Elsevier

Structures

Volume 27, October 2020, Pages 1299-1312
Structures

Lateral distortional buckling in steel-concrete composite beams: A review

https://doi.org/10.1016/j.istruc.2020.07.026Get rights and content

Highlights

  • A critical review of LDB in steel-concrete composite beams is presented.

  • Studies that have investigated the LDB elastic critical moment are compared.

  • Experimental and numerical investigations on the LDB strength were presented.

  • Conservative situation of standard procedures was verified compared to experimental and numerical results.

  • Future research directions were presented.

Abstract

Steel-concrete composite beams, when requested by negative moment, can fail due to Lateral Distortional Buckling (LDB), local buckling, by a combination of these stability modes or achieve the plastic behavior. LDB is a mode of stability in which the web must distort in order for the compression flange to displace and twist during buckling. Several papers were published in an attempt to clarify the LDB behavior of steel-concrete composite beams. These papers can be divided into two strands of studies. The first that seeks to investigate the elastic behavior of the LDB, in an attempt to determine the elastic critical moment, through bifurcational equilibrium analyzes. And the second strand, which investigates the LDB strength of steel-concrete composite beams, through the development of experimental investigations or by non-linear numerical analyzes. However, there is still no consensus regarding the behavior of LDB in steel-concrete composite beams. Researchers who investigated the elastic behavior of LDB show divergences between the methodologies for determining the elastic critical moment. Furthermore, the publications that are aimed at investigating the LDB strength, show inconsistencies in the standard procedures. Therefore, the main objective of this article is to present a critical review about LDB in steel-concrete composite beams. For this purpose, the main studies that analyzed the elastic and inelastic behavior of LDB are presented, in addition to an overview of the main standard procedures. Finally, the future research directions have been discussed, presenting parameters that still need further investigation.

Introduction

The first steel-concrete composite elements used in civil construction were the composite beams. Using the best characteristics of each material, seek an appropriate interaction of them, in order to obtain high performance structures. Steel-concrete composite beams have their established use, through the interaction of the steel profile with different types of slab [1], [2], [3]. In recent years, with the increase in the industrialization of civil construction, the use of steel-concrete composite beams has increased [4], [5], [6]. This increase is due to its construction speed, in addition to structural and economic advantages.

The most common use of steel-concrete composite beams occurs in simply supported elements and therefore subjected to positive sagging moments. Consequently, the concrete slab is in compression and the steel profile is in tension [7]. However, in the construction of buildings the use of rigid and semi-rigid connections has been frequent, causing negative moments in the beams which leads to tensile stresses in the concrete slab and compression in the steel profile [8], [9], [10]. Compression stresses in the bottom flange of the steel profile, without lateral restrain, can cause lateral stability with web distortion, called in this work Lateral Distortional Buckling (LDB) (Fig. 1) [4], [11], [12], [13], [14].

LDB is characterized by a lateral displacement (δ) accompanied by a rotation (θ) of the compressed bottom flange that occurs due to the web distortion, if it is not rigid enough to withstand lateral flexion (Fig. 1) [11], [15]. As a result, LDB in steel-concrete composite beams behaves very differently from the stability modes of steel elements (I-beams), in a way that the well-known Vlasov assumption [16], that the plane-webbed sections still forms a plane, not valid.

In order to solve this problem, investigations were published about LDB in steel-concrete composite beams. These investigations focused on analyzing the elastic behavior of LDB [1], [6], [24], [25], [26], [27], [28], [29], [30], [31], [9], [17], [18], [19], [20], [21], [22], [23], in an attempt to obtain a method for determining the elastic critical moment, or sought to analyze the LDB strength of steel-concrete composite beams [4], [12], [13], [14], [15], [32], [33], [34], [35], [36], [37], [38], [39], [40], [41]. However, it appears that there is still no consensus in the proposed methodologies, since divergences are observed in the determination of the elastic critical moment, when comparing with results calculated by numerical analysis, and also, when the methodologies are compared to each other. Another situation is the verification of divergence between the ultimate moment results obtained through experimental tests or numerical analyzes with the procedures presented by the North American standards [43], [44] (AISC 360-16 and AASHTO 2017) European [45] (EN 1994-1-1-2004), Australian [46], [47] (AS4100: 1998-R2016 and AS/NZS2327-2017) and Brazilian [48] (ABNT NBR 8800: 2008).

Therefore, this paper aims to summarise, review, and assess studies about the theoretical research, numerical simulations, experimental investigations, and standard procedures about the Lateral Distortional Buckling (LDB) in steel-concrete composite beams. At the end, the standard procedures and analytical proposals are compared to each other and an analytical study is carried out with the standard procedures. This paper also highlights the remaining challenges and possible future researches on LDB in steel-concrete composite beams.

Section snippets

Lateral distortional buckling: Review

LDB is fundamentally different from lateral torsional buckling (LTB), because the Vlasov hypothesis [16] that the cross section remains without distortion is not applicable, since the LDB is characterized by a lateral and torsional buckling of the compressed flange accompanied by a web distortion [49]. However, the LDB phenomenon in continuous steel-concrete composite beams is generally conservatively assessed in the standard codes as being a type of LTB. Bradford and Johnson [36] showed that

LDB standard procedures

The standard procedures that address this phenomenon use the conventional lateral-torsional buckling theories for the buckling of partially restrained beams or the inverted U-frame model. Eurocode 4 (EN 1994-1-1) [45] deals with the lateral buckling of continuous composite beams by reducing the section plastic moment resistance at the internal support, Mpl, to a lower value, Mu,dist, referred to the beam buckling strength (Eqs. (16)–(19)). Because the composite beam is one of several parallel

Discussions

The understanding of LDB behavior on steel-concrete composite beams still generates discussions and doubts. As presented, many studies seek to find a way to better determine the LDB strength of steel-concrete composite beams. For this, several researchers have investigated the LDB elastic behavior by determining the elastic critical moment. However, as presented, there is still no consensus in determining the elastic critical moment. Investigations show that the results of elastic critical

Conclusion

This study presents a critical review of LDB in steel-concrete composite beams. The main studies that analyzed the elastic and inelastic behavior of LDB are presented, in addition to an overview of the main standard procedures. Finally, the future research directions have been presented, showing parameters that still need further investigation. In this way, it was concluded:

  • There are divergences between methodologies used to determine the LDB elastic critical moment;

  • Experimental and numerical

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This study was financed by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001.

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