Concrete-filled Steel Tube Research Articles

Efficiency of advanced materials in strengthening of CFST columns: finite elements and artificial neural networks

PurposeThe aim of the current study is to recommend and compare the estimates of finite element model (FEM), analytical model, and artificial neural networks (ANN) model for capturing the LCC of FCSC members. A database comprising 325 FCSC columns was constructed from previous studies to propose FEM and ANN models while the analytical model was proposed based on a database of 712 samples and encasing mechanics of steel tube and FRP wraps. The concrete damage plastic model was used for concrete along with bilinear and linear elastic models for steel tube and FRP wraps, respectively. Analytical and ANN models effectively considered the lateral encasing mechanism of FCSC columns for accurate predictions.Design/methodology/approachThe study aimed to compare the prediction accuracy of finite element (FEM), analytical, and artificial neural network (ANN) models for the load-carrying capacity (LCC) of fiber reinforced polymer (FRP)-encased concrete-filled steel tube (CFST) compression members (FCSC). A database of 325 FCSC columns was developed for FEM and ANN models, while the analytical model was based on 712 samples, utilizing encasing mechanics of steel tube and FRP wraps. FEM used a concrete damage plastic model, bilinear steel tube, and linear elastic FRP models. Statistical accuracy was evaluated using MAE, MAPE, R², RMSE, and a 20-index across all models.FindingsBased on the experimental database, the FEM presented the accuracies in the form of statistical parameters MAE = 223.76, MAPE = 285.32, R2 = 0.94, RMSE = 210.43 and a20-index = 0.83. The analytical model showed the statistics of MAE = 427.229, MAPE = 283.649, R2 = 0.8149, RMSE = 275.428 and a20-index = 0.73 while ANN models portrayed the predictions with MAE = 195, MAPE = 229.67, R2 = 0.981, RMSE = 174 and a20-index = 0.89 for the LCC of FCSC columns.Originality/valueAlthough various investigations have already been performed on the prediction of the load-carrying capacity (LCC) of fiber reinforced polymer (FRP)-encased concrete-filled steel tube (CFST) compression members (FCSC) using small and noisy data, none of them compared the accuracy of prediction of different modeling techniques based on a refined large database.

Influence of damage degree of recycled coarse aggregate concrete-filled steel tube columns strengthened with envelope steel jacket under seismic load

ABSTRACT In order to discuss the influence of damage degree of recycled coarse aggregate concrete-filled steel tube columns strengthened with envelope steel jacket (ESJ) under seismic load, eight columns were designed and manufactured to simulate seismic loading, with the design of ESJ strengthening after pre-damage and destruct tests under seismic load. This experiment was conducive to accurately evaluating the influence mechanism and synergistic effect of seismic damage degree and recycled coarse aggregate on the hysteresis curve, skeleton curve, ductility performance, energy dissipation performance, and bearing capacity performance of each specimens, and a suitable seismic damage model was proposed. The ductility coefficient is from 3.36 and 4.64, satisfying the requirements of seismic design. The research results indicate that the degree of seismic damage and recycled coarse aggregate are unfavorable to improve the seismic performance of recycled coarse aggregate concrete-filled steel tube columns strengthened with ESJ under seismic load; Taking the ductility coefficient of specimen SEJS-0 as the basic data, specimens SEJS-1 to SEJS-3 and FC-0 to FC-3 increased by 22.02%, 20.24%, 8.33%, 18.15%, 38.10%, 35.71%, and 23.51%, respectively. Under moderate and severe damage, the ductility performance of enveloped steel jacket-strengthened seismic-damaged specimens decreased by 15.47% and 15.18%, respectively, and the reduction amplitude of both was similar. As the degree of seismic damage increases, the value of the ultimate bearing capacity first decreases and then increases. The method of using recycled coarse aggregate to replace half of natural coarse aggregate has certain feasibility in the field of concrete-filled steel tube columns. Recycled coarse aggregate has a significant impact on the bearing capacity of each stage, while the degree of seismic damage only has a greater impact on the ultimate stage. The established seismic damage model for recycled coarse aggregate concrete-filled steel tube columns strengthened with ESJ under seismic load is feasible and can be used for quantitative evaluation of the seismic capacity of such components.

High-fidelity simulation of FRP-confined concrete-filled steel tubes: the synergy of empirical and machine learning techniques

Abstract The present research addresses a significant gap in the current literature by overcoming the limitations associated with small, noisy datasets commonly used to predict the axial load-carrying capacity (ALC) of fiber-reinforced polymer (FRP)-encased concrete-filled steel tube compression examples (FCFST). Specifically, the authors present a refined, large-scale database that facilitates the evaluation of the prediction accuracies of three modeling techniques: finite element modeling (FEM), analytical modeling, and artificial neural networks (ANN). This comprehensive comparative analysis, underpinned by a robust experimental dataset, not only enhances predictive accuracy but also provides valuable engineering insights. Unlike previous studies, which often lack data refinement or fail to compare multiple modeling approaches, our work offers a more rigorous and holistic evaluation. The current study aims to recommend and compare the estimates of FEM, analytical model, and ANN model for capturing the ALC of FCFST examples. A database comprising 335 FCFST columns was constructed from previous studies to propose FEM and ANN models while the analytical model was proposed based on a database of 698 samples and encasing mechanics of steel tube and FRP wraps. The concrete damage plastic model was used for concrete along with bilinear and linear elastic models for steel tubes and FRP wraps, respectively. Analytical and ANN models effectively considered the lateral encasing mechanism of FCFST columns for accurate predictions. The FEM exhibited high accuracy with statistical parameters: MAE = 223.76, MAPE = 285.32, R² = 0.943, RMSE = 210.43, and a20-index = 0.83. In contrast, the ANN model outperformed, with MAE = 195, MAPE = 229.67, R² = 0.981, RMSE = 174, and a20-index = 0.89. The R² values between the models indicated strong correlations: FEM vs. analytical (0.876), analytical vs. ANN (0.914), and ANN vs. FEM (0.945), with the ANN model showing the best accuracy.

Experimental analysis on post-fire performance of GRAC filled steel tubular columns and thermal properties of GRAC

This paper presents experimental investigation on the post-fire performance of geopolymeric recycled aggregate concrete filled steel tube (GRACFST) columns and temperature field of GRAC cubes. A total of 10 GRACFST column specimens were tested to investigate their post-fire performance. A total of 10 GRACFST column specimens were tested to evaluate their performance after exposure to fire, considering various parameters: (a) cross-section type (circular and square); (b) testing conditions (ambient temperature test, post-fire test without initial load, and full-coupled post-fire test); (c) target temperatures (20 ℃, 600 ℃, and 800 ℃); and high-temperature exposure durations (30 min and 180 min). The study examined failure modes, temperature evolution, deformation and strain patterns, and post-fire ultimate bearing capacities. The test data revealed the commendable post-fire performance of GRACFST columns, as evidenced by the residual strength index typically falling within the range of 0.83 to 1.11. To calibrate the thermal properties of GRAC materials, a series of temperature field tests of GRAC cubes at different target temperatures (200 ℃, 400 ℃, 600 ℃ and 800 ℃) were conducted. These tests provided data on temperature distribution within the cubes and mass loss due to high temperatures. Using back analysis of these temperature field tests, thermal property models for GRAC, including thermal conductivity, specific heat, and density, were developed and validated by simulating temperature data from existing fire and post-fire tests of GRACFST columns. The proposed thermal property models are crucial for designing this novel composite column type for fire resistance applications.

Experimental investigation on axial compressive performance of rectangular multi-cell stocky concrete-filled steel tubes stiffened with PBL

An experimental investigation on the structural performance of rectangular multi-cell stocky concrete-filled steel tubes (CFSTs) stocky stiffened with perfobond leiste (PBL) under compression. Compression tests were conducted on 12 stocky CFSTs, varying concrete strengths, number of cells, and cross-section shapes. The tests discussed the failure process, load-deformation behaviours, section capacities, ductility factors, and core concrete enhancement factors of the specimens. It was found that all the 12 tested CFSTs experienced local bucking, and owing to the inclusion of PBL, the short sides of the steel tubes exhibited double-wave bulging, while the long sides showed multiple-wave bulging. With the enhancement of concrete strength from 29.4 to 65.1MPa, the section capacity exhibited a significant increase of 18–30%. As the cell number increased from 1 to 3, the section capacity increased by 1.35–1.59 times. When the cross-section of triple-cell CFSTs changed from the I-shape to the L-shape, the section capacity only increased by 3–9%. Moreover, the enhancement factor of the core concrete and the confinement factor showed a significant correlation. The comparison between test capacities and predicted capacities using the methods given in design codes ANSI/AISC 360-16, EN 1994-1-1, and GB 50936-2014, as well as proposed by Zhang, revealed that the capacity ratios of predicted values to experimental values ranged from 0.63 to 0.89, indicating an overly conservative prediction. Considering the confinement factor, a modified design method, based on Zhang’s method was proposed, to more accurately predict the section compressive capacity of rectangular multi-cell stocky CFSTs stiffened with PBL.

Eccentric compression performance of jointed precast concrete-encased concrete-filled steel tube columns with dry connections

Concrete-encased concrete-filled steel tube (CECFST) columns have recently been regarded as the optimum option for high-rise or heavy-loaded buildings due to superior structural resistance over traditional concrete-filled steel tube (CFST) and reinforced concrete (RC). Thus, in developed countries with severe manpower shortages such as Singapore, advanced precast dry connections were proposed for the CECFST columns to facilitate construction and tackle manpower crunch. Moreover, current research shows that the proposed connection has comparable structural resistance with conventional cast-in-place (CIP) connections, demonstrating huge application potential. However, the existing research is only limited to the performance of precast connections without any experimental studies on jointed columns, which hinders the implementation of the precast connections in engineering of practices. In this paper, to address this research gap, a comprehensive experimental programme was initiated, followed by extensive numerical studies. A total of six intermediate and slender jointed precast columns were tested to investigate the effect of precast connections on load-carrying behaviour of the jointed CECFST columns by considering column slenderness, connection detailing, connection position and load eccentricity. Besides experimental studies, extensive 3D finite element (FE) simulations were performed to investigate the relationship between connection integrity, constructability, and load-carrying performance of the jointed CECFST columns. The numerical studies showed that implementing the conventional "Equivalent to CIP" concept into the design of jointed precast CECFST columns would significantly compromise the constructability of such columns. To address this concern, a performance-based design method was proposed for jointed CECFST columns. Parametric studies showed that adopting the performance-based design method could not only improve constructability but also achieve sufficient column resistance.

Thin-walled double-skin concrete-filled steel-box stub columns with perfobond connections: axial compressive behaviour

Thin-walled double-skin concrete-filled steel tube (CFDST) stub columns with perfobond (PBL) ribs stiffened have broad application prospects in prefabricated modular buildings, bridge pylons and tunnels. To evaluate its application potential in engineering, this paper designed nine thin-walled CFDST box stub columns stiffened with PBL ribs and conducted axial loading tests. The failure modes, load-displacement curves, local buckling response, ultimate bearing capacity and ductility of the specimens are discussed. Test results show that PBL ribs constrain the local buckling of columns. Through analysis, the influence of the slenderness ratio, the hole distance and the hole diameter of the PBL rib on the axial compression behavior of the specimen was clarified. In addition, a finite element model was established and the accuracy of the model was verified through experimental results. Subsequently, extensive parametric studies were conducted to obtain the effects of section hollow ratio, steel ratio of the section, steel strength, and concrete strength on the bearing capacity and ductility of PBL ribs stiffened CFDST box stub columns. Finally, a prediction formula for the bearing capacity of PBL ribs stiffened CFDST box stub columns considering local buckling was proposed.

Axially loaded square CFST short columns strengthened with high-strength square steel tubes and concrete jackets

This study investigated the axial compressive performance of square concrete-filled steel tube (CFST) short columns strengthened with high-strength square steel tubes and concrete jackets. 22 columns were tested: 1 reference column, 15 columns strengthened with high-strength steel tubes, and 6 columns strengthened with standard steel tubes. The test results showed significant improvements in the load-bearing capacity, ductility, and stiffness of the CFST columns after strengthening by high-strength steel tubes. For strengthened columns, there was a general upward trend in the improvement of load-bearing capacity when Q460, Q550 and Q690 steel tubes were used for strengthening relative to the use of Q235 steel tubes. However, the specimens strengthened with Q690 steel tubes showed corner cracking during loading resulting in a lower increase in load-bearing capacity of some of their specimens than the specimens strengthened with Q550 steel tubes. Therefore, it is recommended to use high-strength steel tubes with strength grades of Q550 or lower for reinforcement projects. A finite element (FE) model was established and verified using the test results. The FE model showed that utilizing high-strength steel tubes enhanced the synchronization of displacements corresponding to the ultimate load of the original and post-cast concretes and improved the bearing capacity of both. Furthermore, a new formula was proposed to predict the load-bearing capacity of columns strengthened with high-strength steel tubes and concrete jackets. The results of this formula showed strong agreement with those of the experiment and FE model.

Experimental study of steel single skin, double skin and dual tubes stub columns filled with rubberized concrete

This experimental study investigates the performance of rubberized concrete-filled dual steel tubular (RuCFDST) short columns under concentric compression, addressing a gap in existing literature. While previous studies focused on single- and double-skin circular steel tube stub columns, the specific behavior of RuCFDST columns remains largely unexplored. The study compares RuCFDST columns with rubberized concrete-filled steel tubes (RuCFST) and rubberized concrete-filled double-skin steel tubes (RuCFDSST). A total of eighteen specimens were experimentally tested, which consisted of three single-tube configuration, three double-skin configuration, and twelve dual tube configuration. The investigation covers rubberized concrete preparation, material testing, precise measurements, test setup, and result analysis. Key parameters include rubberized ratio (0 %, 10 %, 20 %, and 30 %) and concrete mix variations. The results provide insights into failure modes, load-shortening behavior, ductility, and strength index, with comparisons to the design predictions based on the European standard EC4. The inclusion of rubberized concrete enhances ductility, while RuCFDST columns show promise in combining sustainability and strength. The study also evaluates design predictions, revealing good agreement for lower rubberized content but indicating deviations for higher ratios, suggesting the need for refined design approaches in such cases.

The behavior of uni-axially loaded bolt pre-stressing concrete-filled steel tubular short columns

Concrete-filled steel tube (CFST) columns have superior strength, stiffness, and ductility than traditional reinforced concrete columns. Despite the above merits, a major issue is that the steel-concrete interface bonding will be impaired by the concrete shrinkage and different lateral dilation of steel and concrete under compression. To mitigate the problem, a bolt pre-stressing CFST column is proposed in this study. Eight CFST columns subjected to axial compression with different magnitudes of pre-constraint and steel tube thicknesses were investigated. The results indicated that the initial stiffness and axial load-bearing capacity were significantly improved after applying bolted pre-constraint, while the improvement degree was related to the pre-constraint magnitude. Subsequently, the confining mechanism of the bolt pre-stressing CFST column was further investigated through numerical analysis. Furthermore, a parametric study was performed, which indicated that increasing the pre-constraint magnitude and the yield strength of the steel tube significantly enhanced the initial stiffness and the axial load-bearing capacity of the CFST column, however, the member ductility weakened. Finally, a calculation formula was proposed to determine the axial load-bearing capacity of the bolt pre-stressing short CFST column with satisfactory accuracy.

Experimental Study on the High Temperature Performance of UHPCFST Stub Columns at Different Concrete Age

Fire is one of the serious incidents occurring in the construction phase of Ultra-High Performance Concrete filled steel tubes (UHPCFST) columns, which may cause damage to materials, delays to construction and risk to life. This paper investigates the high temperature performance of UHPCFST columns at different concrete age to simulate the occurrence of fire at construction phase. Axial compression experiments on 24 stub columns are conducted to investigate the effect of temperature levels, age of UHPC on the mechanical response of the UHPCFST columns at different construction stages. The findings reveal that the bearing capacity of the UHPCFST stub columns shows an increase and then a decrease with rising temperatures, and columns of earlier age exhibit a greater increase in fire-resistance bearing capacity. Notably, the load-bearing capacity at room temperature increase with the age of UHPC. At 300 ℃, a marginal increment in capacity correlating with age is observed, whereas at 700 ℃, there is a slight decline. Furthermore, the incorporation of coarse aggregate substantially contributes to the augmentation of load-bearing capabilities across diverse conditions. Meanwhile, a formula for calculating the load bearing capacity and equivalent stress-strain curve of UHPCFST stub columns under elevated temperature at different concrete ages is proposed and validated. This research is expected to provide valuable insights for assessing fire safety and reliability of UHPCFST structure in construction settings.

On the behaviour of diagonally-stiffened concrete-filled steel tube-to-SHS steel brace T-joints: An experimental and numerical investigation

In this paper, the behaviour of the T-joint between concrete filled-steel tube (CFST) chord members with diagonal PBL (Perfobond Leiste) stiffeners and square hollow section (SHS) steel braces is investigated. First, seven T-joint specimens were prepared and experimentally tested under axial load of the steel brace. The results were analysed and discussed with respect to the failure modes, load-displacement responses and load-strain curves. Obviously, the diagonal PBL stiffeners were found to effectively limit the cracking range of concrete, thereby improving the bearing capacity of the T-joints. This is followed by a finite element (FE) analysis for the T-joints using ABAQUS software. FE models were validated using the test results and then parametric studies were generated. These studies included the effects of the ratio of brace-to-chord width (β), the ratio of brace-to-chord thickness (τ), the position and thickness of the PBL stiffeners and the steel and confined concrete material grades. Based on the experimental and numerical results, the bending characteristics were obtained for the steel brace-CFST chord T-joint under the axially compressed steel tube brace. Furthermore, the accuracy of the Chinese, Japanese, American and European specifications to calculate the bending bearing capacity of the T-joints were checked, and the results yielded highly conservative results. Therefore, a new calculation method was currently proposed, which takes into account the strengthening effect of the brace on the upper flange of the chord. The comparisons showed that the obtained results of this proposed method are in good agreement with experimental and FE results, and therefore can safely and reliably be used in design.

Study of bond-slip performance of steel tube with UHPC based on acoustic emission parameter analysis

Conventional methods for assessing bond performance are hindered by challenges in measuring strain and a lack of sufficient sensitivity to internal structural damage. This paper examines the bond behavior between steel and ultra-high-performance concrete (UHPC) based on acoustic emission (AE). The tests included a total of 2 concrete-filled steel tube (CFST) specimens and 4 concrete-encased CFST specimens. The bonding test was analyzed using AE parameters in combination with the damage process, damage morphology, and loading curve of the test specimens. Furthermore, damage correspondence was explored for the AE parameter indexes and the bond damage indexes of the conventional method. The findings reveal that the AE peak frequencies associated with the bond failure between steel tube and concrete span 30–100 kHz, 110–130 kHz, and 220–260 kHz. The AE event rate, cumulative absolute energy, Ib-curve, and percentage of tensile cracks can be used as judgmental and early warning features for interface damage. The damage process at the interface and the concrete crack development can be characterized by the severity index HI and the severity value Sr. The measurement curves obtained from various AE sensor positions exhibit remarkable similarity. A correlation can be discerned between the severity index (Sr) of the AE and the bond damage degree (Dt) ascertained through conventional methods, effectively mirroring the structural damage progression.

Effect of confinement system and recycled aggregates on axial compressive behaviors of CFST columns

The utilization of recycled aggregate concrete (RAC) has emerged as a pivotal technology for global environmental sustainability. Extending RAC’s application to Concrete-filled steel tube (CFST) columns offers an opportunity to strengthen RAC’s inherently weaker attributes. This research investigates the effects of recycled aggregates (RAs), basalt fiber (BF), and various confinement systems on the mechanical performance of CFSTs. A series of experiments were conducted on CFST columns under diverse confinement scenarios, incorporating varying proportions of basalt fiber and RAs. Additionally, numerical analysis was carried out to evaluate the influence of key design parameters on the load capacity of CFSTs, and theoretical discussion was conducted based on experimental results. The findings reveal that incorporating BF into concrete at an optimal dosage of 0.2 % significantly improves compressive, tensile, and flexural strengths across various RA replacement ratios, while the addition of BF results in minimal improvements in load capacity and fracture toughness for CFSTs. Replacing NAs with RAs generally reduces concrete strengths, with the severest reductions observed at higher RA replacement ratios. However, the degradation in the load capacity of CFSTs is less pronounced than the strength decrease observed in concrete. While a 40 % RA replacement in CFSTs has a minimal impact on the stress-strain curve, a 60 % RA replacement significantly alters the stress-strain relationship, leading to an average reduction of 26.3 % in fracture toughness and 13 % in load capacity. The confinement system plays a crucial role in the stress-strain relationship of CFSTs. Increasing the steel tube thickness from 2 mm to 4 mm substantially increases fracture toughness, and the introduction of GFRP wrapping further enhances both load capacity and ductility. The order of load capacity improvement based on confinement systems is as follows: combined confinement with a 4mm-thickness steel tube and GFRP wrapping, a 2mm-thickness steel tube with GFRP wrapping, a 4mm-thickness steel tube, and a 2mm-thickness steel tube. GFRP wrapping proves to be the most effective and economical method for enhancing load capacity compared to other strategies. It is suggested that the confinement stresses from the steel tube and GFRP reinforcement on the core concrete should be estimated independently, as combining them using a single confinement coefficient may not accurately reflect their individual contributions.

Experimental and numerical investigations on the bond-slip behavior of the interface between geopolymer concrete and steel tube

This study conducts push-out tests on eight geopolymer concrete filled steel tube column specimens with varying design parameters to evaluate the effects of steel tube wall thickness, concrete strength, and the presence of welded longitudinal ribs on the bond-slip performance at the interface between geopolymer concrete and steel tube. The study analyzes the influence mechanism of chemical bonding force, mechanical bite force, and friction resistance on bond strength and a three-stage bond-slip constitutive relationship is established. The results indicate that steel tube strain increases with height, with significant strain observed at the welding structure and the fixed end of the steel tube. The length-to-diameter ratio, diameter-to-thickness ratio, concrete strength, and construction measures of the steel tube are identified as key factors in enhancing interfacial bonding performance. The presence of welded longitudinal ribs on the inner wall of the steel tube significantly improves the interface bonding. The calculated bond strength ratios, compared with the test results, fall within an 11% margin, demonstrating good agreement.

Dynamic response analysis of concrete filled steel tube tied arch bridge on a slab foundation under moving train load

The analysis of bridge vibration response under train loads is crucial for the operational safety of railway bridge structures. In this study, a three-dimensional coupled dynamic model of train-track-truss arch bridge is established. Based on the numerical simulation results, the effects of different train axle loads and speeds on the vibration response of the truss arch bridge are analyzed, and the time-history changes of the displacement and stress at critical sections of the bridge are revealed. The results show that: during the train operation, the maximum vertical dynamic stress and maximum vertical displacement are linearly related to the train axle load and speed. The greater the train axle load and speed, the larger the maximum vertical dynamic stress and maximum vertical displacement. The maximum vertical acceleration generated during train operation increases linearly with train speed and exponentially with train axle load. The most unfavorable section occurs at the mid-span of the bridge, where the maximum vertical displacement, maximum vertical dynamic stress, and maximum vertical acceleration are all at their peak. This research has significant implications for engineering safety and operation.

A mode shape sensitivity-based wavelet feature extraction method for interface debonding detection in concrete-filled steel tubes

Abstract The use of concrete-filled steel tube (CFST) composite columns is increasingly prevalent in the construction industry, particularly in high-rise structures. A common issue in CFST columns is interface debonding between the concrete core and the steel tube. If this debonding progresses both superficially and deeply, it can lead to instability and buckling of the column, posing a serious threat to the overall structural integrity. This study presents an innovative and effective method for extracting damage-sensitive features using horizontal, vertical, and diagonal detail coefficients derived from the wavelet analysis of corrected modal signals. The study introduces the total normalized irregularity detection index (NIDIT) as a damage detection metric. The results indicate that NIDIT is highly effective in identifying and detecting debonding regions. NIDIT quantifies the accumulation of irregularities and disturbances in the affected areas, allowing for the detection of concrete surface debonding from the steel tube. The findings show that NIDIT can accurately and efficiently detect damage in middle and end-edge regions, addressing a significant challenge in structural health monitoring with high precision.

Study on eccentric compressive performance of circular double skin concrete filled steel tube connected by thread through inside lining tube

Connection method of lengthening the steel tube of circular hollow sandwich concrete-filled steel tube by inside lining tube and thread is proposed. Twelve circular hollow sandwich concrete filled steel tubular beam-column connected by thread through inside lining tube are designed and fabricated using the length of the thread along the axial direction, the working height of the thread, and the position of the thread as parameters; In addition, one unconnected specimen and two welded specimens also are designed and fabricated to conduct controlled experimental research. The test phenomena and failure modes, axial compressive load-compression curve, axial compressive load-lateral deflection curve, and axial compressive load-strain in steel tube curve, as well as bearing capacity, strength reservation, deflection curve shape, lateral stiffness, ductility and plane section assumption are analyzed. The research results indicate that, within the parameter range studied, the thread connection through inside lining tube is reliable before tripping, and the experimental phenomenon of specimens connected by thread is basically consistent with that of the unconnected specimens. The axial compressive load-compression curve and axial compressive load-lateral deflection curve of all specimens can be approximately divided into elastic stage, elasto-plastic stage, and descending stage. The peak load of all specimens is relatively close, while although experiencing almost the same loading process, the strength reserve of the specimens connected by thread is insufficient. During the entire loading process, the shape of the deflection curve of all specimens is close to the sine half wave curve, and the distribution of longitudinal strain in the steel tube along the height of the middle cross-section basically conforms to the plane section assumption. Calculation method for bearing capacity of circular hollow sandwich concrete filled steel tubular beam-column connected by thread through inside lining tube is suggested.

Numerical analysis of axially loaded concrete-filled steel tubular columns strengthened with CFRP grid-reinforced ECC

Carbon fiber-reinforced polymer (CFRP) and engineered cementitious composites (ECC) are commonly used to reinforce structural elements, with proven effectiveness in enhancing the performance of concrete-filled steel tube (CFST) columns as shown in prior experimental studies. However, the complex interaction among the components of the reinforced columns, including CFRP, ECC, the steel tube, and the concrete core, as well as the underlying mechanical mechanisms, remain insufficiently understood. This research aims to fill these gaps by developing a 3D finite element (FE) model of circular CFST short columns reinforced with CFRP grid-reinforced ECC for comprehensive numerical analysis. Sensitivity analyses are conducted to determine the governing parameters in the numerical simulation, including mesh size and critical plasticity parameters for the concrete damage model, such as the ratio of the second stress invariant on the tensile meridian to that on the compressive meridian (Kc), and the dilation angle (ψ) for both the concrete core and ECC. The model also accounts for the effects of concrete confinement provided by the CFRP grid-reinforced ECC layer and the circular steel tube. The accuracy of the FE model is validated against existing experimental data, and the model is subsequently used to investigate the behavior of reinforced CFST columns under varying geometric and material properties. The study examines failure modes, axial load-displacement responses, stress distributions, and the contribution of each material component to the load-bearing capacity of the strengthened columns. The results indicate an increase in ultimate axial strength ranging from 13% to 20% for the reinforced CFST columns. While the compressive strength of the ECC has a moderate effect on axial resistance, increasing ECC thickness, concrete strength, and steel tube yield strength significantly enhances the columns’ load-bearing capacity. Finally, a novel design model is proposed and validated, which accounts for the confinement effects provided by the CFRP grid and ECC on the concrete core.

Estimation of the axial capacity of high-strength concrete-filled steel tube columns using artificial neural network, random forest, and extreme gradient boosting approaches

Estimation of the axial capacity of high-strength concrete-filled steel tube columns using artificial neural network, random forest, and extreme gradient boosting approaches