Tube Thickness Research Articles

Finite integral transform with homogenized boundary conditions solution of transient heat conduction applied to thermal plug and abandonment of oil wells

After the end of productive life of a geological oil reservoir, a set of operations for well Plug and Abandonment (P&A) is performed to recover the soil layers to its natural state. As traditional P&A techniques are expensive activities, alternative technologies are gaining renewed interest for capital expenditure reduction and leak risks mitigation. Hence, the Thermal Plug and Abandonment (TP&A) procedure is here investigated by focusing on the fulfillment of two intermediate milestones, combining new technology with conventional P&A practices. The first milestone consists in applying a thermite exothermic reaction to generate enough heat for melting the entire thickness of the production tube. The second milestone aims to determine if the resulting molten section has sufficient dimensions to allow for the passage of the cement pumped downhole, thus ensuring the complete sealing of the oil well's cross-section. The thermal investigation was conducted by applying a homogenized form of the Finite Integral Transform (FIT) analytical framework to solve the transient heat conduction equation in 2-D polar coordinates. The well assembly was geometrically discretized as a multilayered circular domain. The thermite reaction was modeled as a theoretical volumetric heat source profile dependent on both time and space, placed in the innermost layer. While a pure FIT approach may only be used to solve Neumann boundary conditions, the combined scheme applied here copes with any type of boundary condition. Hence, the integration of FIT with homogenization satisfies the Dirichlet condition requirement of the TP&A procedure. The methodology was verified through an equivalent Finite Volume Method (FVM) solution obtained using a commercial code. The results evidenced that within the 5 min duration of thermite reaction, the entire circumferential section of the production tube exceeds the steel melting temperature by at least 227 °C, thus fulfilling both milestones set. The research outcomes are part of a series of investigation steps to thoroughly analyze the new TP&A technology with regard to its compliance with the regulatory norms established to P&A operations.

Compressive performance of bamboo scrimber and concrete-filled steel tube columns

The light and high strength bamboo scrimber was buried in the core of concrete-filled steel tube (CFST) to form bamboo scrimber and concrete-filled steel tube column (BCFST), which was expected to reduce the amount of concrete and weight in CFST and promote the use of bamboo scrimber. To investigate the influences of key design parameters on the compressive performance, namely bamboo scrimber dimension, design concrete strength, and diameter to thickness of steel tube, ninety BCFSTs and eighteen CFSTs specimens were tested under axial compression. According to the experimental results, the improvement of the BCFST bearing capacity resulted from the contribution of the inner sandwich concrete and the bamboo scrimber under the constraint from the steel tube. The ultimate load rose with the increase of the bamboo scrimber dimension, concrete strength, and steel tube thickness. Note that the increase range of ultimate load of BCFSTs is 3.9% higher than that of CFSTs by increasing the dimension of bamboo scrimber, with a maximum increase at 43.9%. The damage modes of BCFSTs can generally be categorized into local buckling failure mode and shear failure mode. In addition, owing to the different compactness between the bamboo scrimber and the concrete, the stress-strain curve of the C80 concrete characterized the strain hardening tendency rather than the strain softening tendency in the C50 concrete. According to the load-strain curves of the BCFSTs and the contribution of the composite actions between the three parts of the member to the load-carrying capacity, the characteristic points were defined. A calculation model for accurately predicting the ultimate capacity of BCFSTs was proposed by considering the boundary conditions for both non built-in and fully built-in bamboo scrimber in CFSTs.

Experimental and numerical study on seismic performance of L-shaped multi-cellular CFST frames

Steel-concrete composite frames have been widely used in high-rise buildings. To improve the utilization efficiency of the indoor area, irregular-shaped concrete-filled steel tubular (CFST) columns were proposed for an alternative of the traditional rectangular CFST columns. In this paper, the L-shaped multi-cellular CFST (LM-CFST) frame was proposed, consisting of LM-CFST columns and H-shaped steel beams. Firstly, four LM-CFST frames were tested under combined axial compression and cyclic lateral loads. The local buckling was observed at both the top and bottom ends of the column, and fracture of steel occurred when the drift ratio was large. The hysteresis curves were spindle-shaped with the ductility indexes of 2.61–3.24. Then, a refined finite element model was established and validated against the test results. A parametric analysis was conducted to study the effect of axial compression ratio, web cell length, concrete strength and steel tube thickness on the seismic performance of LM-CFST frames. It was found that the axial compression ratio could affect the seismic performance of LM-CFST frames significantly, while the concrete strength had little effect. Finally, the compression-bending capacities obtained from the sectional analysis method specified in EC4 were compared with those obtained from tests. It was found that this method could predict the compression-bending capacity of the LM-CFST frame under combined axial compression and cyclic lateral loads with reasonable discrepancies.

Theoretical model for spontaneous combustion gangue coarse aggregate concrete filled steel tube stub columns

Spontaneous combustion gangue coarse aggregate concrete filled steel tube (SCGCA-CFST) provides a possibility for the structural application of spontaneous combustion gangue coarse aggregate (SCGCA) concrete. To establish an accurate stress-strain model for SCGCA-CFST, 12 SCGCA-CFST specimens and 18 SCGCA concrete specimens were tested under monotonic axial compression with steel tube thickness and SCGCA replacement ratio (0%, 50%, 100%) as variables. The experimental results demonstrated that as the SCGCA replacement ratio increased, the elastic modulus of SCGCA concrete decreased by 6.65%–11.65%, the cylinder compressive strength decreased by 11%–21.95%, and the axial strain at peak axial stress increased by 7.1%–14.27%. Furthermore, the crack extension forms and dilation properties of the core concrete in SCGCA-CFST differed significantly from those of normal coarse aggregate concrete filled steel tube (NCA-CFST). The incorporation of SCGCA reduces the effectiveness of steel tube confinement, which causes the existing stress-strain models of NCA-CFST overestimate the enhancement effect of steel tube confinement on the strength and deformability of core SCGCA concrete. Based on this, the analysis-oriented stress-strain model for NCA-CFST was modified to be applicable for SCGCA-CFST by incorporating the influence of aggregate characteristics, and the accuracy of that was verified.

Cyclic tests and finite element analysis on hybrid fiber–cement-based composite encased CFST columns

Six hybrid steel–polyvinyl alcohol (PVA) hybrid fiber–cement (HFC)-based composite encased concrete-filled steel tube (CFST) columns were tested for their seismic performance. The impacts of core concrete strength, steel tube thickness, and axial ratio on the seismic performance of the specimens were studied. According to the experimental findings, strengthening the core concrete can enhance the column's lateral bearing capacity and energy dissipation capabilities while also slowing the rate at which the steel tube's strain increases after yielding. Furthermore, HFC-encased CFST columns with a lower axial ratio and a thicker steel tube demonstrated superior seismic performance. An's equation of computation could better forecast the lateral bearing capacity of HFC-encased CFST columns when compared to other calculation methods. Finally, an experimentally validated finite element model of HFC-encased CFST columns was developed. Numerical studies showed that the seismic performance of composite columns can be significantly improved by increasing the strength of the HFC and the volume concentration of the steel fiber, and that PVA primarily acts in the plastic stage.

Crashworthiness of multicellular tubes with tree-like fractal hierarchical structure under axial impact

A new type of tree-like fractal hierarchical multicellular tubes (TFHMTs) is proposed, and the crashworthiness of the structure under axial impact is studied by using a verified Abaqus/Explicit finite element model. The research results show that the TFHMTs have better energy absorption capacity than single-cell tubes of the same thickness and mass under the same conditions. The wrinkle wavelength of the third-order TFHMTs is significantly shorter than that of the single-cell tubes, resulting in more folds. For the same mass, the proposed third-order TFHMTs has a lower peak crush force than a single-cell tube. Moreover, the specific energy absorption is up to 49.40% greater than that of the single-cell tube, and the crush force efficiency is up to 66.18%. Subsequent parameterization research on the layer ratio coefficient and wall thickness on TFHMTs was systematically conducted. Finally, a comparative analysis with typical hierarchical multicellular tubes was performed.

Adhesive reinforced friction stir welded thermoplastic tube-to-tubesheet hybrid joints

Thermoplastic materials are gaining popularity, because of their anti-fouling and chemically inert properties, for use in industrial applications that involve heating and cooling of highly reactive fluids. The current work studies the effect of adhesive reinforcement and radial clearance (RC) on developing friction stir welding (FSW)-based thermoplastic tube-to-tubesheet hybrid joints (TTHJs), which has applications in the thermoplastic heat exchanger and piping industries. The workpieces (sheets and tubes) made of carbon black reinforced high-density polyethylene were used. First, the effect of FSW parameters on the tube pull-out behavior was studied. The fractographic investigations (macroscopic and SEM) suggest that the FSW joints can fail in a brittle, ductile, or mixed manner, depending on the FSW conditions used. The FSW technique provides better load bearing capacity (326 N (0.0 RC), 517 N (0.5 mm RC)) compared to adhesive joints (226 N (0.0 RC), 206 N (0.5 mm RC)). For 0.0 RC, the adhesive reinforcement increased the load bearing capacity by 15.6 %. On the contrary, for 0.5 mm RC, the adhesive reinforcement negatively impacted the load bearing capacity and reduced it by 40.6 %. The FSW technique with 0.5 mm RC provides a higher leak path of 77 % remaining tubesheet thickness (> tube thickness) compared to that of 46.6 % (< tube thickness) achieved at 0.0 RC. However, the adhesive reinforcement can enhance the leak path of 0.0 RC FSW joints to around 100 % remaining tubesheet thickness (> tube thickness) by introducing the adhesive material at the tube-sheet interface.

Seismic performance and bearing capacity calculation of cross shaped concrete columns with built-in T-shaped steel and steel tubes.

Incorporating T-shaped steel and square steel tubes into a cross shaped concrete column can significantly improve the seismic performance of the cross shaped column. However, the experimental samples are limited, so ABAQUS finite element (FE) analysis method was adopted in this paper to study the seismic performance of this cross shaped column, calculate and verify three specimens in the existing reference. Based on the reliable model, parameter analysis was carried out (25 specimens in total). The results show that the established model has a high degree of coincidence in the hysteretic curve, skeleton curve and failure mode, and the error of ultimate bearing capacity and ductility is within 10%. The configuration of T-shaped steel and square steel tubes inside the cross column can meet the ductility requirements specified in the standard under high axial compression ratio. The ultimate bearing capacity of the cross shaped column increases with the increase of the thickness of the square steel tube, but the ductility deteriorates. The increase in steel tube size increases the strength of the concrete in the core area, and the seismic performance of the cross shaped column was improved. Increasing the thickness of the T-shaped steel flange can better improve the seismic performance of the cross shaped column compared to increasing the thickness of the T-shaped steel web plate. Increasing the height of the specimen will significantly reduce its seismic performance. When the shear span ratio is not greater than 4.1, the ductility can meet the standard requirements. The error of the formula for calculating the compression-bending bearing capacity proposed based on existing calculation methods is less than 5%.

Thermal stresses of large-dimension lithium hydride ceramics during the sintering process and strength analysis based on process-based failure assessment diagram

Lithium hydride (LiH) is an important hydrogen storage, heat storage and neutron shielding material. When used in neutron shielding structure, its size and strength have certain requirements, which would be met by LiH ceramics. However, it fails easily during sintering due to severe thermal stress and high brittleness. In this study, the influences of the dimension, furnace temperature cooling rate, and convection condition on the mechanical behavior were systematically examined. The results indicated that larger dimensions and faster furnace temperature cooling rates resulted in higher maximum stresses. Furthermore, convection was beneficial for reducing the thermal stress. Accordingly, a process-based failure assessment diagram method was proposed to evaluate the safety of LiH ceramics, and a bilinear precise temperature control approach was proposed. Based on this method, the tube thickness was increased by 25 % and the cooling time was reduced by 32 % compared to those using linear temperature control in an example. The conclusion and method could be applied to optimize the temperature control for more practical large-dimension sintering.

Experimental study of bond behavior between concrete-filled steel tube and UHPC-encased

This paper examines the bond behavior between steel and ultra-high-performance concrete (UHPC) in members made of UHPC-encased concrete-filled steel tubes (CFST). For the push-out test, a total of ten UHPC-encased CFST specimens, eight normal concrete-encased CFST specimens, and two CFST specimens were designed. The specimen parameters considered for variation include steel fiber content, thickness of the steel tube, anchorage length, thickness of outer concrete, and concrete type. Through experimental observation and measured data, the force failure process and crack development pattern of the specimens were observed, and load-slip curves were obtained for the loading end and the free end. A comprehensive analysis was conducted to examine the influence and mechanism of different parameters on the bonding performance of the specimens. Furthermore, an equation was derived to calculate the bonding strength at the interface between the steel tube and the outer concrete. The findings reveal that both UHPC-encased CFST and normal concrete-encased CFST specimens exhibited bond-anchorage failure, with the load-slip curve exhibiting a sudden change at the peak value, indicating a high degree of brittleness. The bond strength between steel and outer UHPC was found to be twice that between steel and core UHPC, and 1.4 times that between steel and outer normal concrete. Increasing the steel fiber content and the thickness of outer concrete within a certain range effectively improved the bonding performance of the specimens. The thickness of the steel tube did not have a significant effect on the bonding performance of UHPC specimens. Additionally, when the anchorage length reached a certain value, further increases did not significantly enhance the bond strength. Moreover, the influence range of the steel tube's anchorage length and outer UHPC on the bonding performance was smaller compared to outer normal concrete.

Tests and deflection calculation method for circular concrete-filled steel tubular columns under very low-elevation lateral impact loads

An experimental investigation of circular concrete-filled steel tubular (CFST) columns subjected to very low-elevation lateral impacts was performed. Six circular CFST members were prepared for lateral impact tests according to the typical CFST columns in high-speed railway stations in China, and the impact location was at the height of the 2/9 column. The tests had three variables: the thickness of the steel tube, the impact velocity, and the axial load. The failure modes were determined in the tests, along with the time histories of the impact force and the deflection at the impact location. A finite-element analysis was performed to examine the effects of the axial load and scaling on the maximum deflection. The results show that with the increase of axial compression ratio, the impact resistance of the member first increases and then weakens. According to the travelling plastic hinge theory, a three-stage rigid plastic mechanical model was employed to describe the impact process, in which the impact location was at the non-mid-span, and a deflection calculation method for CFST applicable to any impact position was developed. A comparison with the test results indicated that deflections can be calculated with reasonable accuracy using the proposed method.

Experimental study on eccentric compressive behaviors of 6061-T6 aluminum tubular long columns filled with concrete

In this paper, eccentric compressive experiments of 12 circular and 6 square concrete-filled 6061-T6 aluminum tubular (CFAT) long columns were carried out. The influence of the section form, thickness of aluminum tube, slenderness ratio, and eccentricity on the flexural performance of CFAT long columns was investigated. The results showed that all the specimens exhibited flexural-dominated failure. The variation of eccentricity had little impact on the overall failure mode of the aluminum tube, while it dramatically influenced the failure mode of the internal concrete. The internal concrete failed in concrete crushing for all the square columns, while it remained intact for the circular columns. This indicates that circular tubes provide a better constraint effect on the internal concrete, there by increasing the ultimate strain of concrete under compression. It was also found that the increase of eccentricity leads to the weakening of the confinement afforded to the internal concrete, while the increase of slenderness ratio has no obvious effect on the restraining effect. Finally, the applicability of current design provisions for concrete-filled steel tubular (CFST) long columns to CFAT long columns was evaluated, and design suggestions were proposed.

Nectar robbing by bees affects the reproductive fitness of the distylous plant Tirpitzia sinensis (Linaceae).

Nectar robbing can affect plant reproductive success directly by influencing female and male fitness, and indirectly by affecting pollinator behavior. Flowers have morphological and chemical features that may protect them from nectar robbers. Previous studies on nectar robbing have focused mainly on homotypic plants. It remains unclear how nectar robbing affects the reproductive success of distylous plants, and whether defense strategies of two morphs are different. Nectar-robbing rates on the long- and short-styled morph (L-morph, S-morph) of the distylous Tirpitzia sinensis were investigated. We compared floral traits, the temporal pattern of change in nectar volume and sugar concentration, nectar secondary metabolites, and sugar composition between robbed and unrobbed flowers of two morphs. We tested direct effects of nectar robbing on female and male components of plant fitness and indirect effects of nectar robbing via pollinators. Nectar-robbing rates did not differ between the two morphs. Flowers with smaller sepals and petals were more easily robbed. The floral tube diameter and thickness were greater in L-morphs than in S-morphs, and the nectar rob holes were significantly smaller in L-morphs than in S-morphs. Nectar robbing significantly decreased nectar replenishment rate but did not affect nectar sugar concentration or sugar composition. After robbery, the quantities and diversity of secondary compounds in the nectar of S-morphs increased significantly and total relative contents of secondary compounds in L-morphs showed no obvious changes. Nectar robbing could decrease female fitness by decreasing pollen germination rate and thus decreasing seed set. Nectar robbing had no significant effects on male fitness. Robbed flowers were less likely to be visited by hawkmoth pollinators, especially in S-morphs. These results suggest that nectar robbing could directly and indirectly decrease the female fitness of T. sinensis, and different morphs have evolved different defense mechanisms in response to nectar-robbing pressure.

The Influence of Tube Thickness on the Shell Side of the Air preheater As a Form of Corrosion Prevention

Air preheater as a heat recovery technology is generally applied in the powerplant industry and used to heat combustion air, which increases the efficiency of the combustion chamber in the boiler. In this case, air preheater has tubular recuperative type typically located at the bottom of the circulating fluidized boiler for utilizing the lowest temperature exhaust gas. A significant presence of SO2 in the exhaust gas can lead to cold-end corrosion and cause leaks. The low tube thickness in the air preheater provides a good heat transfer performance unfortunately the corrosion issue has not been considered. By increasing the tube thickness, its aimed to extend the life time of the tubes with good corrosion resistance. This study is performed with calculations using empirical equations and validated results using Heat Transfer Research Inc (HTRI) software. Increasing the tube thickness impacts decreasing the heat transfer coefficient, increasing the flue gas (shell) pressure drop, and increasing the fouling factor. The tube thickness which determined for the corrosion prevention design of the air preheater give an overdesign of 18.14%, a heat transfer rate coefficient of 1.726 Btu/hr. ft2. °F, a shell pressure drop of 0.000541 psi, and a fouling factor of 0.114 hr. ft2. °F/Btu.

Simulation study on flexural behaviour of perforated aluminium tubes

A numerical investigation was conducted to compare the flexural capacity of AA6063-T5 aluminum alloy tubes with perforations of different hole diameters (4, 6, 8, and 10 mm), hole spacing (13-26-39-52 mm) and tube wall thickness (0.5, 1, 1.5 and 2 mm) by the finite-element analysis (FEA). As the tube thickness increases, the load-carrying capacity decreases, while the LCC increases as the hole diameter increases. It was observed that the LCC increased as the distance between the holes increased. ANOVA test was used to analyze the influence of hole diameter, hole spacing, and tube wall thickness on tube load-carrying capacity. It is found from the statistical analyses that the most significant factor on maximum load is tube thickness (97.2 %) between parameters of hole diameter, hole spacing, and tube wall thickness. As a result of the second statistical analysis, the most significant factor on maximum load is hole diameter (73.14 %) between parameters of hole diameter and hole spacing. A second important factor is hole spacing on maximum load.

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 %.

Single-polarization single-mode broadband ultra-low loss hollow-core anti-resonant fiber with nested double C-type cladding tubes

A novel five-tube nested double C-type single-polarization hollow-core anti-resonant fiber (HC-ARF) is proposed for single-polarization single-mode, ultra-low loss, and broadband characteristics. Different tube thicknesses are introduced along the orthogonal direction to couple the x-polarized fundamental mode (FM) to the silica modes (SMs). At the same time, the y-polarized FM is tightly bound in the core, achieving a high polarization extinction ratio (PER). In order to achieve large bandwidth, a layer of high-refractive-index silicon material is coated on the inner surface of the cladding tube. To the best of our knowledge, the proposed single-polarization HC-ARF has the highest PER at 1.55μm with a remarkable value of 162486 so far, while the y-polarized FM loss is only 1.4 × 10-3 dB/km. However, the single-polarization bandwidth remains limited. By optimizing the structural parameters on single-polarization bandwidth, the HC-ARF at 1.55μm for single-polarization single-mode transmission is obtained with a high-order mode extinction ratio (HOMER) and PER of 2891, 9531, respectively. In addition, a remarkably high single-polarization bandwidth of up to 150 nm is achieved with ultra-low confinement loss (CL) as low as 2.8 × 10-3 dB/km. Furthermore, the proposed fiber exhibits good bending characteristics, with a bending loss of 6.7 dB/km at the bending radius of 5 cm in the x-direction.

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.

Behavior of longitudinal-seam steel tubular columns with crack defect in weld

An experimental investigation was conducted to investigate the axial compressive behavior of square longitudinal-seam steel tubular (LSST) stub columns with artificial crack defect in weld. The axial compression tests were carried out on 108 square LSST stub columns with crack defect and 3 square LSST columns without crack defect as control groups. The effect of design parameters such as thickness of tube, length and width of crack defect, location of crack defect on axial compressive behavior of square LSST columns were analyzed. Test results involved failure modes, load-displacement behavior, ultimate strength, initial stiffness, and ductility coefficient of all specimens were presented. The corresponding FE models of square LSST columns with crack defect are established and validated by comparison with experimental results. Test results have demonstrated that crack defect often led to stress concentration, causing significantly higher strain intensity at the position of crack defect compared to other areas. Square LSST columns with crack defect exhibited a 26% lower ultimate strength at T = 2.5 mm. The ductility coefficient enhanced with the decrease of length and width of crack defect. However, the location of crack defect had limited effect on axial behavior of LSST columns. In addition, parametric formulae of ultimate strength for square LSST columns with crack defect are proposed, which achieved high accuracy. The research results could provide evaluation reference in design and construction of LSST column.

Experimental investigation of axially loaded circular ultra-high performance concrete with coarse aggregate (CA-UHPC) filled steel tube slender columns

This paper presents an experimental investigation on circular ultra-high performance concrete with coarse aggregate (CA-UHPC) filled steel tube (CA-UHPCFST) slender column subjected to axial compression. A total of 42 specimens were manufactured and tested to determine the effects of CA-UHPC strength, steel tube thickness, steel strength, and length-to-diameter ratio on axial compressive behavior of circular CA-UHPCFST slender columns. The test results show that elastoplastic instability failure with local buckling in the compression region is observed for intermediate columns, while overall buckling failure is occurred for slender columns. The inclusion of steel fibers significantly alleviates the tensile cracking and compressive crushing of CA-UHPC core, which in turn improves the ultimate strength and ductility of CA-UHPCFST slender columns. The ultimate bearing capacity and ductility index decrease remarkably with an increase in length-to-diameter ratio, while increase with steel yield strength and tube thickness. The interaction between steel tube and CA-UHPC core decreases as the length-to-diameter ratio increases, which mainly exists in compression zone but is weak or even nonexistent in tension zone. Finally, the feasibility of current design guidelines concerning the concrete-filled steel tubes for calculating the stability bearing capacity of circular CA-UHPCFST slender columns is evaluated, and a simplified model is proposed to estimate the stability carrying capacity. The simplified model demonstrates good accuracy in predicting the ultimate carrying capacity of axially loaded circular CA-UHPCFST slender columns.