Concrete-filled Square Research Articles

Research on concrete-filled square CFRP steel tube under compressive-torsional hysteresis loading

Concrete-filled CFRP steel tube structures are presently employed on extensively in various engineering practices. This study examines the mechanical performance of concrete-filled square CFRP steel tubes under compressive-torsional hysteresis loads. Through the analysis of nine specimens, the research focuses on failure modes, torque–angle (T–θ) behavior, triaxial strain, and the synergistic effects of the steel tube and CFRP during cyclic loading. A numerical simulation method is initially introduced based on the test data to predict the actions of concrete-filled CFRP steel tube compressive-torsional specimens under hysteresis loading. This method is subsequently verified by contrasting it with the outcomes from representative experiments. In addition, the stress distribution of each material during the entire loading process of the sample is examined. Finally, using data from experiments and finite elements, combined with the trilinear model, a hysteretic model under compressive-torsional hysteresis stresses has been established for square CFRP steel tube filled with concrete. The calculated outcomes of the developed finite element model closely align with those of the hysteretic model.

Impact of steel tube wall thickness on axial compression behavior of reinforced and recycled aggregate concrete-filled square steel tube short columns

Tests and numerical simulations were conducted to investigate the impact of wall thickness of steel tube on the axial load performance of reinforced and recycled aggregate concrete (RAC)-filled square steel tube short columns (R-RACFST). The test groups consisted of R-RACFST, concrete-filled square steel tube (CFST), and RAC-filled square steel tube (RACFST). Each group had five different wall thicknesses of the steel tube, and the RAC infill was made of 100 % recycled coarse aggregate (RCA). Two replicate specimens were prepared for each group and wall thickness. The tests were used to analyze the effect of steel ratio on failure mode, loading performance, and ductility. The analyses clarified that the reinforcement effectively enhanced the confinement effect on RAC, compensating for the inadequate confinement of the square tubes and the brittleness of the RAC with 100 % RCA. To further understand the acting role of reinforcement, numerical parametric studies were conducted. A novel numerical model for R-RACFSTs was established and verified with the tests. A total of 81 models were then simulated, considering the coupling effects between the wall thickness of the steel tube, the amount of reinforcement, and the strength of RAC. Based on the simulations, the coupling relationship between the steel tube and reinforcement, as well as the optimal range of steel ratio, were determined. Additionally, strength prediction equations were studied and proposed. The findings indicate that it is feasible to fill RAC with 100 % RCA in R-RACFSTs; when combined with appropriate reinforcement, R-RACFSTs with thinner tubes can achieve the same or better performance compared to RACFSTs with thicker tubes; the recommended reasonable range for the steel ratio and corresponding confinement coefficient in R-RACFSTs are 6.4 % to 13.7 % and 1.00 to 2.04, respectively; the predictions proposed are accurate and reliable.

Expressions for Stress Concentration Factors for T-Joints of Hollow and Concrete-Filled Square Cross-Sections for In-Plane Axial and Bending Loads

Expressions for Stress Concentration Factors for T-Joints of Hollow and Concrete-Filled Square Cross-Sections for In-Plane Axial and Bending Loads

Behaviour of steel-fibre-reinforced geopolymer concrete-filled square steel tubular stub column under axial compression

Resource utilisation of industrial waste has become a crucial issue in construction aiming for sustainable development. Research on geopolymer concrete-filled square steel tubular (GCFST) structures is limited. Moreover, methods for calculating the bearing capacity of steel-fibre-reinforced GCFST (SFRGCFST) structures require further investigation. This study presents an experimental and analytical investigation of the axial compression performance of SFRGCFST stub columns. Twenty-four specimens were tested to assess the effect of steel tube thickness, steel fibre (SF) volume fraction, SF aspect ratio, and concrete strength grade on failure modes, load–deformation behaviour, load–strain response, ultimate resistance, and ductility of SFRGCFST columns. The results indicated that the failure modes of SFRGCFST columns are influenced by the coefficient index, which varies with the test parameters. When the coefficient index exceeded 0.88, the failure mode of the specimens transitioned from shearing failure to waist-drum-shaped failure. The average ultimate bearing capacity of the SFRGCFST columns increased by 35.13 % compared with that of the plain concrete-filled steel tubes (CFSTs). When the SF volume fraction reached 0.9 %, the ultimate bearing capacity of the SFRGCFST columns increased by 21.85 % compared with that of steel-fibre-reinforced concrete-filled steel tube (SFRCFST) columns. The incorporation of SF significantly improved the deformation capacity and ductility of the SFRGCFST columns and moderated the slope of the post-peak load–displacement and load–strain curves, slowing the descent of the curve. Utilising the multi-axial strength criterion and mechanical equilibrium equation for square CFSTs, a formula for calculating the ultimate bearing capacity of SFRGCFST stub columns was developed. This formula enables accurate prediction of the axial compressive load capacity of SFRGCFST stub columns and provides a basis for revising relevant standards.

Behavior of UHPC filled high-strength square steel tubular stub columns under combined flexural and axial loads

This study experimentally and numerically investigated the behaviors of UHPC-filled high-strength square steel tube stub columns with compact, noncompact and slender sections under combined flexural and axial loads. Eighteen tests were conducted, addressing the gap of limited tests on concrete-filled square steel tubular stub columns with noncompact or slender sections. Additionally, finite element analyses were developed and benchmarked for parametric studies. The results of tests and parametric studies show that (1) steel tube outward buckling and concrete crushing occurred at 1/4–1/2L of the compression zone; (2) the load-axial displacement curves organized into three phases: elastic, elastic-plastic, and recession phase; (3) the compressive strength increased with increasing tube thickness, concrete strength, and steel yield strength. The compressive strength decreased with increasing eccentric ratio and slenderness coefficient. Test and numerical results are utilized to assess the suitability of current design specifications for predicting compressive strength. The evaluation showed that neither GB 50936–2014 nor Eurocode 4 provided reasonable predictions of strength, while AISC 360–16 provided conservative predictions.

Slenderness effects on concrete-filled square steel tube columns strengthened with CFRP grid-reinforced ECC matrix

This study presents an experimental investigation aim at evaluating the slenderness effects on concrete-filled square steel tube columns strengthened with a carbon fiber-reinforced polymer (CFRP) grid-reinforced engineered cementitious composite matrix. Thirteen columns were subjected to axial compression, with the studied parameters including the length-to-width (L/B) ratio, CFRP grid layer number, concrete strength grade, and width-to-thickness ratio of the steel tube. Test results revealed that slender columns experienced an increase in load-bearing capacity ranging from 27.1 % to 32.4 % after strengthening, while the ductility enhancement reached a peak of 52.0 %. A column with an L/B ratio of 5.87 exhibited slight bending deformation in a localized region upon failed, with CFRP grid ruptured at the corner. While columns with L/B ratios of 7.83 and 9.78 failed due to the loss of stability, displaying overall bending deformation. The increase in L/B ratio accelerated the loss of stability, resulting in a decrease in the ultimate load. As the L/B ratio increased from 2.97 to 5.93, 7.91 and 9.89, the ultimate loads of the strengthened columns decreased by 7.4 %, 9.2 %, and 15.4 %, respectively. A load-bearing capacity calculation model of slender strengthened columns was developed using the fiber element method. Through numerical analysis, a stability coefficient was introduced, and a simplified calculation formula was proposed to predict the stability bearing capacity.

Research on Seismic Performance of Concrete-Filled Square Steel Tubular Columns with CFRP Profiles

Research on Seismic Performance of Concrete-Filled Square Steel Tubular Columns with CFRP Profiles

Experimental and Numerical Simulation of Reinforced Concrete-Filled Square GFRP Tubular Columns under Axial Compression.

To investigate the axial compressive behavior of reinforced concrete-filled square glass-fiber-reinforced polymer(GFRP) tubular (RCFSGT) columns, 17 specimens were designed with variations in GFRP tube wall thickness, spiral reinforcement yield strength, and spiral reinforcement ratio. A detailed model was developed using the finite element software ABAQUS, enabling in-depth mechanistic analysis and expanded parameter studies. The results indicate that the failure types of the specimens are all manifested as GFRP square tube cracking, and the core concrete is subjected to crushing or shear failure. The inclusion of a reinforcement cage can significantly enhance the load-bearing capacity and ductility of the specimen. Furthermore, as the yield strength and reinforcement ratio of the spiral reinforcement increase, so does the load-bearing capacity of the specimen. The finite element simulation results align well with the experimental findings. As the wall thickness of the GFRP square tube increases from 2 mm to 6 mm, the load-bearing capacity improves by approximately 19.69%. With the yield strength of the spiral reinforcement rising from 200 MPa to 400 MPa, the specimen's load-bearing capacity shows an increase of approximately 7.55%. However, as its yield strength continues to increase, there is minimal change in the load-bearing capacity. When the stirrup ratio of spiral reinforcement rises from 0.33% to 2.26%, the specimen's load-bearing capacity experiences an increase of approximately 56.90%.

Experimental and numerical investigations on stress concentration factors of concrete filled steel tube X-joints.

An SHS-CFSHS X-joint is fabricated by welding two square hollow section (SHS) braces to a concrete-filled square hollow section (CFSHS) chord. In this paper, the stress concentration factors (SCFs) of SHS-CFSHS X-joints are investigated through experimental tests and finite element analysis (FEA), with the hot spot stress method serving as the analytical approach. Eight specimens are designed and manufactured, with FE models built in software ANSYS. These FE models are validated against the test results. The specimens are tested under brace axial tension to determine the SCFs of the X-joints. It shows that the concrete filled in the chord effectively reduces the SCFs of the X-joints. To further explore various load conditions and the influence of the parameters, FEA is carried out and a total of 64 FE models are built. Based on the FEA results, multiple regression analysis is used to obtain the SCF formulae of SHS-CFSHS X-joints under axial tension load and in-plane bending load in the brace, respectively. Comparison and analysis of the SCF results obtained from experimental tests, the proposed formulae, and FE simulations reveal that the formulae presented in this study are both conservative and suitable for predicting SCFs.

Flexural behaviours of concrete-filled stainless-steel tubular beams under cold-region low temperatures

Applications of concrete-filled square (or circular) stainless-steel tubes keep increasing in cold-region coastal engineering structures. However, their behaviours under low-temperature bending have not been fully investigated, which brings obstacles to their engineering applications. To address this issue, this paper investigated flexural behaviours of concrete-filled square/circular stainless-steel tubular beams (CFSSSTBs/CFCSSTBs) at low temperatures through eight four-point bending tests. The main studied parameters were low temperatures (20∼−60 ℃) and cross-section type (circular or square shape). Test results showed that both CFSSSTBs and CFCSSTBs exhibited flexural failure and exhibited excellent ductility under low-temperature bending benefiting from the excellent ductility of stainless steel; bending resistances of CFSSSTBs and CFCSSTBs were improved by 5% and 22%, respectively. This study also developed finite element models (FEMs) for simulations on flexural behaviours of CFSSSTBs/CFCSSTBs at low temperatures. The FEMs considered both low-temperature material and geometric nonlinearities. Validations against eight tests proved the capacities of FEM simulations on low-temperature flexural behaviours of CFSSSTBs/CFCSSTBs. Finally, the code equations in Eurocode 4 and AISC 360 were used to predict the stiffness and ultimate bending resistances of CFSSSTBs/CFCSSTBs. Validations showed that the code equations underestimated the bending resistances of CFSSSTBs/CFCSSTBs. This study provided fundamental information on the flexural bending mechanism of CFSSSTBs/CFCSSTBs) at low temperatures.

Experimental and analytical investigation on eccentric performance of circular CFST columns jacketed by concrete-filled square tube

This paper presents an experimental and analytical investigation of the eccentric behaviour of circular CFST columns strengthened by a square steel tube and sandwiched concrete jackets. The main parameters include the eccentricity, strength of sandwiched concrete, and thickness of the outer steel tube. The failure modes, load-axial displacement curves, load-lateral deflection curves, and longitudinal strain distributions are presented. The effects of these parameters on the ultimate strength, ductility index, and lateral deflection are discussed in detail. Based on the longitudinal strain results obtained from the experiment and basic hypotheses, the possible positions of the neutral axis in the column section at the ultimate limit state were analysed, and three failure patterns of the specimens were determined. Analytical formulas corresponding to each failure pattern were derived to calculate the eccentric load-bearing capacity of the strengthened columns based on the limit equilibrium theory. Finally, a simplified formula was proposed to serve as the basis for future designs and applications.

Axial compressive behavior of pre-damaged concrete-filled square steel tube columns repaired with section circularization and CFRP composites

This study focused on repair treatments for the effective reuse of damaged concrete-filled square steel tube (CFSST) columns with carbon fiber-reinforced polymer (CFRP) composites. Forty specimens were designed to investigate the effects of pre-damage levels, section circularization, and the number of CFRP layers on the compressive behavior of the repaired CFSST columns. Test results indicated that the method of section circularization and CFRP wrapping effectively restored the degraded initial axial stiffness of the pre-damaged CFSST columns and increased the ultimate bearing capacity of the pre-damaged CFSST columns by 49–180 % compared to their undamaged condition. Considering the influence of the pre-damage level and the contribution of section circularization, the ultimate bearing capacity calculation model was suggested for predicting the compressive behavior of the repaired CFSST columns. The experimental results and collected test data have well verified the accuracy and applicability of the calculation model.

Study of Concrete-Filled Square and Circular Tubes Subjected to Axial Compression Load

Study of Concrete-Filled Square and Circular Tubes Subjected to Axial Compression Load

Seismic behavior of self-centering concrete-filled square steel tubular frame with slit steel plate shear walls

A self-centering concrete-filled square steel tubular frame with slit steel plate shear walls (SC-SSPSW) adopting post-tensioned (PT) column base was proposed in this study. The slit steel plate shear walls (SSPSWs) with edge stiffeners were only connected to the beams. Cycle tests were conducted on three 1/3 scaled single-span two-story specimens to investigate their mechanical and seismic behavior, and the formulas for beam and column internal forces considering frame expansion effects were derived. Finite element (FE) models of SC-SSPSWs were established, and the FE results agreed well with the test results. The results indicate that the hysteretic curves of specimens exhibit a typical double flag shape, and the residual deformation of all specimens is approximately 0.20% when loading to 2.0% story drift. Damage is primarily concentrated in the SSPSWs while other structural members remain elastic, and favorable resilience and energy dissipation capacity are achieved. With an increase in the width-to-thickness ratio or aspect ratio of links while keeping the thickness of SSPSWs unchanged, the energy dissipation decreases, and the self-centering capacity improves. The column that expands in the same direction as the loading direction bears more lateral loads. The theoretical gap opening value, PT tendons force, as well as beam axial force agree well with the test and FE results.

Research on axial compressive behavior of steel-fiber-reinforced recycled concrete-filled square steel tube slender columns

This paper presents an experimental and analytical study of the axial behavior of steel-fiber-reinforced concrete-filled square steel tube slender columns. A total of 25 axially compressive column specimens are manufactured to investigate the effects of the mass replacement percentage of recycled coarse aggregates (Rp), tube wall thickness (Ts), length-to-width ratio of columns (Lc), and steel fiber content (Vsf) on the performance of slender columns. The results show that the effects of Lc and Ts on the compressive behavior of the column specimens are significant owing to changes in the confinement effect and instability. In terms of the bearing capacity, the compressive strength increases by 12.45%–23.19% as Ts increases from 3 to 5 mm but decreases by 4.35%–10.65% as Lc increases from 6 to 12. However, the incorporation of steel fibers improves the post-peak load mechanical behavior of the slender columns by performing anchoring and bridging effects, and when Vsf reaches 1.2%, it tends to compensate for the reduction caused by changes in Lc and Ts. The synergistic action of the column specimens under axial compression is quantified based on an energy consumption indicator. In addition, predictions of the bearing capacity of the slender columns specified in the Eurocode 4, GB 50936-2014, and Han model are compared and discussed. An incremental iteration model is proposed, and the predicted values are similar to the experiment results with reasonable safety margins.

Behaviour of a Sacrificial Cladding with Foam Concrete-Filled Square Tubes under Impact Loads

In this paper, a new sacrificial cladding with foam concrete-filled square tubes (FCFST sacrificial cladding) was developed for dissipating impact energy. The impact experiment was conducted on the FCFST sacrificial claddings using a drop hammer impact experiment system, and the finite element simulation analysis was performed using the explicit nonlinear program LS-DYNA. The deformation modes, force–displacement responses and energy absorption performances of the FCFST sacrificial claddings were discussed. The results indicated that the impact responses of the FCFST sacrificial cladding could be classified into four stages, and the energy absorption performance could be enhanced by increasing the contact area between the sacrificial cladding and impactor. Foam concrete-filled tubes that underwent obvious plastic deformation dissipated more impact energy than other parts of the sacrificial cladding, and three deformation modes could be identified in theses tubes. Furthermore, the effects of the thickness ratio of the top plate to tube, width-to-thickness ratio of the tube and impact location on the impact behaviour of the FCFST sacrificial cladding were numerically studied. It was found that decreasing the thickness ratio of the top plate to tube could enhance the energy absorption performance of the FCFST sacrificial cladding. However, the impact location was found to have little effect on the energy absorption unless it was close to the edge of the sacrificial cladding.

Dynamic response of concrete-filled square steel tubular columns under lateral impact load at flat or corner zone

The dynamic response of columns under lateral impact is of great significance for guiding structural design under accidental loads. The present study aims to investigate the effect of different impact directions on the dynamic response of square concrete-filled steel tubular (CFST) columns by conducting drop hammer tests at flat or corner zones. The main experimental parameters included hammer mass, drop height, indenter radius, built-in steel bars, shear span ratio, width-thickness ratio, and column sizes. The experimental results showed that the impact zone has a significant effect on the dynamic response of CFST specimens. Under higher impact energies, specimens impacted at corner zones were more likely to fracture on the tensile side of the steel tube than specimens impacted at flat zones. And the specimens impacted at the corner zone were more sensitive to the change of indenter radius. Smaller shear span ratios, built-in steel bar, and larger column sizes improved the impact resistance of tested specimens. The 3D finite element models were developed and analyzed by ABAQUS/Explicit to explore dynamic behavior further.

Seismic Behavior Analysis of Recycled Aggregate Concrete-Filled Square Steel Tube Frames.

In this study, the seismic behavior of a recycled aggregate concrete-filled square steel tube (S-RACFST) frame under different design conditions was investigated. Based on previous studies, a finite element model for the seismic behavior of the S-RACFST frame was developed. Moreover, the axial compression ratio, beam-column line stiffness ratio, and yield bending moment ratio of the beam-column were regarded as the variation parameters. It was through these parameters that the seismic behavior of eight S-RACFST frame finite element specimens was discussed. The seismic behavior indexes, such as the hysteretic curve, ductility coefficient, energy dissipation coefficient, and stiffness degradation were obtained-which, in turn, revealed the influence law and the degree of the design parameters regarding seismic behavior. Moreover, the sensitivity of the various parameters with respect to the seismic behavior of the S-RACFST frame was evaluated via grey correlation analysis. The results show that the hysteretic curves of the specimens were fusiform and full with respect to the different parameters. Firstly, with the axial compression ratio increasing from 0.2 to 0.4, the ductility coefficient increased by 28.5%. In addition, the equivalent viscous damping coefficient of the specimen with the axial compression ratio of 0.4 was 17.9% higher than that of the specimen with the axial compression ratio of 0.2, which was 11.5% as well as that with an axial compression ratio of 0.3. Second, when the line stiffness ratio rises from 0.31 to 0.41, the specimens' bearing capacity and displacement ductility coefficient both get better. However, the displacement ductility coefficient gradually decreases when the line stiffness ratio is greater than 0.41. As a result, an optimal line stiffness ratio (0.41) thus exhibits good energy dissipation capacity. Thirdly, with the increase in the yield bending moment ratio from 0.10 to 0.31, the bearing capacity of the specimens improves. In addition, the positive and negative peak loads increased by 16.4% and 22.8%, respectively. Moreover, the ductility coefficients were all close to three, thus demonstrating good seismic behavior. The stiffness curve of the specimen with a large yield bending moment ratio with respect to the beam-column, is higher than those that possess a small beam-column yield moment ratio. In addition, the yield bending moment ratio of the beam-column possesses a significant influence on the seismic behavior of the S-RACFST frame. Furthermore, the yield bending moment ratio of the beam-column should be considered first in order to ensure the seismic behavior of the S-RACFST frame.

Lateral impact resistance of full-scale concrete-filled weathering steel tube columns

This paper conducted lateral impact tests on 10 concrete-filled weathering steel tubular (CFWST) columns and studied the effect of prestressing on their resistance to lateral impact. The results indicate that by using prestressed cantilever members, the impact resistance of the column can be significantly improved. This is mainly due to the reduction of tensile stress level in the steel tube at the fixed end of the cantilever column and of the overall plastic deformation of the member, which is achieved through the application of prestress. Furthermore, the test process was also simulated numerically. Based on verifying the correctness of the numerical simulation, the parameters of the full-scale model are analyzed. The impact resistance of the model was evaluated by considering various factors such as impact angle, impact point height ratio, prestress ratio, width-thickness ratio, slenderness ratio, and mass ratio. Based on these analyses, empirical formulas for the lateral ultimate displacement and bending moment of the cantilever members were derived. Particularly, considering the difference in yield strength between tension and compression sides, the theoretical calculation of plastic limit bending moment of concrete-filled square steel tubular members is modified. Additionally, the damage level of the component is defined, and the damage limit value of the concrete-filled steel tubular cantilever column is given based on the different damage grades. On this basis, considering the bending bearing capacity and displacement response of the component, an impact resistance design approach based on the performance of the component is proposed.

Research on eccentric-compressive behaviour of steel-fiber-reinforced recycled concrete-filled square steel tube short columns

This study, a total of 25 specimens, aims to assess the influence of the mass replacement percentage of recycled coarse aggregates (0%, 50%, 75%, and 100%), steel tube thickness (3 mm, 4 mm, and 5 mm), load eccentricity (0.10, 0.25, and 0.40), and volume fraction of steel fiber (0%, 0.6%, 1.2%, and 1.8%) on the eccentric-compressive behaviour of steel-fiber-reinforced recycled concrete-filled square steel tube short columns. The post-peak mechanical behaviour, deformation ability, and energy consumption degrade with increasing mass replacement of recycled coarse aggregate; the load eccentricity is detrimental to the ultimate compressive strength and aggravates the lateral deflection; thicker steel tubes and the incorporation of steel fiber improve the ultimate compressive strength, deformation ability, and energy consumption. Moreover, an incremental iteration model is proposed to calculate the ultimate compressive strength of steel-fiber-reinforced recycled concrete-filled square steel tube short columns under eccentric-compressive load. Compared to current codes, the predicted values using the proposed model are close to experimental values and are inclined toward the safe side.