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High-strength concrete-filled steel tubular (HCFHST) square columns are commonly used as critical members in super high-rise and high-rise structures. These columns are susceptible to being impacted by vehicles in service, resulting in column damage and even structural collapse. Therefore, a lateral impact test of HSCFST columns is conducted using a rigid test truck. The failure mode, impact force, deformation and energy dissipation capacity are analyzed to reveal its dynamic response. Then, the refined finite element models are established, and the damage evolution law, energy dissipation mechanism, and dynamic distribution of internal load of HSCFST columns under different span-to-height ratios (H/L) are analyzed to reveal its working mechanism. The effects of H/L on column dynamic responses with varying impact mass, velocity, steel and concrete strength, steel ratio, and section size are investigated. The results indicate that HCFHST specimens display bending deformation and superior impact resistance. Based on internal force distribution laws, the failure section of HCFHST columns is close to the support. When H/L < 0.25, the column dynamic performance changes, and the failure mode gradually shifts from bending failure to shear failure. Therefore, it is suggested to locally reinforce the support to prevent the fixed-fixed supported HCFHST columns from a shear failure. Additionally, the section size and the steel tube thickness are the critical factors that influence the impact resistance and energy dissipation capability of the column under different H/L. A calculation formula for evaluating the energy dissipation capacity of HCFHST columns is proposed based on the data regression method. • Conduct impact tests on HCFHST specimens under impact with fixed-fixed support. • Analyze the failure mode and dynamic response of HCFHST column under impact loading. • Analyze the effect of span-to-height ratio on the dynamic response of HCFHST column. • Propose a calculation formula to evaluate the energy dissipation capacity of column. [ABSTRACT FROM AUTHOR]

Using ultra-high-strength materials in the concrete-filled steel tubular columns has potential to optimize cross-sectional dimensions and improve the performance and sustainability of offshore structures under the complex marine conditions. This study investigated the behavior and performance of ultra-high-strength concrete-filled square steel tubular (UHSCFST) stub columns when subjected to eccentric compressive loads using experimental tests and finite element analysis. Six UHSCFST column specimens were tested considering variations in material strength and eccentricity. The column response to the eccentric loads was analyzed, taking into account the failure mode, load-lateral deflection response, and longitudinal and transverse strains obtained from the tests. Additionally, finite element models of the tested UHSCFST columns were developed and validated by comparing the numerical and experimental results. Baseline simulations were conducted to extensively analyze the stress distributions of each component and identify the load-transfer mechanism during the loading process. The column models were also used to examine the effects of key parameters on the eccentric compression behaviors of the UHSCFST stub columns and determine the dominant parameters for developing design suggestions. These findings provide valuable information on the utilization of ultra-high-strength materials in CFST members for performance improvement. Furthermore, the results serve as references for the further design and evaluation of UHSCFST columns under different loading conditions. • Using ultra-high-strength materials in CFST stub column for coastal structures. • Eccentric compression testing of UHSCFST stub column. • Examining capacity and load transfer mechanism of UHSCFST stub column. • Creating and validating numerical model of eccentrically loaded UHSCFST stub column. • Conducting parametric studies on column mechanical behaviors for design suggestions. [ABSTRACT FROM AUTHOR]

This study conducts experimental and numerical investigations into the response of ultra-high-strength (UHS) concrete-filled ultra-high-strength steel tubular (UHSCFST) columns under eccentric loading, varying the slenderness ratio, to develop effective design guidelines for engineering applications. A series of eccentric compression tests were conducted on twelve UHSCFST columns with varying slenderness ratios to identify failure mechanisms and load-bearing characteristics. In the experimental program, critical influencing factors, including load eccentricity ratio, slenderness ratio, and UHS steel strength, were considered. Finite element models of eccentrically loaded UHSCFST columns were developed using ABAQUS and validated through a comparison of tested and simulated results to analyze load-sharing ratios and stress distribution for each column component. The findings indicated that UHSCFST column failure modes were characterized by compression-controlled and flexure-dominated damage under the combined effects of slenderness ratio and load eccentricity ratio. UHS concrete played a dominant role in bearing the eccentric load, and a judicious selection of UHS steel yield strength can improve column capacity and resistance. Additionally, these validated models were employed to conduct parametric studies that evaluated the effects of design and load parameters on the eccentric load capacity of UHSCFST columns. Design equations were developed based on tested and simulated results to predict the ultimate load capacity of UHSCFST column with varying slenderness ratios under eccentric loading conditions. • Conducting eccentric compression tests and nonlinear numerical simulations on UHSCFST column • Evaluating effects of slenderness ratio and load eccentricity on column behaviors • Extensive studies of capacity, load transfer mechanism, and failure mode for columns • Identifying compression-controlled and flexure-dominated damage for UHSCFST column • Proposing design equations for estimating eccentric load capacity [ABSTRACT FROM AUTHOR]

This study presents experimental and numerical research on the dynamic behaviors and resistances of square concrete-filled steel tubular members internally strengthened by I-shaped CFRP profile (SCFST-CFRP) with fixed boundary conditions subjected to lateral impact loads. Dynamic impact tests were conducted on five SCFST-CFRP specimens and a traditional concrete-filled steel tubular (SCFST) specimen, examining their dynamic responses with respect to deformation modes, impact force, displacement, and strain distribution at different levels of impact energies and impact momentums. The test results indicated that the deformation of the specimens was concentrated in the impact region, approximately 0.38 L above the base, due to the transient localized characteristics of the lateral impact load. In terms of displacement and impact force, the SCFST-CFRP member exhibited better impact resistance compared to the SCFST member. Finite element models of the SCFST-CFRP members were created using LS-DYNA and validated against the impact tests. These validated models were then utilized to explore the damage patterns, dynamic bending moment, and load transfer mechanism of the SCFST-CFRP member under lateral impact loading. Additionally, a parametric study was conducted to evaluate the effects of load and structural parameters, including CFRP profile, impact energy, and impact momentum, on the impact resistance and dynamic flexural capacity of the SCFST-CFRP member. The results demonstrate that the enhancement in impact resistance caused by the inner CFRP profile was more significant under higher impact energy. Based on the parametric analysis results, empirical equations were proposed to predict the dynamic flexural capacity of lateral impact-loaded SCFST-CFRP members. • Impact tests of CFST member strengthened with CFRP profile under fixed boundaries. • Evolutions and distributions of deformation and internal force were summarized. • Impact load transfer mechanisms of the composite member were revealed. • Effects of load and structural parameters on the impact resistance were evaluated. • An equation for the dynamic flexural capacity of the composite member was proposed. [ABSTRACT FROM AUTHOR]

• Conduct impact tests on CFSTS-CFRP members to study the effect of velocity and CFRP. • In-depth analyze the working mechanism of CFSTS-CFRP members under impact loading. • Clarify the contribution of each part to the impact resistance of CFSTS-CFRP members. • Propose a simplified dynamic flexural capacity model of CFSTS-CFRP members. • Propose a maximum deflection prediction model of CFSTS-CFRP members. Concrete-filled steel tubular simply supported members stiffened with encased I-shaped CFRP (CFSTS-CFRP members) have been developed due to their excellent mechanical performance, promoting promising applications in bridge and building structures. However, these members are susceptible to collision impacts during service, leading to serious accidents. This paper aims to investigate the structural behavior of CFSTS-CFRP members subjected to transverse impact loading, utilizing experimental, numerical, and theoretical studies. Drop hammer impact tests were conducted on three CFSTS-CFRP specimens with varying impact velocities, while a CFST specimen was used as the benchmark. The experimental results demonstrate that all CFSTS-CFRP specimens experienced bending failure. The cooperation between the I-shaped CFRP and CFST members was observed, with the mechanical properties of CFSTS-CFRP specimens being fully utilized. The working mechanism of CFSTS-CFRP members is revealed by numerical simulation results obtained from the FE models of the tested CFSTS-CFRP members, which consist of the analyses of failure mode, inertia force, sectional moment, energy absorption, etc. Furthermore, by investigating the effects of different parameters on the structural response of CFSTS-CFRP members, predicted models for dynamic flexural capacity and maximum deflection are proposed for the purpose of impact design. Additionally, the contribution of the steel tube, concrete, and I-shaped CFRP to the transverse impact resistance of CFSTS-CFRP members is clarified. This clarification provides a scientific basis for determining the respective weight coefficients in subsequent damage assessment research. The findings from the experimental, numerical, and theoretical analyses contribute to the understanding of their mechanical performance and assist in the development of more efficient design approaches. [ABSTRACT FROM AUTHOR]

The impact behavior of building and bridge structures is already a growing concern due to the frequent occurrence of vehicle collision accidents. Concrete-filled square steel tube stiffened with encased I-shaped carbon fiber reinforced plastic profile (CFST-CFRP) is suitable for building and bridge structures due to its high bearing capacity and small section size. Thus, this study experimentally and numerically presents the dynamic responses for CFST-CFRP columns under lateral impact to evaluate their impact resistance. Firstly, three CFST-CFRP columns and one CFST column were tested in a rigid vehicle impact device, with variations in impact velocity, impact type, impact impulse of the rigid vehicle, and CFRP profile. The impact force-displacement curve and failure mode of CFST-CFRP columns were obtained. Additionally, finite element analysis (FEA) models were built by ABAQUS and verified against tested results. Then, the working mechanisms of CSFT-CFRP columns under impact load were further revealed in-depth by analyzing displacement, impact force, inertia force, bending moment, shear force, and dissipated energy. Based on the working mechanisms, the effect of the CFRP profile on the dynamic response of CFST-CFRP member subject to different parameters was discussed. The results indicated that all the specimens fail at the support. With the additional CFRP profile in the CFST column, the failure pattern of the steel tube was transformed from fracture to local buckling. CFRP profiles enhance the impact resistance of CFST columns (incremented by 17%), and the increasing ratio rises with the decreasing steel ratio and steel strength of members. Steel tubes can share 72% and 78% of energy absorption and bending moment, which is the main impact-resistant component. For this study, valuable experimental data can be supplied for CFST-CFRP columns subjected to vehicle collision. Meanwhile, a theoretical reference for impact resistance design in the future is also provided. [ABSTRACT FROM AUTHOR]

Using high strength materials in concrete filled steel tube (CFST) columns is expected to achieve better structural performance and fulfil the requirements of sustainable construction. To study the mechanical behaviour of eccentrically loaded high strength concrete filled high strength square steel tube (HCFHSST) stub columns, this paper describes 12 tests with different eccentricity ratios and steel ratios. The cubic strength of high strength concrete under investigation was 110.5 MPa, and the yield strength of the high strength steel was about 434 MPa. Curves of load-lateral deformation were presented, along with values of ductility index, and the minimum ductility index based on the steel ratio of columns was suggested. Finite element analysis (FEA) software ABAQUS was applied to simulate HCFHSSTs. The analytical results were in good agreement with the experimental ones. The load-lateral deformation curve was divided into four stages: elastic, elastic-plastic, plastic hardening and descending. The confinement effect of steel tube at various stages was analysed. The parametric studies were carried out to evaluate the influences of the eccentricity ratio, concrete compressive strength, steel yield strength and steel ratio on the strength reduction factor (SRF), concrete contribution ratio (CCR), P-M and P/P u - M/M u interaction curves of the HCFHSST members. The bending moments at balanced points of P/P u - M/M u curves calculated by the plastic stress distribution models (PSDM) and FEA models were compared. The ultimate bearing capacities obtained from the tests and the values calculated from the AISC 360, GB 50936 and CECS 28: 90 design codes were compared. Finally, the formulas were proposed to predict the P/P u - M/M u curves for the HCFHSST stub columns subjected to eccentric load. The proposed formulas’ predictions agreed well with the test results. [ABSTRACT FROM AUTHOR]

To study the mechanical behavior of high-strength concrete filled high-strength square steel tube (HCFHST) under pure bending load, six specimens with different steel ratio were tested. The corresponding nonlinear finite-element models were established to analyze the mechanical properties. The load-displacement curves obtained from the numerical analyses are consistent with the experimental results. In addition, the influences of different materials are analyzed in this paper. The moment-curvature relationship can be divided into three stages: elastic stage, yield stage and hardening stage. And the ultimate bearing capacity increased with the steel ratio, steel yield strength and concrete compressive strength. Moreover, the ultimate bearing capacity of the experiment and finite-element analysis (FEA) model is compared with the requirements of codes: AISC-LRFD (1999), AIJ (1997), EC4 (1994) and GB50936-2014 (2014). The test and FEA result were the most compatible to the calculated result of EC4 (1994). And find the results in this paper is the most compatible to the code EC4 (1994). [ABSTRACT FROM AUTHOR]

• Conducted eccentric compression tests on 18 CFSST-CFRP long column. • Investigated eccentrically loaded behavior and resistance of CFSST-CFRP column. • Evaluated effects of slenderness ratios and load eccentricity ratio. • Analyzed load bearing capacity and load-transferring mechanism. • Performed parametric studies on column bearing capacity. • Developed design equations to predict ultimate eccentric load capacity. This study investigated behavior of concrete filled square steel tubular (CFSST) columns encased with I-shaped CFPR under eccentric compression. Full-scale eccentric compression tests were conducted on eighteen column specimens consisting of square steel tube, concrete, and an I-shaped CFRP profile. The test program considered effects of load eccentricity ratio and column slenderness ratio. The eccentrically loaded column behavior was investigated with respect to the mid-height deflection, load, and failure modes. The development and distribution of longitudinal strain and neural axis for the column were also studied. Finite element models were developed and validated against tested results to further analyze the load-transferring mechanism of the composite column and perform detailed parametric studies. The results indicated that the CFSST column encased with I-shaped CFRP behaved in a ductile manner with the improved capacity and increased stability. Finally, design equations were developed using tested and simulated data to estimate ultimate bearing capacity of the CFSST column encased with I-shaped CFRP when subjected to eccentric compression. The predicted column capacities using the design equations matched well with the tested and simulated capacities. [ABSTRACT FROM AUTHOR]

• High-strength CFSST stub column with an encased I-shaped CFRP profile was proposed. • Axial compression test was performed on HCFHSST-CFRP stub column. • Investigated effects of material strengths and steel ratio on column behavior. • The combinations of high-strength materials and CFRP improved column resistance. • Formulas were proposed to predict ultimate axial load capacity. A new composite column that consists of high-strength square steel tube, high-strength concrete, and carbon fiber reinforced polymer (CFRP) profile with a I-shaped cross section was developed and investigated in this study. This paper experimentally and numerically investigated axially loaded behavior of high-strength concrete filled high-strength steel tubular (HCFHSST) stub column with an encased I-shaped CFRP profile. In the experimental study, axial compression tests were completed on eight specimens to examine the axial load response of the composite column, including the load–displacement curves, failure mode, and strain distribution. Finite element models of the composite column were developed using ABAQUS and validated by comparing numerical results with experimental data. The validated models were used to further investigate the load sharing and transferring mechanism for each component of the composite column. Results showed that the composite column comprehensively used the advantageous merits of concrete, steel tube, and CFRP as a unit to share the applied load at different loading stages: linearly elastic, elastic–plastic, hardening, post-peak descending, and residual plateau stage. Parametric studies were performed that assessed influences of critical design parameters on the axially loaded behavior of the stub column. The examined parameters included the compressive strength of high-strength concrete, yield strength of high-strength steel, and steel ratio. Finally, empirical equations were proposed to determine the ultimate vertical strain and the ultimate axial load capacity of the HCFHSST stub column encased with a I-shaped CFRP profile. [ABSTRACT FROM AUTHOR]

Concrete-filled square steel tubular (CFSST) stub column stiffened with an encased I-section carbon fiber-reinforced polymer (CFRP) is a new composite member that consists of a square steel tube, concrete infill, and an encased CFRP profile. This paper conducted investigations that experimentally and numerically examined the behavior of CFSST stub column with an inner I-section CFRP profile under biaxial bending. Seven column specimens were tested using biaxially eccentric compression tests in the experimental study. The parameters considered in the test were the load eccentricity, steel yield strength, and steel tube thickness. Numerical models were developed to investigate the column load-carrying mechanism using ABAQUS and validated against experimental results. Results indicated that the CFSST column stiffened with an encased CFRP profile has favorable capacity and ductility when subjected to biaxial bending. Furthermore, parametric analyses were performed to assess the effects of steel yield strength, concrete compressive strength, and steel ratio (steel thickness) on the load bearing capacity and P / P u - M / M u curve of stub column under biaxial bending. Finally, formulas to predict the P / P u - M / M u curves of the composite column under bi-axial bending were proposed in this study. • Concrete-filled square steel tubular stub column stiffened with an encased I-section CFRP profile was proposed. • Biaxially eccentric compression test was performed on CFSST stub column stiffened with an encased I-section CFRP profile. • Effects of concrete compressive strength, steel yield strength, and steel ratio were investigated. • Parametric studies were conducted to study the mechanical behavior of the new composite stub column. • Formulas were proposed to predict the P / P u - M / M u curves. [ABSTRACT FROM AUTHOR]

Damage modes of the rectangle concrete-filled steel tube (RCFST) long columns under the eccentric compression were investigated by combining the finite element method (FEM) and the extended finite element method (XFEM) on the ABAQUS platform. The three-dimensional (3D) aggregates and the interfacial transition zone (ITZ) were generated at the middle height of RCFST. The parametric analyses were performed to test four RCFST long columns by varying the eccentricity ratio (γ). The results agreed well with the experimental results. The proposed multi-scale numerical simulation procedure can be used to understand the instability behavior of the RCFST long columns. [Display omitted] • Rectangle concrete-filled steel tube long columns have many instability modes. • Eccentricity ratio dominates concrete-filled steel tube long columns instability modes. • Python script process can set up a concrete-filled steel tube long columns multi-scale platform on ABAQUS. [ABSTRACT FROM AUTHOR]

Many old concrete-filled steel tube (CFST) arch bridges constructed using common concrete, the fluidity before initial setting and dry shrinkage during use create ring gaps at the interfaces of concrete core column (CCC) and spiral welding tube (SWT), and air voids in CCC. Also, unfavorable conditions of nature increase the number of gaps and voids, create more serious defects, decrease arch rib stiffness, and even change the dynamic properties of the whole bridge structure. Therefore, a finite element analysis (FEA) verified by scale-model experiments on CFST arch bridge rib members with air void and ring gap composite defects was conducted to determine the tangential stiffness of the structure. Secondly, the natural vibration and frequency of the whole bridge were analyzed using tangential stiffness and the influences of various defects on the dynamic performance of bridge was investigated. Therefore, a novel trans-scale determine system was developed for the detection of the tangential stiffness of bridges with composite defects in CFST ribs, so as to evaluate the influences of these defects on the dynamic performance of bridges. This study can provide a strong foundation for the maintenance repair of CFST arch bridges. Unlabelled Image • Bearing capacity of a CFST rib with ring gap and air void composite defects under axial compression was studied. • Influence of the composite defects on the dynamic performance of the bridge was described through frequency analyses. • A novel trans-scale determine system of the bridge with composite defects in CFST ribs was proposed. [ABSTRACT FROM AUTHOR]