Steel Tube Short Columns Research Articles

Axial compression performance of slurry‐wrapping recycled aggregate concrete‐filled steel tube short columns under freeze–thaw cycles

<scp>Axial</scp> compression performance of slurry‐wrapping recycled aggregate concrete‐filled steel tube short columns under freeze–thaw cycles

Study on mechanical properties of locally corroded square steel tube short column

To investigate the axial compressive properties and failure modes of 18 locally corroded square steel tube short columns, salt spray corrosion tests were conducted. The findings indicate that local corrosion in the horizontal direction significantly impacts the ultimate bearing capacity of the specimens, with all failures occurring in the corroded areas. However, the influence of the corrosion area on the ultimate bearing capacity and ductility of the specimens is not evident. A local corrosion model for square steel tube short columns was developed using the finite element method. The ultimate bearing capacity determined through finite element simulation closely aligns with experimental results, validating the reliability of the simulation approach. Moreover, a comparison is made between the prediction models of the BP neural network and the GA-BP neural network, with the prediction effectiveness of each model evaluated using the leave-one-out method. The verification results indicate that the GA-BP neural network model demonstrates superior predictive performance, with an average error of 3.14%.

An analytical model for axially compressed circular concrete-filled steel tubular (CFST) short columns with varied confinement factors

Accurate evaluation of the load-strain behavior of axially compressed concrete-filled steel tube (CFST) short columns is pivotal for engineering structures, and depends on precise prediction of the hoop-axial strain response. This study introduces a two-stage hoop-axial strain relationship that incorporates the initial Poisson's ratio and elastic limit to account for the initial linearity of concrete, and a reduction coefficient to take into account the effect of concrete strength on lateral deformation properties, based on a widely used hoop-axial equation. Experimental validation across a definite concrete strength range of 28 MPa to 125.3 MPa reveals improved predictions for the dilation rate of CFST columns subjected to axial compression, particularly for those columns fabricated with high-strength concrete (> 100 MPa). Subsequently, an analytical model consisting of the proposed two-stage strain relationship, a confined concrete model with inflection-point strain and residual strength, and the biaxial stress-strain relationship of steel tube is then established to estimate the compressive behavior of circular CFST short columns. Experimental verification over a range of confinements (confinement factor from 0.289 to 2.138) demonstrates the ability of the proposed analytical model to accurately capture the load-strain curves of circular CFST short columns, especially the post-peak behavior of those with confinement factors less than 1. The performance of the established analytical model in assessing the axial load-carrying capacity of circular CFST stub columns is investigated using a database assembled from available studies.

Experimental study on the axial compression behavior of circular steel tube short columns under coastal environmental corrosion

This study adopts experimental, numerical, and algorithmic methods to investigate the compressive behavior and failure mode of corroded circular steel tube short columns. The study establishes an equivalent relationship between electrochemical accelerated corrosion and natural coastal corrosion environments. The effects of current intensity, sodium chloride concentration, and energizing time on corrosion equivalent duration and mechanical properties of specimens are analyzed. The results demonstrate that the ultimate bearing capacity and energy absorption capacity of the specimens are significantly reduced with increasing current intensity and energized time. However, the NaCl concentration has minimal effect on the mechanical properties of the specimens. After natural corrosion in a coastal area with medium salinity for 19.2 years, the ultimate bearing capacity, ductility, initial stiffness, and energy absorption capacity of circular steel tube short columns decreased by 49.5 %, 63.1 %, 48.9 %, and 85.6 %, respectively. A novel corrosion pit generation algorithm is suggested to accurately simulate the distribution of corrosion pits and determine the ultimate bearing capacity of circular steel tube short columns. This algorithm demonstrates improved accuracy and stability compared to traditional simplified methods. Subsequently, a corrosion pit random generation model is developed using this method, and the accuracy of the finite element model is validated against experimental results. Furthermore, the impact of the diameter thickness ratio on the ultimate bearing capacity of corrosion specimens is thoroughly analyzed.

The influence of basalt fiber on the mechanical performance of concrete-filled steel tube short columns under axial compression

With rapid economic and social development, both concrete-filled steel tube (CFST) composite structures and basalt fiber (BF) have been widely applied in the field of civil engineering. To investigate the laws and characteristics of the influence of chopped BF on the mechanical properties of CFST columns and further promote the application of BF in CFST structures, the axial compressive bearing capacity test of 18 CFST short columns was carried out, and the influence of BF of different lengths on their structural mechanical properties was analyzed. The test results were compared with the theoretical calculation results and the finite element analysis results to verify the reasonableness of the test results. The results reveal that the axial compressive bearing capacity of the CFST short column after adding BF is significantly improved compared to the ordinary CFST short column, in which the bearing capacity and the ductility coefficient are increased by approximately 8.1% and 31.6%, respectively, on average. In addition, changing the length of BF has less effect on the bearing capacity of CFST short columns, the rate of increase in bearing capacity decreases with an increase in the steel ratio of CFST, and the coefficient of ductility increases with the increase in the steel ratio.

Axial compressive behavior of CFRP reinforced concrete filled steel tube short columns with a circumferential gap

Carbon fiber reinforced polymer (Carbon Reinforced Polymer Plastic) can effectively use its own tensile properties to provide stronger restraint for concrete, and can delay the buckling of steel pipes after yielding, and has been widely used in engineering repair and reinforcement. For the CFST composite structure with annular void defects, whether the reinforcement of CFRP can make up for a series of problems caused by void defects is still a fog. In order to explore the axial compression performance of CFRP (carbon fiber cloth) reinforced concrete-filled steel tubular short columns with circumferential void defects, 12 CFRP-reinforced CFRP short columns with circumferential void defects were proposed to be reinforced with a void ratio of 1.1-2.2%. The axial compression performance test was carried out to analyze the influence of parameters such as void ratio and the number of reinforcement layers on the axial compression performance, and a corresponding finite element model was established to assist in analyzing its working mechanism. The test results show that with the increase of the void ratio, the ultimate bearing capacity and the corresponding displacement of the components show a downward trend, and the deformation capacity is also greatly weakened. The ductility of the empty specimen is significantly improved, and the ductility of the specimen is also strengthened. With the increase of the number of reinforcement layers, the buckling deformation restraint effect of CFRP on the steel pipe becomes more and more significant, and it also provides better hoop restraint for the core concrete. To a certain extent, CFRP can reduce the effect of annular voiding defects.

Axial compression performance of high-temperature-exposed concrete-filled steel tubular columns repaired with carbon fiber reinforced polymer

Axial compression tests were conducted on high-temperature-exposed round concrete-filled steel tube (CFST) short columns repaired with carbon fiber reinforced polymer (CFRP) to test the influence of temperature, CFRP-wrapped layers and concrete strength on compressive performance. The experimental data were plotted as load–displacement and load–hoop strain curves, and the variation laws of the curves were analyzed. The load–displacement curves contain elastic, elastoplastic, and plastic strengthening phases. A finite element model of a high-temperature-exposed CFST column repaired with CFRP was established to analyze the stress changes in the CFRP, steel tube, and concrete. CFRP improves the bearing capacity, stiffness and ductility of CFST columns that were damaged by high temperatures. As the number of CFRP layers increased, the bearing capacity of the repaired columns improved, and deformation was delayed. Taking into account the damage of temperature and the restraint effect of CFRP, an equation was developed to evaluate the axial compression bearing capacity of high-temperature-exposed CFST columns repaired with CFRP.

Axial compression experiment and numerical simulation of CFST short columns at an ultra early age

To study the axial compression performance of ultra-early-age concrete-filled steel tube (CFST) short columns, axial compression tests were carried out on short columns of CFSTs with different wall thicknesses of steel tubes and different concrete ages. The load-displacement curves and failure modes of CFST short column specimens under different concrete ages were obtained. The influence of wall thickness and concrete age on the mechanical properties of ultra-early-age CFST specimens was analyzed. The calculation formula for the bearing capacity of mature CFST short columns in GB50936–2014 was extended, and a new calculation formula for calculating the bearing capacity of ultra-early-age CFST short columns was proposed. Considering that there is no known concrete stress-strain expression for ultra-early-age CFST short columns in existing literature, this paper has adjusted the constitutive model of the core concrete in ordinary CFSTs and advanced a stress-strain relationship suitable for the core concrete in ultra-early-age CFST short columns.

Axially-compressed behavior of carbon-FRP strengthening CFT short columns having circumferential void defects

To clarify the viability of externally bonding carbon-fiber-reinforced polymer (FRP) for strengthening the structural integrity of concrete-filled steel tube (CFT) short columns having circumferential void defects, this study comprehensively explores the strengthening effectiveness of various wrapping parameters (i.e., carbon-FRP strength, wrapping layers, and wrapping ratio) on the axially-compressed CFT short columns with various void ratios, material strengths, and geometric parameters by numerical method. Detailed mechanical responses, encompassing failure patterns, load-shortening (N-Δ) curves and stress distribution, are delved to reveal the strengthening mechanisms. Finally, strength prediction formulas for these composite columns are proposed rooted in the ring extension and local force transmission theories. Results show that the presence of initial voids delays the occurrence of steel-concrete contact stress (p) and weakens the p-value at peak load, thus reducing the axial resistance of column. Particularly when the void ratio exceeds 0.2%, the longitudinal strain when the concrete contacts with outer tube is beyond the concrete's peak compressive strain, thus the shape of the N-Δ curve is obviously changed, exhibiting two peaks. Externally bonding carbon-FRP strips can obviously improve the peak load of the column with a void ratio ≤ 0.2%. If the void ratio exceeds 0.2%, externally bonding carbon-FRP strips can also improve the column's second peak load, even exceeding the strength of pure CFT column, while it has no effect on the first load. The formulas proposed herein have a satisfactory accuracy based on the tested validation, which are expected to guide the design of strengthening scheme in engineering.

Axial behaviour of CFRP strips confined lithium-slag concrete filled square steel tube stub columns

10 square columns with different lithium slag (LS) content were designed and tested under axial load condition to investigate the compressive behavior of lithium slag concrete filled steel tube (LSCFST) short columns externally confined by CFRP strips. It is found in this paper that the failure mode of CFRP strips confined square LSCFST stub column is CFRP strip fracture and local buckling of square steel tube. The confinement of CFRP strips is able to limit dilation tendency of columns, more layers and smaller spacing allow their bearing capacity to obtain a greater enhancement rate. And columns with LS replacement rate of 20% have the best bearing capacity, ductility and initial stiffness. A calculation method for the ultimate strength of this kind of columns was put forward eventually.

Axial compression behavior and stress–strain relationship of slurry-wrapping treatment recycled aggregate concrete-filled steel tube short columns

Abstract The utilization of recycled concrete can effectively solve the problems of large accumulations of construction waste and the constant consumption of natural aggregates. Slurry-wrapping modification and concrete-filled steel tubes (CFSTs) are effective approaches to enhance the utilization ratio of recycled concrete. The study involved 4 ordinary CFST columns and 16 slurry-wrapping recycled aggregate concrete-filled steel tube (SRACFST) columns. The variable parameters included the slurry-wrapping recycled aggregate replacement ratio and the section form. The result shows that the ultimate strength of the specimens reached the minimum and maximum at 25 and 100% aggregate replacement ratio. The favorable strength performance of the SRACFST columns is attributed to the dominant positive effect of the slurry-wrapping treatment in reducing matrix porosity over the negative impact of the recycled aggregate’s complex interface transition zone. Due to the hoop factor, the residual bearing ratio peaks at a 25% substitution ratio. Four design standards were used to predict the ultimate strength, with GB50936 and EC4 yielding more accurate estimations, while AISC360-10 and AIJ provided conservative estimations. This study presents the equations of the stress–strain curve for the whole axial compression process, which can be directly applied in the theoretical and numerical analysis of RACFST columns.

Confinement-based direct design method for fibre reinforced polymer confined CFST short columns

The paper presents a detailed analysis of the behaviour of circular and square concrete filled steel tube (CFST) short columns strengthened externally with carbon or glass fibre reinforced polymer sheets (CFRP or GFRP, respectively). A thorough review of existing test information is presented and discussed, and the most salient parameters in terms of the overall strength are identified. There are a large number of influential and inter-related parameters which affect the load-carrying capacity, including the geometry, cross-sectional shape, type of steel, concrete strength, boundary and loading conditions, and type of FRP. It is shown that existing design approaches do not reliably predict the strength for the full range of possible parameters. Therefore, this paper proposes a new design model to calculate the axial compressive strength of FRP-confined concrete filled steel tubular (CFST) short columns with either a circular or square cross-section. The method accounts for the various complexities which affect the behaviour, yet presents a user-friendly, performance-based design expression. It is based on an evaluation of the lateral confining pressure provided by the both the FRP and the steel tube to the concrete core. This is employed in the confinement-based direct resistance calculations. The paper validates the approach by comparing its capacity predictions with a large database of experimental results and alternative design models available in the literature. The results show that the proposed model provides much accurate strength predictions with greater reliability for the full range of parameters examined, than existing methods.

Performance of SSC filled circular steel tube short columns under axial compression

Steel slag concrete (SSC) filled steel tube (SSC-FST), reusing the waste steel slag, is a new type of composite members, therefore shows advantages in sustainable use of resources. In order to investigate axial compressive performance of this new types of SSC-FST short columns with circular section, ten specimens with varied steel slag aggregate (SSA) replacement ratio and cross-sectional steel ratio (α) were tested. The failure patterns, load versus deformation relationship and mechanical indexes (axial capacity, elastic modulus and ductility) of the specimens were recorded and analyzed. The test results indicate that, generally, replacing natural aggregates with SSAs and improving α lead to better structural performance of circular SSC-FST short column specimens. Moreover, a refined finite element (FE) model considering the initial strain of core concrete before loading was established to simulate the performance of circular SSC-FST short columns under axial compression, and the FE model was validated through experimental results from this research and the literature. Based on the verified FE model, the mechanism of axially compressed circular SSC-FST short columns was further analyzed. Finally, simplified equations were proposed to predict the axial capacity of circular SSC-FST short columns, and generally the calculated results show good agreement with the numerical/experimental results.

Loading performance of reinforced and recycled aggregate concrete-filled circular steel tube short column with different steel ratios

Experimental and numerical studies were conducted to clarify the influencing law of steel ratio on the mechanical properties of reinforced and recycled aggregate concrete (RAC)-filled circular steel tube short columns (R-RACFST) with 100% recycled coarse aggregate (RCA) replacement. Concrete-filled steel tube (CFST), RAC-filled steel tube (RACFST) and R-RACFST test series were designed using five different wall-thicknesses of steel tube with two replicates for each wall-thickness. Based on the test, the influencing law of steel ratio on the failure, loading performances and ductility was analyzed, and the improving effect of reinforcement on the behavior of R-RACFSTs was confirmed, and the finite element (FE) model was developed, and the FE simulations were then performed considering the coupling effect between the wall-thickness of steel tube, reinforcement and strength of RAC. The strength prediction equations of CFSTs from codes such as T/CECS 625, GBT51446-2021, GB50936-2014, ANSI/AISC A360-16, AIJ, Eurocode 4 and AS/NZS 5100.6 were studied and their applicability to RACFSTs was confirmed. Meanwhile, novel equations for predicting the strength of R-RACFSTs were proposed and verified. The results demonstrate that: R-RACFST makes it possible to fill RAC with 100% RCA; when combined with an appropriate amount of reinforcement, R-RACFSTs with thinner steel tube performs as well or better than RACFSTs with thicker steel tube; reasonable ranges of steel ratio and confinement index for R-RACFSTs are recommended as 6.2%∼12.8% and 0.78 ∼ 1.53, respectively; the proposed equations are accurate and reliable, and can be applied to design the load bearing capacity of axially loaded R-RACFSTs.

Axial compressive behavior and design of high-strength square concrete-filled steel tube short columns with embedded GFRP tubes

This paper proposed a hybrid column by embedding glass fiber-reinforced polymer (GFRP) tube into high-strength square concrete-filled steel tube (CFT), named as high-strength square steel-concrete-GFRP concrete (SCFC) column. A total of 13 high-strength square SCFC short columns were tested. The test parameters included diameter and thickness of GFRP tube, width and thickness of steel tube, yield stress of steel, and compressive strength of concrete. Results showed that high-strength square SCFC short columns exhibited post-yield strengthening behavior and stable residual strength. The axial strength, confining effect, and ductility were improved because of the embedded GFRP tube. Detailed finite element models were developed and benchmarked to investigate the strength contribution of each component and conduct parametric studies. It was shown that: (i) the concrete infill and the steel tube contributed >90% to the overall compressive strength and (ii) the strength improvement by embedding GFRP tube was closely related to the section size ratio, confinement ratio of the GFRP tube, and confinement ratio of the steel tube. Evaluation of the current equations showed that they were not accurate enough to estimate the axial compressive strength of high-strength square SCFC short columns. New equations were then proposed.

Research on eccentric-compressive behaviour of steel-fiber-reinforced recycled concrete-filled square steel tube short columns

This study, a total of 25 specimens, aims to assess the influence of the mass replacement percentage of recycled coarse aggregates (0%, 50%, 75%, and 100%), steel tube thickness (3 mm, 4 mm, and 5 mm), load eccentricity (0.10, 0.25, and 0.40), and volume fraction of steel fiber (0%, 0.6%, 1.2%, and 1.8%) on the eccentric-compressive behaviour of steel-fiber-reinforced recycled concrete-filled square steel tube short columns. The post-peak mechanical behaviour, deformation ability, and energy consumption degrade with increasing mass replacement of recycled coarse aggregate; the load eccentricity is detrimental to the ultimate compressive strength and aggravates the lateral deflection; thicker steel tubes and the incorporation of steel fiber improve the ultimate compressive strength, deformation ability, and energy consumption. Moreover, an incremental iteration model is proposed to calculate the ultimate compressive strength of steel-fiber-reinforced recycled concrete-filled square steel tube short columns under eccentric-compressive load. Compared to current codes, the predicted values using the proposed model are close to experimental values and are inclined toward the safe side.

Axial compressive performance of seawater sea sand concrete-filled CFRP-stainless steel tube short columns

In order to improve the bearing capacity and durability of thin-walled stainless steel structures, the internal and external walls of stainless steel tube were pasted with CFRP to form CFRP-stainless steel composite tube, and the axial compressive mechanical properties of seawater sea sand concrete-filled carbon fiber-reinforced polymer (CFRP)-stainless steel tube (SCSST) short columns were investigated in this study. Twenty-one specimens were tested with the CFRP pasting methods and the number of CFRP pasting layers as the variation parameters. The results indicate that the failure modes of the specimens without CFRP and internal CFRP specimens were shear damage, while the external CFRP specimens were waist drum damage, all CFRP were fractured. CFRP and stainless steel tube had good cooperative performance. The bearing capacity, damage and energy absorption suppression of specimens were improved with the increase of CFRP layers, but the ductility and initial stiffness increased first and then decreased. With the same layers of CFRP, the mechanical properties of internal CFRP specimens were better than those of external CFRP specimens, and the ultimate bearing capacity could be increased by 5.5% and 8.8%. Finally, the strain-hardening effect of stainless steel was considered and a bearing capacity calculation formula of SCSST short columns based on the limit balance method was proposed, and 115 data samples were collected to verify the calculation formula.

Optimum reinforcement ratio of axially loaded reinforced concrete-filled square steel tube column

For the purpose of clarifying the influencing mechanisms of the longitudinal reinforcement on loading performances of Reinforced Concrete-Filled Square Steel Tube (R-CFSST) short columns under axial load, experimental and numerical studies were performed. Setting the longitudinal reinforcement ratio as parameter, ten R-CFSSTs with five different ratios and three Concrete-Filled Square Steel Tube (CFSST) specimens for comparison were fabricated and tested. Based on the test, the influencing law of longitudinal reinforcement on failure, loading behavior, stiffness, peak load, composite efficiency, ductility and stress state of steel tube of R-CFSSTs were theoretically investigated. A novel material model and simulation method for concrete core was proposed and verified against the test, and thereafter 32 model specimens with four wall-thicknesses of steel tube coupling with eight reinforcement ratios were simulated. The strength prediction equations from ANSI/AISC A360–16, Eurocode 4 and AS/NZS 5100.6 and GB 50936–2014 were studied, modified and compared each other, and based on the test and simulation results, novel equations were proposed and validated against the experiment. The results demonstrate followings: longitudinal reinforcement significantly impacts the behavior of R-CFSSTs as the steel tube does, and thus it is recommended to configure reinforcements in CFSST for the improved performances; proper ratios of longitudinal reinforcement enable the R-CFSSTs to acquire better balance between performance and construction cost, and a range for the optimum ratios is recommended between 1.0% and 3.2%, regardless of wall-thickness of steel tube; the proposed equations are recommended for more accurate and stable prediction of load bearing capacity of R-CFSSTs.

Behaviour and design of high-strength octagonal CFST short columns subjected to combined compression and bending

A systematic experimental and numerical investigation on the behaviour of octagonal concrete-filled steel tube short columns fabricated with S690 high-strength steel and C90 high-strength concrete, and subjected to combined compression and bending is reported in this paper. Experiments were firstly performed on twelve short column specimens with different plate width-to-thickness ratios. The experimental results and observations including the ultimate loads, load versus displacement responses and failure modes of the specimens were discussed. In supplementary to the experimental investigation, numerical investigation using a validated finite element model was performed to examine the behaviour of the structures with a wide range of plate width-to-thickness ratios, yield strength of high-strength steel and compressive strength of high-strength concrete that subjected to various combinations of compression and bending. Based on the experimental and numerical results, the applicability of existing design approaches in standards was also evaluated. The assessment shows that the design approaches provide conservative strength predictions for the high-strength octagonal concrete-filled steel tube short columns under combined compression and bending and can be applied to provide safe designs for the structures.

A theoretical model for predicting mechanical properties of circular concrete-filled steel tube short columns

Circular concrete-filled steel tube (CCFST) short columns have superior mechanical properties and broad application prospects. To rapidly predict its mechanical properties, this paper introduced both the similarities and differences of existing models, evaluated the influence of debonding effect and radial stress on CCFST short columns, selected mechanical properties for materials, considered the stress-path dependence of concrete and the strain hardening of steel tubes, and proposed a theoretical model calculated by an incremental-iterative program. Results suggest that ignoring the radial stress and the de-bonding effect has little effect on the mechanical properties of CCFST short columns without local buckling. As the axial strain increases, the influence of the stress-path dependence on the concrete increases. The concrete in CCFST short columns has no stress-path dependence when the confinement factor is greater than 2.5. In the prediction of hoop strains, load components, load-axial strain curves, and axial load capacity, the proposed model is effective and accurate and is superior to the existing models.