Tube Columns Research Articles

Axial compressive behavior of GFRP composite spiral ties-reinforced ECC-encased HCFST columns

Aiming to solve the issues of conventional concrete-encased high-strength concrete-filled steel tube (HCFST) columns, a novel GFRP composite spiral ties (GC)-reinforced engineered cementitious composite (ECC)-encased HCFST column was proposed and tested under axial compression in this study. The test variables included encasing cement-based materials, the thicknesses of ECC and steel tube, the compression strength of HSC, and the tie configuration. The test results indicated that the failure mode of the composite columns changed after replacing the outer concrete with ECC, showing that the ECC-encased HCFST columns had excellent integrity. When ECC with the same compression strength was used instead of concrete, the bearing capacity, strength index (SI), ductility ( μ) and energy dissipation ( E d.) of the composite columns were increased by 14.2%, 7.7%, and 81%, respectively. Increasing the thicknesses of ECC and the steel tube significantly improved the composite columns' bearing capacity, and the latter was superior in enhancing the μ and E d. of the columns. Compared with other tie configurations, GC had an outstanding performance in improving μ and E d., reflecting the excellent restraint performance of GC. Furthermore, a calculation method for the axial compressive bearing capacity of GC-reinforced ECC-encased HCFST columns was proposed based on the composite constraint model and the unified theory of strength.

Research advance of solid-phase microextraction based on covalent organic framework materials

Solid-phase microextraction (SPME) is a fast and simple sample preparation technique that enables the enrichment of analytes, and it is used in combination with other detection techniques to provide accurate and sensitive analytical methods. SPME is widely used in environmental monitoring, food safety, life analysis, biomedicine, and other applications. The extractive coating is the core of the SPME technique, and the properties of the extractive coating greatly influence extraction selectivity and efficiency, as well as the enrichment effect. Therefore, the development of new and efficient extractive coating materials remains a hot topic in the analytical chemistry and sample preparation fields. Covalent organic frameworks (COFs) are a kind of porous crystalline network polymer materials formed by covalent bonds. Owing to the advantages of large specific surface area, high porosity, good stability, high designability, simple synthesis and post-modification, etc., it has been widely used in gas adsorption, catalysis, sensing and drug delivery. In recent years, COFs have attracted much attention in the field of sample preparation. A variety of novel COF-based SPME materials had been developed for extracting and enriching various types of analytes through π-π interaction, hydrophilic/hydrophobic interaction, electrostatic adsorption, and hydrogen-bonding, as well as pore effects. In this paper, the research advances of COFs for using in fiber-, in tube-, and membrane-based SPME over the past three years were discussed. Fiber surfaces had been modified with functionalized COFs or COF-hybrid materials for use in SPME through physical coating, in-situ growth, and chemical-bonding approaches. The combination of SPME fiber and chromatographic analysis can be used to detect a variety of analytes such as polycyclic aromatic hydrocarbons, phthalates, polychlorinated biphenyls, and pesticides in environmental and food samples, with good enrichment effects, wide linear ranges, and high sensitivity. Based on in tube-SPME, COFs-based monolithic column and fiber-filled tube as the extraction tubes were combined with high performance liquid chromatography online to develop highly sensitive detection methods for synthetic phenolic antioxidants and bisphenol compounds, respectively. In addition, COFs had also been used in membrane SPME technique, showing high efficiency in the extraction of trace polychlorinated biphenyls in environmental water. Finally, the development trends of COFs in the field of SPME was prospected.

Symbolic regression for strength prediction of eccentrically loaded concrete-filled steel tubular columns

Concrete-filled steel tube (CFST) columns are widely employed in high-rise buildings, long-span bridges, and seismic-resistant structures due to their superior load-bearing capacity, structural efficiency, and resilience under extreme loading conditions. This study uses symbolic regression with structural design code provisions to predict the eccentric strength of concrete filled-steel tubular columns with circular shape (CCFST) and rectangular shape (RCFST). Previous studies have used two distinct approaches for estimating eccentric strength: explainable models based on theoretical derivations and black-box models derived from machine learning (ML) methods. This study proposes a hybrid model derived from the design code standards, with performance enhanced by the symbolic regression technique. This model is based on a comprehensive experimental database of 464 tests for CCFST columns and 313 tests for RCFST columns under eccentric loading from various research papers. The developed code-based symbolic regression (C-SR) displays both robust and interpretable, demonstrating high prediction accuracy with mean values of the prediction-to-actual ratios of 1.006 and 0.997 and coefficient of variation (CoV) values of 0.117 and 0.098 for CCFSTs and RCFSTs, respectively, while providing explainable mathematical expressions that align with the mechanical principles of code provisions. The developed C-SR model is benchmarked against EC4 and AISC360 standards and evaluated against the various ML techniques, demonstrating acceptable performance. The results highlight the C-SR model’s effectiveness in providing reliable predictions and valuable insights for practical engineering applications.

Experimental Study on the Axial Compression Performance and Bearing Capacity Calculation Method of Concrete Filled CFRP-PVC Square Tube Column

Abstract To explore the mechanical characteristics of carbon fiber reinforced polymer–polyvinyl chloride (CFRP-PVC) square tube confined concrete columns, a set of nine specimens was meticulously crafted, varying in parameters such as the quantity of CFRP layers as well as the width and spacing of CFRP strips. Axial compression tests were conducted to gauge the response of the specimens under stress. Detailed observation of the complete failure process yielded crucial parameters including axial load displacement, peak bearing capacity, ductility coefficient, and axial compression stiffness. The results unveiled distinct failure patterns: specimens under strong restraint exhibited tearing failure at the corners of the CFRP-PVC tube, whereas those with weaker restraint experienced buckling failure of the PVC tube. Moreover, adding a greater number of CFRP layers led to a substantial 46.7 % growth in maximum peak bearing capacity, albeit at the cost of a 34.5 % reduction in ductility. Similarly, widening the CFRP strip resulted in a significant 41.8 % boost in maximum peak bearing capacity and a 9.6 % growth in ductility, surpassing those of specimens lacking CFRP. Remarkably, among specimens with equivalent CFRP content, those featuring CFRP strips spaced at 50 mm and with a width of 50 mm showcased superior mechanical properties. The finite element analysis adeptly replicated the observed cracking behavior. Drawing from the experimental findings and established literature calculation methods, a robust method for determining the axial compressive bearing capacity of CFRP-PVC square tube confined concrete columns is proposed.

Prediction of load-bearing capacity of FRP-steel composite tubed concrete columns: using explainable machine learning model with limited data

The complex interaction mechanism between the FRP jacket, steel tube, and confined concrete in the FRP-steel composite tubed concrete (F-STC) column makes the prediction of its mechanical behaviour a challenging task. This paper specifically investigates the application of machine learning models to predict the load-bearing capacity of F-STC columns. Since relatively few experimental works are performed on F-STC columns, the database established based on the test results from previous research contains only 69 data samples. In order to circumvent the training difficulties caused by the relatively small database, the application of the Gaussian process regression (GPR) model is trialled in this study. To make the predictions of the GPR model explainable, the Shapley additive explanations (SHAP) approach is incorporated with the GPR model in this study. Besides, four contrasting prediction models based on artificial neural network (ANN), support vector regression (SVR), decision tree (DT), and random forest (RF), are also proposed. The k-fold validation and test results indicate that the GPR model provides strong potential in predicting the load-bearing capacity of F-STC columns with high prediction accuracy and generalisation capability. Besides, 95% and 99% confidence intervals obtained by the GPR model are provided to show the uncertainty of the prediction results. Furthermore, the effect of the database size on the prediction performance of GPR, ANN, and SVR models is further examined by gradually reducing the number of data samples, and the comparisons illustrate the superiority of the GPR model.

Tests and analysis of HSC-filled steel tube columns strengthened by CFRP and angle steel frame under eccentric compression

Tests and analysis of HSC-filled steel tube columns strengthened by CFRP and angle steel frame under eccentric compression

Finite Element Modeling of the Behaviors of Concrete-Filled Steel Tube (CFT) Columns at Elevated Temperatures

Concrete-filled steel tube (CFT) columns are widely used as structural systems because of their high load-bearing capacity and material efficiency. However, under fire conditions, elevated temperatures degrade the mechanical properties of both steel and concrete. When combined with initial geometric imperfections, these factors significantly affect the load distribution and the fire resistance of the structure. Understanding how material properties and geometric factors change in CFT columns at elevated temperatures is essential for ensuring safe and efficient design. This study used the ASTM E119-88 fire curve to establish the relationship between the surface temperature of the structure and the fire resistance duration of the CFT column. Heat transfer and mechanical analyses of the structure were conducted using ABAQUS 2024 software. A comparison of simulation and experimental data showed that the numerical model was highly accurate. The study also addressed the effects of initial geometric imperfections, considering amplification factors of L/1000 and L/500, and compared the simulation results with the experimental data. The results demonstrated that initial geometric imperfections significantly influenced the fire resistance of the columns. Additionally, this study examined the material properties under high-temperature conditions as specified in the AISC 360-22 standard. The study compared the simulation results with the Eurocode standards and experimental data. The findings suggested that utilizing the material properties specified in the AISC 360-22 standard resulted in more conservative predictions of fire resistance for CFT columns, compared to the Eurocode standards. Furthermore, Appendix 4 of the AISC 360-22 standard was used to calculate the fire resistance rating of the CFT column. These calculations were compared with the simulation and experimental results to evaluate the reliability of using ABAQUS 2024 simulation software.

Evaluating Axial Strength of Cold-formed C-Section Steel Columns Filled with Green High-performance Concrete

Concrete-filled steel tube (CFST) columns that experience outward local buckling under high axial stress remain a significant concern, particularly when thin steel sections are used, as opposed to semi-compact and compact sections. This study investigated the performance of column systems by comparing single- and double-C-section configurations with both hollow and concrete-filled designs. Two types of infill materials were investigated: normal concrete and recycled material concrete, which included 10% waste glass powder as a cement replacement, 8% black high-density polyethylene beads as a sand substitute, and 10% pumice stone as coarse aggregate. To enhance the strength of the proposed CFS column, steel strips and screws were used to connect the flanges of the C-sections. Nine columns were tested experimentally under static axial load. Additionally, finite element analysis software was used to model and evaluate the effects of parameters beyond those investigated in the tests. The results indicated that the load capacity of the double face-to-face section was approximately 3% higher than that of the double back-to-back section. The addition of steel strips, used to connect the lips of the C-section flanges, enhanced the axial strength of the column by approximately 2% compared with the unstrengthened corresponding specimen and delayed buckling in the most vulnerable areas. Furthermore, the recycled infill concrete material had a minimal impact on the axial performance of the analyzed CFS columns compared to the control concrete, with a difference of less than 2.2%. The findings confirm that recycled waste material concrete can achieve performance comparable to that of the conventional concrete. Doi: 10.28991/CEJ-SP2024-010-014 Full Text: PDF

Experimental and Numerical Investigation on the Ultimate Bearing Capacity of Axially Compressed Steel Tube Columns with Local Corrosion

Experimental and Numerical Investigation on the Ultimate Bearing Capacity of Axially Compressed Steel Tube Columns with Local Corrosion

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.

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.

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.

Increasing the operating time of pumping units of water-reducing wells through the use of self-cleaning filters

Relevance. At enterprises engaged in open-pit mining, water-reducing wells equipped with submersible installations of electric submersible pumps are widely used in drainage systems. A significant content of particles of mechanical impurities in the pumped-out well fluid causes intense hydro-abrasive wear of the working stages of the electric submersible pumps. Among the existing methods of combating hydro-abrasive wear of submersible pumps in water-reducing wells, the simplest, most economical and effective is the use of filters of various designs. An urgent task is to increase the operating time of submersible electric submersible pumps while reducing the time and costs for cleaning or replacing filters. Aim. Justification of the designs and operating parameters of a self-cleaning filter and tubing string extension included in the electric submersible pump assembly of a dewatering well. Methods. Static calculations of deformation of the tubing column and the tubing column extension under the influence of overpressure. Results and conclusions. The authors have carried out the analysis of an electric submersible pump functioning in the dewatering wells of quarries during the development of mineral deposits by the open method. It was revealed that the main reason for the failure of the electric submersible pumps is the hydro-abrasive wear of the working stages of the submersible pump. The authors propose a method to increase the operating time of the electric submersible pumps in dewatering wells complicated by intensive removal of particles of mechanical impurities by using a self-cleaning filter of the original design. It is noted that a promising direction of development of the drive for self-cleaning filters is the use of deformation of the tubing column. Based on the calculations carried out, it was concluded that the small depths of dewatering wells cause an insufficient amount of deformation of the tubing string to clean the filter element. To increase the length of the reciprocating movement of the electric submersible pumps relative to the production string of a dewatering well, it is proposed to use a tubing string extension of an original design. The operating parameters of the tubing string extension were calculated, which showed the possibility of providing the required amount of controlled reciprocating movement of the electric submersible pumps in the well to restore the throughput of a self-cleaning filter.

Axially loaded rectangular FRP-concrete-steel hybrid multi-tube concrete stub columns: Performance, confinement mechanism, and design-oriented model

This paper presents an experimental investigation of rectangular glass fiber-reinforced polymer (FRP)-concrete-steel hybrid multi-tube concrete columns (MTCCs) subjected to monotonic axial compression to explore their mechanical behavior and confinement mechanism. Sixteen rectangular MTCCs and eight concrete-filled FRP tube columns (CFFTs) were tested. Four experimental variables, namely aspect ratio, FRP thickness, steel volume ratio, and steel tube configuration, were taken into consideration. The experimental results demonstrated that rectangular MTCCs’ load-bearing capacity and deformability diminished with increasing aspect ratio, as it reduced the effective confinement area of FRP tube to concrete. Additionally, the confined concrete’s compressive strength and axial deformability of rectangular MTCC (with a 6.4% steel volume ratio) enhanced by 21.5% and 32.9%, respectively, compared to the corresponding CFFT. This demonstrated the effectiveness of additional steel confinement. Furthermore, the confinement mechanism of rectangular MTCCs was clarified based on the full-range compressive behavior and dilation property of confined concrete. It included unconfined stage, transition stage, and hardening stage. Finally, a stiffness-based design-oriented model for rectangular MTCCs was established with favorable accuracy.

Ductility and shape effect of steel tube column filled with reactive powder concrete

In recent years, a modern obstetrics of concrete has been progressing, named Reactive Powder Concrete (RPC). This research presents the effect of this type of concrete on the behavior of filled steel tube columns under concentric loads. The eight columns were tested in this study, three of these columns were control specimens tested without filled concrete, with different three shape (square, rectangular, and circular) cross section with constant length (750 mm) and length to diameter ratio (10). The other five columns consist of one square column with a compressive strength of (54 MPa) that is filled with RPC without steel fibers, and the remaining four columns included two rectangular and two circulars, each one of these two columns filled with RPC without steel fiber have a compressive strength (54 MPa) and the other filled with RPC with 1.5 % steel fiber with compressive strength (92 MPa) respectively. The parameters studied in this test, ultimate stress, the effect of shape column on the load- deflection behavior, ductility index, strength index and toughness. The results obtained from this research, that an enhancement in the behavior of filled columns with increase in the ultimate strength when compare with steel columns which reached the highest percentage about 238.33 % for circular columns with compressive strength (54 MPa) and this columns had a better behavior compared with other shapes. Also, the results showed an improvement in the ductility index, strength index and toughness when filled columns with RPC, that a maximum increase of about 22.12 %, 222 %, and 680.62 % respectively.

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.

Prediction and reliability analysis of ultimate axial strength for outer circular CFRP-strengthened CFST columns with CTGAN and hybrid MFO-ET model

This study develops a novel hybrid machine learning model to estimate the ultimate axial strength and conduct a reliability analysis for outer circular carbon fiber-reinforced polymer (CFRP)-strengthened concrete-filled steel tube (CFST) columns. The experimental datasets are collected and enriched using the conditional tabular generative adversarial network (CTGAN). The column length, the steel properties (cross-section diameter, thickness, and yield strength), the CFRP properties (thickness, tensile strength, and elastic modulus), and concrete strength are selected as input variables to develop the Extra Trees (ET) model hybridized with Moth-Flame Optimization (MFO) algorithm for the ultimate axial strength estimation. The results reveal that the CTGAN can efficiently capture the actual data distribution of CFRP-strengthened CFST columns and the developed hybrid MFO-ET model can accurately predict the ultimate axial strength with a high accuracy (R2 of 0.985, A10 of 0.867, RMSE of 182.810 kN, and MAE of 124.534 kN) based on the synthetic database. In addition, compared with the best empirical model, the MFO-ET model increases the R2 by (6.78% and 13.48%) and A10 by (108.19% and 122.88%) and reduces the RMSE by (68.19% and 66.24%) and MAE by (71.33% and 68.48%) based on real and synthetic databases, respectively. Notably, a reliability analysis is performed to evaluate the safety of the developed MFO-ET model using Monte Carlo Simulation (MCS). Finally, a web application tool is created to make the developed MFO-ET model easier for users to design practical applications.

Influence of Compressive Strength and Steel-Tube Thickness on Axial Compression Performance of Ultra-High-Performance Concrete-Filled Stainless-Steel Tube Columns Containing Coarse Aggregates

With the increasing use of concrete-filled steel tubular (CFST) structures, exposed steel tubes are highly susceptible to corrosion, posing potential safety hazards. This study innovatively proposes the use of stainless-steel tubes instead of traditional carbon-steel ones and introduces coarse aggregates into ultra-high-performance concrete (UHPC), forming a coarse aggregate-incorporated ultra-high-performance concrete-filled stainless-steel tube (CA-UFSST). The inclusion of coarse aggregates not only compensates for the shortcomings of UHPC but also enhances the overall mechanical performance of the composite structure. Twenty sets of specimens were designed to analyze the influence of four parameters, including the coarse aggregate content, compressive strength, stainless-steel-tube thickness, and stainless-steel type on the axial compression performance of UHPC. The experimental results indicate that the failure mode of UHPC is related to the confinement ratio. As the confinement ratio increases, the failure mode transitions from shear failure to bulging failure. The addition of coarse aggregates enhances the stiffness of the specimens. Furthermore, this paper discusses the applicability of six current codes in predicting the bearing capacity of CA-UFSST and finds that the European code exhibits the best prediction performance. However, as the confinement ratio increases, the prediction accuracy becomes notably insufficient. Therefore, it is necessary to establish a more accurate calculation model for the axial compression bearing capacity.