Elsevier

Thin-Walled Structures

Volume 167, October 2021, 108193
Thin-Walled Structures

Full length article
Stability behavior of Steel–concrete Composite Beams subjected to hogging moment

https://doi.org/10.1016/j.tws.2021.108193Get rights and content

Highlights

  • Buckling and post buckling numerical analyses are performed.

  • LDB and LB were the failure modes observed.

  • Divergences between the values of LDB elastic critical moment obtained in the buckling analysis and analytical procedures were verified.

  • The slab height is an important factor for the analysis of steel–concrete composite beams under hogging moment.

  • The SSRC ”2P” design curve provides more realistic results of LDB strength than ECCS curves.

Abstract

The behavior of Steel–concrete Composite Beams (SCCB) under the action of hogging moment is not yet fully understood. In this condition, these structural elements may be subjected to local buckling or Lateral Distortional Buckling (LDB). LDB is a mode of stability in which the web must distort in order for the compression flange to displace and twist during buckling. The classic LDB standard procedures start from the determination of the elastic critical moment and subsequently use empirical curves to determine the LDB strength. However, investigations show that there is no consensus in determining the LDB elastic critical moment. In addition, studies indicate that the use of the same empirical curves obtained for the analysis of steel I-beams leads to the conservative results of the LDB strength in SCCB. In this context, this paper investigates the behavior of SCCB under the action of hogging moment through the development of buckling and post-buckling numerical analyses with the ABAQUS software. In the parametric study, the effects of the I-section, the unrestrained length, the reinforcing ratio, the concrete slab height and the slab topology were investigated. The investigations showed divergences between the elastic critical moment and ultimate moment when compared with classic procedures. In addition, the influence of the analyzed parameters is presented. These results can provide a reference for future research and specification reviews.

Introduction

Steel–concrete composite beams (SCCB) under hogging moment may fail due to the occurrence of Local Buckling (LB) modes, Lateral Distortional Buckling (LDB) or through the combination of these buckling modes [2], [3]. LDB (Fig. 1) is characterized by a web distortion due to lateral displacement (δ) and rotation (θ) of the unrestricted bottom flange [1], [4], [5], [6], [7], [8]. This displacement and rotation occur due to the fact that the top flange is totally restrained, through the concrete slab, to the lateral displacement [9]. As a result, LDB in SCCB behaves very differently from the stability modes of steel I-beams, in a way that the well-known Vlasov assumption [10], that the plane-webbed sections still forms a plane, not valid.

In order to solve this problem, investigations were carried out about LDB in SCCB. These investigations focused on analyzing the elastic behavior [4], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26] in an attempt to obtain a method for determining the elastic critical moment, or sought to analyze the LDB strength of SCCB [1], [2], [6], [7], [8], [27], [28], [29], [30], [31], [32], [33], [34]. The correct determination of the LDB elastic critical moment is fundamental to resolve the LDB strength. The current standard procedures require the elastic distortional critical moment determination to estimate the LDB strength of SCCB. In the EC4 [35] previous version (EN 1994-1-1:1992), the methodology proposed by Roik et al. [16] to determine the elastic distortional critical moment was adopted. This methodology is still used in the Brazilian code [36] (ABNT NBR 8800:2008). However, studies [11], [20], [21] have shown divergences between elastic distortional critical moment, obtained through numerical analysis, when compared with the methodologies proposed by Roik et al. [16], Svensson [13], Williams and Jemah [14] and Hanswille et al. [18]. Therefore, the use of these methodologies for the elastic distortional critical moment estimation can result in the mistaken obtaining of the strength of SCCB under the action of hogging moment by the standard procedures. In addition, standard codes such as Eurocode 4 [37], AISC [38], AASHTO [39], NBR 8800:2008 [36] and Australian codes [40], [41] make use of the same design curves proposed for steel elements to determine the LDB strength of SCCB. Rossi et al. [2], Zhou and Yan [1] and Liu et al. [8] showed very conservative situations in the standard codes when compared with FEA (Finite Element Analysis) results obtained for SCCB subjected to uniform hogging moment. In this context, there is a need for further investigation into the instability modes of SCCB, as the estimation of the strength of these elements is not yet fully understood.

Therefore, this paper aims to investigate the behavior of SCCB under the action of hogging moment. For this, buckling and post-buckling numerical analyzes with the ABAQUS [42] software were developed. With the buckling analysis it is possible to determine the elastic critical moment, which is compared with the analytical procedures present in the literature. In the post-buckling numerical analysis, the initial geometric imperfection, residual stress, real shear connector, geometric nonlinearity, and material nonlinearity were considered. These results are compared with standard and analytical procedures. The beams are considered simply supported, with restrictions on lateral slab displacement and are subjected to a uniform hogging moment distribution. The influences of the following parameters are analyzed: longitudinal reinforcement ratio, different I-sections, unrestrained span length, the slab height and the differences in the use of solid slabs and precast hollow core slabs. The analyses showed in this work can provide a reference for future research and specification reviews.

Section snippets

Literature review

SCCB can be used as simply supported elements and therefore subjected to sagging moments. Consequently, the concrete slab is in compression and the steel I-section is in tension [43]. However, in the construction of buildings the use of rigid and semi-rigid connections has been frequent, causing hogging moments in the beams which leads to tensile stresses in the concrete slab and compression in the steel I-section [4], [44], [45]. Compression stresses in the bottom flange of the steel

LDB standard and analytical procedures

The standard procedures that address the LDB 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) [37] considers the inverted U-frame model in determining the LDB elastic critical moment and uses the same design curves developed for the LTB analysis in I-beams. The Brazilian standard code, ABNT NBR 8800:2008 [36], is also based on the inverted U-frame model to determine of the

Numerical model

For the development of numerical analyses, the ABAQUS software [42] was used. With this software it is possible to develop elastic buckling analyses and post-buckling analyses (physical and geometric nonlinear analyses). For the elastic buckling analysis, the buckle linear perturbation method was used to estimate the critical elastic stability load by obtaining eigenvalues and their eigenvectors. In this method, the critical elastic stability load is obtained by the product of the first

Numerical model verification

The numerical model developed to analyze the behavior of SCCB with solid slab under hogging moment was validated in the previous papers, Rossi et al. [2], [58], through the experimental tests of Tong et al. [66]. However, as no experimental study in SCCB with PCHCS under hogging moment has been found in the literature, Lam’s [75] experimental tests (sagging moment), also presented by Lam, Elliott and Nethercott [76], were analyzed to verify the validity of the numerical model developed with

Parametric study

In the parametric study, the LDB elastic critical moment and the LDB strength of SCCB was investigated. For this, buckling and post-buckling numerical analysis were performed in the ABAQUS software. The influence of the following factors on the stability phenomenon of SCCB was investigated: I-section, unrestrained length, longitudinal reinforcement ratio, the slab height and the possible influence of solid slabs and PCHCS on the behavior of SCCB under hogging moment. The composite beams were

Results and discussion

The analysis developed in this paper aimed to investigate the stability behavior of SCCB under the action of uniform hogging moment distribution by analyzing the occurrence of LDB and local stability modes. The following parameters were investigated: I-section, unrestrained length, longitudinal reinforcement ratio, the slab height and the possible influence of solid slabs and PCHCS. The results of the numerical buckling analysis were compared with the elastic critical moment values obtained by

Conclusion

This study investigated the stability behavior of SCCBs under uniform hogging moment. Buckling and post-buckling numerical analyses were performed using ABAQUS software. The following parameters were investigated: I-section, unrestrained length, longitudinal reinforcement ratio, the slab height and the possible influence of solid slabs and PCHCS. The buckling analysis results were compared with the LDB elastic critical moment values obtained by analytical procedures. Posteriorly, the

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.

Acknowledgment

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

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