Steel Tube-reinforced Concrete Research Articles

Behaviour of steel tube reinforced-concrete short bridge columns under cyclic loading

The results of an experimental study focused on the cyclic shear behaviour of steel tube reinforced-concrete (STRC) short bridge columns are presented. Seven STRC column specimens were tested under constant axial load and cyclic-reversed lateral displacement to investigate the effects of the axial load ratio, volumetric stirrup ratio, longitudinal steel ratio, sectional steel tube ratio and shear span ratio. An additional reinforced-concrete (RC) short column was also tested to evaluate the effectiveness of the steel tube at enhancing the column behaviour. Damage progression and failure modes of the specimens are described, along with a detailed discussion on their seismic indexes with regard to shear strength, ductility, stiffness degradation and energy dissipation. The test results demonstrated improved seismic resistance and mitigated damage extent for the STRC specimens relative to the RC counterpart. It was also found that the STRC short bridge columns with rational structural configurations possessed satisfactory deformability, ductility and energy dissipation capacity and can thus be utilised in regions of moderate to high seismicity. Based on the test results, a simplified superimposition model and the corresponding expressions are developed for shear strength prediction of STRC short bridge columns.

Displacement ductility of staged construction-steel tube-reinforced concrete columns

The steel tube-reinforced concrete (ST-RC) column is consist of a concrete-filled steel tube embedded in reinforced concrete. As an innovative type of composite structures, there is still a lack of information on the behavior and ductility of ST-RC columns, particularly on staged construction-steel tube-reinforced concrete (SC-ST-RC) columns. This paper studied the mechanism of two types of ST-RC columns in a 15 storey building. A finite element (FE) model with proper material constitutive relationship was proposed for SC-ST-RC columns subjected to combined axial compressive force and lateral loading. The material nonlinearity and the interaction between steel tube and concrete were considered. The proposed FE model was able to predict the lateral stiffness, strength and deformation capacities of SC-ST-RC columns with a reasonable level of accuracy. Then, the effects of different parameters on displacement ductility were discussed in detail. Finally, a simplified formula for calculating the displacement ductility of SC-ST-RC columns was developed based on the parametric analysis, the predictions of the proposed formula fitted well with a large number of test results. Utilizing the proposed formula, the demand of displacement ductility under different seismic design grade in current ST-RC specification was presented, which may provide a useful reference for the seismic design of the SC-ST-RC structures.

Mechanical behavior of a steel tube-confined high-strength concrete shear wall under combined tensile and shear loading

The steel tube-reinforced concrete (STRC) shear wall is a type of composite shear wall that consists of a reinforced concrete shear wall embedded into high-strength concrete-filled steel tube (CFST) columns in the boundary element and/or the center of a shear wall. The use of STRC walls has gained popularity in the construction of high-rise buildings because their performance is superior to conventional reinforced concrete (RC) walls. To study the influence of various parameters (i.e., the number of CFSTs embedded in the shear wall, the shear span ratio, the ratio of the vertical reinforcement, the strength of the concrete outside the embedded steel tube, and the initial tensile stress) on the mechanical properties of an STRC composite shear wall under combined tension and shear forces, tensile shear tests were conducted on 9 specimens whose shear span ratios were less than or equal to 1.0. The experimental results demonstrated that the STRC shear wall retained its high shear capacity and its good ductility under a high axial tensile force. Using statistical analyses, a formula to calculate the bearing capacity of an STRC shear wall was proposed. The calculated values are in good agreement with the experimental results.

Hysteretic behavior and modified design of square TSRC columns with shear studs

The tubed steel reinforced concrete (TSRC) column is a composite member consisting of the concrete core reinforced by a steel shape and the outer thin-walled steel tube which is made slightly shorter than the column to avoid direct axial loading and acts as a confining steel for the concrete. In this paper, the hysteretic behavior of square TSRC columns was investigated experimentally and analytically. Five square TSRC columns, in which high-strength concrete with fcu,150 = 85.4 MPa was used and the thin-walled steel tube in potential plastic hinge zones was stiffened by steel plates, were tested under constant axial compression and cyclic lateral loads. The influences of shear studs on the steel shape, axial load ratio, width to thickness (D/t) ratio were also considered in the test. The test results indicated that the confinement from steel tubes effectively improved the ductility and plastic deformation ability of the specimens, while the shear studs on the steel shape effected little on the co-working behavior between the concrete and the steel shape. A fiber-based element model using OpenSEES software was developed and a good agreement was achieved between the test and predicted results. Utilizing the numerical model, the limiting axial load ratio was analyzed to ensure that the square TSRC columns had the sufficient ultimate deformation capacity. To account for the improvement of strength and ultimate strain in the concrete core resulting from the tube confinement, relevant development methods for N-M interaction diagrams, such as those in the ACI and EC4, were modified for square TSRC columns.

Seismic behavior of circular TSRC columns with studs on the steel section

The tubed steel-reinforced-concrete (TSRC) column can be interpreted as a special steel-reinforced-concrete (SRC) column where the reinforcement cage is replaced with an outer encased thin-walled steel tube for confining the concrete core. In this study, seven circular TSRC columns using high-strength concrete (fcu,150=97.6MPa) were tested under combined constant axial compression and lateral cyclic load. Two primary system parameters, the axial load ratio and the arrangement of shear studs, were considered in this test. The test results indicate that the TSRC specimens exhibit excellent ductility and plastic deformation ability. The deformation of the steel section develops coherently with the high-strength concrete for both the specimens with shear studs on the steel section and those without, due mainly to the confinement from the steel tube. The lateral strength, ductility, and deformability of the circular TSRC specimens are not effectively enhanced by installing shear studs on the steel section. The axial load-moment interaction diagrams of the specimens were developed according to the ACI and EC4 methods. The predictions from the EC4 method appear to better match with the experimental results.

Axial load behavior and stability strength of circular tubed steel reinforced concrete (SRC) columns

The tubed steel reinforced concrete (SRC) column is a composite column in which the outer steel tube is mainly used to provide confinement on the core concrete. This paper presents experimental and analytical studies on the behavior of circular tubed SRC (TSRC) columns subjected to axial compression. Eight circular TSRC columns were tested to investigate the effects of length-to-diameter ratio (L/D) of the specimens, diameter-to-thickness ratio (D/t) of the steel tubes, and use of stud shear connectors on the steel sections. Elastic-plastic analysis on the steel tubes was used to investigate the mechanism of confinement on the core concrete. The test results indicated that the tube confinement increased the strength and deformation capacity for both short and slender columns, and the effects on strength were more pronounced for short columns. A nonlinear finite element (FE) model was developed using ABAQUS, in which the nonlinear material behavior and initial geometric imperfection were included. Good agreement was achieved between the predicted results using the FE model and the test results. The test and FE results were compared with the predicted strengths calculated by Eurocode 4 and the AISC Standard. Based on the analytical results, a new design method for this composite column was proposed.

Behavior and Strength of Circular Tubed Steel-Reinforced-Concrete Short Columns under Eccentric Loading

This paper presents the results of experimental studies on circular tubed steel-reinforced-concrete (TSRC) short columns subjected to axial and eccentric loading. A total of 12 columns with the key parameters of eccentricity ratio and diameter-to-thickness ratio of the steel tube were tested. The effect of shear studs on the co-work behavior of concrete and shaped steel was studied. The test results indicated that the shear studs affected little on the failure mode, bearing capacity and ductility of the eccentrically loaded circular TSRC short columns. Elastic-plastic analysis for the steel tube showed that the tubes at the compression side began to yield when the load approximately reached 90% of the peak load. Fiber-based numerical models for circular TSRC short columns were established and the results accorded well with the experimental results. Furthermore, the whole section plastic assumption in EC4 was adopted to determine the section capacity interaction diagram for circular TSRC columns.

Behaviour and design method of short square tubed-steel-reinforced-concrete columns under eccentric loading

The tubed-steel-reinforced-concrete (TSRC) column is a kind of special concrete-encased steel composite columns using the thin-walled steel tube instead of a reinforcement cage to confine the concrete core. The steel tube discontinues at the beam-column joints and thus does not carry any direct axial load. In this study, twelve short square TSRC columns were tested to investigate their load-carrying and deformation capacities under eccentric compression. The studied parameters are width-to-thickness ratio of the steel tube, eccentricity of the axial load, and the flange shear studs. The test results indicate that the encased steel shape works with the concrete compatibly due to the confinement from the steel tube, and the flange shear studs are not effective in enhancing the flexural stiffness and the axial resistance. To account for the inelastic behaviour of structural steel and concrete materials, a numerical model based on the fibre sectional analysis was developed, which predicts the results in general agreement with the test results. Parametric analysis is carried out based on the numerical model. Moreover, a new simplified method to estimate the capacity interaction diagram of a square TSRC section is proposed.

Behavior of square tubed steel reinforced-concrete (SRC) columns under eccentric compression

This paper presents experimental and analytical studies on the behavior of square tubed SRC (TSRC) columns subjected to eccentric compression. Eight square TSRC columns were tested to investigate the effects of eccentricity ratio of the compression force, width-to-thickness ratio (B/t) of the steel tubes, and use of shear connector studs on the steel sections. The test results indicated that local buckling of the square tubes was delayed effectively since axial load was not directly applied on the steel tube. Buckling of the tube initially occurred when the load reached the ultimate value for the specimens with B/t ratio of 100, and buckling occurred earlier for the specimens with B/t ratio of 133 when the load reached 88% to 94% of the ultimate load. A nonlinear finite element (FE) model was developed using ABAQUS, in which the nonlinear material behavior and initial geometric imperfections were included. Good agreement was achieved between the predicted results using the proposed FE model and the test results. A modified Eurocode 4 design method was adopted to calculate the ultimate strength of square TSRC columns.

Mechanical Properties of the Section from Steel Tube-Reinforced Concrete Pier

To research the impact of inner concrete filled steel tubular (CFST) on the reinforced concrete (RC) pier confined by stirrups, a Matlab program based on fiber model was written to calculate the moment-curvature (M-ϕ) relationship. The program was utilized to compute theM-ϕrelationships of three piers with same longitudinal bars and stirrups, and the three piers were an ordinary RC pier confined by stirrups、a high strength reinforced concrete (HSRC) pier confined by stirrups and a steel tube-reinforced concrete (ST-RC) pier respectively. The rules about bearing capacity of section and curvature ductility along with axial loadNwere deliberated by comparing the numeral results of three piers. The ratio of peak momentMkto yield momentMywas defined as super coefficientλs, and the disciplinarian ofλsalong withNwas discussed. Participation factorξreferred to the ratio of the moment provided by inner CFST to the total moment of ST-RC pier, and the laws ofξaffected byϕandNwere researched. The results show that ST-RC pier has higher ductility and higher bearing capacity of section, and ductility decreases more slowly than other piers with the increase ofN.λsof ST-RC pier is highest among three piers in most cases. On conditions of differentN,ξshows different variation trend with curvatureϕup, and the maximum of participation factorξmaxis reckoned to be not affected byNbasically.

Effect of cumulative seismic damage to steel tube-reinforced concrete composite columns

The steel tube-reinforced concrete (ST-RC) composite column is a novel type of composite column, consisting of a steel tube embedded in reinforced concrete. The objective of this paper is to investigate the effect of cumulative damage on the seismic behavior of ST-RC columns through experimental testing. Six large-scale ST-RC column specimens were subjected to high axial forces and cyclic lateral loading. The specimens included two groups, where Group I had a higher amount of transverse reinforcement than Group II. The test results indicate that all specimens failed in a flexural mode, characterized by buckling and yielding of longitudinal rebars, failure of transverse rebars, compressive crushing of concrete, and steel tube buckling at the base of the columns. The number of loading cycles was found to have minimal effect on the strength capacity of the specimens. The number of loading cycles had limited effect on the deformation capacity for the Group I specimens, while an obvious effect on the deformation capacity for the Group II specimens was observed. The Group I specimen showed significantly larger deformation and energy dissipation capacities than the corresponding Group II specimen, for the case where the lateral cyclic loads were repeated ten cycles at each drift level. The ultimate displacement of the Group I specimen was 25% larger than that of the Group II counterpart, and the cumulative energy dissipated by the former was 2.8 times that of the latter. Based on the test results, recommendations are made for the amount of transverse reinforcement required in seismic design of ST-RC columns for ensuring adequate deformation capacity.

Application of compactness detection to complicated concrete-filled steel tube by ultrasonic method

An example of using ultrasonic method to detect the compactness of complicated concrete-filled steel tube in certain high-rise building was discussed in this study. Because of the particularity of the complicated concrete-filled steel tubular column, the plane detection method and embedded sounding pipe method were adopted in the process of effectively detecting the column. According to the results of the plane detection method and embedded sounding pipe method, the cementing status of steel tube and concrete can be concluded, which cannot be judged by the hammering method in the rectangular steel tube-reinforced concrete.

Behavior of steel tube-reinforced concrete composite walls subjected to high axial force and cyclic loading

This paper proposes an innovative composite shear wall, named the steel tube-reinforced concrete (ST-RC) composite wall, with steel tubes embedded at the wall boundary elements and fully anchored within the foundation. This arrangement is supposed to enhance the wall’s seismic performance. A series of quasi-static tests were performed to examine the behavior of the ST-RC walls when subjected to high axial forces and lateral cyclic loads. The area ratios of steel tube and of concrete filled steel tube (CFST) (i.e. the ratios of the cross-sectional areas of steel tubes and of CFSTs over that of the wall boundary element, respectively), axial force ratio, and cross-sectional shape of walls were taken as major test variables. All specimens failed in a flexural mode, characterized by tensile yield of the vertical rebars and steel tubes in the boundary elements and compressive crushing of concrete at the wall bottom. The test results showed that the ST-RC composite walls had larger load-carrying and deformation capacities relative to the RC wall counterpart. The deformation capacity of the rectangular-shaped composite walls increased with an increase in the area ratios of steel tube and of CFST and decreased with an increase in the applied axial force ratio. The barbell-shaped composite wall that was configured with edge columns had much larger deformation and energy dissipation capacities than the rectangular-shaped composite walls. In addition, simplified formulation was proposed to evaluate the lateral load-carrying capacity of the ST-RC composite walls. The evaluated results showed good agreement with the test results, with errors no more than 10%.

Experimental Study and Theoretical Analysis on Seismic Performance of RC Shear Wall with STRC Columns and Embedded Steel Plate

RC shear wall with STRC (steel tube-reinforced concrete) columns and embedded steel plate has been proposed and used in the project of an International Conference Center. In order to ascertain the seismic performance of this kind of composite shear walls with different openings in the practical engineering, four 1/7 scale specimens with shear span ration 2.0 were tested under low-frequency cyclic loading. The load-carrying capacity, ductility, stiffness and its attenuation, hysteretic property, energy dissipation capacity and failure mode of the specimens were analyzed. The effect of the embedded steel plate and the concealed steel trusses on the seismic performance of the walls was studied. The results show that the ductility and load-carrying capacity of RC shear wall are improved greatly by setting the embedded steel plate or concealed steel trusses in the wall; The embedded steel plate and the concrete work very well through the stud connectors welded on the steel plate and the tie bars inserted in the walls; The STRC columns have the advantage of higher load-carrying capacity, not easy to crack and better ductility; The new composite shear wall has good seismic performance and important practical value. It is suitable for large and complex application of high-rise buildings in the seismic regions.

Application and Experimental Study on Seismic Behavior of Composite Core Walls with STRC Columns

According to the structural design in a project in Dalian, experimental study on seismic behavior of composite core walls with steel tube-reinforced concrete (STRC) columns were carried out. Five 1/6 scale composite core wall specimens with different steel reinforced details in the walls and different openings on the walls were designed and tested under cyclic loading. Based on the experiment, hysteretic property, load-carrying capacity, ductility, energy dissipation capacity and damage characteristics of the five specimens were compared and analyzed. The results show that the core walls with STRC columns have good seismic behavior. And the seismic behavior can be greatly improved by setting concealed steel trusses in the walls.

Application and Experimental Study on Seismic Behavior of Composite Core Walls with STRC Columns

According to the structural design in a project in Dalian, experimental study on seismic behavior of composite core walls with steel tube-reinforced concrete (STRC) columns were carried out. Five 1/6 scale composite core wall specimens with different steel reinforced details in the walls and different openings on the walls were designed and tested under cyclic loading. Based on the experiment, hysteretic property, load-carrying capacity, ductility, energy dissipation capacity and damage characteristics of the five specimens were compared and analyzed. The results show that the core walls with STRC columns have good seismic behavior. And the seismic behavior can be greatly improved by setting concealed steel trusses in the walls.

Experimental Study and Theoretical Analysis on Seismic Performance of RC Shear Wall with STRC Columns and Embedded Steel Plate

RC shear wall with STRC (steel tube-reinforced concrete) columns and embedded steel plate has been proposed and used in the project of an International Conference Center. In order to ascertain the seismic performance of this kind of composite shear walls with different openings in the practical engineering, four 1/7 scale specimens with shear span ration 2.0 were tested under low-frequency cyclic loading. The load-carrying capacity, ductility, stiffness and its attenuation, hysteretic property, energy dissipation capacity and failure mode of the specimens were analyzed. The effect of the embedded steel plate and the concealed steel trusses on the seismic performance of the walls was studied. The results show that the ductility and load-carrying capacity of RC shear wall are improved greatly by setting the embedded steel plate or concealed steel trusses in the wall; The embedded steel plate and the concrete work very well through the stud connectors welded on the steel plate and the tie bars inserted in the walls; The STRC columns have the advantage of higher load-carrying capacity, not easy to crack and better ductility; The new composite shear wall has good seismic performance and important practical value. It is suitable for large and complex application of high-rise buildings in the seismic regions.

Axial load behavior and strength of tubed steel reinforced-concrete (SRC) stub columns

This paper presents experimental and analytical studies on the behavior of tubed SRC stub columns subjected to axial compressive load. Fourteen circular tubed SRC (CTSRC) and fifteen square tubed SRC (STSRC) stub columns were tested to investigate the failure mode and axial loaded behavior of tubed SRC columns. The effect of diameter/width to thickness ratio of the tubes was studied. The effect of height to diameter/width ratio of the separated tubes in tubed SRC columns was studied to investigate the effect of bond and friction between tube and concrete on the behavior of tubed SRC columns. The test results indicated that tubed SRC stub columns exhibited higher axial load capacity than common SRC columns with the same volumetric steel ratio. Elastic–plastic analysis on the steel tube was employed to study the mechanism of tubed SRC stub columns subjected to axial compression. Equations for the prediction of the axial load strength of tubed SRC stub columns were also proposed based on the proposed experimental results.

Experimental Study on the Torsional Behavior of RC Composite Core Walls with Steel Tube-Reinforced Concrete Columns and Concealed Steel Trusses Subjected to the Combined Action of Multi-Directional Stresses

An experimental study on the torsional behavior of two 1/6 scale core walls: one reinforced concrete core wall with concealed steel trusses and steel tube-reinforced concrete columns, and one normal reinforced concrete core wall, was carried out under eccentric horizontal cyclic loading. The torsional load-bearing capacity, torsional angle ductility, torsional hysteresis characteristics, torsional stiffness and its deterioration process, torsional energy dissipation and damage characteristics of the two specimens are herein discussed. Results show that the torsional performance of RC core walls can be improved by embedding the concealed steel trusses in the walls and setting the steel tube-reinforced concrete columns as boundary-columns.

Experimental Research on Eccentric Compressive Performance of Steel Tube-Reinforced Concrete Column

Eccentric loading experiment of 13 steel tube-reinforced concrete columns and a reinforced concrete column is implemented. The whole process from the start load on the steel tube-reinforced concrete column until damage has been researched. Change of ultimate bearing capacity with eccentricity, longitudinal reinforcement ratio, position coefficient has been studied, and deflection curve and load-vertical displacement curve under eccentric compressive load were obtained. Failure characteristics of steel tube-reinforced concrete were divided into two different type, small eccentric damage and big eccentric damage. With the same conditions, when steel tube ratio of steel tube-reinforced concrete was 2%, its ultimate bearing capacity was nearly double of reinforced concrete columns.