Concrete-filled Steel Tube Stub Research Articles

Axial local bearing behavior of circular reinforced concrete filled steel tube stub columns

In this work, the axial local compression of circular reinforced concrete-filled steel tube (CRCFT) stub columns is studied. Sixteen specimens, including one circular reinforced concrete stub column (CRCC) specimen and fifteen CRCFT specimens, were prepared, considering different variables, such as the local compression area ratio β, sectional steel ratio α, volume stirrup ratio ρv, longitudinal reinforcement ratio ρ, and concrete strength fc. The axial local compression of specimens were experimentally investigated in terms of the damage process, failure mode, load-displacement relationship, ultimate bearing capacity, stiffness, deformation capacity, and strain characteristic. The finite element model of the CRCFT was also developed and validated. The parametric analysis of the local compression area ratio β, sectional steel ratio α, and volume stirrup ratio ρv facilitated the further investigation of the axial local compression behavior of CRCFT. The results showed steel tube buckling and concrete shear failure exhibited by CRCFT specimens. With the increasing local compression area ratio β, the ultimate bearing capacity reduced by 3.6–47.9 %, whereas the local compression strength improvement coefficient βcl increased by 11.8–273.9 %. With the increase in section steel ratio α and volume stirrup ratio ρv, the ultimate bearing capacity, stiffness, and deformation capacity were improved. Longitudinal reinforcement ratio ρ and the concrete strength fc also influenced the stiffness of CRCFT specimens. A simplified calculation method for the ultimate bearing capacity of CRCFT specimens was also presented.

Compressive axial load performance of GFRP–confined recycled aggregate concrete–filled steel tube stub columns

This study examined the axial compressive properties of glass–fiber reinforced plastic (GFRP)–confined recycled aggregate concrete–filled steel tube (RACFST) stub columns. The differences in the failure modes, load–displacement curves, and load–strain curves of the composite columns with different parameters were analyzed, including the number of GFRP layers, steel tube thickness, recycled aggregate substitution rate, and recycled aggregate concrete compressive strength. The results revealed a bulging failure mode in the middle of the GFRP–confined RACFST stub columns. With the increasing substitution rate of recycled aggregate, the bulging deformation of the specimen increased. This eventually resulted in a reduction in the stiffness and bearing capacity but an improvement in the ductility at a later stage. The early stiffness and ultimate bearing capacity of the specimen can be increased by thickening the steel tube or strengthening the recycled aggregate concrete. However, the ductility is greatly reduced in the later stage. Based on the axial compression test of GFRP–confined RACFST stub columns, the axial compression bearing capacity formula was derived. Compared with the existing formula, the formula presented in this paper has greater accuracy. In addition, a finite element (FE) model of the composite column was established to analyze the stress development during the compression process.

Theoretical model for spontaneous combustion gangue coarse aggregate concrete filled steel tube stub columns

Spontaneous combustion gangue coarse aggregate concrete filled steel tube (SCGCA-CFST) provides a possibility for the structural application of spontaneous combustion gangue coarse aggregate (SCGCA) concrete. To establish an accurate stress-strain model for SCGCA-CFST, 12 SCGCA-CFST specimens and 18 SCGCA concrete specimens were tested under monotonic axial compression with steel tube thickness and SCGCA replacement ratio (0%, 50%, 100%) as variables. The experimental results demonstrated that as the SCGCA replacement ratio increased, the elastic modulus of SCGCA concrete decreased by 6.65%–11.65%, the cylinder compressive strength decreased by 11%–21.95%, and the axial strain at peak axial stress increased by 7.1%–14.27%. Furthermore, the crack extension forms and dilation properties of the core concrete in SCGCA-CFST differed significantly from those of normal coarse aggregate concrete filled steel tube (NCA-CFST). The incorporation of SCGCA reduces the effectiveness of steel tube confinement, which causes the existing stress-strain models of NCA-CFST overestimate the enhancement effect of steel tube confinement on the strength and deformability of core SCGCA concrete. Based on this, the analysis-oriented stress-strain model for NCA-CFST was modified to be applicable for SCGCA-CFST by incorporating the influence of aggregate characteristics, and the accuracy of that was verified.

Prediction of ultimate bearing capacity of concrete filled steel tube stub columns via machine learning

Prediction of ultimate bearing capacity of concrete filled steel tube stub columns via machine learning

Axial compressive behaviour of ultra-high performance concrete filled steel tube stub columns at elevated temperatures

Ultra-high performance concrete (UHPC) has many advantages such as high strength, good plasticity and toughness, and excellent durability. However, it is more likely to experience explosive spalling at high temperatures than ordinary concrete due to its low porosity. The ultra-high performance concrete-filled steel tubes (UHPCFSTs), where steel tubes are placed outside of UHPC to reduce its high-temperature spalling, could be an effective structural type to make full use of the advantages of both steel and UHPC. Most of the existing fire protection design codes for concrete-filled steel tube structures are based on ordinary concrete, and the performance and failure mechanisms of UHPCFSTs under high temperatures are still unclear. On this basis, an experimental study on the axial compressive performance of UHPC filled circular steel tube stub columns at constant elevated temperatures was carried out. The effects of temperature, steel tube thickness and coarse aggregate content on the compressive properties and failure modes of UHPCFST members were analysed. The results have shown that the UHPCFST mainly suffered from the overall pier coarse type and drum type failure modes. The failure characteristics were highly influenced by temperature magnitude, and 400℃ was the critical temperature where the structural performance change significantly beyond this point. The constraint effect of the steel tube on UHPC increased with the increase of thickness of steel tube, but it would be weakened with the increase of temperature or the coarse aggregate content. Finally, based on the average temperature method, a formula for calculating the ultimate load bearing capacity and equivalent stress–strain relationship of an UHPCTST stub column under a constant high temperature was proposed.

INFLUENCE OF BOND AND FRICTION ON TENSILE STRENGTH OF PERFORATED STEEL PLATE CONNECTOR UNDER CONFINEMENT

Concrete-filled steel tube (CFST) columns are commonly used in Japan, which utilize onsite full-strength welded splices between columns. However, onsite welding requires high technical skill and a controlled environment. Further, this type of splice is expensive and, in most cases, is not necessary for dependable building performance under severe earthquake loading conditions. Recently, new types of CFST column splices have been developed that enhance constructability and avoid the need for onsite welding. In the proposed column splice method, perforated steel plates are placed on each column half and are welded into place. To evaluate the performance of this splice, it is important to determine the pull-out strength and behavior modes of the perforated steel plates embedded into the CFSTs. In this paper, a pull-out experiment with perforated steel plates embedded into a square CFST stub is conducted. The experimental parameters are the bond between the steel plate and the concrete, the embedded length of the perforation, and the extra length of the steel plate. The effect of the bond and friction strength between the steel and concrete are discussed, and a design formula for the pull-out strength of the perforated steel plate is examined.

Performance of fly ash and silica fume self-compacting concrete filled steel tube stub columns under axial compression

Experimental research on the performance of fly ash and silica fume selfcompacting concrete filled steel tube (FSS CFST) stub columns under axial compression were conducted. The main parameters varied in the tests are steel tube’s diameter to thickness ratio, D/t (from 20 to 33), and yield strength (from 275.83 MPa to 350.51 MPa). The self-compacting concrete grade used as infill is M60 concrete with 50% and 10% addition of fly ash and silica fume, as partial replacement of Portland cement. The performance of FSS CFST stub columns is examined via the axial compression capacity, load-shortening response, and mode of failure of 12 specimens. The results indicate that the ultimate axial load capacity of the columns increases as the D/t ratio decreases. The FSS CFST columns have a maximum concrete contribution ratio of 3.72, a strength index greater than unity, and a ductility index of 2.431 and below. The predicted values obtained using Eurocode 4 closely estimate the test results with a mean of 0.927 and a standard deviation of 0.073. Conversely, the predicted values using ACI code are more conservative with a mean of 1.341 and a standard deviation of 0.089.

Analysis of Finite Element Mechanism of Axial Compressive Behavior of T-Shaped Stiffened Concrete-Filled Steel Tubular Stub Columns After Uniform Fire Exposure

Based on the reasonable determination of material constitutive relationship and interaction model between concrete and steel tube, a finite element model of T-shaped stiffened concrete-filled steel tube (TSCFST) stub column exposed to uniform fire was established, and model reliability was verified. Through the FE model, the working mechanism of the model in the whole process of loading was analyzed in detail. In the process of axial compression, the load distributions of steel tube and concrete, and the interaction between steel tube and concrete were discussed. This paper analyzed the effects of the main factors on residual bearing capacity of TSCFST stub columns, and put forward the calculation formula of the residual bearing capacity of TSCFST stub columns after uniform fire exposure.

Axial compression behaviour of CFRP confined reactive power concrete filled steel tube stub columns

The axial compression behaviour of circular carbon fiber reinforced polymer (CFRP) confined reactive powder concrete (RPC) filled steel tube stub columns was investigated. The mechanical tests of 12 CFRP confined steel tube-RPC stub columns, 4 steel tube-RPC stub columns and 4 steel tube stub columns were performed with the number of the CFRP layers and the steel tube thickness as parameters. The load-displacement curves were used to analyze the effects of the CFRP layer number and the steel tube thickness on the ultimate load and deformation capacity of the specimens. Subsequently, the performance indicators such as improvement coefficient, CFRP strain efficiency and ductility coefficient were discussed. Finally, a model of CFRP confined steel tube-RPC stub columns was proposed by increasing the coefficient associated confinement ratio. The experimental results indicate that the bearing capacity and deformation capacity of the CFRP confined steel tube-RPC stub columns are significantly improved by CFRP. In contrast to the CFRP confined concrete filled steel tube (CFRP confined steel tube-C), the CFRP confined steel tube-RPC exhibites a decrease in CFRP strain efficiency, and its ductility is worse than the CFRP confined steel tube-C. Based on the bearing capacity of steel tube-RPC, a practical model for calculating the bearing capacity of CFRP confined steel tube-RPC stub columns is proposed.

Unified solutions on axial bearing capacity of round-ended concrete-filled steel tube short columns with binding bars

Based on the unified strength theory, according to the characteristics of axial bearing capacity of round-ended concrete-filled steel tubular stub short columns with binding bars, the cross shaped section was divided into a rectangular section which has bars and two round-ended sections which have no bars. Considering intermediate principal stress, the ration of width to thickness of pipe to the bearing capacity of steel tube was in consideration too, the paper analyzed force mechanism. In the end, the mathematical formulation of bearing capacity for the round-ended concrete filled steel tube stub column with binding bars was obtained. The formula calculation values were in good agreement with the value of the relevant literature. Theoretical formulas are expected to be helpful for engineering applications.

Compressive Behaviour of Circular, Square, and Rectangular Concrete-Filled Steel Tube Stub Columns

In this paper, the compressive behaviour of circular, square, and rectangular concrete-filled steel tube stub (CFSTS) columns is assessed. Nonlinear three-dimensional finite element models for simulating the behaviour of the columns are developed with the aid of the finite element analysis package ABAQUS. Modelling result is compared with the experimental test result to validate the modelling. It is found that the obtained load-axial strain curves of the columns from the finite element analysis and experimental test are notably close to each other and the modelling is finally validated. Then, the analyses of the developed models of the columns are done in accordance with the validated method. Various parameters are adopted in the analyses including the load eccentricity, cross-sectional shape, and steel tube thickness. It is concluded that as the load eccentricity of the columns is increased, their ultimate load-carrying capacity, energy absorption capacity, and stiffness are decreased. Also, the circular columns have generally better performance than their rectangular and square counterparts. The hierarchy of the cross-sectional shapes of the columns from the ultimate load-carrying capacity and energy absorption capacity viewpoints is the circular, rectangular, and square shapes. Although the initial stiffness and slope of the stiffness curves of the rectangular and square columns are slightly higher than those of the circular columns, their stiffness distribution is non-uniform. Furthermore, thicker steel tube leads to greater ultimate load-carrying capacity, energy absorption capacity, and stiffness. Failure modes of the columns are achieved and discussed as well.

Study on circular CFST stub columns with double inner square steel tubes

This paper presented axial compression tests on the behavior of the circular concrete filled steel tube stub columns with double inner square steel tubes (DIS-CFST). A total of 27 DIS-CFST stub columns with different eccentricity ratio (e), hollow area ratio (ψ) and concrete compressive strength (C) were tested. The study mainly investigated the failure modes, ultimate bearing capacity, load-strain curves, load-displacement curves, initial stiffness at elastic stage (ki) and ductility of the DIS-CFST stub column. The failure mode of DIS-CFST stub columns observed from the tests was local buckling and no crack was observed on the surface of the specimens. It was found that concrete compressive strength had remarkable influence on ductility and ultimate bearing capacity of DIS-CFST stub columns. However, eccentricity ratio had little influence on the behavior of DIS-CFST stub columns. Experimental results showed that when the hollow ratio was small, it had little effect on the ultimate load-carrying capacity of DIS-CFST stub columns. However, the ultimate bearing capacity of specimens significantly decreased when hollow area ratio was large. The eccentricity ratio, hollow area ratio and the concrete compressive strength had slight influence on initial stiffness at elastic stage. Furthermore, the ductility of DIS-CFST stub columns increased with the decrease of hollow area ratio. A simplified formula was proposed to calculate the ultimate bearing capacity of DIS-CFST stub columns. The predicted ultimate bearing capacities were in good agreement with DIS-CFST stub column test results. By comparing with the existing strength calculation formula, it can be concluded that the ACI code, EC4 and Han's method were more satisfied with the requirements of the design.

Axial compression behavior of hybrid fiber reinforced concrete filled steel tube stub column

Previous studies indicate that the use of hybrid fiber has the potential to improve the properties of concrete. This paper investigates the effect of steel-polypropylene hybrid fiber on the axial compression behavior of concrete-filled steel tube (CFST) columns. Sixteen hybrid fiber reinforced concrete filled steel tube (HFRCFST) stub columns are tested under axial load. The variables considered in the tests are the steel fiber volume percentage and polypropylene fiber quality percentage. The failure mode, ultimate capacity, ductility and energy dissipation capacity of HFRCFST column are investigated. Experimental results show that hybrid fiber has negligible effect on the failure mode and ultimate capacity, delays the failure process and improves the energy dissipation capacity. The fiber hybridization has a favourable reinforcement effect on the ductility over the sum of the individual single fibers. Therefore, using hybrid fiber reinforced concrete is a more effective method to improve the ductility of the CFST columns than single fiber.

Mechanical behavior of circular and square concrete filled steel tube stub columns under local compression

This paper presents a combined experimental and numerical study on the behavior of both circular and square concrete-filled steel tube (CFT) stub columns under local compression. Twelve circular and eight square CFT stub columns were tested to study their bearing capacity and the key influential parameters. A 3D finite element model was established for simulation and parametric study to investigate the structural behavior of the stub columns. The numerical results agreed well with the experimental results. In addition, analytical formulas were proposed to calculate the load bearing capacity of CFT stub columns under local compression.

Shape effect on the behaviour of axially loaded concrete filled steel tubular stub columns at elevated temperature

Concrete filled steel tubular columns have been extensively used in modern construction owing to that they utilise the most favourable properties of both constituent materials. It has been recognized that concrete filled tubular columns provide excellent structural properties such as high load bearing capacity, ductility, large energy-absorption capacity and good structural fire behaviour. This paper presents the structural fire behaviour of a series of concrete filled steel tubular stub columns with four typical column sectional shapes in standard fire. The selected concrete filled steel tube stub columns are divided into three groups by equal section strength at ambient temperature, equal steel cross sectional areas and equal concrete core cross sectional areas. The temperature distribution, critical temperature and fire exposing time etc. of selected composite columns are extracted by numerical simulations using commercial FE package ABAQUS. Based on the analysis and comparison of typical parameters, the effect of column sectional shapes on member temperature distribution and structural fire behaviour are discussed. It shows concrete steel tubular column with circular section possesses the best structural fire behaviour, followed by columns with elliptical, square and rectangular sections. Based on this research study, a simplified equation for the design of concrete filled columns at elevated temperature is proposed.

Concrete filled steel tube stub columns under combined temperature and loading

Abstract A finite element analysis (FEA) model was developed to predict the load versus deformation relationships of concrete filled steel tube (CFST) stub columns subjected to a combination of temperature and axial compression. This model was used to simulate a set of CFST stub column experiments under various thermal and mechanical loading conditions, including tests at high temperature, tests on the residual strength of specimens subjected to uniform heating, and tests on specimens exposed to the ISO-834 standard fire without initial loads. Comparisons between the predicted results and the test results show that this model can predict the load versus deformation relationships with reasonable accuracy. The FEA model was then used to investigate the behaviour of CFST stub columns in a complete loading history including initial loading, heating and cooling by examing the cross-sectional stress distribution and confinement stress development at different loading phases. All specimens were loaded to ultimate strength after cooling and the residual stress index was studied with respect to a group of parameters. It can be found that the ultimate strength when considering the mutual actions of temperature and loading was slightly lower than that after exposure to fire without initial load, but the peak strain corresponding to the ultimate strength was increased significantly.