep and shrinkage of the concrete slab, and in which the effects of partial shear interaction (PI) at the interface between the slab and the steel joist are included in the analysis. By making recourse to an algebraic representation of the viscoelastic response of the concrete, the formulation in this paper leads to a unique and useful solution of the problem in closed form, which follows from the establishment of a second order linear differential equation. The solution therefore does not require a discretisation along the beam as is usually required for numerical techniques, but only one discretisation in the time domain, and furthermore the resulting solution is generic in the sense that it may be applied for a variety of loading and restraint conditions. Specific solutions, which are validated against a numerical technique reported elsewhere, are presented for the cases of a simply supported beam, an encastré beam and for a propped cantilever.

Nucor Corp.

AbstractMetal Works (MIC: 11.3 SIC: 3312 NAIC: 331111)Nucor is engaged in the manufacture and sale of steel and steel products. Co.'s principal products from the steel mills segment are hot‐ and cold‐rolled steel, while the steel products segment produces steel joists and joist girders, steel deck, cold finished steel, steel fasteners, metal building systems and light gauge steel framing. Steel joists and hoist girders, and steel deck are sold to general contractors and fabricators domestically. Cold finished steel and steel fasteners are sold primarily to distributors and manufacturers, and hot‐rolled steel and cold‐rolled steel are sold primarily to steel services centers, fabricators and manufacturers in the U.S.

Nucor Corp.

Mergent's Dividend AchieversVolume 3, Issue 2 p. 204-204 U.S. Company Reports Nucor Corp.† First published: 20 April 2006 https://doi.org/10.1002/div.4012 † Contact: : Peter C. Browning — Chmn. Address: : 2100 Rexford Road, Charlotte, NC 28211 Web Site: : www.nucor.com AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Abstract Metal Works (MIC: 11.3 SIC: 3312 NAIC: 331111) Nucor is engaged in the manufacture and sale of steel and steel products. Co.'s principal products from the steel mills segment are hot- and cold-rolled steel, while the steel products segment produces steel joists and joist girders, steel deck, cold finished steel, steel fasteners, metal building systems and light gauge steel framing. Steel joists and hoist girders, and steel deck are sold to general contractors and fabricators domestically. Cold finished steel and steel fasteners are sold primarily to distributors and manufacturers, and hot-rolled steel and cold-rolled steel are sold primarily to steel services centers, fabricators and manufacturers in the U.S. Volume3, Issue2Spring 2006Pages 204-204 RelatedInformation

Strengthening Open-Web Steel Joists

The paper presents procedures and suggested details for the strengthening of open web steel joists. Strengthening of open web steel joists is often required due to the addition of roof top units, under hung conveyors, or other loading increases not contemplated in the original specification for the joists. Three basic methods of strengthening a joist or joist system are discussed: load redistribution, adding new joists or beams, and reinforcing existing joists.

Nucor Corp.

AbstractMetal Works (MIC: 11.3 SIC: 312 NAIC: 31111)Nucor is engaged in the manufacture and sale of steel and steel products. Co.'s principal products from the steel mills segment are hot‐ and cold‐rolled steel, while the steel products segment produces steel joists and joist girders, steel deck, cold finished steel, steel fasteners, metal building systems and light gauge steel framing. Steel joists and hoist girders, and steel deck are sold to general contractors and fabricators domestically. Cold finished steel and steel fasteners are sold primarily to distributors and manufacturers, and hot‐rolled steel and cold‐rolled steel are sold primarily to steel services centers, fabricators and manufacturers in the U.S.

Time analysis of structural concrete elements using the equivalent displacement method

This paper presents a modelling technique referred to as the equivalent displacement method (EDM) which describes the behaviour in time of structural concrete elements, such as reinforced concrete beams and composite beams with full shear interaction, accounting for time effects, such as creep, of the concrete component. The time-dependent behaviour of the concrete is modelled using the algebraic representations, such as the age-adjusted effective modulus method (AEMM), while the steel joist and reinforcement are assumed to behave in a linear-elastic fashion. The main advantage of the EDM method is that it requires only one analysis to obtain the deformation state of the structural system at one step in time based on the AEMM methods, instead of the two required by available modelling techniques (i. e. one performed at timet 0 and one performed one step in timet). The EDM method is then applied to the analysis of structural concrete elements using the stiffness analysis and the results obtained based on this modelling technique are validated against other modelling methods. The advantages of using the EDM method in design applications are also illustrated.

Nucor Corp.

AbstractMetal Works (MIC: 11.3 SIC: 3312 NAIC:331111)Nucor is engaged in the manufacture and sale of steel and steel products. Co.'s principal products from the steel mills segment are hotand cold‐rolled steel, while the steel products segment produces steel joists and joist girders, steel deck, cold finished steel, steel fasteners, metal building systems and light gauge steel framing. Steel joists and hoist girders, and steel deck are sold to general contractors and fabricators domestically. Cold finished steel and steel fasteners are sold primarily to distributors and manufacturers, and hot‐rolled steel and cold‐rolled steel are sold primarily to steel services centers, fabricators and manufacturers in the U.S.

Nucor Corp.

AbstractMetal Works (MIC: 11.3 SIC: 3312 NAIC:331111)Nucor is engaged in the manufacture and sale of steel and steel products. Co.'s principal products from the steel mills segment are hot‐ and cold‐rolled steel, while the steel products segment produces steel joists and joist girders, steel deck, cold finished steel, steel fasteners, metal building systems and light gauge steel framing. Steel joists and hoist girders, and steel deck are sold to general contractors and fabricators domestically. Cold finished steel and steel fasteners are sold primarily to distributors and manufacturers, and hot‐rolled steel and cold‐rolled steel are sold primarily to steel services centers, fabricators and manufacturers in the U.S.

Nucor Corp.

AbstractMetal Works (MIC: 11.3 SIC: 3312 NAIC:331111)Nucor is engaged in the manufacture and sale of steel and steel products. Co.'s principal products from the steel mills segment are hot‐ and cold‐rolled steel, while the steel products segment produces steel joists and joist girders, steel deck, cold finished steel, steel fasteners, metal building systems and light gauge steel framing. Steel joists and hoist girders, and steel deck are sold to general contractors and fabricators domestically. Cold finished steel and steel fasteners are sold primarily to distributors and manufacturers, and hot‐rolled steel and cold‐rolled steel are sold primarily to steel services centers, fabricators and manufacturers in the U.S.

Strength and Design of Open Web Steel Joists with Crimped-End Web Members

Open web steel joists are prefabricated truss-type members economical for use in floor and roof support systems for lightly loaded structures. Joists are designed in accordance with the specifications and standard load tables published by the Steel Joist Institute. An experimental study was conducted to determine strength and general flexural behavior of open web steel joists having L1 in.×1 in.×1/8 in. single angles with crimped ends for web members. Crimping the ends of the web members allows them to be aligned symmetrically with respect to the centerline of the joist, thereby eliminating the effects of eccentric loading in the web members. The purpose of the tests was to observe overall flexural behavior based on failure loads, deflections, and strains in the top and bottom chords. Outcomes from the study show that there is considerable rotational restraint in the web members at the panel points. Based on the parameters tested, an effective length factor is recommended that is less than that corresponding to a pin ended column. Finally, using the more accurate measure of rotational stiffness at the joints, revised service loads are recommended.

Composite Steel Joists

Composite steel construction has been recognized for a number of years as one of the most economical systems for constructing building floors. Three options have evolved over the years to meet the requirements for building height limitations and the need to run complex heating, ventilating, electrical, and communication systems: (1) Composite wide flange beams with web openings; (2) Stub girders; and (3) Open web steel joists and joist girders. This paper focuses on the advantages associated with composite open web steel joists, development and testing of open web steel joists, behavior of welded shear studs observed while testing composite joists, case histories of projects using composite joists, unique vibration considerations associated with joist floors, and current status of composite joist specification development.

Development of a new damper to reduce resonant vibrations in lightweight steel joist floors

Floor vibrations annoying to humans often occur in lightweight constructions. A number of methods to solve the problem of resonant vibrations are reported in the literature. Tuned mass damper, semi-active tuned vibration absorber and active control system are all examples of existing methods. A new method has been tested in laboratory environment on a prefabricated floor containing a resilient ceiling with a size up to 6.8×4.8 m 2. The method takes advantage of small pieces of visco-elastic material connected between the ceiling joists and the primary beams. A finite element model is used to calculate the correct amount of visco-elastic material. The new damper is especially effective in damping mode shapes where the ceiling oscillates out of phase relative to the floor but shows improvements for other mode shapes as well.