Strength Steel Tubes Research Articles

Reliability Analysis of Axial Compressive Strength of Concrete-Filled Steel Tube (CFST) under Coupled Corrosion and Load Effects

This paper presents a finite element analysis (FEA) of and reliability study on concrete-filled steel tube (CFST) members under the combined effects of corrosion and compressive loading. First, a stochastic-based FE model is established through the proposed secondary development program based on ABAQUS 2021 software. The model could account for the uncertainties of material, geometric, and corrosion effect on CFST members. The reliability of the built model was validated through experimental data of corroded CFST members under compression loading. Subsequently, the compressive performance of CFST under a combination of corrosion and loading was further investigated by numerical parameter analysis. A total of 1800 models were created to clarify the coupling mechanism among the core concrete strength, the steel tube strength, the steel ratio, and the maximum strength of the CFST member. Three theoretical formulas presented in classical design standards were used to calculate the axial compressive strength of the corroded CFST, and the uncertainty parameters μkp and δkp were also obtained for the discussed design formulas. Finally, the First Order and Second Moment (FOSM) method was employed to estimate the reliability indices β across different standards. The calculations revealed that the reliability indices β according to European standard ranges from 2.93 to 5.52, with some results falling below the target reliability index βT of 3.65. In addition, the multi-parameter coupling effects on reliability index β were investigated, and the main influencing factors were obtained. By leveraging the reliability analysis, reasonable design requirements can be proposed for CFST members under the coupling effects of corrosion and external load, which provides a design basis for the CFST member.

Eccentric load capacity of ultra-high strength concrete-filled steel tubular lattice short columns

To explore the behavior of ultra-high strength concrete filled steel tubular (UHSC-FST) lattice short columns under eccentric compressive loads, experimental analyses on four specimens and 276 finite element models using ABAQUS were conducted. The study focused on the effects of steel tube wall thickness, concrete strength, steel tube strength, and load eccentricity on failure modes, load-displacement curves, and ultimate load-bearing capacity. Results showed that for columns with minor eccentricity-induced compressive failure, the reduction coefficient of ultimate load capacity has a weak correlation with the parameters. However, for columns with significant eccentricity-induced tensile failure, the reduction coefficient increases with steel tube thickness and strength and decreases with concrete strength. The center-to-center distance of the columns has a minor effect. Based on these findings, a comparative analysis of existing standards was conducted, leading to the development of an accurate method for calculating the ultimate load-bearing capacity of eccentric CFST lattice columns. This method is applicable to various cross-sectional dimensions, material strengths, and steel tube wall thicknesses, with calculation errors within 10 %, ensuring it meets engineering precision requirements.

Waste rubber recycling in concrete-filled steel tube members: mechanical performance, reliability and life cycle assessment

This paper focuses on the axial compression mechanical performance, reliability analysis and environmental impact of rubber concrete-filled circular steel tube (RuCFST) columns. Initially, the research of the axial compression performance reveals that enhancing the wall-thickness or yield strength of steel tubes variably increases the yield, peak, and ultimate loads of RuCFST columns. The degree of enhancement of each characteristic point by growing the wall thickness of the steel tube is 5% to 44%, 6% to 44%, and 9% to 44%, respectively; while the degree of enforcement is 5% to 55%, 23% to 53%, and 24% to 61%, respectively, upon yield strength increase. Reliability analysis indicates that higher concrete grades decrease the probability of axial compression failure in RuCFST columns. Raising the yield strength and wall-thickness of steel tubes leads to a reduction in the reliability index. Both larger and smaller live-to-dead load effect ratios adversely impact the reliability index. In addition, the life cycle assessment method was used to evaluate the environmental impact of RuCFST columns, and the analysis was made after considering the superposition effect of waste rubber incineration and recycling into rubber aggregates.

Data-driven axial bearing capacity analysis of steel tubes infilled with rubberized alkali-activated concrete

This study aims to employ machine learning algorithms to analyze the axial bearing capacity of rubberized alkali-activated concrete filled steel tubes. A dataset encompassing 327 synthesized instances and seven input features is adopted for training and testing six machine learning models, including Decision Tree, Random Forest, Extremely Randomized Trees, Adaptive Boosting, Gradient Boosting Decision Trees (GBDT), and eXtreme Gradient Boosting Trees (XGBoost). The SHapley Additive exPlanation algorithm is employed to elucidate the prediction process of machine learning models and to analyze the influence of each parameter on axial bearing capacity. Comparison of evaluating metrics shows that GBDT and XGBoost models achieve highest accuracy and generalization capabilities when their Coefficient of Determination values surpassing 0.98 and Mean Absolute Percent Error remaining below 3%. Moreover, the explanation analysis of machine learning models reveals that diameter/width of the cross section, rubber content, yielding strength and thickness of steel tubes are critical variables that affect the axial bearing capacity, while compressive strength of alkali-activated concrete, specimen height, and shape of cross section show negligible impact. Besides, GBDT model overemphasizes the effect of specimen height and might lead a conservative prediction for specimens with smaller heights. Finally, compressive strength of alkali-activated concrete and diameter/width, thickness, and yielding strength of steel tubes are positively correlated with axial bearing capacity, and the increase of rubber content in alkali-activated concrete leads to the decrease of capacity.

Behavior of Circular Hollow Steel-Reinforced Concrete Columns under Axial Compression

The circular hollow steel-reinforced concrete (HSRC) column consists of an inner circular hollow steel tube and outer circular hollow reinforced concrete (RC). This design provides several advantages, including being lightweight, having a wide sectional profile, and having a high flexural stiffness. This paper aims to investigate the behavior of the circular HSRC columns under axial compression through testing and finite element (FE) modeling. An FE model was established to simulate the circular HSRC columns under axial compression, which was validated against the test data. Additionally, the load distribution and the interface stress between the outer hollow RC and inner steel tube were analyzed. Subsequently, a systematic parametric analysis was conducted on the diameter (d) and thickness (t) of the steel tube; slenderness ratio (λ); strength of concrete (fcu); yield strength of steel tube (fsy), longitudinal rebar (fly), and stirrup (fgy); as well as the stirrup spacing (s). The critical influencing factors of the circular HSRC columns under axial compression were identified. fcu, λ, d, fly, and fsy dramatically influence the bearing capacity, and the stiffness is notably affected by λ and fcu. Finally, three simplified design methods were summarized and evaluated for calculating the bearing capacity of the circular HSRC columns under axial compression.

Fire test and simulation of circular steel tube confined steel-reinforced concrete columns

Steel tube confined steel-reinforced concrete (STCSRC) columns are novel steel-concrete composite columns where the steel tubes are disconnected at beam-column connections. Few researches have been conducted on the fire behaviour of STCSRC columns by now, though there are some relevant studies on the fire performance of steel-reinforced concrete-filled steel tubular (SR-CFST) columns. However, the mechanical behaviour of STCSRC columns under fire exposure differs from that of SR-CFST columns due to the discontinuous external steel tube. It is essential to carry out a study on the fire performance of STCSRC columns. The fire tests of four axially loaded STCSRC columns were carried out in this paper, and the failure mode, distribution of cross-sectional temperature, fire resistance, and lateral deflection were discussed. A finite element model was developed and validated with test results, and then a parametric analysis of the STCSRC stub and slender columns under fire exposure was performed. The load ratio, steel tube strength, the area ratio of steel tube to concrete, and slenderness ratio have an adverse effect on the fire resistance of STCSRC columns, whereas cross-sectional dimension, area ratio of steel section to concrete, and strength of steel section have a favourable impact. Concrete strength has a different influence on the fire resistance of STCSRC stub and slender columns. Finally, based on the specifications JGJ/T 471-2019 and EN 1994-1-2, simplified calculation methods for assessing the fire resistance of STCSRC columns were proposed.

Eccentric compression capacity of bolt-welded joints in concrete-encased CFST

The new bolt-welded joint in concrete-encased Concrete-Filled Steel Tube (CFST) without cutting flange demonstrates great mechanical properties and durability, which is also easily constructed at high altitudes or in long-span arch bridges. It is crucial to study the mechanical properties of composite member made of the bolt-welded joint and outer concrete. In this study, a parametric analysis on bearing behavior of bolt-welded joints in concreted-encased CFST under eccentric compression was explored, based on experiments and a validated finite element model. Furthermore, a simplified calculation formula for the eccentric bearing capacity of the bolt-welded joint in concreted-encased CFST was proposed. The results indicated that the bearing capacity increased with the increase of steel tube strength, core concrete strength, reinforcement strength, outer concrete strength, steel ratio, and reinforcement ratio. Increasing the steel ratio and the steel tube diameter-section ratio can enhance the ductility of the member. A rise in stirrup spacing had a detrimental impact on both bearing capacity and ductility. An excessive amount of eccentricity diminished the bearing capacity of the member and alter its failure mode. The proposed simplified calculation formula for eccentric bearing capacity was in strong agreement with both experimental and numerical results.

Flexural behavior of high-strength RCFST column-to-column connections

This paper investigates the flexural behavior of high-strength rectangular concrete-filled steel tubular (RCFST) column-to-column connections with different configurations. Based on the tests, 35 additional finite element analysis (FEA) models were developed to perform the parametric analysis varying with the cross-sectional size effect of (D), the width-to-thickness ratio of steel tube (D/t), steel tube strength (fs,y), steel bars strength (fr,y), concrete strength (fc,r), length of steel bars (L), arrangement and quantity of steel bars, respectively. The current code underestimated the yield and plastic bending moment compared with the calculated results from GB 50010–2010, ACI 318–19, EN 1992–1-1:2004, and JSCE-SSCS-2007. Finally, the strain coordination method and the full plastic section method were proposed to calculate the yield and plastic bending moment of the connection.

Passive stress-strain model and ultimate strength prediction for short steel tube confined concrete (STCC) columns allowing for size effect

Steel tubes can significantly enhance the strength and ductility of concrete-filled steel tube (CFST) and steel tube confined concrete (STCC) columns. Existing research work have mainly focused on the former type while the later type of members not only avoid longitudinal steel bulking but also provide better ductility performance to resist seismic loads which is further investigated in this paper. Based on partial-interaction shear-friction mechanics, a passive stress-strain model for short steel tube confined concrete columns is proposed. The main benefit of the proposed model is that it is based on mechanics for rectangular and circular cross-sections which could allow for the size effect. Besides, this model also gives the ultimate strength of steel tube confined concrete columns and is further simplified as a design-oriented approach. The proposed passive stress-strain model and the simplified model for the ultimate strength of concrete columns show good correlation with experimental data. Compared with three other existing approaches, the simplified model could enhance the computing efficiency to a new level. Then a parametric study is conducted to investigate the effect of specimen size on the behaviour of steel tube confined concrete columns.

Behaviour of Slender Hybrid Rubberised Concrete Double Skin Tubular Columns under Eccentric Loading

Rubberised concrete, utilised as infill material within single- or double-skin confinements, has emerged as a sustainable solution, offering improved ductility in structures. Past studies have indicated promising results regarding the axial response of hybrid columns comprising filament wound exterior tubes, rubberised concrete infill, and steel interior tubes. This paper investigates the response of such hybrid columns under eccentric compression using validated numerical techniques. An extensive parametric study is conducted to explore the effects of load eccentricity, rubber percentage, concrete strength, and steel tube strength. Results show that despite credible increases in rubber percentage and load eccentricity, the columns have reasonably good performance. The findings facilitate the prediction of the eccentric behaviour of these hybrid columns across varying rubber percentages, confirming its viability for practical applications under realistic eccentric load conditions. The results further affirm the suitability of this hybrid column in scenarios that necessitate higher ductility.

Axial compression behavior of square section concrete-filled steel tubes reinforced with internal latticed steel angles

The axial compression behavior of square CFSTs (concrete-filled steel tubes) reinforced with internal latticed steel angles was investigated in this study, and the test results including load-displacement and load-strain behavior, failure modes, and ultimate load were obtained. The experimental results demonstrated that the steel angles exerted an additional confining effect on the enclosed concrete, and altered the stress distributions of the adjacent concrete. The corresponding finite element model was established subsequent to the experiment, and the analysis and discussion of the axial compression mechanisms was conducted. The parametric analysis was performed to evaluate the influence of main parameters on the load-displacement behavior, and the analysis results revealed that the concrete made the highest contribution to the ultimate load. Additionally, the formulas for calculating the ultimate load were proposed according to the superposition method, and the calculation results demonstrated that the design formula derives from the unified theory of CFSTs exhibit enhanced accuracy and reduced deviation. Finally, a reliability analysis was conducted to evaluate the feasibility of the proposed design formula, and the analysis results indicated the calculated reliability index decreases with an increase in the steel ratio, and for specimens with a higher steel ratio, a lower yield strength of steel tube leads to a lower reliability index.

Experimental research on load separation of concrete-filled circular steel tube short columns

In recent years, scholars from various countries have conducted extensive experiments and analytical studies on the axial compressive behavior of circular concrete-filled steel tube (CFST) columns. However, the existing research has been based on overall loading analysis of circular CFST columns, making it difficult to accurately measure the loads borne by the steel tube and the core concrete separately. In order to better study the axial compressive behavior of circular CFST columns, this paper adopts the load separation device proposed by Hong-Song Hu and prepares 16 specimens with different concrete strengths for axial compression tests, directly measuring the load components of circular CFST columns under axial compression. The feasibility of the superposition principle is revealed at the experimental level. Furthermore, the compressive strength of the concrete and the compressive strength of the steel tube in circular steel tube concrete columns are analyzed. The results indicate that there is a certain discrepancy between the calculated steel tube strength based on existing formulas and the experimental values. However, for safety considerations, a reasonable estimation of the steel tube compressive strength can be made. Utilizing the measured stress-strain values of concrete and steel, the existing stress-strain models are evaluated, and a more reliable stress-strain model is established.

Mechanical properties of CFST column with bolt-welded joints under eccentric compression

With the increase of arch bridge span and difficulty in welding construction, the traditional connection method of arch rib steel tube cannot satisfy the requirements of construction safety and economy. In this paper, a new bolt-welded connection method for arch rib of long-span Concrete Filled Steel Tubular (CFST) arch bridge is proposed, which can avoid the stress redistribution of joints of arch rib caused by cutting the joint flange in the traditional connection method. In order to study the mechanical properties of the bolt-welded joint of CFST, the eccentric compression scale tests were carried out, and the finite element model is validated based on the experiment. The parameter analysis was performed and the calculation formula of eccentric bearing capacity of bolt-welded joint of CFST is proposed. The results show that the bolt-welded joint can significantly improve the stiffness, stability and effectively avoid buckling at the joint. With the increase of steel tube strength, core concrete strength and steel ratio, the bearing capacity of bolt-welded joints of CFST significantly improved, and the bearing capacity of bolt-welded joints under small eccentric is better than welded joints. The bolt-welded area ratio is recommended not to exceed 0.3. The calculation results of the proposed formula are consistent with the experimental and simulated results.

High-strength concrete-filled steel tube columns with tie bars: Seismic behavior and design

The current study reports the utilization of tie bars to connect the opposite faces of steel tubes in the plastic hinge regions to strengthen the deformability of square high-strength concrete (HSC)-filled steel tube (CFST) columns. To evaluate the seismic performance of square HSC-filled steel tube columns with tie bars, four CFST columns with tie bars (TBCFST) and four CFST counterparts with concrete strength of about 125 MPa were examined. The test variables included the tie bar spacing, steel tube strength, and axial load ratio. It was found that when the height of the tie bar-confined region was equal to the steel tube width and the tie bar confinement index (λm) was in the range of 0.09 to 0.17, the local buckling of steel tube and concrete crushing were primarily concentrated in the unconfined zone adjacent to the tie bars. Finite element analysis was also conducted and showed that the ultimate drift ratio (θu) of the columns enhanced linearly with the increase in λm and confinement index of CFST (ξs), but diminished swiftly with an increase in the axial load ratio (n). For a given value of λm, θu increased with the increase in the tie bar columns (ntb). The flexural moment capacity ratio (Mtu/M0u) of the TBCFST column to the CFST counterpart increased as λm increased. The ratio Mtu/M0u did not follow a clear trend with the variation of ξs and n, but increased slightly with the increase in ntb. The minimum requirements for the design of tie bars were proposed.

Behavior of semi-prefabricated steel-tube double-layer concrete columns under eccentric compression

ABSTRACT To promote the application of steel-reinforced-concrete structures in prefabricated concrete structures, the semi-prefabricated steel-tube double-layer concrete (SPSTDC) column was proposed. The eccentric compression mechanical behavior was studied through theoretical analysis, experiments, and numerical simulations. Three possible failure modes, namely, compression failure, total yield failure, and tension failure, were obtained. Then, corresponding calculation methods of the bearing capacity (N u) were established and their effectiveness was verified through comparison with test results. The analysis results showed that N u decreased with the increase in the eccentricity. N u increased with the precast concrete strength, and its effect on N u diminished with increasing eccentricity. The post-cast concrete strength had a smaller effect on N u than the precast concrete strength. N u increased with the increase in the steel ratio α a, while the steel tube strength had little influence on N u. The N–M curve of the SPSTDC column could be divided into three segments, corresponding to the three failure modes. For the compression failure mode, the ultimate load N s decreased with the increase in the ultimate bending moment M s. For the other two failure modes, the pattern was the opposite. The eccentricity had a significant impact on the horizontal lateral deflections of the SPSTDC columns. With the increase in the eccentricity, the horizontal lateral deflection corresponding to N u increased. The horizontal lateral displacement of the mid-height section remained the largest compared with those of other sections. The lateral stiffness increased with the increase in the concrete strength, steel strength, and steel ratio. The impact of the precast concrete strength was the most significant while the influence of the steel tube strength was the weakest.

Seismic performance of composite jacket-confined square high-strength concrete-filled steel tube columns

Adding external confining jackets in the potential plastic hinge regions is a practical approach to improving the deformation capacity of square concrete-filled steel tube (CFST) columns with high-strength concrete (HSC). To investigate the seismic behavior of composite jacket-confined square CFST columns with HSC, three jacket-confined CFST (JCCFST) columns and two CFST counterparts with concrete compressive strength of approximately 125 MPa were tested. The test variables included the jacket configuration and steel tube strength. The test results demonstrated that both the jacket-confined region and the adjacent unconfined region could be damaged when the jacket length was 1.25 times the steel tube width. Finite element analyses were also performed to comprehensively investigate the influence of the parameters on the column behavior. It was found that the ultimate drift ratio, θu, increased approximately in proportion to the effective jacket confinement index, λm, and the confinement index of the CFST section, ξs, and decreased rapidly as the axial load ratio, n, increased. The ratio of the moment capacity of a JCCFST column to that of the corresponding CFST column, Mju/M0u, increased as λm increased. The influence of n and ξs on Mju/M0u was not significant. Formulas for designing the confining jacket were also developed.

Experimental study on torsional behavior of tapered high strength thin-walled concrete-filled double-skin steel tubular columns

Comparing with traditional straight concrete-filled double-skin steel tubular (CFDST) members, tapered CFDST members have been increasingly used in the domain of power industry due to esthetics and special spatial experience. In addition, the utilization of high strength materials can reduce cross-sectional area and further lower construction cost. In this paper, the torsional behavior of tapered high-strength thin-walled CFDST (THSTW-CFDST) columns with or without longitudinal stiffeners was investigated and a total of twenty tapered THSTW-CFDST specimens were tested. The failure modes, torque-torsional angle curves and torsional capacity of the THSTW-CFDST columns were investigated. The results demonstrate that the installation of stiffeners can significantly improve the local stability of thin-walled steel tubes, but reduce the torsional capacity of the members. Compared with THSTW-CFDST specimens without stiffeners, the torsional capacities of those with stiffeners have been apparently reduced. Based on the experimental results, the finite element (FE) model was developed and verified, and then utilized to ascertain the force-transfer mechanism and the stress development process of each component of THSTW-CFDST columns. In addition, the effects of the various parameters including hollow ratio, diameter-to-thickness ratio, inner steel tube strength to outer steel tube strength ratio, concrete strength the torsional behavior of THSTW-CFDST members were quantitatively assessed. Finally, the accuracy of the existing methods for predicting the torsional capacity of THSTW-CFDST members was evaluated.

Parameter analysis and design on socket CFST column-cap beam joint with UHPC grouted connection

The excellent mechanical properties of concrete-filled steel tube (CFST) make it a competitive alternative to column-cap/foundation cap socket connections in accelerated bridge construction (ABC). To investigate more research parameters and facilitate the seismic design of socket CFST column joints, a detailed numerical analysis model of socket column-cap beam joint was established and verified by experimental data, and the bearing capacity and failure modes of socket joints under the dimensions of the CFST parts and their material properties were investigated as well. It is found that the size of steel tube, the strength of steel tube, the socket depth of CFST, and the type of forming hole have significant effects on the strength and failure modes of column to cap beam socket joints. This study also proposed a moment calculation method for socket joints that can accurately predicts the bearing capacity under different failure modes. Finally, a design process was developed to facilitate the widespread application of this socket CFST column-cap beam joint with Ultra High-Performance Concrete (UHPC) grouted connection.

Application of ensemble model in capacity prediction of the CCFST columns under axial and eccentric loading

Understanding the load-carrying capacity of circular concrete-filled steel tube (CCFST) columns is crucial for designing CCFST structures. However, traditional empirical formulas often yield inconsistent results for the same scenario, causing confusion for decision makers. Additionally, simple regression analysis is unable to accurately predict the complex mapping relationship between input and output variables. To address these limitations, this paper proposes an ensemble model that incorporates multiple input features, such as component geometry and material properties, to predict CCFST load capacity. The model is trained and tested on two datasets comprising 1305 tests on CCFST columns under concentric loading and 499 tests under eccentric loading. The results demonstrate that the proposed ensemble model outperforms conventional support vector regression and random forest models in terms of the determination coefficient (R2) and error metrics (MAE, RMSE, and MAPE). Moreover, a feature analysis based on the Shapley additive interpretation (SHAP) technique indicates that column diameter is the most critical factor affecting compressive strength. Other important factors include tube thickness, yield strength of steel tube, and concrete compressive strength, all of which have a positive effect on load capacity. Conversely, an increase in column length or eccentricity leads to a decrease in load capacity. These findings can provide useful insights and guidance for the design of CCFST columns.

Analysis of dumbbell-shaped CFST members subjected to combined compression and torsion loadings

In a study examining the mechanical behavior of dumbbell-shaped concrete-filled steel tubes (CFST) under combined compression and torsion, four concrete-filled steel tubes were fabricated and tested. The test results revealed that after the completion of loading, the specimens exhibited significant torsional deformation but no apparent signs of damage, allowing them to continue loading in subsequent stages.The dumbbell-shaped CFST model was analyzed using the finite element method, and the accuracy of the finite element results was confirmed by comparing them with the existing test results. Based on this, the impact of various factors on ultimate torque was investigated, including steel tube strength, concrete strength, axial compression ratio, slenderness ratio, and steel ratio. In conjunction with the analysis of finite element parameters, a straightforward calculation formula for the compression-torsion correlation curve of dumbbell-shaped CFST was proposed.