Capacity Of Columns Research Articles

Experimental investigation of CFRP-confined partially encased composite columns under axial compression

The use of fiber reinforced polymer (FRP) confinement techniques to repair partially encased composite (PEC) columns can prevent outward local buckling and corrosive damage in their flange plates. This study investigated the effects of three different carbon FRP (CFRP) strengthening schemes (including hoop, longitudinal, and bidirectional combined bonding of CFRP) on the axial compressive behavior of PEC columns with varying slenderness ratios. Fifteen specimens were tested to analyze their failure modes, bearing capacities, load-deflection responses, and load-strain responses. The results show that CFRP hoop wraps effectively enhance the strength of short columns. Longitudinal bonding of CFRP significantly improves the flexural stiffness of slender columns. Optimal load-bearing capacity enhancement can be achieved through the synergistic effect of bidirectional combined bonding of CFRP. A simplified calculation formula for the axial load bearing capacity of CFRP-confined PEC columns was also proposed, which shows a good agreement with the experimental results.

Breakthrough curve analysis of phosphorylated hazelnut shell waste in column operation for continuous harvesting of lithium from water

In batch-scale operations, biosorption employing phosphorylated hazelnut shell waste (FHS) revealed excellent lithium removal and recovery efficiency. Scaling up and implementing packed bed column systems necessitates further design and performance optimization. Lithium biosorption via FHS was investigated utilizing a continuous-flow packed-bed column operated under various flow rates and bed heights to remove Li to ultra-low levels and recover it. The Li biosorption capacity of the FHS column was unaffected by the bed height, however, when the flow rate was increased, the capacity of the FHS column decreased. The breakthrough time, exhaustion time, and uptake capacity of the column bed increased with increasing column bed height, whereas they decreased with increasing influent flow rate. At flow rates of 0.25, 0.5, and 1.0 mL/min, bed volumes (BVs, mL solution/mL biosorbent) at the breakthrough point were found to be 477, 369, and 347, respectively, with the required BVs for total saturation point of 941, 911, and 829, while the total capacity was calculated as 22.29, 20.07, and 17.69 mg Li/g sorbent. In the 1.0, 1.5, and 2.0 cm height columns filled with FHS, the breakthrough times were 282, 366, and 433 min, respectively, whereas the periods required for saturation were 781, 897, and 1033 min. The three conventional breakthrough models of the Thomas, Yoon-Nelson, and Modified Dose-Response (MDR) were used to properly estimate the whole breakthrough behavior of the FHS column and the characteristic model parameters. Li's extremely favorable separation utilizing FHS was evidenced by the steep S-shape of the breakthrough curves for both parameters flow rate and bed height. The reusability of FHS was demonstrated by operating the packed bed column in multi-cycle mode, with no appreciable loss in column performance.

Strength prediction and stochastic analysis of ultra-high performance concrete columns under the explosive blast load

The performance research based on numerical and experimental studies on ultra-high performance concrete (UHPC) generally considers it as an isotropic material, which is obviously different from what it really is in practical engineering. A database of UHPC compressive strength was investigated, having the same UHPC mix proportion as the field blast experiment, to show how the strength of UHPC varies in compression. It is found that Weibull distribution is the best fit of its probability model. A combination of Monte-Carlo and Finite Element method is used, adopting the available UHPC compressive strength, to reproduce the field blast test on UHPC columns. Both the non-spatial and spatial variability of material properties of the UHPC columns are under consideration to conduct the UHPC column strength prediction under blast loads. The residual loading capacity, damage index and failure mode of UHPC columns with different sizes damaged by different explosion severities are obtained by non-spatial simulation and spatial simulation respectively. It can be concluded that compared with the non-spatial model, the numerical simulation results of the spatial model are closer to the experimental situation. Therefore, inclusion of spatial variability is recommended for reliability-based blast-resistant design for UHPC column.

Numerical Investigation of the Ultimate Load-Carrying Capacity of Square Concrete-Filled Steel Tube Columns Considering Initial Stresses Generated during Construction

During construction, newly cast concrete exerts lateral pressure on the steel plates of concrete-filled steel tube (CFST) columns, resulting in non-negligible initial circumferential stresses. Finite element analysis, in which lateral pressure is applied using a user-defined load subroutine, was conducted to comprehensively investigate the effects of initial stresses, including circumferential stresses, on the structural behaviors of a square CFST column under the action of compressive load. This study also provides guidance for the numerical simulation of CFST columns under complicated construction scenarios. The analysis revealed that the steel tube plates were more sensitive to lateral pressure, which should be limited during construction, compared with gravity loads. Under the action of compressive load, the presence of initial stresses altered the failure modes of the square CFST columns and reduced their ultimate load-carrying capacities (ULCCs). For columns with slenderness ratios of 18 and 37, the ULCCs were essentially inversely proportional to the initial stress ratio β, ranging from 0.1 to 0.5. However, for columns with a larger slenderness ratio of 55, the initial stress level did not influence their ULCCs. Finally, a simple method for calculating the ULCCs of square CFST columns considering initial stresses is proposed for design purposes.

Influence of elevated temperature on buckling capacity of mild steel-based cold-formed steel column sections– experimental investigation and finite element modelling

PurposeThe capability of steel columns to support their design loads is highly affected by the time of exposure and temperature magnitude, which causes deterioration of mechanical properties of steel under fire conditions. It is known that structural steel loses strength and stiffness as temperature increases, particularly above 400 °C. The duration of time in which steel is exposed to high temperatures also has an impact on how much strength it loses. The time-dependent response of steel is critical when estimating load carrying capacity of steel columns exposed to fire. Thus, investigating the structural response of cold-formed steel (CFS) columns is gaining more interest due to the nature of such structural elements.Design/methodology/approachIn this study, experiments were conducted on two CFS configurations: back-to-back (B-B) channel and toe-to-toe (T-T) channel sections. All CFS column specimens were exposed to different temperatures following the standard fire curve and cooled by air or water. A total of 14 tests were conducted to evaluate the capacity of the CFS sections. The axial resistance and yield deformation were noted for both section types at elevated temperatures. The CFS column sections were modelled to simulate the section's behaviour under various temperature exposures using the general-purpose finite element (FE) program ABAQUS. The results from FE modelling agreed well with the experimental results. Ultimate load of experiment and finite element model (FEM) are compared with each other. The difference in percentage and ratio between both are presented.FindingsThe results showed that B-B configuration showed better performance for all the investigated parameters than T-T sections. A noticeable loss in the ultimate strength of 34.5 and 65.6% was observed at 90 min (986℃) for B-B specimens cooled using air and water, respectively. However, the reduction was 29.9 and 46% in the T-T configuration, respectively.Originality/valueThis research paper focusses on assessing the buckling strength of heated CFS sections to analyse the mode of failure of CFS sections with B-B and T-T design configurations under the effect of elevated temperature.

Mechanical behavior and design applicability of ultra-high-performance concrete-filled circular steel tubular short columns under axial compression

This paper presents the results of axial compression tests conducted on 12 short columns made of ultra-high-performance concrete-filled steel tubes (UHPCFST) with different diameter-to-thickness (D/t) ratios and steel fiber contents. The study aimed to investigate the interaction between infilled concrete and steel tubes as well as the confinement effect on the compressive behavior of UHPCFST short columns. Two types of load–displacement curves were observed in the test, which were related to the D/t ratio of the steel tube. Besides, the results showed that columns with smaller D/t ratios exhibited higher strength enhancement and better post-yield performance due to increased concrete confinement. Furthermore, the presence of steel fibers improved the post-yield ductility of the columns but did not significantly contribute to the strength enhancement. Owing to the longer elastic branch and less lateral dilation of UHPC compared to normal-strength concrete (NSC), the establishment of confining effect to UHPC core is relatively later than the yielding of steel tube, leading to a redistribution between axial stress and hoop stress. The test results were compared with current design codes, including Eurocode 4, Chinese code GB 50936, and American code AISC 360. The results showed that Eurocode 4 and GB 50936 overestimated the axial load-bearing capacity when considering the confinement effect of the steel tube, while the calculations by Eurocode 4 without considering the confinement effect and AISC 360 were closer to the test results. Therefore, the consideration of the confinement effect in design is not recommended and a reduction factor of UHPC is suggested to obtain a reliable prediction of the axial load-bearing capacity of UHPCFST short columns as safe as that of the CFST short columns infilled with NSC.

Square concrete-filled steel tube strengthened with carbon fiber-reinforced polymer grid-reinforced engineered cementitious composite under axial loading

This paper presents an investigation on axial compression behavior of square concrete-filled steel tube (CFST) columns strengthened with carbon fiber-reinforced polymer (CFRP) gird-reinforced engineered cementitious composite (CFGRE). A total of 19 columns, including 3 un-strengthened CFST columns, 1 CFST column strengthened with CFRP sheets, and 15 CFST columns strengthened with CFGRE, were prepared and tested. The main test parameters involved the strengthening strategy, number of CFRP grid layers, width-to-thickness ratio of the steel tube, and concrete strength grade. The CFST columns strengthened with CFGRE showed a ductile failure, with the CFRP grid rupturing at the corner. The CFGRE provided confinement to the original column in the transverse direction and, along with the bearing load contribution of engineered cementitious composite in the longitudinal direction. This resulted in a significantly greater enhancement in load-bearing capacity compared to the CFST columns strengthened with CFRP sheets. The CFST columns strengthened with CFGRE demonstrated a similar developing trend in load–deformation curves as the CFST columns during the entire loading process, indicating its strong adaptability to the original structural system. A finite element model was established to evaluate the failure process of the strengthened columns. A calculation formula was proposed to predict the load-bearing capacity of the CFST columns strengthened with CFGRE, taking into account the effect of the uneven confining pressure on the confinement provided by CFGRE.

Prediction and Interpretation of Residual Bearing Capacity of Cfst Columns under Impact Loads Based Interpretable Stacking Fusion Modeling

The utilization of Concrete-filled steel Tubular (CFST) columns is increasingly widespread. However, the assessment of the residual bearing capacity of CFST columns currently relies mainly on costly and time-consuming experiments and numerical simulations. In this study, we propose a machine learning-based model for rapidly identifying the residual bearing capacity of CFST columns. The results demonstrate that the predictions of the proposed Stacking-KRXL model align well with the actual values, with most prediction errors falling within ±10%. The RSquared value of 0.97 significantly surpasses that of other methods. The stability and robustness of the model are analyzed. Additionally, the Shapley additive explanations method is applied for global and local interpretations, revealing positive or negative correlations between different parameters and the residual bearing capacity of CFST columns, mainly influenced by the concrete area in the core region.

A unified formulation for axial compression of steel tube-confined concrete and concrete-filled steel tube stub columns

Steel-confined concrete (STCC) columns and concrete-filled steel tube (CFST) columns have different load boundary conditions. In STCC columns, the steel tube transmits minimal axial load. Existing design practices employ different formulas to predict the axial load-bearing capacity of STCCs and CFSTs based on these varying load boundary conditions. However, there has always been a practical and challenging demand for researchers and engineers to develop a unified design formula that accommodates composite columns with different sections and load boundary conditions. This demand aligns with the contemporary design concept of continuous structural design optimization. This paper proposes an analytical solution for the elastic deformation of circular STCCs under axial compression, considering the specific load boundary conditions in circular STCC columns. This solution is then extended to encompass polygonal sections, resulting in a unified formula for determining the strength of STCC columns. Additionally, the influence of load boundary conditions on the confined effect of the core concrete is quantified by reformulating and simplifying the proposed formula. These adjustments are informed by the formulation for the axial load capacity of CFST columns proposed by Yu Min et al. Finally, a simple and convenient unified formulation for calculating the axial compressive strength of both STCC columns and CFST columns is proposed for practical engineering applications.

Eccentric bearing capacity of steel reinforced reactive powder concrete columns after high temperature exposure

The three-dimensional nonlinear finite element model of steel reinforced reactive powder concrete (SRRPC) column was created to analyze mechanical properties after high temperature. Effect of temperature on mechanical behaviors of RPC, section steel and steel bars were taken into account in model. Accuracy of the temperature distribution and the prediction of eccentric bearing capacity after high temperature was verified by comparing experimental results with numerical results. Effects of eccentricity, loading angle, RPC strength, section steel strength and steel ratio on eccentric bearing capacity after high temperature were analyzed. Findings indicate that: there are two typical failure modes of SRRPC columns after high temperature under different eccentric loads, including small and large eccentric compression failure. As eccentricity has increased, residual bearing capacity declines obviously. Increase of RPC strength will greatly increase residual bearing capacity, and improve ductility to a certain extent. Increase of section steel strength and steel ratio can improve residual bearing capacity to a certain extent. Residual bearing capacity is mostly unaffected by the loading angle. Finally, the calculation formula of normal section bearing capacity of SRRPC bias column after high temperature was established based on limit state design method, which has high accuracy and can provide reference for identifying and strengthening composite structures following fire.

Performance of round-ended recycled aggregate CFST stub columns after fire exposure

The post-fire performance of round-ended recycled aggregate concrete-filled steel tubular (RE-RACFST) short columns has been investigated experimentally and numerically. The test parameters included cross-section aspect ratios, recycled aggregate replacements and steel ratios. Twelve short columns were first heated for 90 min following ISO 834 standard fire, followed by natural cooling. Subsequently, axial compressive tests were performed to obtain the damage mode, load versus axial deformation, and strain development of the columns. The test results revealed that a higher level of recycled aggregate content resulted in decreased bearing capacity and elastic stiffness of RE-RACFSTs, and an earlier onset of the confining effect. Furthermore, finite element (FE) models were established and benchmarked against the experimental results. Parametric investigations were then conducted to study the effects of key factors on the residual load-carrying capacity. Finally, according to the experimental and FE results, a simplified formula was proposed to estimate the post-fire residual capacity of RE-RACFST stub columns.

Investigation the influence of geometric parameters on the bearing capacity of partially encased composite columns in fire condition according to Eurocode 4

In this article the method to determine the bearing capacity of composite steel-concrete columns in fire conditions according to Eurocode 4 (EC4) was introduced. Some work examples are presented to clarify the influence of geometric parameters (effective length, axis distance of reinforcement bar) on the bearing capacity of partially encased composite columns in fire condition.

Cyclic Behavior of Square CFST Columns-Based Joint

This paper investigates the cyclic behavior of six square concrete-filled steel tube (CFST) columns that take the effect of width–thickness ratio (D/t = 30, 40, and 60), slenderness ratio (λ = 19.63 and 24.25), and axial force ratio (n = 0.6, 0.4, and 0.2) into consideration. The failure modes, hysteretic behavior, energy dissipation capacities, stiffness degradation, and ductility of these specimens have been discussed and studied. The results revealed that a bigger D/t could reduce the energy dissipation capacities and bearing capacities of the columns. With increasing λ, the energy dissipation capacities and bearing capacities of columns reduced, and the stiffness deteriorated rapidly. The axial force ratio could enhance the bearing capacities but weaken their energy dissipation capacities and stiffness. Calculation formulae for ultimate moment strength of square CFST columns were exhibited to compare to the test results.

Axial compression behavior of square CFST short column with triangular-corner gap

In order to investigate the impact of the triangular-corner gap between the outer steel tube and the core concrete on the axial compression behavior of square concrete-filled steel tubular (SCFST) columns, this study conducted axial compression tests on 117 SCFST columns and three reference hollow steel tubes. The main test parameters included steel tube thickness, concrete strength, side length of the triangular gap, and axial gap depth. The test results revealed four typical damage modes in the SCFST columns with triangular-corner gaps. The presence of the gap defect had a significant effect on the ultimate bearing capacity of the SCFST columns, causing a decrease in the range of 1.66 %–17.72 % when the gap ratio ranged from 0.45 % to 12.50 %. Moreover, the influence of the gap ratio on the ductility and initial stiffness of the SCFST with triangular-corner gaps was dependent on the concrete strength and the steel tube thickness. Finally, a simplified formula for calculating the ultimate bearing capacity of SCFST columns with triangular-corner gaps was proposed based on the test data and force analysis. The maximum error between the theoretically calculated value and the test value is within 15 %.

Behavior of circular concrete-filled steel tubular columns with different end moment ratios: Modelling and discussion

This paper develops a nonlinear model for the analysis of circular CFST columns under equal and unequal end moments using fiber beam element (FBE) method. An iterative process adopting Newton’s method combined with secant method was proposed to improve the calculation efficiency. A test database was collected to assess the accuracy of the proposed model regarding the prediction of axial load-bearing capacity, deflection curves and load–deflection curves. The verified model was then further used to investigate the behavior of CFST columns under different end moments. It was found that the normalized sectional locations of maximum deflection of CFST columns are only significantly affected by the end moment ratio, whereas those of critical sections are also influenced by the axial load. The specimen with a larger end moment ratio, steel strength, L/D ratio and/or a smaller e1/D ratio, D/t ratio experiences more significant second order effect. The bending stiffness of CFST columns is hardly affected by the end moment ratio. Moreover, the current codes, i.e., EC4 and AISC 360, may underestimate the capacities of CFST columns under unequal end moments.

Damage prediction of RC columns with various levels of corrosion deteriorations subjected to blast loading

Coastal structures are often exposed to harsh environmental conditions such as saltwater, high humidity, and coastal winds, leading to corrosion damage to the reinforcing steel and degradation of concrete. The blast risk is characterized by a relatively low likelihood but a significant consequence. The blast resistance of structural members with deteriorated properties due to corrosion and the corresponding post-blast performance is of significance to evaluate the lifecycle structural safety facing explosion threats. In this study, the damage of reinforced concrete (RC) columns of coastal structures with various corrosion degrees subjected to blast loading is investigated. The corrosion effect was modelled by considering the deterioration of rebar diameter and yield strength, bond strength between rebar and concrete, and rust expansion pressure effect. The numerical model was validated by simulating drop weight impact tests of RC beams with different corrosion degrees. Based on the validated model, the finite element (FE) models of corroded RC columns with the maximum corrosion degree of 15% were established and their responses and damage to blast loads of various blasting scenarios were calculated. It is found that the blast response of the column increases with the degree of corrosion. The blast damage mode may change from combined shear and flexural damage to concrete spalling damage with the increment of corrosion degree. Furthermore, the residual axial loading capacity and stiffness of post-blast columns were calculated and it is found that they degrade as the corrosion degree increases. A blast damage index is defined in terms of the residual axial loading capacity of the column, which is found to increase with the corrosion degree. The damage amplification factor due to corrosion deterioration (CAF) is then proposed as a function of corrosion degree, TNT equivalent mass, standoff distance, concrete strength, and reinforcement ratio to predict the blast damage of corroded columns.

Cyclic loading tests and seismic behaviors of steel-reinforced recycled aggregate concrete filled square steel tube composite columns

To investigate the seismic performance of steel-reinforced recycled aggregate concrete (RAC) filled square steel tube composite columns, the cyclic load tests were conducted for nine columns. The effects of steel ratio of profile steel, width thickness ratio of square steel tube, the replacement rate of recycled coarse aggregate (RCA) and axial compression ratio on the seismic performance of composite columns were investigated in detail. The failure characteristics, hysteretic curves, performance indexes and stress-strain distribution of columns were analyzed in detail. The results show that an obvious plastic hinge is generated at the column base and present a compression-bending failure mode. The hysteretic curves of columns present a full shuttle shape, showing that the columns have good energy dissipation capacity and ductility. The use of RCA has little impact on the seismic performance of composite columns. In particular, the bearing capacity of columns with fully RCA is only 1.57% lower than that of ordinary concrete columns. With the increase of profile steel ratio or the decrease of width thickness ratio of square steel tube, the ductility and energy dissipation capacity of columns obviously improve. Increasing the axial compression ratio is conducive to improving the bearing capacity of columns to some extent, but not conducive to improving the energy dissipation and deformation capacity of columns. Based on the failure mechanism of composite columns, combined with AISC specification, the modified formula on the horizontal bearing capacity of steel-reinforced RAC filled square steel tube composite columns is proposed, which is well verified by the test results.

Seismic performance of reinforced self-compacting concrete-filled circular steel-tube columns

Reinforced self-compacting concrete-filled circular steel-tube (RSCCFST) columns are used globally. The aim of this paper was to analyze the seismic performance of RSCCFST columns. One self-compacting concrete-filled circular steel-tube (SCCFST) column and seven RSCCFST columns were subjected to a low-frequency cyclic load. The experimental results indicated that the hysteretic curves of the RSCCFST columns were plump, and the columns exhibited good seismic performance. Parametric studies were also conducted to reveal the effects of the axial compression ratio, steel tube thickness, and the longitudinal reinforcement ratio on the seismic behavior of the RSCCFST columns. The parameter analysis indicates that increasing the reinforcement ratio and steel tube thickness can improve the load capacity and ductility of RSCCFST columns. Based on the above analysis, the entire process analysis method for RSCCFST columns under low-frequency cyclic loads was proposed using the Fortran language. The calculated results showed high accuracy compared to the experimental results; the average value of the ratio between the calculated and experimental values was 0.942, with a mean square error of 0.034. This proves that the computing programs written in Fortran are efficient for analyzing RSCCFST columns.

Post-fire performance of circular steel tube confined steel-reinforced concrete slender columns: Testing, simulation and design

Steel tube confined steel-reinforced concrete (STCSRC) stub columns offer good residual bearing capacity, great ductility, and large stiffness after fire exposure because inner steel profiles are unaffected by exterior temperature. Nonetheless, instability issues exist in STCSRC slender columns, and study into the mechanical characteristics of post-fire slender specimens is critical. At present, no relevant study on the axial performance of STCSRC slender columns after fire exposure has been reported. In this paper, nine circular STCSRC slender columns that had been exposed to fire were tested under axial load. The failure modes, axial load–displacement relationship, and lateral deflections of STCSRC columns were discussed. Furthermore, heat transfer analysis models and mechanical analysis models were established, and the effects of crucial variables on the buckling responses of STCSRC slender columns were explored. Among the parameters studied, sectional diameters and steel profile to concrete area ratio have a significant impact on buckling capacity. To calculate the buckling capacity of the post-fire STCSRC slender column, a simplified calculation method according to JGJ/T 471–2019 was proposed.

Behaviour of glass fiber reinforced polymer (GFRP) structural profile columns under axial compression

Abstract Glass fiber-reinforced plastic (GFRP) structural profiles in the construction industry are a promising alternative to conventional building materials due to their high strength-to-weight ratio, high tensile strength, insulation properties, chemical resistance, fatigue properties, and lower maintenance cost. This study aims to evaluate the compression behaviour of semi-compact and slender glass fiber-reinforced plastic I-sections. Short, intermediate, and long columns of both slender and semi-compact I-sections were subjected to axial compression, and the experimental capacity was compared to available theoretical results. It was found that the experimental capacity of short, semi-compact, and long columns were 27 %, 49 %, and 40 % lower than the theoretical capacity of semi-compact I-sections. Short slender sections had an ultimate experimental capacity 55 % greater than the theoretical results. However, lower ultimate capacities were achieved for intermediate and long columns in the case of slender sections when compared to the theoretical capacity. Slender sections were prone to both global and local buckling, whereas semi-compact sections failed by global buckling alone. The study also concludes the need for proper section classification of glass fiber-reinforced plastic sections to consider buckling characteristics. The existing theoretical equations to estimate the load-carrying capacity was found to be overly conservative; hence it is necessary to conduct numerical and parametric studies to develop equations that are more in agreement with the experimental results.