Steel Tube Research Articles

Experimental investigation on seismic performance of embedded column base for circular CFST

Embedded column bases for concrete-filled steel tubes play an essential role in the structural safety of high-rise and super-high-rise buildings. However, the working mechanism and design methods of embedded column bases remain unclear. This paper presents an experimental investigation of five embedded column base specimens subjected to axial compression load and cyclic lateral load, to thoroughly reveal the seismic performance of such column bases with varied parameters. The failure modes, hysteretic curves, energy dissipation capacity, stiffness degradation, and strain developments were discussed. The test results revealed that increasing the embedded depth ratio and utilizing anti-punching shear reinforcements led to an improvement in the seismic performance of the embedded column base. Moreover, the axial load ratio only influenced the seismic performance of the column when the embedded depth was sufficient. Finally, a calculation method was proposed to determine the ultimate strength of the embedded column base. The method considered the resistances resulting from the horizontal interaction between the steel tube and foundation concrete, vertical interaction between the endplate and foundation concrete, and axial deformation of anchor bolts. The predicted results were found to agree well with the test results.

Effect of vertical stiffeners on the seismic performance of T‐shaped CFST column to steel beam joint

SummarySpecial‐shaped concrete‐filled steel tubular (SCFST) columns have recently been developed for efficient steel‐concrete composite construction. In this study, a novel vertical stiffener joint for the SCFST column and steel beam frame structure is proposed. Five SCFST columns with H‐section beam joints were investigated under cycling loading. The test parameters mainly consider the column stiffening form, vertical stiffener type, and the column axial load. The failure pattern, hysteretic curves, and strain development of specimens are analyzed. Experimental results demonstrate the proposed joint with vertical stiffeners can develop the steel beam's full plastic flexural capacity and exhibit favorable seismic performance. In addition, a finite element (FE) model is developed to explore the effects of the following parameters on the hysteretic performance: vertical stiffener sizes, width‐to‐thickness ratio of column steel tube, and the column axial load. Based on the experimental and FE analyses, a stress and deformation model of the joint steel tube was established. To facilitate the practical applications, a calculation formula for joint strength was also put forward, considering the contribution of vertical stiffener, and front and side steel plates of the joint steel tube.

Numerical analysis on seismic behavior of a novel steel-timber composite frame column

Steel-timber composite structures are a novel hybrid structural system that combines the advantages of both steel and wood structures, holding great promise for various applications. In this paper, the seismic behaviors of steel- timber composite columns are investigated based on finite element analysis. The reliability of the finite element model is validated by quasi-static test results. Numerical analysis results indicate that the proposed steel- timber composite systems is with high ultimate bearing capacity, full hysteresis loops, and strong displacement ductility, demonstrating excellent seismic performance. The axial compression ratio, steel tube thickness, and flexural point height significantly influence the seismic resistance of the structure.

Optimization for Offshore Prestressed Concrete–Steel Hybrid Wind Turbine Support Structure with Pile Foundation Using a Parallel Modified Particle Swarm Algorithm

The prestressed concrete–steel hybrid (PCSH) support structure, which replaces the lower part of the traditional support with a concrete segment, is a prospective support structure solution for ultrahigh wind turbines. Taking a 5.5 MW wind turbine support structure founded on a jacket substructure with pile foundation as an example, an optimized design of the corresponding PCSH support structure with pile foundation for offshore wind turbine is conducted considering the soil–structure interaction (SSI) and the effect of water pressure. The construction cost of the proposed structure is treated as the objective function and minimized with a parallel modified particle swarm optimization (PMPSO) algorithm where the physical dimensions of each part of the PCSH wind turbine support structure are treated as optimization variables. Eleven optimization constraints are considered under both the serviceability limit state (SLS) and the ultimate limit state (ULS) according to relevant specifications and industry standards. A penalty function strategy is introduced to make sure that these constraints are fulfilled. The mechanical behavior and the cost of the optimal PCSH support structure with pile foundation are analyzed and are compared with those of the original design with a traditional steel tube tower founded on a jacket substructure. The results show that the cost and levelized cost of energy (LCOE), a comprehensive evaluation, of the optimized PCSH support decrease obviously with the PMPSO algorithm, which can provide advanced mechanic behavior including natural frequency, top deformation, and anti-overturning capacity. Compared with the PSO algorithm, the PMPSO algorithm has better performance in the procedure of PCSH support for offshore wind turbine optimization.

Feasibility of using superelastic shape memory alloy in plastic hinge regions of steel bridge columns for seismic applications

AbstractThis paper contributes to the further development of seismic resilient infrastructure by introducing a novel prototype bridge which integrates tubular steel piers with superelastic shape memory alloy (SMA). The proposed bridge pier is composed of a circular steel tube which is bonded to a superelastic SMA tube in regions of high stress. The pier is distinguished by its ability to minimize residual drifts following inelastic deformations induced by cyclic loading. Three‐dimensional continuum finite element (FE) models are utilized to examine its lateral behavior. Experimental data is used to demonstrate the effectiveness of the continuum FE procedure in replicating the cyclic response and capturing both global and localized behaviors. A novel composite material model is proposed to represent the degradation of strength and accumulation of irreversible strains in the cyclic response of superelastic SMAs. An iterative procedure for the calibration of this material is presented. Investigations, employing the calibrated FE procedure, focus on the quasi‐static cyclic response of steel piers with superelastic SMA in the plastic hinge zone, aiming to identify the optimal length of the SMA tube for achieving a self‐centering response with reduced residual deformation. The study is then further expanded to examine the seismic response of a bridge structure incorporating such piers. Development of the FE model for the prototype bridge includes the modelling of the piers using continuum elements, while the superstructure, bearing units, abutment walls, and backfill material are modelled using discrete elements. Nonlinear time history analyses are undertaken to investigate the effects of column wall thickness and materials used in the plastic hinge zones of the piers. Dynamic FE study results indicate that bridges employing such piers are capable of returning to their original position, provided the SMA tube is of adequate length.

Investigation on axial compression performance of self-compacting fly ash concrete filled square steel tube column: Tests and numerical simulation

Self-compacting concrete has the advantages of high fluidity, high uniform density, and low porosity. To promote the engineering application of self-compacting concrete, this article studies the axial compression test of ten square steel tube self-compacting concrete columns. The effects of design parameters such as different grades of concrete strength and internal structures of circular steel tubes, square steel tubes, and H-shaped steel on the mechanical properties of self-compacting fly ash concrete filled square steel tube columns are studied. The failure mode, characteristic load and characteristic displacement, ductility, and energy dissipation capacity of each specimen are analyzed. On the basis of the test, the finite element analysis model of steel tube self-compacting concrete column is established, and the test results and simulation results are compared and analyzed. The results show that: the failure mode of the square steel tube specimen is the multilayer middle and upper ring buckling failure. Internal structural measures of square steel tube and H-shaped steel can improve the bearing capacity, ductility, and energy dissipation capacity of the specimen. It is not recommended to use the specimen with an outer square and an inner circle design. The results of the finite element simulation have a high degree of matching with the test results, which intuitively reflects the changes in force of each component.

Seismic behavior of double-cell CFST columns with table tennis racket-shaped cross section

Multicell concrete-filled steel tube (CFST) columns with excellent mechanical performance have been used in super high-rise buildings in recent years. According to the requirements of a 265-m tall building, the double-cell CFST columns with an innovative cross section of table tennis racket were applied. Hence, six columns were designed according to the prototype columns and subjected to low-frequency cyclic loading. The impacts of different shear-span ratios (SSRs), axial load ratios (ALRs), and steel ratios on the seismic behavior were elaborated and clarified. The test results indicated that the seismic performance varied in different loading directions owing to the asymmetric cross section, and the columns performed better in the positive loading direction resulted from earlier and more sufficient confinement of the circular steel tube, which was also reflected by the measured strain development. With SSR deceasing from 2.5 to 1.7, earlier and more severe damage was recorded. The resisting capacity and stiffness were significantly improved at a cost of ductility loss. Increasing ALR from 0.2 to 0.4 brought about more damage and worse deformability. However, a proper increase in axial load was beneficial to the resisting capacity and stiffness, and its influence on the restoration capacity was associated with SSR. Increasing the steel ratio (by 33.36%) could effectively postpone and alleviate the local buckling of steel tube, thereby comprehensively improving the seismic performance. A finite element (FE) analysis of such columns was performed to carry out the damage evolution and parametric study, and provide references for their application in practical engineering.

Joining by forming technology for thermal applications: A case study of finned tube heat exchanger

Heat exchangers are essential for various thermal applications, and their performance could be improved by optimization of layout/operating conditions or materials. The layout/operating conditions optimization has been widely subjected to research and development, while the implementation of different materials has been limited to the available joining solutions. Joining by forming allows to circumvent the existent limitations, since it utilizes plastic deformation to produce multi-material mechanical joints between thin sheets and thin-walled tubes. Here, joining by forming is adopted for the first time, to manufacture multi-material transversal finned tube heat exchangers. The numerical-experimental analysis explores the production of tube compression beads obtained by plastic instability to fix and support fins, and therefore manufacture a novel design of finned heat exchanger with improved performance. A case study is carried out with the help of computational fluid dynamics simulations to find an optimal layout. Then, finite element simulations are employed to analyse the joining by forming process. A prototype model of transversal finned tube heat exchangers was finally manufactured and experimentally tested. Results show considerable gains in comparison with conventional finned tube heat exchangers made from steel tubes and fins, being the multi-material heat exchanger effectiveness doubled with respect to traditional designs.

Analysis-oriented stress-strain model for concrete in steel tubed geopolymer concrete (STGC) columns

To alleviate the brittleness of geopolymer concrete and further promote its engineering application for environmental benefits, a novel type of column, i.e., steel tubed geopolymer concrete (STGC) column, has been proposed recently. Note that an accurate axial stress-strain model is necessary for a comprehensive understanding of the compressive behavior of STGC columns. However, the existing analysis-oriented models are all developed for the conventional concrete-filled steel tube (CFST) columns, and the confinement mechanism of steel tubed concrete columns is significantly different from that of concrete-filled steel tube columns since the axial deformation of steel tube and core concrete is not synchronized for steel tubed concrete columns during the loading process due to the discontinuous steel tube. Furthermore, the dilation properties of STGC columns at the initial loading are significantly overestimated by the existing lateral-axial strain models. Besides, steel-confined geopolymer concrete (GPC) experiences a more remarkable softening behavior resulting from the more significant brittleness of GPC than that of ordinary concrete. Thus, the deformation models are proposed in this study and the active-confinement base model is also developed for GPC based on the mechanical characteristics of STGC columns under axial compression. Then a new analysis-oriented model is proposed for steel tubed geopolymer concrete. Comparisons between the theoretical calculations and the test results indicate that the proposed model can provide reasonable predictions for both steel stress evolution and the stress-strain relationship of STGC.

Effects of seawater corrosion on compression-induced buckling performance of FRP-CFST columns

This study experimentally investigated axial compression-induced buckling performances of FRP confined concrete filled steel tube (FRP-CFST) columns after exposure to seawater corrosion environment. Sixty-three stub FRP-CFST are manufactured, and sixty of them were exposed to three simulated seawater corrosion conditions with 120, 240, 360 days. Four-stage failure mode of the axial compression-induced buckling tests was observed and analyzed. Comparative analysis indicated that FRP-CFST can effectively resist normal seawater corrosion, while weaker durability is observed from columns in triple-salinity seawater environments, particularly with wet-dry cycles conditions. Under the same corrosion conditions, CFST columns wrapped with Carbon Fiber reinforced polymer (CFRP) exhibited preferable buckling resistance performance than those with Basalt Fiber reinforced polymer (BFRP). Based on mechanism analysis of the axial compression-induced buckling tests, a theoretical evaluate model for compression-induced buckling performances of FRP-CFST after seawater corrosion is proposed and verified. The outcomes of this research can provide experimental and theoretical basis for evaluating the durability of FRP-CFST under seawater corrosion environment.

Torsion and Combined Torsion-Axial Load Behaviour of Concrete Filled Steel Tube Columns with and without ECC/CFRP Wrap

ABSTRACT Concrete-filled tube columns may experience coupled torsion and axial compression under seismic and wind loading. Fifteen square, rectangular, and circular concrete filled steel/aluminium tube (CFST/CFAT) are tested under pure torsion to understand the behaviour and develop/validate finite element (FE) models. Parametric studies under pure torsion are conducted using FE models to study the effect of geometric (tube cross-section, length, and thickness) and tube/concrete material parameters on torsional strength, stiffness, and tube-concrete composite interaction. FE models are used to study strength, stiffness, and failure modes of CFST columns under combined torsion and axial compression load at various preload levels of axial and torsion. Coupled torsional preloading and subsequent axial load reduce the axial load capacity significantly, while coupled axial preloading and subsequent torsional loading have shown no significant influence on the torsional strength of CFST columns. Implementation of FE models developed for CFST columns with engineered cementitious composite (ECC) and carbon fibre reinforced polymer (CFRP) wraps showed significant enhancement of axial strength and stiffness compared to control (without wrap) even under high torsional preload level. The energy absorption capacity and ductility of the CFRP wrapped CFST column are about 1.38 and 1.1 times higher than its counterpart with ECC wrap of same axial load capacity. Overall, the results suggest that use of both CFRP and ECC wrap is an effective approach to enhance the torsional behaviour and ductility of CFST columns under combined torsion and axial loading conditions. However, high crack resistance and better post-peak ductility of ECC wrapped CFST compared to sudden CFRP rupture failure in CFRP-wrapped counterpart should be taken into consideration for seismic applications.

Stress Concentration Factors of Concrete-Filled Double-Skin Tubular K-Joints

Tubular joints are important connecting parts of a welded steel tube structure. The S-N curves based on the hot spot stress (HSS) method are often used to evaluate the fatigue life of tubular joints in practical engineering. The stress concentration factor (SCF) is a key parameter to calculate HSS. In this paper, stress concentration tests of hollow-section and concrete-filled double-skin tubular (CFDST) K-joints were carried out, respectively, and then finite element models of K-joints considering the weld were established. The developed models were validated with the experimental results. The influence of key geometrical parameters, such as the diameter ratio of brace to chord β, the diameter to thickness ratio of chord γ, the wall thickness ratio of brace to chord τ, brace angle θ, and hollow section ratio ζ on the distribution and key position of SCFs along the weld toe, was discussed. Parametric studies were conducted to obtain the calculating equations for the SCF values of CFDST K-joints. The results demonstrate that infill concrete can effectively reduce SCFs along the weld on the chord. When the hollow section ratio was reduced to 0.317, the SCF was reduced by 77.2%. Notably, the SCF reduction rate was sensitive to γ and θ, with a decrease observed as γ increased. The hollow section ratio ζ had a less pronounced effect on SCF distribution patterns, but as ζ decreased, the chord’s stiffness improved, suggesting a potential approach to enhance joint performance. The distribution of SCFs is similar for joints of the same type but different geometric configurations. The innovatively integrated hollow section ratio in the CFDST design equation significantly simplifies and enhances the precision of SCF calculations for CFDST K-joints.

Eccentric compressive performances of circular steel-reinforced concrete-filled stainless steel tubular column

Steel-reinforced concrete filled stainless steel tube (SRCFSST) columns are predicted to offer excellent durability, load bearing capacity, ductility, fire resistance, impact resistance, and seismic performance. Therefore, eccentric compressive tests of 18 circular SRCFSST columns were carried out to investigate the effects of the slenderness ratio, load eccentricity, and embedment of carbon-profiled steel (CPS) on circular SRCFSST columns. The ultimate strength and ultimate deflection of the composite columns were improved significantly after the CPS was embedded. A finite element (FE) model was established and the FE analysis indicated that the CPS was proved to be an effective means of constraining concrete. Based on the FE parametric analysis, it was shown that the stability coefficient decreased with increasing concrete strength, proof strength of stainless steel, and CPS yield strength, but increased with increasing rotation radius-diameter ratio. The greater the concrete strength, the more similar the N∼M interaction curves of the SRCFSST columns and reinforced concrete columns. The higher the CPS yield strength, stainless-steel ratio, slenderness ratio, carbon steel ratio, or proof strength of stainless steel, the more similar the interaction curves of the SRCFSST columns and profiled steel columns. Finally, the simplified model was refined to forecast the carrying capability of a circular SRCFSST specimen under the eccentric compression.

Experimental study on the bond-slip behavior of steel tube-coal gangue concrete

This study investigated the bond-slip behavior at the interface between steel tubes and coal gangue concrete, considering the coal gangue coarse aggregate replacement rate, the strength grade of coal gangue concrete, and the bond length as variable parameters. Eleven groups of push out tests were conducted on steel tube coal gangue concrete specimens. The bond slip curve and the longitudinal strain distribution curve of the steel tubes were obtained, and the effects of these parameters on bond strength were analyzed. The results showed that the load-slip curves at both the loading and free ends of the specimens were similar, with slip occurring earlier at the loading end. The regularity of the test curves in repeated experiments indicated that interfacial bond stress was primarily determined by friction in the later stages. The longitudinal strain of steel tubes was approximately exponentially distributed along their length. The interfacial bond strength increased with the increase of coal gangue aggregate replacement rate and was more pronounced in specimens with higher strength coal gangue concrete. Longer bond lengths resulted in greater bond failure loads, with a lower rate of increase in higher strength coal gangue concrete specimens compared to those with lower strength. Based on the three stage bond stress-slip relationship for steel tube-concrete, a bond-slip constitutive model for steel tube-coal gangue concrete was established. This provided a reference for mechanical analysis and interface performance design of steel tube-coal gangue concrete.

Experimental and numerical investigation on the impact response of bolt-ball joints

The densely populated space lattice structure requires reliable performance under impact loads. The bolt-ball joint serves a crucial role in connecting members at various angles, significantly contributing to the overall safety of the structure. However, there is limited literature available on the impact resistance of the bolt-ball joint. In this study, the drop hammer impact test system was employed to conduct impact tests on 11 specimens of bolt-ball joints. Comprehensive records were maintained, including the final deformation states, video recordings of the impact process, and data on impact force, displacement, and strain. Additionally, numerical simulation analysis was conducted to expand the scope of the study. Five failure modes were observed: global bending deformation, bolt fracture, local denting, coupling deformation of local denting and global bending deformation, bolt and tube fracture. When the impact applied at the bolt ball or conical head and steel tube welding positions, the impact process was categorized into three stages: inertia, global bending deformation, and elastic recovery/bolt fracture. When the impact position was the steel tube, coupling deformation and elastic recovery/ bolt and tube fracture were observed. The energy absorption during the impact test was analyzed, revealing a positive correlation between the degree of specimen failure and the proportion of energy absorbed relative to the work done by the impact force. The effects of impact velocity, impact position, bolt dimension and impact angle on the dynamic response of the specimens were thoroughly analyzed.

Predicting the fire-induced structural performance of steel tube columns filled with SFRC-enhanced concrete: using artificial neural networks approach

Predicting the axial Shortening strength of concrete-filled steel tubular (CFST) columns is an important problem that this study attempts to solve for civil engineering projects. We suggest using a deep learning-based artificial neural network (ANN) model to address this issue, taking into account the intricate relationship between steel tube and core concrete. The model, called ANN-SFRC (Steel Fibre Reinforced Concrete), surpasses an R2 threshold of 0.90 and achieves impressive R2 values across different types of CFST columns. Compared to traditional linear regression methods, the ANN-SFRC model significantly improves accuracy, with an observed inaccuracy of less than 3% compared to actual values. With its reliable approach to forecasting the behavior of CFST columns under axial compression, this high-performance instrument enhances safety and accuracy during the design and planning stages of civil engineering.

Performance of multi-ribbed composite wall incorporating reactive powder concrete-filled steel tubular columns under axial compression

In this study, axial compression researches of an innovative composite shear wall, named multi-ribbed composite wall incorporating reactive powder concrete-filled steel tubular columns, were conducted using theoretical analyses as well as experimental and numerical investigations. This precast hybrid system embedded reactive powder concrete-filled steel tubular columns as boundary elements of multi-ribbed composite wall. A novel approach, namely the unified strength theory, was adopted in consideration of various materials diversity. The outcomes of unified strength theory were utilized to predict the ultimate compressive capacity of multi-ribbed composite wall equipped with reactive powder concrete-filled steel tubular columns. The proposed theoretical formulas were validated against the experimental results reported in this paper. Despite the fact that the calculated formula with b= 0 was obtained to predict the closest capacity value of the test specimen infilling ordinary concrete. The calculations with different values of b clearly indicated that the intermediate principal stress effect should be rationally considered. Experimental observations suggested that the frame column significantly contributed to improving the compressive performance throughout the entire process and maintained the wall integrity. Meanwhile, finite element models were developed using the ABAQUS program, followed by the elaboration of its numerical implementation. The numerical predictions of ten shear wall specimens infilling reactive powder concrete were found to be reasonably in agreement with the calculated results corresponding to b= 0.5. These findings revealed the characteristics of multiple defensive lines of "block-ribbed column-frame column" under axial compression. Following the successful validation of finite element models, parametric studies were carried out to evaluate the influences of the filled block compressive strength, steel tube wall thickness and height-width ratio. The results show that the axial compression capacity of multi-ribbed composite wall incorporating reactive powder concrete-filled steel tubular columns can be noticeably improved with an increase in block strength and tube thickness. The proposed composite wall demonstrates favorable cooperative working performance and desirable displacement ductility. Subsequently, the primary objective of this pilot study aimed at developing a reliable theoretical calculation formula and conducting numerical simulation verification of the innovative composite wall. The aforementioned conclusions are intended to provide insights for the guidance and optimization of engineering structures.

Investigation on bearing resistance of thin-walled circular steel tube subjected to eccentric loading

In the engineering structures using circular steel tube (CST), the eccentric loading of CST members often occurs due to installation error and structural form. Existing research mainly focuses on the bearing resistance of circular steel pipes under the condition of eccentricity at one end. In practical application, both ends of CST members also may be eccentric. And with the increase in eccentricity, material yielding may occur prior to flexural buckling. So far, it’s lack of reports about the mechanical behavior of CST members subjected to eccentric loading at both ends and the boundary between material yielding and flexural buckling. This paper presents experimental, numerical and theoretical studies on bearing resistance of thin-walled circular steel tube with slenderness ratio of 30, 40 and 50, subjected to eccentric loading at one end and both ends, respectively. The study reveals a significant discrepancy in the prediction of bearing resistance for circular tubes subjected to eccentric loading at both ends according to existing design codes. Considering the synthesis of bending moment and deflection caused by eccentric loading at both ends, the calculation method of the bearing resistance based on flexural buckling of CST is established, which enhances the prediction accuracy of test verification. In addition, a theoretical boundary between the two failure modes appearing in CST members under eccentric loading at one and both end(s) - flexural buckling and reaching the material yielding strength - was established as dominated by the slenderness ratio and loading eccentricity.

Strength design of built-up radially battened columns subject to axial compression and arbitrary directional bending moment

Built-up radially battened columns (RBCs), comprising several identical circular steel tubes interconnected by multiple radial-shaped battens, represent an innovative column design that combines aesthetic appeal with exceptional load-bearing capacity. This makes them well-suited for architectural applications in large public buildings such as stations and airports. The axial compressive strength design methods for the built-up RBC have been extensively explored in the authors' prior studies. However, in real-world engineering applications, built-up RBCs may experience simultaneous axial compression and varying directional bending moments, particularly when considering potential eccentric compression or wind and earthquake loads in public buildings. Currently, strength design methods for this loading condition are still lacking. To address this deficiency, this paper primarily delves into the failure mechanism and strength design methods for built-up RBCs experiencing combined axial compression and arbitrary directional bending moments. Initially, the sectional strength of the built-up RBC is investigated by using a shell finite element model (FEM) for the built-up RBC. It is revealed that the compression-bending sectional strength of the built-up RBC exhibits significant differences with varying bending directions and tube numbers. Moreover, in some bending directions, the M-N sectional strength curve of the built-up RBC exhibits convexity. By integrating theoretically derived equations grounded in the principles of materials mechanics with FEM numerical calculations, concise and practical design equations are proposed for accurately predicting the sectional strength of the built-up RBC under combined axial compression and arbitrary directional bending moments. Subsequently, The buckling strength of the built-up RBC is studied using the FEM, considering initial geometrical imperfections consistent with first-order flexural buckling and accounting for geometric nonlinearity. It is noted that the bending direction of the built-up RBC may deviate during loading. Besides, the M-N buckling strength curve of the built-up RBC is not as convex as its M-N sectional strength curve. Based on calculations from numerous examples, practical design equations for predicting the buckling strength for the built-up RBC under axial compression and any directional bending moments are introduced. The key findings of this paper contribute to the compression-bending strength design of RBCs, enriching RBC design theory and promoting the widespread application of built-up RBCs in actual engineering projects.

Experimental Investigation and Numerical Analysis of the Axial Load Capacity of Circular Concrete-Filled Tubular Columns

This paper focuses on the experimental investigation of the axial load capacity of CFT (concrete-filled steel tube) columns under actual construction conditions during building reconstruction. A total of four samples were loaded up to failure. The varied parameters were the column length and absence/presence of the concrete infill within the steel tube. Further, the analysis is extended to developing a numerical model in the finite element-based software ABAQUS version 6.9. This numerical model includes material and geometrical nonlinearities and was validated with the experimental results. The contribution of the concrete core to the column capacity and the concrete core confinement effect are discussed. Finally, the column capacity was calculated according to several design codes: the Eurocode 4 with and without considering the confinement effect, American specifications, Australian standards, the American Institute of Steel Construction, and the Architectural Institute of Japan. The Eurocode 4 considering the confinement effect provides the closest results to those obtained in the tests.