Scholarly article on topic 'Review of Experimental Studies of Cold-Formed Steel Channels with Slotted Webs under Bending'

Review of Experimental Studies of Cold-Formed Steel Channels with Slotted Webs under Bending Academic research paper on "Civil engineering"

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{"Thermal studs" / "channel beams" / "slotted webs" / "perforated webs" / bending / "direct strength method"}

Abstract of research paper on Civil engineering, author of scientific article — N.V. Degtyareva

Abstract The paper presents a review of experimental studies of cold-formed steel channels with perforated webs under bending. In the experimental studies five channels were tested under four-point bending and two channels were subject to a uniformly distributed load. A distortional buckling failure was observed in the tested channels. The flexural strength of the tested perforated channels was calculated using the direct strength method equations and compared with the test results. The direct strength method equations for beams with holes allowed to define precisely the flexural strength of the slotted channels for specimens tested under four-point bending.

Academic research paper on topic "Review of Experimental Studies of Cold-Formed Steel Channels with Slotted Webs under Bending"

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Procedia Engineering 206 (2017) 875-880 ^ ^

www.elsevier.com/locate/procedia

International Conference on Industrial Engineering, ICIE 2017

Review of Experimental Studies of Cold-Formed Steel Channels with Slotted Webs under Bending

N.V. Degtyareva*

South Ural State University, 76, Lenin Avenue, Chelyabinsk 454080, The Russian Federation

Abstract

The paper presents a review of experimental studies of cold-formed steel channels with perforated webs under bending. In the experimentpl studie s five channels were tested under four-point bending and two channels were subject to a uniformly distributed load. A distortiunal buckling failure was obsdrved in the testnd channels. The flexural strength of thc tested peeforated channels wad calculated using the direct strength method equations and compared wlth the test results. The direct strength method equations for beams with haies allowed to define precisely the flexuralstrength of the slotted channels her specimens testem under four-point bending.

©20 1 7 The Audhors. PuSKshed by Elsevier Ltd.

Pe2w-review nnd^r responsibilijy of the scientific committee of the International Conference on Industrial Engineering Keywords: Thermal studs; channel beams; slotted webs; perforated webs; bending; direct strength method.

1. Introduction

Cold-formed ste el channels with slotted webs aire used in building constructions to improvd their thermal aetfosmance ^3]. In spite of a widespread occurrence of these structures, they aae undersftidied. The existing deeign standards [4,I] lack recommendations on calculation of* coldmocmed steel channels with slotted webs. The compression and shear strength of such structures wed studied experimentany and theoreticany [6-][0]. The flexural strength of the cold-foemea steel structures with sk)tted webs was mainlm studied experimentally [11-14].

Detesmination of* the ultimate ben^ng capacity is cennected with material yielding, loc al bucking, distortional buckling, lateral-torsional buckling, and combinations thereof [11]. For open cross-sections distortional buckling is

* Corresponding author. Tel.: +7-351-267-9742 E-mail address: degtyareva_nv@mail.ru

1877-7058 © 2017 The Authors. Published by Elsevier Ltd.

Peer-review under responsibility of the scientific committee of the International Conference on Industrial Engineering. 10.1016/j.proeng.2017.10.566

determinant. Perforation in the beam web reduces the critical elastic distortional buckling moment, M& consequently, the distortional buckling capacity is also reduced [16].

Currently, there are formulas of the direct strength method [16] to determine the flexural strength of beams with holes. The direct strength method is an alternative to the effective width method and allows to define the flexural strength by the values of critical elastic buckling moments.

The objective of this paper is to review the results of the tests covering slotted channels under bending and to check applicability of the direct strength method equations for defining the flexural strength of cold-formed steel beams with slotted webs.

Nomenclature

H channel overall depth

B1 channel top flange width

B2 channel bottom flange width

t base steel thickness

Fy yield stress of steel

Fu tensile strength of steel

E modulus of elasticity (Young's modulus) of steel

L span length

Lload distance between two loading points

My yield moment

Mcrd critical elastic distortional buckling moment

Mcrf critical elastic local buckling moment

Mcre critical elastic lateral-torsional buckling moment

Mni nominal flexural strength for local buckling

Mne nominal flexural strength for lateral-torsional buckling

Mnd nominal flexural strength for distortional buckling

Mn nominal flexural capacity of channels

2. Review of Experimental Studies of Cold-For med Steel Channels with Perforated Webs

Cold-formed steel beams are generally tested under four-point bending [13,15,16]. However, in the paper [14] the beams were subject to a uniformly distributed load. Besides, in the paper [12] roof elements were subject to testing. The load was distributed using dividing beams. Two roof elements had the length of 5.4 m, other two roof elements were 7.2 m long. All the test specimens showed signs of local, distortional and lateral torsional buckling. The authors noted that it was difficult to determine, which type of buckling was the ultimate failure mode [12].

The papers [13,14] contain the fullest information on the initial data and test results. Therefore, these tests will be further considered.

2.1. Test Specimens, Test Set-Up, and Test Procedure

The paper [13] covered testing of five specimens of cold-formed steel beams. All the tested channels had webs stiffened with one longitudinal stiffener. The channel depth, thickness and span length varied. Cross-sections of the tested channels are shown in Fig.1(a,b). The channels had the nominal depths of 145 and 195 mm and the nominal thickness of 1.0, 1.3 and 1.5 mm. The perforation patterns of the channels are shown in Fig. 2 (a, b). The webs had nine and six staggered rows of perforations for the channels with the nominal depth of 195 mm and 145 mm, respectively.

The work [14] covered testing of two specimens of cold-formed steel beams with flat webs. The channels had the nominal depths of 150 and the nominal thickness of 1.0 mm. The cross-section of the tested channels is shown in

Fig. 1(c). Two perforation regions were provided in the webs of the channels. Each perforation region consisted of four staggered rows. The perforation pattern of the tested channels is shown in Fig. 2 (c).

The actual dimensions of the specimens and the mechanical properties of steel are given in Table 1.

f r-ll

9/ i ^ ■

Fig. 1. Cross-sectional dimensions of the channels with (a, b) stiffened [13] and (c) unstiffened [14] webs.

Fig. 2. Perforation patterns of the channels with (a, b) stiffened [13] and (c) unstiffened [14] webs. Table 1. Actual specimen properties and test results

Specimen H (mm) B1 (mm) B2 (mm) t (mm) Fy (MPa) Fu (MPa) E (MPa) L (mm) Lload (mm) Mtest (kNm)

PA-145-1.0 145.5 51.2 51,2 0.96 412 520 197453 3450 665 2.65

PA-145-1.5 145 51.05 51.05 1.46 405 493 199498 3450 665 5.42

PA-195-1.0 196 49.72 49.72 0.96 412 520 197453 3950 665 3.92

PA-195-1.5 195 51.3 51.3 1.46 405 493 199498 3950 665 6.80

PA-195-1.3 194.5 53,07 53,07 1.25 369 482 201733 2550 665 4.22

F19 148.5 39.25 43.5 0.98 350 - - 2500 - 1.55

F20 148.5 39.0 43.75 0.99 350 - - 2500 - 1.59

In the paper [13] all the specimens were tested under four-point bending. The distance between two loading points was the same for all the specimens. Beyond the constant moment region, the channel top and bottom flanges were fastened together with straps made of L20x20x2. The test set-up is shown in Fig. 3.

In the paper [14] both specimens were subject to a uniformly distributed load. The span length comprised 2500 mm. The channel top and bottom flanges were connected together with gypsum plasterboard plates. The load was gradually applied in ten points until the specimen was destroyed. The test set-up is shown in Fig. 4.

Fig. 3. Test set-up [13].

Roller support \ Plywood sheets 200\600xI b mm Pinned support/

Fig. 4. Test set-up [14].

2.2. Test Results

Table 1 presents flexural strengths of the channels tested in the studies [13,14].

Fig. 5 shows a failure mode of specimen F19. At the initial loading stages shear buckling near the supports was observed in specimens F19, F20. However, they were destroyed under distortional buckling. The specimens with the length of 3450 and 3950 mm tested in the paper [13] were also destroyed under distortional buckling. A rotation of the flange at the flange/web junction was observed.

Fig. 5. Failure mode of tests specimens [14].

3. Comparisons of the Test Results with the Available Design Equations

In order to define the flexural strength of cold-formed steel beams with holes the direct strength method equations are used [16]. In order to define the flexural strength of cold-formed steel channels it is necessary to use critical elastic buckling moments Mcre, Mcrl, and Mcrd determined by the finite element method. The nominal strength of a cold-formed steel channel with holes is a minimum value of the nominal flexural strength for lateral-torsional buckling, Mne, local-global buckling, Mnh and distortional buckling, M^.

In order to define critical elastic buckling moments Mcre, Mcrl, and Mcrd finite element models were created for each specimen. All tested beams were fully braced against lateral-torsional buckling therefore Mne = Mynet. The values of Mcre, Mcrh and Mcrd, the calculation results and a comparison with the test results are shown in Table 2.

Direct strength method predicted distortional buckling failure for all tested specimens. The distortional buckling capacity of specimens PA-145-1.0, PA-145-1.5, PA-195-1.0, PA-195-1.5 was defined with a high accuracy. The direct strength method resulted in an overestimated flexural strength for specimen PA-195-1.3. The value of MteJMn ratio comprised 0.73. It is connected with the fact that it was shorter than the remaining ones, therefore, it was probably destroyed under combined bending and shear. The direct strength method significantly underestimated the flexural capacity of specimens F19 and F20. The maximum value of Mtes/Mn ratio comprised 1.42.

Table 2. DSM nominal flexural strength of slotted channels with elastic buckling loads from ANSYS compared with Mtest.

Specimen My (kNm) Mcrd (kNm) Mcrl (kNm) Mne (kNm) h Mnl (kNm) hd Md2 (kNm) Mnd (kNm) Mn (kNm) Mtest/ Mn

PA-145-1.0 4.75 3.44 3.75 4.70 1.12 3.70 1.17 4.67 3.20 3.20 0.83

PA-145-1.5 6.8 6.94 12.06 6.73 0.75 6.73 0.99 6.69 5.35 5.35 1.01

PA-195-1.0 6.94 4.16 3.81 6.82 1.34 4.76 1.29 6.76 4.28 4.28 0.92

PA-195-1.5 10.31 7.46 12.20 10.13 0.91 9.15 1.18 10.04 6.95 6.95 0.98

PA-195-1.3 8.20 6.47 9.52 8.06 0.92 7.23 1.13 7.99 5.75 5.75 0.73

F19 3.55 0.57 0.26 3.40 3.60 1.16 2.49 3.32 1.10 1.10 1.41

F20 3.57 0.59 0.27 3.42 3.56 1.17 2.45 3.33 1.12 1.12 1.42

4. Conclusion

The literature review has shown that there are no recommendations on determination of the flexural strength of cold-formed steel channels with slotted webs. Therefore, this work reviews tests of cold-formed steel channels with perforated webs under bending. Only several works deal with tests of cold-formed steel channels with slotted webs under bending. However, they are valuable, whereas they can form the basis for creation and validation of finite element models for numerical studies.

The direct strength method allowed to define with a high accuracy the flexural strength of the channels with the span length of 3450 and 3950 mm tested under four-point bending. The direct strength method significantly underestimated the flexural capacity of the channels subject to a uniformly distributed load. The comparison is insufficient to make a conclusion on applicability of the direct strength method for determination of the flexural strength of perforated channels. A wider data set is needed for a better comparison.

Therefore, within the framework of further researches we will create and validate finite element models to carry out numerical and parametric studies.

Acknowledgements

The work was supported by Act 211 Government of the Russian Federation, contract # 02.A03.21.0011.

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