Aggregate Concrete-filled Steel Tube Columns Research Articles

Eccentric compression behaviors of iron tailings and recycled aggregate concrete-filled steel tube columns

This paper presents a sustainable method for using iron ore tailings (IOTs) sand and recycled coarse aggregate (RCA) in concrete and concrete-filled steel tube (CFT) columns. The study first examines the impact of RCA replacement ratios (0 %, 50 %, 100 %) on concrete's mechanical properties, finding that both compressive and tensile strengths decrease with higher RCA content due to the negative effects of old interfacial transition zones and adhered cement in RCA. Then, twelve iron tailing and recycled aggregate concrete-filled steel tube (ITRAC-CFT) columns were tested under eccentric compression to assess the effects of varying RCA replacement ratios, eccentricity ratios (0.3, 0.5), and slenderness ratios (12.12, 19.05). Results indicate that RCA ratios have minimal impact on failure modes, ultimate bearing capacity, and stiffness, although ductility increases with higher RCA content. As slenderness ratios increase, the ultimate bearing capacity decreases by 5.3 % and 6.8 % for eccentricities of 0.3 and 0.5, respectively. The study further validates these findings through the finite element method (FEM), showing strong agreement between experimental and predicted results, average value, standard deviation, and coefficient of variation of Nu/NFE were 1.02 %, 0.04, and 3.92 %, respectively. Finally, a comparison with existing design codes (EC4, AISC 360, and GB 50396) reveals that AISC 360 provides the most accurate predictions of the ultimate bearing capacity of ITRAC-CFT columns. The research concludes that the comprehensive use of IOTs sand and RCA in CFT structural concrete is a highly viable and eco-friendly solution, offering potential benefits for sustainable construction practices.

Recycled aggregate concrete-filled steel tube columns with small-diameter circular FRP-confined sea-sand concrete cores: Conceptual and experimental investigations

Recycled aggregate concrete (RAC) prepared from waste concrete can achieve the green recycling of resources; however, its inferior material properties hinder its applications. Sea-sand concrete (SSC) can help alleviate the resource shortage of fresh water and river sands but is prone to steel corrosion. To address these challenges, this study developed a new RAC-filled steel tube column with a small-diameter circular fibre-reinforced polymer (FRP)-confined SSC core. This paper presents and discusses the results of the axial compression tests conducted on RAC-filled steel tube columns, with and without small-diameter circular FRP-confined SSC cores. The study investigated the effects of the configuration of the FRP-confined SSC core, diameter-to-thickness ratio of the FRP tubes, compressive strength of RAC and SSC, and cross-sectional shape of the column. The results revealed that using small-diameter circular FRP-confined SSC cores to partially replace RAC was effective in improving the compressive performance of RAC-filled steel tube columns. The increase in the number of FRP tubes, in-filled concrete strength, and confinement stiffness of the steel and FRP tubes contributed to improvements in the structural strength and ductility, resulting in progressive ladder-shaped declines in the post-peak curve. Finally, a reasonable load–capacity model is presented for the proposed columns.

Seismic behaviors of tailings and recycled aggregate concrete-filled steel tube columns

To alleviate the shortage of river sand and the pollution of construction waste, this paper proposed the tailings and recycled aggregate concrete (TRAC) and its application in concrete-filled steel tube (CFT) columns. Six full-scale TRAC filled square steel tube (TRACFST) columns were tested under axial static load and lateral cyclic load, and the results were verified by the finite element method(FEM). The principal parameters were substitution rate of RAC (0%, 50%, 100%) and axial load ratio (0.3, 0.5). The failure mode of the specimens was presented. Based on the experimental data, the hysteresis curves, skeleton curves, ductility, energy dissipation capacity, and stiffness degradation of the specimens were analyzed. The difference of peak bearing capacity of specimens with different RAC substitution rates was no more than 5%. The average ductility coefficient of the specimens with 100% substitution rate increased by 1%-7% compared with the specimens with 0% substitution rate. The TRACFST columns exhibit remarkable seismic performance.

An experimental investigation and machine learning-based prediction for seismic performance of steel tubular column filled with recycled aggregate concrete

Abstract This work presents the design and application of a low-cycle reciprocating loading test on 23 recycled aggregate concrete-filled steel tube columns and 3 ordinary concrete-filled steel tube columns. Additionally, a systematic study on the influence of various parameters (e.g., slenderness ratio, axial compression ratio, etc.) was conducted on the seismic performance of the specimens. The results show that all the specimens have good hysteresis performance and a similar development trend of skeleton curve. The influence of slenderness ratio on the seismic index of the specimens is more significant than that of the axial compression ratio and the steel pipe wall thickness. Furthermore, artificial intelligence was applied to estimate the influence of parameter variation on the seismic performance of concrete columns. Specifically, Random Forest with hyperparameters tuned by Firefly Algorithm was chosen. The high correlation coefficients (R) and low root mean square error values from the prediction results showed acceptable accuracy. In addition, sensitivity analysis was applied to rank the influence of the aforementioned input variables on the seismic performance of the specimens. The research results can provide experimental reference for the application of steel tube recycled concrete in earthquake areas.

Dynamic response of square recycled aggregate concrete-filled steel tube columns subjected to close-range blast loads

To study the dynamic response of square recycled aggregate concrete-filled steel tube (RACFST) columns under explosion loads, explosion examinations and numerical analyses were performed. Based on the measured longitudinal strain and residual displacement of the columns, the effects of recycled aggregate replacement percentage, steel tube thickness, explosive charge weight, blast center distance, and explosion height on the dynamic response of square RACFST columns are analyzed, and the failure modes are investigated. Then, the established numerical model was verified through test results, and further explore the dynamic response of square RACFST columns. It indicates that square RACFST columns suffer localized damage after detonation, and no obvious global deformation occurs. The localized failures, including blast pit, steel tube bulge or rupture, and weld fracture, could be observed on these columns. The square RACFST columns strain and displacement values are positively correlated with TNT equivalent and RA content, while negatively correlated with steel tube thickness and blast center distance. Furthermore, the concrete absorbs most of the total energy, implying the important role of core concrete in the explosion resistance of RACFST columns.

Seismic performance evaluation of recycled aggregate concrete-filled steel tubular columns with field strain detected via a novel mark-free vision method

In this study, low cycle reciprocating load tests were conducted on nine recycled aggregate concrete-filled steel tube columns (RACSTCs) and a solitary ordinary concrete-filled steel tube contrast column (OCSTC). The axial compression ratio and steel-tube wall thickness were considered as the parameters of interest. Accordingly, the failure mechanism, hysteresis performance, skeleton curve, ductility coefficient, energy consumption performance, and stiffness degradation of the two types of columns were compared. A vision measurement system was developed to track the full field deformations of specimens, and a quadocular vision system was constructed to determine the concrete column deformations. The deformations were compared with those obtained from laser measurements using an image and point cloud stitching algorithm. The results show that the hysteresis curves of RACSTCs are non-pinched with large ductility coefficients for all the specimens and the equivalent viscous damping coefficients are in the range of 0.462–0.975. RACSTC specimens exhibit good seismic and deformation performance. A three-fold restoring force model was established for RACSTC specimens based on skeleton curve test data. The theoretical hysteresis curve obtained using the skeleton curve model and hysteresis rule shows good agreement with the hysteresis curve obtained from experiment. This can be used as a reference for research on the restoring force characteristics of RACSTCs. The results obtained using the vision measurement system show that the measured mean relative error values are less than 0.504%. This confirms that the multiple vision measurement method can be used to accurately measure curved surface deformations as well as the full field strain values of RACSTCs. Therefore, the proposed method can be used to evaluate the asymmetric deformation of structures subjected to vibrations, impact, and other load types, thereby providing early warning decision data.

Seismic Behaviors of Tailings and Recycled Aggregate Concrete-Filled Steel Tube Columns

Seismic Behaviors of Tailings and Recycled Aggregate Concrete-Filled Steel Tube Columns

Residual axial capacity of square recycled aggregate concrete-filled steel tube columns after blast loads

To study the residual axial capacity of square recycled aggregate concrete-filled steel tube (RACFST) columns after close-range explosion loads, the explosion tests and the axial compression tests were performed. Firstly, 18 square RACFST columns were fabricated, and 15 of them were subjected to explosion tests. Secondly, the axial loads were applied to 3 intact columns and 9 blast-damaged columns. The curves of the load-displacement, the load-strain, and the load-mid-span deflection of all columns are analyzed. After the tests, the failure modes of the columns and core concrete were analyzed. Furthermore, the theoretical axial capacity of the RACFST columns was calculated according to the Chinese standard GB50936-2014. Based on the residual load-bearing capacity, the damage index is adopted to assess the damage degree of 9 blast-damaged columns. It indicates that both the blast-damaged and intact columns show diagonal shear failure under axial compression; the range of bearing capacity loss of the blast-damaged columns is approximately 1.9–32.1%, of which 5 columns are slightly damaged and 4 columns are moderately damaged, indicating that the columns still maintain a strong axial capacity reserve after explosion loads.

Study on the hysteretic behavior of recycled aggregate concrete-filled steel tube columns containing ferronickel slag

To study the hysteretic behavior of recycled aggregate concrete-filled steel tube (RACFST) columns containing ferronickel slag (FNS), this paper designed and fabricated nine specimens with the recycled coarse aggregate replacement ratios (RCAs), diameter-thickness ratio, and axial load ratios as the design parameters, which were tested using low-cycle reciprocation loading tests. The damage patterns of all specimens were observed; the hysteresis and skeleton curves of each specimen were obtained. Comparative analyses of the ultimate strength, hysteretic behavior, ductility, stiffness degeneration, energy dissipation capacity, and other seismic parameters were performed. Additionally, a series of numerical models of RACFST columns were established and the relevant parametric studies were discussed. The test results showed that the damage position of the specimen was located in the plastic hinge area at the bottom of the column, which was mainly characterized by the bulging and fracturing of steel tubes. The hysteresis curves of all specimens were relatively full, and the RCAs had a negligible influence on the hysteretic behavior of the columns. With the increasing axial loading ratio, the degeneration rates of ultimate strength and stiffness were accelerated, the deformation capacity was inversely deteriorated, while the hysteretic energy dissipation was unexpectedly enhanced. As the diameter-thickness ratio declined, both the ultimate strength and ductility of the columns were improved accordingly. Furthermore, an applicable numerical model was established and compared with the test results. The numerical results were in good agreement with the test results and especially could reflect the hysteretic behaviors of columns. Moreover, the results obtained from the parametric analyses showed that the slenderness ratio, axial load ratio, and steel ratio all exhibited a relatively large effect on the ultimate strength and ductility of the specimens, while the effect of the RAC strength was relatively small.

Research on the Bond Behavior of Preplaced Aggregate Concrete-Filled Steel Tube Columns.

In order to investigate the bond behavior of preplaced aggregate concrete-filled steel tube (CFT-PAC) columns and the difference of bond behavior between CFT-PAC columns and normal concrete-filled steel tube (CFT-NC) columns, a total of 11 columns were prepared and the push-out tests were conducted. The experimental parameters included the type of concrete (preplaced aggregate concrete and normal concrete), concrete strength (C40, C50 and C60), cross-section dimension (D = 219 mm, 299 mm and 351 mm) and the thickness of steel tube (t = 6 mm and 8 mm). The results indicated that the CTF-PAC columns had a similar load-slip curves with CFT-NC columns. The bond stresses of the CFT-PAC columns were higher than that of the PAC-NC columns at the same concrete strength. Increasing compressive strength of PAC increased the critical bond strength and bond strength of CFT-PAC columns. With an increase of the L/D ratio, both of the slip corresponding to peak load and bond strength of CFT-PAC columns exhibited an increasing trend. A rise in the D/t ratio led to a decrease in the bond stress of CFT-PAC columns and an increase in slip corresponding to the peak load of CFT-PAC columns. The proposed bond stress–slip relationship model considerably matched the bond stress–slip relationship of CFT-PAC columns.

Axial behaviour of semi-lightweight aggregate concrete-filled steel tube columns - A DOE approach

The main purpose of this paper is to present the experimental investigation on the axial behaviour of concrete-filled steel tube columns using semi-lightweight aggregate concrete as an infill type. The paper describes the effect of variation in the diameter (D), width (B), thickness (t) and length-to-diameter (L/D) ratio of steel tube with a special type of core concrete on the ultimate axial load (Nue) and the associated axial shortening (δue) for both the circular and the square CFST columns. The experimental campaign involves, finding the mechanical properties of steel, concrete and the Axial compression tests conducted on the CFST specimens. The 2k factorial design; a DOE approach is implemented primarily. Subsequently ANOVA, a statistical tool is used to analyze and compare the different combinations for reducing the error variance and finding the most influential factor on Nue and δue. Basic prediction models are proposed to predict the response Nue and δue for the CFST columns and further, the Response surface method is implemented to revise the models for interaction between the different combinations. Comparisons are made with the existing design codes like ANSI/AISC 360-10 and EN-1994 (Eurocode 4) to validate. The proposed model predictions thus, validate the experimental results with good accuracy. The tests confirmed the considerable influence of semi-lightweight aggregate concrete on the performance of CFST columns. In addition, the confinement improves the strength of the infill concrete and thus validates the use of semi-lightweight aggregate concrete as an infill to the CFST columns for structural purpose and particularly for reduced self-weight.

Cyclic Loading Test on Beam-to-Column Connections Connecting SRRAC Beams to RACFST Columns

This paper presents an experimental study conducted on the seismic behavior of beam-to-column connections based on the components of steel reinforced recycled aggregate concrete beams and recycled aggregate concrete-filled steel tube columns. The main test parameter of the specimens is the replacement ratio of recycled aggregate. The experiment process and failure modes of all specimens were investigated in detail. Several parameters such as hysteretic behavior, bearing capacity, strength and stiffness degradation, ductility coefficients, and energy dissipation were also analyzed. The test results showed that slipping appeared between the steel tube and beam concrete (sandwiched between the circumferential stiffening plates) while the specimen yielded. The shapes of the moment versus rotation hysteresis curve at the end of the beam were plump, which runs through a linear, reverse “S”-shaped and spindle-shaped deformation stages. Analysis of the seismic evaluation index showed that the replacement ratio of the recycled aggregate had no significant effect on the seismic performance. Moreover, a simulation study was also carried out using FEM, and the results showed good agreement with the skeleton curves obtained from the test. Finally, a simplified calculation model was established and the bearing capacity calculation equation of connections was proposed. Compared with the test results, the calculation equation can satisfy engineering application requirements. The results presented in this paper can be used as reference for engineering practice.

Axial compression behavior of circular recycled concrete-filled steel tubular short columns reinforced by silica fume and steel fiber

This paper presents an experimental work for short circular steel tube columns filled with normal concrete (NAC), recycled aggregate concrete (RAC), and RAC with silica fume and steel fiber. Ten specimens were tested under axial compression to research the effect of silica fume and steel fiber volume percentage on the behavior of recycled aggregate concrete-filled steel tube columns (RACFST). The failure modes, ultimate loads and axial load- strain relationships are presented. The test results indicate that silica fume and steel fiber would not change the failure mode of the RACFST column, but can increase the mechanical performances of the RACFST column because of the filling effect and pozzolanic action of silica fume and the confinement effect of steel fiber. The ultimate load, ductility and energy dissipation capacity of RACFST columns can exceed that of corresponding natural aggregate concrete-filled steel tube (NACFST) column. Design formulas EC4 for the load capacity NACFST and RACFST columns are proposed, and the predictions agree well with the experimental results from this study.

Seismic performance of recycled aggregate concrete–filled steel tube columns

In this study, low cyclic loading tests were performed on nine seamless steel tube columns filled with recycled aggregate concrete (RAC) and two steel tube columns filled with normal concrete to analyse their seismic performance and damage mechanism. The hysteresis behaviour, skeleton curve, ductility coefficient, stiffness degradation, and energy dissipation capacity of the steel tube columns were studied. The influence of the axial compressive ratio, steel strength, and steel thickness on the seismic performance of the steel tube columns was discussed. In addition, the failure mode and damage mechanism of the specimens were investigated; a skeleton curve–fitting formulation based on the Boltzmann mathematical model was proposed. A damage degree–based model was built for representing the damage degree quantitatively. The results indicate that the RAC-filled steel tube columns exhibit a full hysteresis loop, the equivalent coefficient of viscosity ranges from 0.402 to 0.572, and the coefficient of energy dissipation ranges from 2.617 to 3.595. The comparisons between the two types of steel tube columns indicate that the seismic performances of the RAC-filled steel tube columns are similar to those of the corresponding normal concrete–filled steel tube columns and that the RAC-filled steel tube columns even have appreciably better lateral bearing capacity, better ductility, and slightly lower energy dissipation ability at the same displacement level. These results consistently indicate that desirable seismic performance is achieved, and they serve as a potential reference for the structural design and application of RAC components in seismic areas.