Concrete-filled Steel Tube Columns Research Articles

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.

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.

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.

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, but the existing analysis-oriented models are all developed for the conventional concrete-filled steel tube (CFST) columns. Nevertheless, the confinement mechanism of steel tubed concrete columns is significantly different from that of CFST 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 model. 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. 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.

Structural performance of circular CFST columns with circumferential gap imperfections

The present study investigated the influence of circumferential uniform gap imperfections (≤ 1.0%) on the structural behavior of circular concrete-filled steel tube (CFST) columns under axial compression. The study involved testing 20 CFST columns with circumferential uniform gaps with varying gap ratios (0.2%–1.0%), diameter-to-thickness ratios (18–43), and concrete strength (68.5 MPa and 114 MPa). The presence of uniform gaps (0.2%–1.0%) reduced the confinement effect of steel tube on core concrete, and peak load capacity decreased by 9.0%–24.0%. The normalized concrete strength in high-strength concrete specimens with gap ratios ranged between 0.89 and 0.99, showing no interaction between steel tube and core concrete due to the less deformable nature of high-strength concrete. Core concrete exhibited a combination of vertical splitting and diagonal cracks distributed across the height of specimens with an increase in gap ratio, and local steel tube bulging was dispersed around the edge regions. A theoretical procedure was developed to assess the impact of uniform gaps on the stress state of steel tube and core concrete by determining their respective load contributions. The suggested approach reasonably estimated the gap ratio's nominal influence on the behavior of steel tubes and its considerable influence on the behavior of core concrete. Considering the experimental limitations, gap ratios were broadened through finite element modelling to investigate the gap ratio effect further. After examining the confinement mechanism of CFST columns and finite element results, an analytical formulation to predict the peak load capacity of CFST columns with circumferential uniform gaps was proposed and verified.

Finite Element Analysis on the Seismic Performance of Concrete-Filled Steel Tube Columns with a Multiple-Chamber Round-Ended Cross-Section

This study proposes a form of concrete-filled steel tube column with a multiple-chamber round-ended cross-section (M-CFST). Longitudinal and transverse stiffening ribs divide the circular-ended section into different chambers, strengthening the steel tube’s confinement effect on the core concrete and improving the component’s seismic performance. A three-dimensional finite element (FE) solid model of the M-CFST is created by employing the FE software ABAQUS. Quasi-static analysis is conducted to investigate the influence of parameters, such as chamber arrangement, aspect ratio, and axial compression ratio, on flexural hysteresis performance. Moreover, the failure modes, hysteresis curves, skeleton curves, strain development, and energy dissipation of the components are analyzed. The results show the following: (1) The FE model presented in this study can simulate the quasi-static behavior of CFST columns accurately, and the calculated results are in good agreement with the measured values. (2) The seismic performance of the composite column is excellent, with a large number of chambers leading to a robust hysteresis curve for the composite columns, resulting in increased bearing capacity and energy dissipation capacity. However, the energy dissipation performance of the specimen with a two-chamber arrangement is slightly lower than that with a single-chamber arrangement. (3) The results of the finite element analysis suggest that the long and short sides of the CFST columns with a large length–width ratio should be arranged to be relatively close in length.

Experimental and simulation study on seismic performance of steel‐PVA hybrid fiber cementitious composites‐encased CFST

AbstractSix hybrid steel and PVA fiber cementitious composite (S&PFCC)‐encased concrete‐filled steel tube (CFST) columns were designed and fabricated, and the effects of axial compression ratio, core concrete strength grade and steel tube thickness on the seismic performance of composite columns were studied. The test results show that the increase of core concrete strength can obviously improve the bearing capacity and energy dissipation capacity of composite column and can restrain the strain growth rate of steel tube after yielding. Low axial compression ratio and thicker steel tube thickness can improve the overall seismic performance of composite columns. Three calculation methods are modified, and the modified An method can predict the lateral bearing capacity of composite column well. Finally, based on the OpenSees finite element software, the seismic performance of the CFST column wrapped in S&PFCC is simulated to verify the test, and the numerical study shows that the seismic performance of the composite column can be optimized by increasing the steel fiber content, while PVA fiber has a weak effect in the elastic stage, and can effectively improve the ductility of the composite column in the plastic stage.

Satin bowerbird optimizer-neural network for approximating the capacity of CFST columns under compression

Concrete-filled steel tube columns (CFSTCs) are important elements in the construction sector and predictive analysis of their behavior is essential. Recent works have revealed the potential of metaheuristic-assisted approximators for this purpose. The main idea of this paper, therefore, is to introduce a novel integrative model for appraising the axial compression capacity (Pu) of CFSTCs. The proposed model represents an artificial neural network (ANN) supervised by satin bowerbird optimizer (SBO). In other words, this metaheuristic algorithm trains the ANN optimally to find the best contribution of input parameters to the Pu. In this sense, column length and the compressive strength of concrete, as well as the characteristics of the steel tube (i.e., diameter, thickness, yield stress, and ultimate stress), are considered input data. The prediction results are compared to five ANNs supervised by backtracking search algorithm (BSA), earthworm optimization algorithm (EWA), social spider algorithm (SOSA), salp swarm algorithm (SSA), and wind-driven optimization. Evaluating various accuracy indicators showed that the proposed model surpassed all of them in both learning and reproducing the Pu pattern. The obtained values of mean absolute percentage error of the SBO-ANN was 2.3082% versus 4.3821%, 17.4724%, 15.7898%, 4.2317%, and 3.6884% for the BSA-ANN, EWA-ANN, SOSA-ANN, SSA-ANN and WDA-ANN, respectively. The higher accuracy of the SBO-ANN against several hybrid models from earlier literature was also deduced. Moreover, the outcomes of principal component analysis on the dataset showed that the yield stress, diameter, and ultimate stress of the steel tube are the three most important factors in Pu prediction. A predictive formula is finally derived from the optimized SBO-ANN by extracting and organizing the weights and biases of the ANN. Owing to the accurate estimation shown by this model, the derived formula can reliably predict the Pu of concrete-filled steel tube columns.

Confinement-based direct design of axially-compressed octagonal concrete-filled double skin steel tubes

Prior research has highlighted distinctions in the confinement mechanism for concrete-filled double-skin steel tube (CFDSST) columns with octagonal sections compared to circular and square sections. Current design codes primarily address the models for the design of square and circular sections in columns made of concrete-filled steel tube (CFST). This study addresses this gap by presenting a novel confinement-based direct design model specifically developed for octagonal CFDSST columns, encompassing both unstiffened and stiffened outer steel tubes. Initial data collection involved experimental and numerical results of axially-compressed octagonal CFST and CFDSST columns sourced from literature. Subsequently, ultimate compressive resistance, as determined by international design codes (EC4, ACI-318, AISC-360, GB-50936, T/CCES-7, AS/NZS-2327, CSA-S16, AIJ) and existing analytical models, underwent comparison with test results. The results reveal that existing codes and models generally offered accurate predictions, but their consistency across the entire side width-to-thickness (w/to) ratio range varied. The study proposes a new confinement design model for predicting the compressive resistance of octagonal CFDSST columns. Although the new model does not outperform existing ones, it demonstrates satisfactory prediction scatter throughout the w/to ratio and compressive strength (fc′) range, particularly excelling in high-strength concrete (HSC) and ultra-high-strength concrete (UHSC) scenarios. Notably, the proposed formula incorporates the influence of stiffening ribs on the confinement of the octagonal steel tube on concrete, making it applicable for practical design considerations for both unstiffened and stiffened octagonal CFDSST columns.

Interface debonding defect detection for CFST columns based on EMI measurements: Experiment, numerical simulation and blind inspection in practice

Concrete-filled steel tube (CFST) members have been widely used in skyscrapers and long-span bridges. Non-uniformly distributed hydration heat during curing, inadequate compaction during construction and unavoidable shrinkage and creep of mass concrete in service most likely lead to interface debonding defects between concrete core and steel tube, which has been a common concern. The development of effective non-destructive inspection methods for interface bonding condition of existing CFST members is critical. In this study, an interface debonding defect detection method based on electromechanical impedance (EMI) measurement using surface-mounted piezoelectric-lead-zirconate-titanate (PZT) sensors is proposed at first. Then, experimental study on the feasibility of the proposed approach is carried out with scaled CFST specimens with artificially mimicked interface debonding defects. EMI of surface-mounted PZT sensors at different frequency bands are measured and compared to verify the detectability of the proposed approach for the mimicked interface debonding defects. Thirdly, a multi-physics CFST-PZT coupling finite element model (FEM) with interface debonding defects is established, and EMI of surface-mounted PZT sensors at different locations is simulated. The influence of interface debonding defects on EMI measurements is illustrated. Finally, a blind inspection on the interface bonding condition of selected CFST columns in an existing skyscraper in service using the proposed approach is carried out. Both bonding and debonding defect in the tested CFST columns are detected correctly and validated with drilling hole observation. Experimental, numerical and engineering application results show the proposed approach is effective for interface debonding detection of CFST members and sensitive to minor debonding defect of 0.3 mm in CFST members.

Dynamic responses of concrete-filled steel tubes impacted horizontally by a rigid vehicle: Experimental study and numerical modelling

Concrete-filled steel tubes (CFSTs), composed of an outer tube made of steel as the confining material and an inner concrete core, have been popularly utilised as high-rise building columns and urban bridge piers owing to their superior structural behaviour. Since the invention of CFSTs, their mechanical performance under static and seismic loading conditions have been extensively studied, while the investigation on their dynamic behaviour under impact loading is relatively limited. Of these limited studies about CFSTs under impact loading conditions, most experiments were completed using a drop-hammer testing facility or a pendulum-hammer testing device. Against this background, this study investigated six large CFSTs being impacted horizontally by a rigid vehicle to analysis their dynamic response. All specimens were vertically placed with the bottom pedestal fixed on the lab floor and the top end free. The main parameters of these CFSTs included the impact velocity (i.e., vi = 3.16–7.18 m/s), the CFST section size (i.e., D = 180–300 mm), as well as the CFST column height (i.e., hc = 1500–2100 mm). Test results revealed that, (1) all CFSTs experienced a bending-dominant failure when impacted horizontally by a rigid vehicle; (2) the impact velocity had a positive correlative trend with the peak impact force Fpeak and the peak lateral displacement δpeak of the CFST column; (3) a larger section size of the CFST column resulted in a higher flexural stiffness and a larger flexural capacity, thus leading to a higher Fpeak, a smaller time duration T and a smaller δpeak; (4) the column height would affect the inertial response of the CFST column; a larger column height led to a larger Fpeak caused by the larger inertia effect of the CFST segment above the impact point. Finite-element model was established on the platform of LS-DYNA to simulate these CFSTs under horizontal impact loading, which was able to predict both impact force–time history curves and lateral displacement–time history curves with reasonably accuracy.

Behavior of Concrete-Filled Steel Tube Columns with Multiple Chambers and Round-Ended Cross-Sections under Axial Loading

Concrete-filled round-ended steel tubes (CFRTs) are a unique type of composite stub columns, which have the advantage of aesthetics and a well-distributed major–minor axis. Thus, the structure has been widely employed as piers and columns in bridges. To improve the mechanical performance of CFRTs with a large length–width ratio and to enhance the restraint effect of steel tubes on concrete, this study investigates the compressive property of multi-chamber, concrete-filled, round-ended steel tubular (M-CFRT) stub columns using a combination of experimental and numerical analyses. A detailed compression test on eight specimens is conducted to examine the compressive property of M-CFRT stub columns. The study focuses on understanding the influence of some key parameters on ultimate bearing capacity, failure stage, damage modes, and ductility. Additionally, the accuracy of the finite element modeling method in simulating the ultimate bearing capacity of the structure is verified. Finally, the calculating formula for the ultimate bearing capacity of M-CFRT stub columns is proposed on the basis of the experimental and numerical findings. Results of the formula calculation are consistent with the experimental data. These research findings serve as a valuable reference for designing similar structures in engineering practice.

Axial Compression Tests for Circular Concrete-Filled Steel Tube (CFST) Columns with Notch Imperfection

Axial Compression Tests for Circular Concrete-Filled Steel Tube (CFST) Columns with Notch Imperfection

A Review of Research on Recycled Aggregate Concrete Filled Steel Tube

Recycled aggregate concrete filled steel tube as a new combined structural form, can effectively improve the inherent defects of recycled aggregate concrete. Existing studies are mainly theoretical analysis, experimental research and numerical simulation to investigate the mechanical properties and deformation capacity of recycled aggregate concrete filled steel tube columns. Based on the review of the current research status of recycled aggregate concrete filled steel tube columns in recent years, the basic mechanical properties, durability, seismic performance, fire and high temperature resistance of recycled aggregate concrete filled steel tube are described, and suggestions are made for future research directions.

Seismic performance and design of an innovative dual vertical diaphragms joint between flat CFST column and H-beam

Steel-concrete composite structure is one of the research hotspots in the structural engineering field in recent years. Among the various types of composite structures, flat concrete-filled steel tube (CFST) column structures are preferred for residential buildings owing to the smooth elevation to coordinate with the indoor decoration. The seismic performance of beam-to-column joints is momentous as a key part of flat CFST column structures. This study provided a new type of joint between flat CFST column and H-beam with dual vertical diaphragms through the column. The design procedure for the vertical diaphragms was proposed to design the test specimens. An experimental study on the seismic behavior of the innovative joint under cyclic load was performed on three full-scale specimens. The seismic performance of the joint, including the failure mode, hysteretic and skeleton curves, ductility and energy dissipation capacity, was observed and discussed in detail. Subsequently, nonlinear finite element models (FEMs), based on the specimens, were developed using the ABAQUS/Standard program and validated by comparing the numerical results with the test ones. The experimental and numerical results demonstrated that the proposed joint exhibited satisfactory seismic performance and all the specimens exhibited a ductile failure mode. The failure process and damage distribution of the joint under earthquake were revealed based on the validated FEM. Furthermore, a mechanical model was established to predict the load-bearing capacity of the shear force and bending moment of the proposed joint. The mechanical model was validated to be accurate and reliable by comparing the numerical simulation results with the theoretical ones. This study provided a practical joint between flat CFST column and H-beam as well as its design method, which was beneficial for the promotion of the flat CFST column structures.

Investigation on behavior of concrete-filled double steel tubular columns infilled with nanomaterial-based concrete subjected to axial compression

Nanotechnology has been applied in construction to enhance the mechanical properties of concrete by using nanomaterials. A new stiffening scheme called catty-cornered propped concrete-filled steel tube (CFDST) column was proposed and analyzed under axial compression. The steel tube of CFDST specimens was filled with normal and nano material-based concrete, including nano-silica (NS), carbon nanotubes (CNT), and nano-titanium dioxide (NT). The study collected data on ultimate capacity, load vs strain behavior, and load vs deformation response, as well as ductility index (DI), secant stiffness, composite interaction, and confining effect variation. The results showed that the proposed stiffening scheme increased the ultimate capacity of unstiffened CFDST by approximately 14%, and the use of nanomaterials in CFDST infill concrete resulted in an approximately 7% increase in load capacity. Increasing the number of stiffening bars improved the ductility and stiffness of the column section, while the inclusion of nanomaterials decreased the ductility index and improved the stiffness of the section. The proposed stiffening scheme resulted in better composite interaction and increased confinement. The study concluded that the utilization of nanomaterial-based concrete as an infill in the stiffened CFDST column could enhance its performance under axial compression loading.

Impact force curve feature and failure mode identification method of concrete-filled steel tube members under lateral impact

A collision accident caused by derailed trains is a potential safety hazard for the structure adjacent to high-speed rail lines. Concrete-filled steel tube (CFST) columns are frequently utilized in modern high-speed railway stations, however CFST station columns may suffer severe damage from train collisions because of their high impact energy. Therefore, the method of identifying CFST members' failure modes under large impact energy was investigated in this paper. Adopting numerical simulation by LS-DYNA, the corresponding relationship between the local indentation and impact process was researched, the characteristic impact force time-history curve was proposed, and the effects of impactor and CFST specimen parameters on impact force feature were analyzed. The plateau proportion was established and quantified, then the mapping relationship between plateau proportion and failure degree was acquired. Research results indicated that local indentation developed primarily at impact force plateau stage. CFST specimens showed bending deflection when plateau proportion was below 67.5%, experienced fracture failure when it was above 77%, and exhibited crack failure when it was in between respectively. Finally, the empirical formulas for plateau proportion and maximum deflection were established, and a simplified approach for predicting the failure modes was put forward. The research provides suggestions for identifying damage patterns and strengthening CFST columns subjected to lateral impact loads.

Sectional strength design of l-shaped irregularly concrete-filled steel tube column under axial compression and any directional moment

Authors’ previous research proposed a new kind of L-shaped irregularly concrete-filled steel tube column (L-ICFSTC) and conducted the experimental and numerical investigation into it under eccentric compression. In this paper, authors further study the sectional strength capacity of L-ICFSTC under axial compression and any directional moment and establish a complete set of design formulas for it. The FE model validated by the authors’ previous experimental results is adopted to the parameter analysis of this study. The involved parameters include the length of two column limbs, the thickness of steel tube, the material strength and the axial compressive ratio, and consider the possibility of unequal length between two column limbs. Due to the irregularly-shaped section and two materials with different properties, the load-bearing behavior of L-ICFSTC is significantly related to the angle of moment, making its interaction curves and design formulas much more complex than current those of rectangular or circular CFST columns. Therefore, we start from the capacity of L-ICFSTC under pure unidirectional moment, and then study the capacity of L-ICFSTC under axial compression and unidirectional moment, and based on this, we finally obtain the capacity of L-ICFSTC under axial compression and any directional moments. The complete set of design formulas is established by theoretical analysis and fitting the N-M curves and Mx-My curves obtained by FE model. The formula results can agree well with the FE investigation results, demonstrating its applicability to the engineering design of L-ICFSTC.

A study on low-frequency vibration mitigation by using the metamaterial-tailored composite concrete-filled steel tube column

The bandgap properties exhibited by local resonant metamaterials provide a potential approach for structural vibration reduction. In this work, we introduce the local resonance mechanism into the composite structure for the first time and propose a novel metamaterial column with 33.8–47.2 Hz low-frequency vibration mitigation based on practical engineering materials and utilizing material shear deformation. By vertically arranging metamaterials, the metamaterial concrete-filled steel tube column with low-frequency vibration reduction bandgap is designed. Its equivalent bandgap model is proposed by combining the Timoshenko beam and Bloch theorem. The bandgap formation mechanism and vibration mitigation effect of the metamaterial are clarified by finite element analysis. It is revealed that the bandgap generation depends on the contrary motion between the resonator and the substrate, thus the reaction force from the relative motion can cancel the external excitation. Then, the bandgap vibration mitigation effect of the metamaterial column is proved by shaking table tests at different amplitudes. This also supplies a feasible solution for vibration mitigation control and even earthquake protection for buildings, bridges, and major infrastructures. Finally, the theoretical, numerical, and experimental results are discussed to verify the validity of the theoretical approach and numerical model, and the rubber damping is found to widen the bandgap but weaken the vibration reduction capacity.

Experimental study on the seismic performance of concrete-filled steel tube columns with a multiple-chamber round-ended cross-section

Reinforced concrete bridge piers with round-ended sections are susceptible to bending, bending–shear, and shear failure after earthquakes in high-intensity areas, thus necessitating improved seismic performance. This study introduced a novel design for a concrete-filled steel tube (CFST) column, featuring a multi-chambered, round-ended cross-section. The use of longitudinal and transverse stiffeners divided the column section into distinct chambers, thereby enhancing the seismic performance of the columns. A total of 12 groups of static tests were performed to examine the effect of chamber layout, axial compression ratio, and aspect ratio on columns’ hysteresis behavior, and the hysteresis curves, skeleton curves, failure modes, stiffness degradation, ductility, and energy dissipation capacity were obtained. Results demonstrated the favorable seismic performance of composite columns. Additionally, an increase in chambers led to a full hysteresis curve, enhancing bearing and energy dissipation capacities. The displacement ductility coefficient (μ) ranged between 3.88 and 7.45, and the design parameters have minimal influence on the stiffness degradation of the composite beam. Based on the results, the long and short sides of the CFST columns with a large length–width ratio should be arranged to be relatively close in length.