Elsevier

Structures

Volume 28, December 2020, Pages 863-877
Structures

Compressive behavior of steel-reinforced concrete-filled circular steel tubular stub columns

https://doi.org/10.1016/j.istruc.2020.08.012Get rights and content

Abstract

Steel-reinforced concrete-filled circular steel tubular (SRCFT) stub columns is a novel type of composite columns, which have a great potential to be used as piers or columns in practical engineering. Hence, it is essential to comprehend the compressive performance of SRCFT stub columns and suitably predict the compressive strength for the engineering design and applications. This paper aims to investigate the compressive behavior of SRCFT stub columns through combined experimental and numerical studies. A total of 8 specimens were tested to investigate the compressive performance of SRCFT stub columns in detail, in terms of the axial load-strain curve, ultimate bearing capacity, ductility, strength-weight-ratio and strain ratio. The SRCFT stub columns exhibited better ductility than CFT stub columns. The inserted steel section can effectively prevent shear cracks in the core concrete from propagating quickly. Furthermore, finite element model was established and verified by comparing the experimental and FE results. Then, the complex composite action among the steel tube, core concrete and steel section was discussed and clarified comprehensively. In addition, the capacity of the energy dissipation for SRCFT stub columns was discussed. Finally, a novel simplified formula was proposed to predict the ultimate bearing capacity of SRCFT stub columns. The studies may provide a considerable reference for designing this type of structures in engineering practice.

Introduction

Steel-concrete composite structure such as concrete-filled steel tube (CFT) column have been widely used as modern structure members in building structures and bridges [1], [2], [3], [4], [5], even in regions with high seismic risk [6], [7], [8]. This is mainly attributed to the optimum usage of steel and concrete [9], [10], [11]. First of all, the CFT require no reinforces cage and no formwork, the steel tube can act as permanent and integral formworks, reducing the labour costs, materials and construction time simultaneously. Secondly, due the lateral confinement effect provided by the steel tube, the compressive strength and deformation performance of the core concrete were enhanced. What’s more, the infill concrete can add stiffness to the steel tube, and prevent or delay the occurrence of local buckling [12], [13], [14], [15]. Therefore, the mechanical performance of CFTs has caught more and more research attentions.

So far, extensive experimental and numerical studies [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28] on the compressive behavior of CFT columns have been carried out. Tao et al. [16] performed a nonlinear analysis of concrete-filled square stainless steel stub (CFSST) columns under axial compression, and presented a formula for calculating the ultimate bearing capacity. El-Heweity [17] investigated the compressive performance of circular high strength steel tubes filled with concrete (CFT) based on the numerical methods, indicating that both concrete strength and ductility of CFT columns are enhanced but to different extents. Yuan et al. [18] presented the experimental investigation and numerical analysis on the performance of concrete-filled double skin composite tube columns (CFDSCT) under axial loading. Uenaka [21] investigated the characteristics of concrete filled elliptical/oval steel tubular stub (CFEST) columns under centric loading, and proposed a method to predict the axial loading capacity induced by confinement effects of the in-filled concrete. Zhao et al. [23] proposed a novel strength design formula to calculate the ultimate bearing capacity of circular hollow centrifugal concrete-filled steel tubular short column by collecting previous experimental data, in which a confinement coefficient representing the enhancing of the infilled concrete strength was considered. Pi et al. [24] carried out experimental investigation on the behavior of the circular concrete filled steel tube stub columns with double inner square steel tubes. And a simplified formula was developed to calculate the compressive strength. Li et al. [25] investigated numerically the compressive behavior of concrete-filled double-skin steel tubular stub column, in terms of parametric studies and mechanical analysis. Ding et al. [26], [27], [28] presented a combined experimental and numerical investigation on compressive behavior of CFT stub columns with different cross-sections. Finally, design formula for the ultimate bearing capacity was derived.

However, with the increase of the bridges span and buildings height in the practice engineering, the cross area of composite column is often designed bigger to meet the higher requirement of bearing capacity, ductility and stiffness. For example, the diameter of CFT column in the first story of the Shenzhen Saige Plaza Building even reached 1600 mm. Such a large cross section may result in reduced the useful indoor space [29], [30]. Thus, a novel form of composite column, namely steel-reinforced concrete-filled circular steel tube tubular (SRCFT) column [31], was proposed, attempting to combine the advantage of the steel reinforced concrete (SRC) column and the concrete-filled steel tube (CFT) column, as shown in Fig. 1. Compared with previous studies as mentioned above, limited studies have been conducted on the performance of SRCFT column. Wang et al. [31] investigated experimentally the compressive behavior of SRCFT columns with different parameters, and a formula was proposed to calculate the compressive strength. Besides, Cai et al. [32] investigated numerically the influence of some parameters on the compressive behavior of SRCFT column, and also presented a new formula to estimate the compressive strength. Nevertheless, it is necessary that the composite action between the steel tube and core concrete, core concrete and steel section still be clarified for SRCFT columns.

With the advancement of computing techniques to conduct research more efficiently and economically, the finite element analysis is becoming more and more popular to simulate the behavior and predict the response of steel–concrete composite structural, because which can simulate the case that are difficult and/or complex. Chang et al. [33], [34] conducted numerically the performance of composite structures using ABAQUS program. Hassanein et al. [35], [36] performed a numerical investigation on the compressive behavior of circular concrete-filled double skin tubular short columns with external stainless steel tubes. Pagoulatou et al. [37] adopted finite element computer core to establish the FE models, which can capable to accurately predict the capacity of circular concrete-filled double-skin steel tubular stub columns. Hence, the ABAQUS program will be employed to attempt to analyze the behavior of SRCFT stub column in this paper.

Therefore, the objective of this paper is to rationally investigate the compressive behavior of SRCFT stub column, and to develop a more concise and precise formula to calculate the ultimate bearing capacity accordingly. More specifically, based on the experimental and numerical research from our team [26], [27], [28], the main contents of this paper are listed below: (1) Compression tests on 8 specimens are conducted to investigate the behavior of SRCFT stub columns, in terms of failure mode, ultimate bearing capacity, strain ratio and so on. (2) FE models are established to investigate further the composite action between constituent components deeply, and parametric study is conducted in detail. (3) A simplified formula to estimate the ultimate bearing capacity is proposed based on the limit equilibrium method.

Section snippets

Specimen design and materials

In order to study the compressive performance of SRCFT stub columns, a total of 8 specimens were designed to test, including 4 circular concrete filled steel tubular (CFT) stub columns and 4 steel-reinforced concrete-filled circular steel tubular (SRCFT) stub columns, where the effect of concrete strength and steel section are considered in this study. The details of specimens are listed in Table 1, where D, t and L represent the diameter of the circular section, the wall thickness of steel

Complete curve analysis (Axial load vs. Strain curves)

Based on the test observation and obtained axial load vs. strain curves of all the specimens, as shown in Fig. 2, the specimens under axial loading were considered to experience three stages until failure: elastic stage, elastic–plastic stage and post-peak stage.

Elastic stage: At the initial loading stage, all the specimens were in elastic phase, indicating that the axial load increased linearly with the increase of the displacement. The compressive stiffness of specimens in this stage was

FE models

Finite element (FE) models are established using ABAQUS version 6.1 [41], which have been extensively adopted to simulate the compressive behavior of composite columns. In those models, the 8-node reduced integral format 3D solid element (C3D8R) is adopted to model the steel tube, core concrete, steel tube and loading plates for all specimens.

The loading plate is modeled as rigid bodies. A surface-based interaction with hard contact in the normal direction and the Coulomb friction coefficient

Formulation

From the above analysis, it can be found that the steel section is almost under uniaxial loading, and the mechanical properties of SRCFT stub columns are consistent with those of CFT stub columns. After that, the SRCFT stub column can be regarded as a combination of CFT stub column and steel section. Therefore, the practical formula for the ultimate bearing capacity of SRCFT stub columns can be deduced based on the limit equilibrium method through combined the strength calculation formula of

Conclusion

This paper presented a combined experimental and theoretical study on the compressive behavior of SRCFT stub columns, in terms of complete curve analysis, failure mode, parametric studies, and composite action and so on. Based on the limited results from the current study, the following conclusions can be drawn:

  • (1)

    Based on the experimental phenomenon and measured axial load vs. strain curves for all specimen, the specimens generally is considered to experience three stages until failure, including

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 research work is financially supported by the National Natural Science Foundation of China, Grant No. 51978664, and the National Key Research program of China, Grant No. 2017YFC0703404. The experiments are conducted in National Engineering Laboratory for High Speed Railway Construction at Central South University. The support is gratefully acknowledged. The authors sincerely appreciate the construction comments and suggestions by the reviewers, which is quite beneficial for improving this

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