Concrete-filled Double Skin Research Articles

A machine learning based interaction model to predict robustness of concrete-filled double skin steel tubular columns under fire condition

Concrete-filled double skin steel tubular (CFDST) column is a hollow composite structure component, which shows better performance than traditional reinforced concrete and steel columns due to the favorable composite action between steel and concrete. In the current study, a machine learning based interaction model combine with the extended Rankine method is developed to predict fire resistance of eccentrically loaded CFDST cylinder columns. The prediction of the reliable shear bond parameter was conducted by back propagation artificial neural network (BP-ANN) and Extreme Gradient Boosting Tree (XGBoost). To perform a reliable production, the architecture and the parametric setting of both models were constructed. Furthermore, the results of the prediction were verified by experimental results and finite element analysis. The results show that the proposed method can predict the behavior of the eccentrically load CFDST columns under fire attack with reasonable accuracy.

Machine learning models for predicting axial compressive capacity of circular CFDST columns

Machine learning (ML), widely recognized for its advanced predictive capabilities, is progressively being employed in structural design. Concrete-filled double skin steel tubular (CFDST) members are extensively utilized due to their exceptional mechanical behavior. However, existing formulas encounter challenges in accurately calculating the axial compressive capacity of circular CFDST members, particularly when high-strength concrete and steel materials are involved, leading to complexity and low accuracy. This paper presents a data-driven framework that leverages the superior predictive performance of machine learning approaches to predict the axial compressive capacity of circular CFDST columns. Finite element models are developed through secondary development of ABAQUS using custom script, which are then validated against experimental data, confirming their effectiveness and applicability. A general database is established, comprising 226 test results and 550 finite element results obtained from the script, to facilitate the prediction of axial compressive capacity for circular CFDST columns. By incorporating the physical mechanisms of CFDST members and conducting correlation analysis, the input parameters for the machine learning models are determined. Decision Tree, Artificial Neural Network (ANN), K-nearest neighbor (KNN) and two ensemble methods including Random Forest, XGBoost, are trained and optimized using the database to provide accurate predictions. The results demonstrate that the KNN model exhibits superior performance and high accuracy, outperforming the four commonly used calculation formulas in the field, particularly for circular CFDST columns using high-strength materials. The proposed data-driven framework shows promising potential for achieving outstanding predictive performance.

Hysteretic performance of circular high-strength concrete-filled double skin steel tubular columns: Experiment

In marine structures, utilizing high-strength materials in concrete-filled double skin steel tubular (CFDST) members can provide an optimized solution upon the tendency of light self-weight and high performance. The cyclic load in the marine environment usually determines the safety margin for whole offshore structures. Therefore, this paper experimentally investigated the hysteretic performance of circular high-strength concrete-filled double skin steel tubular (HCFDST) columns with out-of-code diameter-to-thickness ratios. The typical failure mode appeared with the infill material crushing, steel fracture and local buckling of outer tubes. Subsequently, the detailed analysis of hysteretic curves, skeleton curves and ductility, energy dissipation, stiffness degradation, and lateral force reduction was conducted to reflect the influences of hollow ratios, axial compression ratios, and infill types, e.g., increasing the hollow ratio from 0.54 to 0.68 and 0.82, respectively reduced the bearing capacity by 6.25% and 11.20%, and the ductility coefficient had an apparent decrease of 19.27% and 26.61%. The out-of-code HCFDST columns with reasonable design could behave with favorable hysteretic performance. A theoretical model considering the tensile strength effect of engineered cementitious composite (ECC) was finally established and verified to predict the moment-resisting capacity of HCFDST columns using ECC. The reported research on HCFDST columns can provide significant references to marine structure applications.

A Seismic Risk Assessment of Concrete-Filled Double-Skin Steel Tube (CFDST) Frames with a Beam-Only-Connection for Reinforced Concrete Shear Walls (BRWs)

The beam-only connected reinforced concrete shear wall (BRW) is used as a reinforcing component to enhance the seismic performance of concrete-filled, double-skin steel tube (CFDST) frames. The effects of the BRW on seismic risks of CFDST frames are investigated. Three performance levels of limit states are defined and described according to the typical failure of test specimens and the existing definition of current guidance. A simplified numerical model is calibrated for CFDST frame-BRW structures, and test results validate it. Nonlinear dynamic analyses on a nine-story CFDST-BRW building are performed to investigate the effects of BRW on reducing the seismic risk of CFDST buildings. The results show that the BRW reduces the probability of collapse of the CFDST frame to 2.76% in 50 years, which can effectively reduce the probability of different degrees of damage in the service cycle of the structure. The results provide information for risk-informed decision-making on the design of CFDST frame-BRW structures.

Research on the Concrete-Filled Double Skin steel Tubular (CFDST) columns subjected to axial force after fire

This article investigates the structural performance of Concrete-Filled Double Skin Steel Tubular (CFDST) columns after fire under the axial compress. 13 experiments were conducted on the residual bearing capacity of CFDST columns under axial compression after different fire duration time. The variation parameters included the hollow ratio, fire duration time and strength of concrete. The effect of different parameters on the axial load and displacement changes after fire was revealed. The experimental and finite element simulation results were compared and analyzed, and they were in good agreement. The results indicate that CFDST columns have good fire resistance, and the strength of concrete has little effect on the residual bearing capacity of CFDST columns after the fire. With the increase of hollow ratio from 0 to 0.72, the axial residual bearing capacity of CFDST columns increases first and then decreases after the same fire duration time. Compared with the column without initial load, the residual bearing capacity of CFDST columns will increase with an initial load before fire, but different initial loads have no significant impact on the ultimate bearing capacity after fire.

Experimental study and numerical analysis on the dynamic response of steel tube confined concrete with a circular hollow section (STCC-CHS) under transverse impact loading

The dynamic response to lateral impact of steel tube confined concrete with a circular hollow section (STCCCHS) was investigated via pendulum impact tests in the laboratory. Nine STCCCHS columns and two concrete-filled double skin steel tubes (CFDST) were tested under lateral impact. The hollow ratio, the thickness of the outer steel tube, the impact height, and axial load ratio were varied. The failure pattern was observed along with the time histories of the impact force and the mid-span deflection. Strain development in the outer steel tube was quantified. The failure mechanism was integral bending and local buckling under lateral impact. Increasing the outer wall thickness and adopting an appropriate hollow ratio can effectively improve the impact resistance of such columns. Changes in impact energy have a significant influence on the plastic deformation of the members. Modest axial loading has little effect on the impact resistance. The test results were used to tune a finite element simulation of the process. A whole dynamic response investigation of STCCCHS columns under impact loads was carried out, and compared with the impact resistance of CFDST columns.

Experimental and numerical investigation on strengthening mechanism of rib-reinforced round-over-round RCFDST column jointed with steel beam under cyclic loading

This paper involved both experimental and numerical investigations on the behaviour of twelve types of recycled-concrete filled double-skin steel tubular (RCFDST) structures subjected to the cyclic loading with reinforced ribs at the column–steel beam joints, of which the damage pattern and seismic performance were analysed by varying the ratio of beam–column flexural linear stiffness, axial compression ratio, hollow ratio, type and strength of the concrete, and the length of ribs. The results indicate that the specimens primarily exhibited the damage pattern of the plastic hinge at both ends of the beams, and that the horizontal load–displacement hysteresis curves with full loop at the top of the column were observed. Moreover, the structures composed of recycled concrete from 40 MPa to 60 MPa presented no reduction in ultimate load as well as the joint ductility to those of the ones with normal concrete. Regarding the performance of RCFDST, the optimal ratio of beam–column flexural line stiffness (ki) is found in the range of 1.0 to 1.5. This study demonstrated that the recycled concrete made from the industrialized aggregate formed by crushing waste concrete from road bases has potential application prospects in Concrete-filled double skin steel tubular (CFDST) structures due to its low cost and good seismic performance, including high ultimate load capacity and low energy consumption.

Analytical model for axially compressed circular concrete-filled double skin steel tubes (CFDSTs): Insights from concrete non-uniformly confined states

Concrete-filled double skin steel tube (CFDST) is becoming a competitive structural concept in deep-sea and deep-ground engineering structures. However, the passive non-uniform confinement of the sandwiched concrete needs to be further clarified and quantitatively described to achieve better design efficiency of CFDSTs in sophisticated application scenarios. This investigation suggests a development approach for the analytical model of the axially compressed circular CFDSTs considering the non-uniform confinement effect. The strength and deformation characteristics of the concrete subjected to constant lateral stresses have been first systematically analyzed through the extensively collected experimental database, and the corresponding constitutive models have been formulated accordingly. The stress distributions of the sandwiched concrete and the influence of the cross-sectional geometric properties have been discussed, and then the calculation method for the non-uniform confining factor has been developed. An efficient analytical model has been established on the basis of an incremental-iterative procedure, with the steel tube-concrete interaction and bonding behavior appropriately considered. The proposed analytical model has been verified through the widely collected experimental data of axially compressed CFDSTs, and the results show that it could effectively simulate the full-range axial load–strain curves and improve the prediction accuracy of ultimate loads by about 5% to 16% compared with the existing design formulas.

Hysteretic energy distribution model of CFDST composite frame with metallic dampers using coupled shear-flexural beam model

Novel steel–concrete composite structures have drawn increasingly attention in recent years especially in high-rise buildings owing to its superior structural performance over conventional concrete and steel structures. Moreover, energy dissipation devices such as metallic dampers and buckling-restrained braces (BRB) were necessarily added in this type of structure to resist seismic loads. However, the existing research regarding to the dual system consisting of composite frame and energy dissipation was limited. In this paper, the dual system consisting of concrete-filled double skin steel tubular (CFDST) composite frame and metallic damper was set as the research subject, especially focusing on the analysis of hysteretic energy distribution along the height. The 10- and 20-story dual systems were designed with different parameters revealing the influence of semi-rigid connection and metallic damper. Nonlinear models of structures established by Opensees software were validated by the test results. Afterwards, the energy distributions of all stories were discussed. It demonstrated that the metallic damper could absorb considerable energy under seismic loads while a semi-rigid connection with relatively high moment strength had a detrimental effect on the column. Moreover, the semi-rigid connection in the span without metallic damper in high story exhibited significantly larger rotation than that in the span with metallic damper. Finally, the method to estimate the energy distribution estimation of the dual system was developed, in which the lateral displacement pattern was observed by the coupled shear-flexural beam model to fully consider the flexural deformation of the dual system. An equivalent distribution of the shear and bending stiffness was also proposed considering the effect of the semi-rigid in the span without metallic damper. The predicted results from the model were validated by the analysis results derived from the nonlinear model. The theoretical and analytical results of the paper could activate the application of the dual system and provide a reasonable method to estimate the hysteretic energy distribution of the dual system.

Compressive–Flexural Failure Mechanism and Bearing Capacity Calculation of Over-Ranging Tapered CFDST Members for Support Structures of Offshore Wind Turbines

Upon the higher requirement on high-performance structures of large-scale supporting structures of offshore wind turbines, the systematic analysis on the compressive-flexural behavior and ultimate bearing capacity of tapered concrete-filled double skin steel tubular (CFDST) members designed by over-ranging parameters was performed. Investigating the entire-process mechanism, e.g., the moment–deformation response, stress development, interaction stress, and subassembly contribution, was based on the finite element (FE) analysis, where the moment–deformation curve can be distinguished by four characteristic points, and the transverse local buckling of outer tube partly weakens distribution height of interface pressure in compression zone compared to that in tension zone. Influences of material strengths and geometric parameters were examined by the parametric study, e.g., increasing tapered angle (ψ) slightly reduces the bearing capacity; the higher axial compression ratio (n) contributes a noteworthy action on the post-peak behavior and carrying capacity, e.g., the bearing capacities at n = 0.9 and n = 0.5 reduce by 64.14% and 18.44% compared to capacity at n = 0.1, respectively; influence of Do/to ratio is more significant than Di/ti ratio. Subsequently, the modified cross-sectional stress integration (CSI) method was proposed to predict the moment–strain (M-ε) curves of tapered CFDST members; meanwhile, a confined concrete model with transverse confinement stress as an explicit parameter was modified, and influences of different confined concrete models on predicting M-ε curves were compared. Finally, design methods based on the modified CSI method and limit state method were proposed as a simplified calculation method to determine the correlative relationship of axial compressive strength and moment-resisting capacity (N-M curve).

Shaking table test on seismic behavior of posttensioned precast segmental Concrete-Filled double skin steel tubular piers

Posttensioned precast segmental bridge piers have proven to be an attractive solution for accelerated bridge construction and seismic resilience. Although extensive research efforts have been made to understand the seismic performance of such piers under quasi-static loading and unidirectional/bidirectional ground motions, there is limited information available regarding to their dynamic behavior when subjected to tri-directional ground motions. Therefore, this study performed shaking table tests on an innovative posttensioned precast segmental concrete-filled double skin steel tubular (CFDST) pier to explore its seismic behavior under a set of tridirectionally applied far-field ground motions. A total of six 1/5 scaled piers were investigated with different design details, including one monolithic pier as reference, two posttensioned precast segmental piers without internal energy-dissipating (ED) bars but different amounts of prestressing tendons, and three posttensioned precast segmental piers with different amounts of ED bars. It has found that the relative displacement responses decreased with increase in amounts of prestressing tendons or ED bars. The segmental piers without ED bars twisted obviously when PGA reached 0.3 g under tri-directional ground motion excitations, while the segmental piers with ED bars did not due to additional shear resistance across joints provided by ED bars. Moreover, the dynamic responses of segmental piers with and without vertical ground motion excitation were compared in details to investigate the effect of vertical ground motion on their seismic behavior. It has found that the change in vertical acceleration response due to vertical ground motion excitation was a significant importance compared to the change in lateral accelerations, relative displacements and tendon force increment. In consequence, the axial compressive force as well as shear resistance across joint provided by dead load reduced by almost 33% due to appearance of vertical ground motion at the PGA of 0.7 g.

Numerical study of seismic performance of steel-concrete composite rigid-frame bridge with precast segmental CFDST piers crossing fault-rupture zones

Although seismic performance of bridges crossing fault-rupture zones has been studied in recent two decades, there is still no effective solution to mitigate the hazard of fault-crossing effect. Recently, a new type of post-tensioned precast segmental (PTPS) concrete-filled double skin steel tube (CFDST), known as PTPS-CFDST column, has been proposed and verified to exhibit excellent performance with respect to seismic resilience. Moreover, PTPS-CFDST columns can accommodate torsional deformation through joint slip and are thus considered as a promising structural solution for bridges crossing fault-rupture zones. This study aims to investigate the performance of a steel–concrete composite rigid-frame bridge (SCCRFB) with PTPS-CFDST piers subjected to across-fault ground motions through numerical simulations. Two detailed three-dimensional (3D) finite element (FE) bridge models are developed using the explicit FE code LS-DYNA. In particular, Bridge 1 uses the new PTPS-CFDST pier, while Bridge 2 serves as a reference model with monolithic CFDST piers. Two types of across-fault ground motions with strike- and dip-slip mechanisms are used as seismic inputs, and the influence of fling-step is parametrically investigated. Structural responses, including the global seismic responses, seismic damages, energy absorption, and local joint slip and opening, are systematically discussed. The numerical results indicate that, compared to the monolithic CFDST piers, PTPS-CFDST piers exhibit advantages in terms of seismic resilience, with lower damage and outstanding self-centering performance, which facilitates post-earthquake recovery after experiencing across-fault ground motions. This study provides valuable references for the seismic design of bridges with PTPS-CFDST piers crossing fault-rupture zones.

Axial compressive behavior of circular composite columns with external confinement

With the advance of externally confined composite columns, a generic model that can predict the ultimate axial compressive strength of both circular concrete-filled steel tube (CFST) and concrete-filled double skin steel tubes (CFDST) short columns with external confinement is very attractive. For this purpose, a rich experiment database of composite columns is assembled, guides to build up this database are outlined, and its limitations are also summarized. Based on some fundamental considerations, a simple formula for estimating ultimate axial compression of circular composite short columns is proposed first. The hoop and longitudinal stresses of outer and inner (if any) steel tubes are then determined by the stress analysis, from which the assumption frequently used in previous studies that the sandwiched concrete in a CFDST column is under uniform confinement is demonstrated to be unreasonable. Besides, the additional external confining pressure provided by external confinement in the form of steel spirals, rings, jackets, or tie bars is thoroughly investigated. Further, to comprehend the triaxial strength of infilled concrete in both CFST and CFDST columns, a novel concept of equivalent confining stress that can reflect both uniform and non-uniform confinement effects is defined, with which a modified Power-law failure criterion is established. Model validations illustrate that this generic model can reasonably estimate the strength of externally confined CFST and CFDST columns. Although it currently slightly underestimates the strength of ring-enhanced CFDST columns, this limitation can be easily overcome by recalibrating some coefficients without rebuilding the proposed framework.

Testing, numerical analysis and design of CFDST cross-sections with square stainless steel outer tubes in bending

The structural performance and design of concrete-filled double skin tubular (CFDST) cross-sections with square stainless steel outer tubes are studied herein. A total of 17 four-point bending tests on CFDST cross-sections with varying concrete grades, together with accompanying material tests, were first conducted. The details of the test rig and procedures, as well as the key experimental results are reported. Following the physical testing, a numerical modelling campaign was carried out. A finite element (FE) model was initially validated against the tests, and then adopted to conduct a parametric study to acquire further FE data, covering a broader spectrum of material strengths and cross-section slendernesses. The obtained test and FE results were used to evaluate the applicability of the general design provisions for concrete-filled carbon steel members in the current European and American design codes. Overall, the examined design codes are shown to provide unduly conservative (less so for the higher concrete grades) and rather scattered moment resistance predictions, though some moment resistances predicted using the European code were on the unsafe side. Modifications to the European design treatment in relation to the assumed stress distribution, to take due account of the partial spread of plasticity in the outer tube, and the effective compressive strength of the concrete infill, to reflect the reduced relative effectiveness of using higher concrete grades, are proposed and shown to improve the consistency of the resistance predictions.

Analytical behavior and bearing capacity research on out-of-code tapered CFDST members under pure torsion and compression-torsion combination

Facing the apparent enhancement of rated power of offshore wind turbines, the increasing rotor diameter and blade length gradually pose severe challenges to its support structure for resisting extreme loads. Due to the remarkable composite effect, the recently developed tapered concrete-filled double skin steel tubular (CFDST) members can provide a high-performance structural type and competitive application prospect compared to traditional steel tower barrels. Therefore, this paper conducted the numerical and theoretical research on out-of-code tapered CFDST members under pure torsion and compression-torsion combination. The finite element (FE) model was established to examine the full-range mechanism including torque versus deformation response (T-θ curve), interaction behavior and component contribution, indicating that four characteristic points can distinguish the T-θ curve under pure torsion, and slight contact pressure between the inner tube and sandwich concrete exists along the height direction. The parametric study was performed to investigate the influences of geometric-physical parameters, e.g., by increasing tapered angle (ψ) 0.2°, the torsional capacity obtains a reduction of 5%; hollow ratios (χ), axial compression ratios, and diameter-to-thickness (D/t) ratios of double-skin tubes obviously affect the torsion resistance; altering steel yield grade influences torsional capacity than concrete grade. Subsequently, a theoretical multilayered cylinder model as the simplified design tool was proposed to simulate full-range T-θ curves of tapered CFDST members. Moreover, a modified design method for calculating N-T correlation curve was developed and validated by introducing the refined equations of pure torsion resistance (Tu), where the design methods in current codes displayed a quite conservative prediction for tapered CFDST members with out-of-code parameters (e.g., hollow ratios or D/t ratios). The above research on out-of-code tapered CFDST members can offer valuable design guidelines for its engineering applications.

Study on axial behaviour of concrete filled steel tubular columns

Concrete-filled steel tube (CFST) columns have gained wide acceptance in the construction of high-rise buildings due to their exceptional ability to withstand axial load. They are commonly employed as columns in large-span high-rise buildings, bridges, and piers. This research aims to investigate the performance of concrete-filled steel tube (CFST) columns when subjected to axial load. One key advantage is that the steel tube serves as a permanent confinement for the concrete. The concrete filling inside the tube prevents local buckling and enhances the lateral stability of the member. Moreover, the external steel tube acts as a formwork. Eight composite columns were constructed, comprising four CFST columns and four CFDST (Concrete-filled Double Skin Tubular) columns, and were subjected to axial loading for evaluation. The experimental study was conducted to determine the relationship between load, axial displacement, and lateral displacement, as well as the ultimate load-carrying capacity. Furthermore, finite element analysis using Abaqus was performed to investigate the composite columns analytically. A parametric study was also carried out, considering the diameter-to-thickness ratio and grade of concrete. Confinement significantly enhances the load-carrying capacity, and the presence of concrete infill reduces the lateral deflection of long columns.

Experimental and numerical investigation on hysteretic behavior of posttensioned precast segmental Concrete-filled double skin steel tubular piers

The posttensioned precast segmental concrete-filled double skin steel tubular (CFDST) piers proposed in this study combines the advantages of posttensioned precast segmental piers and composite CFDST piers, in such way to reduce on-site construction burdens, increase section modulus, and reduce self-weight. To investigate the hysteretic behavior of this new type of bridge pier, one posttensioned precast segmental CFDST pier was designed and tested under cyclic lateral loading, with one cast-in-place CFDST pier as reference. Test results show that the proposed posttensioned precast segmental pier performs well with good ductility, satisfactory energy dissipation, and small residual displacement. The damage to precast segments is effectively avoided by using CFDST members. Moreover, a numerical study was also conducted to investigate the influences of different design parameters on the hysteretic behavior of posttensioned precast segmental CFDST piers. The design parameters studied in this paper included the pier aspect ratio, amount of energy-dissipating (ED) bars, axial load ratio due to gravity, axial load ratio due to prestressing force, initial stress level in prestressing strands and CFDST cross-sectional parameters. It has been found that the amount of ED bars, axial load ratio due to gravity and axial load ratio due to prestressing force are the more important factors on energy dissipation and self-centering capacities. The pier aspect ratio being greater than 7 has a negative effect on residual drift ratio of posttensioned precast segmental CFDST piers due to P-Δ effect. The initial stress level in prestressing strands has little effect on energy dissipation and self-centering capacity, but influences the failure mode and deformation capacity.

Experimental and analytical research on seismic performance of ECC-filled high-strength double skin steel tubular columns with out-of-code D/t ratios

Against the offshore construction requirement on light weight and high performance, using high-strength (HS) steel in concrete-filled double skin steel tubular (CFDST) members usually results in out-of-code diameter-to-thickness (D/t) ratios and performance uncertainty. A quasi-static cyclic loading test was therefore conducted to investigate the seismic performance of circular-in-circular ECC-filled high-strength double skin steel tubular (EFHDST) columns with out-of-code D/t ratios. Typical failure mode, hysteretic curves, bearing capacity and ductility were analyzed. Subsequently, the finite element (FE) model incorporating material damage effect was established and verified to conduct further parametric study. Influence of geometric parameters (e.g., wall thickness and hollow ratio), material strength and axial compression level was discussed in detail. Finally, a simplified restoring force model was developed to predict the seismic behavior of EFHDST columns. The result indicates that: the EFHDST columns fail by the ECC crushing, steel fracture and local buckling of double-skin tubes; the steel yield strength and thickness of outer tube, axial compression level and hollow ratio obviously affect the hysteretic performance (e.g., the bearing capacity and ductility) through the test and FE analysis, e.g., increasing hollow ratio from 0.54 to 0.82 the bearing capacity and ductility coefficient of test respectively decrease by 11.20% and 26.61%; the dimensionless skeleton curve, unloading stiffness degradation and hysteretic rule are proposed to form the restoring force model, where a strength model considering effect of ECC tension strength is included, and the reasonable agreement is achieved by the comparison results. The displayed research on EFHDST columns can provide significant references to its engineering applications.

Numerical investigation of concrete-filled double skin steel tubular (CFDST) structure subjected to underwater explosion loading

With the increasing applications in the offshore industry such as oil and gas jackets, submarine pipelines and wind turbine foundations, concrete-filled double skin steel tubular (CFDST) structures are encountering the ever-increasing risk of threats to underwater explosions (UNDEX). This study presents a systematical investigation on the structural behaviors and design recommendations of the CFDST structures subjected to UNDEX loadings through finite element analysis (FEA) approaches. Finite element models have been developed, where the non-linear material properties of the constitutive steel and concrete parts and the composite actions in-between have been considered. The FEA models are verified against the experimentally determined shock wave pressure history, the deformation shapes, and the residual strength. The full-range analyses were firstly carried out on the structural responses of CFDST structures, including the typical damage patterns and residual strength of the specimen after UNDEX. Then, the parametric studies show that the cross-section hollow ratio, charge weight, and explosion distance play great roles in determining the residual strengths. Thereafter, damage indexes considering the parameter of the hollow ratio and the scaled explosion distance has been formulated, and design recommendations have been suggested accordingly.

Circular concrete-filled double skin steel tubes under concentric compression: Tests and FEA parametric study

Circular concrete-filled double skin steel tubes under concentric compression: Tests and FEA parametric study