Review articleStudy of bolts used as shear connectors in concrete-filled steel tubes
Introduction
Concrete Filled Steel Tube (CFST) columns are widely used in civil construction due to their advantages. Among these advantages are the high strength capacity, the possibility of smaller cross-sections, reduction in the structural weight and the expenses with additional fire resistance systems, good ductility, and high energy absorption [1], [2], [3]. The latter is why these kinds of structures have been used in bridges, underground construction, and high-rise buildings, even in places with seismic phenomenon [3], [4], [5].
In beam-to-CFST connections, the shear force is transmitted directly to the steel tube, requiring the concrete core’s load transference. The need for bond strength between the materials is mostly necessary for the load introduction area, according to the Eurocode [6], guaranteeing the composite action.
The longitudinal shear strength transferred can be made either through the natural bond or using a mechanical connector. If that load exceeds the natural bond strength, it must adopt mechanical shear connectors [7], [8].
Studies of bolts used as shear connectors in CFSTs includes researchers as [9], [10]. They have concluded through numerical and experimental analysis that these bolts increase the load transferring between steel tube and concrete core compared to the natural bond. Other authors included in their analysis the interference of other parameters that contribute to this increase. According to [9], [11], [12], [13], [14], [15], [16], [17], increasing the bolt’s diameter also increases the bolt’s capacity in transferring load between the steel and the concrete. Authors as [9], [11], [12], [14], [15], [17] concluded that the bolt’s capacity to transfer load between the steel and the concrete also increases when increasing the bolt’s length. The increase in the number of bolts used as shear connectors also increases the load transfer capacity between steel and concrete [11], [12], [15], [17], [18]. Raising the steel tube thickness also raises the bolt connector’s load capacity due to the increase in confinement forces, steel resistance, and stiffness of the connection between the steel tube and bolts [11], [14], [15], [17].
This paper presents a numerical analysis of bolts used as shear connectors in circular CFST columns. The numerical models were developed using the finite element method in the software Abaqus 6.14.
The numerical models were validated with the calibration through experimental analysis results from Xavier, et al. (2019) [12]. Subsequently, with a reliable calibrated model, an analysis was developed to investigate the influence of parameters such as the bolt’s length and position and the steel tube thickness.
Section snippets
Cross-section, geometry, and experimental test scheme
The experimental program of CFST columns with bolts used as shear connectors developed by Xavier et al. (2019) [12] was based on twelve prototypes with six different configurations, two prototypes for each configuration. Fig. 1 exhibits the prototype’s geometry containing four and eight bolts, divided into one and two levels, respectively. The bolts used had a diameter of ½″ and lengths of 2″ and 4″. Two different types of concrete strength were also used. Table 2 exhibits the characteristics
Numerical analysis
The numerical model was developed using the Abaqus software based on the finite element method. The model consists of a circular concrete-filled steel tube with bolts used as mechanical shear connectors. The symmetry of the CFST and resources in the software made it possible to model only a quarter of the prototype, reducing computational costs.
The numerical model calibration was primarily used in one experimental model, and then the same characterization was applied to the other five models
Results and discussion
The same attributions were applied to all six models and compared with the experimental results. On the steel tube and bolts were used elasticity modulus, E, as 200,000 GPa and Poisson’s ratio, ν, equal to 0.3. Table 2 shown the nomenclature and the properties of the numerical models and the experimental results.
The nomenclature comprises a sequential number of the model, the number of bolts, the bolt's length, and the concrete's strength.
The numerical models' results were compared with the
Study of the influence of other variables in the behaviour of the CFST
Other models were constructed with the same parameters previously discussed, using the nominal values of materials' resistance in all three components (bolt, steel tube, and concrete. The new numerical models were defined with modifications in the geometry, such as the thickness of the steel tube, the connector's length, and the connectors' disposition.
Conclusions
This study investigates the resistance capacity per bolt used as a shear connector in concrete-filled steel tube columns. It was analyzed his behavior with different bolt lengths and concrete strengths. The numerical study was developed using the Abaqus 6.14 software. The models were calibrated with the experimental test results to better reliability of the numerical model's response.
The CDP (concrete damage plasticity) model used for the concrete modeling involved many parameters, 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
The authors acknowledge the support provided by the National Council for Scientific and Technological Development (CNPq), Coordination for the Improvement of Higher Education Personnel (CAPES), the company Vallourec and the Federal University of Ouro Preto.
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