Tube-reinforced Concrete Columns Research Articles

Nonlinear finite element and machine learning modeling of tubed reinforced concrete columns under eccentric axial compression loading

There is still insufficient data on the behavior of tubed-reinforced concrete columns (TRCCs) under the eccentric compression. Thus, this research work comprehensively examines the eccentric compression behavior of TRCCs using nonlinear finite element modeling and machine learning (ML). To do this, numerical simulation and parametric analysis based on existing investigations were conducted. In addition to the existing 22 specimens with limited test variables, additional 188 specimens were developed to cover a wide range of parameters, including the load eccentricity, transverse reinforcement spacing, columns’ slenderness ratio, yield strength of steel, and outer steel tube diameter. Additionally, six ML models were created to estimate the ultimate load results. The results indicated that increasing the outer steel tube yield strength and diameter, and reducing the load eccentricity, slenderness ratio, and spacing of the transverse reinforcement enhanced the load-carrying capacity of the columns. The Gaussian process regression model demonstrated superior performance metrics in comparison to other ML models, with the highest R2 values (0.998613 in training and 0.99823 in testing stages) and lowest root mean square error values (0.007213 in training and 0.008471 in testing stages). To save money, time, and resources compared to laboratory testing, an online-based prediction program is finally presented to predict the columns’ ultimate load.

Influence of Confinement Interaction on the Compressive Behavior of Steel Tube–Reinforced Concrete Columns

Influence of Confinement Interaction on the Compressive Behavior of Steel Tube–Reinforced Concrete Columns

Behavior of eccentrically-loaded tubed reinforced concrete short columns with high-strength concrete and reinforcement

Compared with traditional reinforced concrete (RC) columns, the concrete ductility in tubed reinforced concrete (TRC) columns is significantly improved and higher ultimate compressive strain matching with the high yield strain of high-strength steel rebars (HSSRs) can be attained. Therefore, high-strength concrete (HSC) and HSSR are suitable and recommended for use in TRC columns. In this study, a total of twelve circular TRC column (CTRC) specimens with the concrete compressive strength of 81 MPa and rebar yield strength above 527 MPa were tested under eccentric loading. The investigated parameters include the diameter-to-thickness ratio of steel tube and load eccentricity, whose effects on the failure mode, load capacity, and ductility are described and discussed. A fiber-based finite-element model was established and verified for conducting parametric studies and investigating the stress development of the HSSRs in CTRC columns. The study results show that all test specimens fail in a ductile manner due to the tube confinement, and the load eccentricity is a primary factor affecting the failure location, load capacity, and ductility. With the parameters considered, the longitudinal rebars in the compression region yield before the column reaches its load capacity, indicating that the strength of HSSRs can be fully utilized. Based on the study results, calculation methods are suggested to determine the strength of eccentrically-loaded CTRC columns with HSC and HSSR.

Test and design of eccentrically-loaded slender circular tubed columns filled with high-strength concrete and reinforcement

The tubed-reinforced concrete (TRC) column is an original reinforced concrete column in which the stirrups are mostly replaced with the steel tube to enhance the confinement to the concrete core. In this study, the eccentrically-loaded behavior of slender circular TRC (CTRC) columns with high-strength materials was experimentally and numerically investigated. Six slender columns with high-strength concrete of 81 MPa and high-strength rebar of 583 MPa were tested to failure under eccentric loading, considering the main parameters of length-to-diameter ratio and load eccentricity. A three-dimensional finite element (FE) model was established and verified for conducting parametric studies and investigating the moment magnification and eccentricity magnification which reflect the second-order effect on the strength of slender columns. The results indicate that all columns fail in a bending mode and show good deformability, even with the use of high-strength materials, and the strength of high-strength rebars can be fully utilized due to the enhanced concrete compressive strain and ductility. Based on the test results and parametric study, a design method is proposed to assist designers to evaluate the load capacity of slender CTRC columns.

Assessment on the seismic performance of circular tubed reinforced concrete column to steel beam frames using numerical modeling

Tubed reinforced concrete (TRC) is an innovative steel-concrete composite structure in which the steel tube acts as the transverse confinement rather than directly carries the axial load. To study the seismic performance of TRC columns in high-rise buildings, the static and dynamic analyses of the frames containing circular tubed reinforced concrete (CTRC) columns and steel beams were performed in this study. Representative frame analysis models with both the building height and the maximum elastic story drift ratio close to the code-specified limits were established using the software OpenSees. The effectiveness of the finite element model was verified through component and frame tests. The failure mechanisms, story drift ratios, and collapse margins of different frames were compared and analyzed, with the reinforcement ratio and column-to-beam strength ratio considered as the main parameters. In addition, the seismic behaviors of the frames containing CTRC columns (i.e., CTRC frames) were compared with those containing concrete-filled steel tubular (CFST) columns (i.e., CFST frames) under the same column steel ratio. It is shown that the load-bearing capacity, ductility coefficient, and collapse margin of a properly designed CTRC frame are similar to those of a CFST frame; and increasing the column reinforcement ratio is more effective in improving the load-bearing capacity and ductility of CTRC frames, compared with the use of thicker steel tubes. Moreover, when the CTRC frame is designed based on the lateral stiffness, its collapse margin is generally stable as the column-to-beam strength ratio decreases from 1.52 to 0.85. Based on the analysis results, suggestions on the seismic design of CTRC frames, including the allowable building height, maximum story drift ratio, and effective column section forms, are proposed.

Structural fire design of square tubed-reinforced-concrete columns with connection to RC beams in composite frames

The tubed-reinforced-concrete (TRC) column is an innovative type of steel-concrete composite column that is gaining increasing engineering usage, and structural fire performance should be an important consideration of its design. As affected by the adjacent members and beam-to-column joints, the fire behaviour of TRC columns integrated into a frame may largely differ from that of isolated columns with idealised end conditions. However, the fire performance of TRC columns in composite frames has not been studied, except for some work done on the fire performance of isolated TRC columns with certain end restraints. This paper presents finite element analysis on single-storey and single-span non-sway frames with square TRC columns, employing the software package ABAQUS. The thermal and deformation behaviour, development of axial stress, axial force and bending moment during heating, working mechanism and failure mode of the frame exposed to fire are numerically investigated. The difference between the fire performance of TRC columns in a frame and those of equivalent isolated columns is quantified. The fire resistance of the framed column is found to lie between those of the columns with rotational end restraints and columns with idealised pinned ends. The complex effects of the connected RC beam on the fire behaviour of TRC columns, e.g. the beneficial restraining effect and the negative effect due to restrained differential thermal expansion, are clarified. Finally, a practical fire resistance design approach is proposed for TRC columns considering the continuity and interactions between structural elements within a composite frame.

Experimental and numerical investigations on seismic behavior of circular tubed reinforced concrete column to RC beam frames

AbstractThe tubed reinforced concrete (TRC) column is a special kind of concrete‐filled tube (CFT) column where the steel tube is disconnected at the beam–column connection, thereby not directly carrying the axial load while maximizing the confinement effect. Extensive research has been conducted to study the static and seismic performances of TRC columns and their mechanical properties. However, little attention has been paid to study the whole structural system containing TRC columns. To fill this lacking information, an experimental program on the seismic behavior of circular tubed reinforced concrete (CTRC) column to reinforced concrete (RC) beam frames (CTRC frames) was presented in this study for the first time. Two half‐scale two‐story CTRC frames, with two bays in each frame, were designed and tested under quasi‐static loads. The first frame has strong columns and weak beams; while the second frame has rather weak columns and strong beams, implying that plastic hinges may form in the columns under seismic action. The test results indicate that both frames are sufficiently ductile to effectively dissipate energy. However, for the second frame, more severe damages of beams and columns in the first floor were observed, resulting in the instability of the overall frame. A fiber‐based finite‐element model is established using OpenSees; and the numerical results are generally in good agreement with the test results. Utilizing the numerical model, a parametric study is conducted and the preliminary design suggestions on TRC frames are proposed.

Hysteretic behavior of circular tubed reinforced concrete column to steel beam frames

Tubed reinforced concrete (TRC) columns have good deformability and energy dissipation capacity under horizontal cyclic loads; and even with plastic hinges formed at the column ends, the corresponding frame structure may still have sufficient inter-story deformation capacity. Extensive research has been conducted on the static and seismic performances of TRC columns. However, little attention has been paid to the structural system containing TRC columns. To overcome this shortcoming, an experimental study on the seismic behavior of circular tubed reinforced concrete (CTRC) column to steel beam frames (referred as “CTRC frames”) is described first in this study. Based on the previous studies on CTRC columns and joints, two double-bay two-story CTRC frames of 1/2 scale were designed and tested under quasi-static loading: one frame with stronger flexural strength in columns than the beams and the other frame is the opposite. The test results indicated that although the frame failed in column plastic hinge mode had the ductility coefficient of 3.56, a weak story with the maximum story drift ratio of 1/18 formed in this frame, which increased the collapse risk of the overall structure. Therefore, considering the unfavorable deformation mode, the column plastic hinge mode should be avoided in practical designs; and the control of frame deformation modes should be considered when proposing a suitable column-beam strength ratio for CTRC frames. A fiber-based element model using OpenSees software was developed, which showed a good agreement with the test results. Utilizing the numerical model, the affecting parameters to the hysteretic behavior of CTRC frames, such as the axial load ratio, concrete compressive strength, and column-beam strength ratio, were further investigated.

Fire performance of eccentrically-loaded square and rectangular tubed-reinforced-concrete columns

Tubed-reinforced-concrete (TRC) columns are gaining increasing popularity in engineering constructions, however, research on their fire performance is still limited and mainly focused on concentrically-loaded columns. In this study, extensive numerical analysis was carried out to investigate the performance of square and rectangular TRC columns under eccentric loading and exposed to ISO 834 standard fire. A sequentially-coupled thermo-mechanical finite element analysis (FEA) model was developed in ABAQUS and validated well against fire testing results. The high-temperature overall deformations, internal bending moments and cross-sectional load redistributions of square TRC columns with different load eccentricities were analysed. Parametric studies were conducted to investigate the influences of load eccentricity ratio, sectional aspect ratio, bending direction, fire protection thickness, sectional dimension, load ratio and slenderness ratio on the fire resistance of square and rectangular TRC columns. Load eccentricity was found to have a greater effect on the fire resistances of columns of lower slenderness than those of columns of higher slenderness. Rectangular TRC columns of sectional aspect ratios no larger than 2 could generally achieve identical buckling resistance as that of the equivalent square sections. The influences of sectional aspect ratio and bending direction on the column fire resistance were insignificant. A design method was then proposed for both the ambient-temperature and high-temperature designs of eccentrically-loaded square and rectangular TRC columns. The fire design method could cover both protected and unprotected TRC columns. The design method has been thoroughly validated against detailed FEA modelling and yields excellent agreements with the modelling results.

Structural fire safety design of square and rectangular tubed-reinforced-concrete columns

The tubed-reinforced-concrete (TRC) columns have gained increasing use in the high-rise buildings and large-span stadiums in China, whereas the structural fire design method for square and rectangular TRC columns is still missing. Finite element analysis of the fire performance of square and rectangular TRC columns was conducted using a sequentially-coupled thermo-stress model. This model yielded good predictions against the experimental results of square TRC columns. Fire tests on two rectangular TRC columns were also conducted and presented in this paper, to further calibrate the model. Parametric studies were then conducted, through which it was found that the fire resistance of square and rectangular TRC columns decreases with the increase of load ratio or slenderness ratio and increases as the sectional dimension enlarges. Sectional aspect ratio has a minor influence on the fire resistance of rectangular TRC columns. A practical design method was proposed, for the first time, to determine the fire resistance of square and rectangular TRC columns with or without fire protection. The buckling reduction coefficient could be determined by the EC3 buckling curve (c) or the JGJ/T471 buckling curve. The heat transfer equations given in the Japanese AIJ recommendation were modified to determine the temperatures of the steel tube and rebars and equations were proposed to determine the equivalent temperatures of the concrete core.

ISO 834 standard fire test and mechanism analysis of square tubed-reinforced-concrete columns

The tubed-reinforced-concrete (TRC) column is an innovative steel-concrete composite column and its steel tube is terminated at beam-to-column connections to mainly work as hoop reinforcements without sustaining axial load directly. Fire performance of TRC columns differs from that of concrete-filled steel tubular (CFST) columns since the axial deformation behaviour of the TRC columns would mainly depend on the inner reinforced concrete and local buckling of steel tube is minimised. However, no research has been reported on the behaviour of square TRC columns under fire exposure. Five slender square TRC columns subjected to standard fire and axial loading were tested in this study and the effects of load ratio and load eccentricity were investigated. Failure mode of the test specimens was dominated by global flexural buckling, whereas tube local buckling was also observed. The experimental results show that load ratio has a significant influence on the fire resistance of test specimens while the influence of load eccentricity is marginal. A sequentially-coupled thermo-mechanical finite element analysis (FEA) model was developed using ABAQUS. This FEA model was validated well against the test results when using the measured column end rotations as realistic boundary conditions. Different from the case of a CFST column, the axial load applied to a TRC column in fire is mainly sustained by the concrete and reinforcing bars and the high-temperature capacity contribution of steel tube is neglectable. With the increase of exposure time, the applied load gradually transfers from concrete to reinforcements until the yielding of re-bars.

New connection system for circular tubed reinforced concrete columns and steel beams

A new connection system for circular tubed reinforced concrete (TRC) columns and steel beams is proposed, where crossing diaphragms are introduced to withstand the moment at beam ends and interior diaphragms are added to withstand the shear at the interfaces between beam and joint. Interior diaphragms are more convenient for placement of curtain walls and architecturally desirable. The joint tube is used to improve the joint strength and the holes through the interior diaphragms are pre-drilled at the locations where the longitudinal reinforcing steel bars in column pass through. This relatively new configuration represents a diaphragm-through connection between circular TRC column and steel beam. In this study, the quasi-static reversed cyclic loading test was performed on five one-third scaled specimens and the feasibility of proposed connection was verified. A finite element model was then developed and validated with the experimental results, where the peak lateral load was accurately obtained. Furthermore, a shear-resistance model for the connections is suggested, from which theoretical formulas for predicting the shear resistance of connection are established.

Axial compressive performance of RAC-encased RACFST composite columns

A new type of composite column, recycled aggregate concrete (RAC)-encased recycled aggregate concrete-filled steel tube (RACFST) composite columns, promotes the RAC extensive utilization considering synergistic effect between the RAC and the steel tube, which is an attempt to develop environmentally sustainable concrete in high-rise buildings. In this paper, experimental research investigated the axial compressive behavior of RAC-encased RACFST composite columns. Twenty 1:3-scaled specimens were fabricated to test until failure under axial compressive loading. The main variable parameters affecting the behaviour of specimens were recycled coarse aggregate replacement ratio (range from 0% to 100% with 10% increase), stirrup spacing (s = 50 mm, 70 mm, 100 mm, 120 mm), diameter of steel tube (D = 89 mm, 114 mm), concrete strength grade (RC40, RC60) and longitudinal reinforcement ratio (4▪12, 8▪12). The failure modes, the whole load-deformation curves and the mechanical performance of specimens were also obtained based on static loading experiments and theoretical analysis. It was found that RAC-encased RACFST composite columns, which were subjected to identical axial loads, exhibited more favorable bearing capacity and deformation than those of a comparative reinforced recycled aggregate concrete columns (RACC). The replacement ratio of RCA had a slight effect on the mechanical performance of RAC-encased RACFST composite columns, the optimal substitution ratio of RCA was 50–60%. Based on the previous theory of superposition, the concrete cover is considered, and a calculation formula with double reduction coefficients of the axial load-bearing capacity of composite columns is proposed. Compared to the simplified superimposition method and the Chinese code Technical specification for steel tube-reinforced concrete column structure (CECS188:2005), the calculated results of axial compression bearing capacity by the proposed formula are in more agreement with the experimental values, with errors no greater than 15%.

Simplified method for analysis of circular steel tubed-reinforced-concrete columns under eccentric compression

This paper develops a simple and general approach to analyse circular steel tubed- reinforced-concrete (TRC) columns including calculations of peak loads and plots of ascending branch of load-deflection curves. The proposed model relates cross-sectional capacity to actual column capacity by introducing a stability parameter so that column N-M curves can be determined directly. This stability parameter is calculated by establishing a rational mid-height deflection limit, which can be obtained through strain-compatibility and geometric relationship. It also provides a theoretical background to the classical Rankine formula. Moreover, a smooth transition of load-carrying capacity from short to slender columns is obtained. To generate the load-deflection curves, mid-height deflection is increased from 0 to the deflection limit while cross-sectional capacity is kept the same. The proposed method is validated against three series of test data including a total number of 40 TRC columns. It shows that the predictions compare well with the test results in three aspects, namely, mid-height deflection at peak load, peak load and ascending branch of the load-deflection curve. Moreover, the proposed method has a wide range of applications for TRC columns filled with both normal and high strength concretes with column slenderness ratio ranging from low to high. Most importantly, this model can be implemented using spreadsheet, which provides a simple and robust numerical tool for engineers to determine strength of TRC columns.

Cyclic Behavior of Composite Joints Between Circular Hollow Steel Tube-Reinforced Concrete Columns and H-shaped Steel Beam

Hollow steel tube-reinforced concrete columns have been more and more used in real structures. However, the researches on these kinds of composite joints are still relatively less. Based on the appropriate selection of material constitutive relation, element type and contact model, 3 nonlinear finite element analysis models are set up which are used for the whole loading process of hollow steel tube-reinforced concrete column to steel beam joints under constant axial load on the top of column and cyclic load at the beam ends. Based on these finite element analysis results, an intensive research can be done for the stress and strain relation of each component.

Axial capacity of steel tube-reinforced concrete stub columns

The steel tube-reinforced concrete (ST-RC) column is an innovative composite structure that has been increasingly applied in high-rise buildings and bridge piers in China. This study aims to investigate the axial capacity of the ST-RC stub column by means of a modified superposition method. Primarily, the sectional confining force equilibrium was elaborated to explain the confinement mechanism of the ST-RC column under concentric compression, which involves the confining stress induced from the inner steel tube and secondary confining stress induced from the peripheral steel hoops. Thereafter, a modified method for predicting the axial capacity of the ST-RC column, considering the secondary confinement, was developed according to a stress and strain analysis. Thirdly, 41 published specimens were collected to verify the accuracy of the proposed method. It was demonstrated that the current method fitted strongly with the tests results and exhibited satisfactory adaptability. Finally, four other methods according to ACI 318, AIJ, EC 4, and CECS 188-2005 were verified in the same scenario. It was found that the current method exhibited superior correlation with the experimental results compared with conventional approaches. It will be favorable to obtain the viable axial capacity of the ST-RC column by using the presented solution.

Seismic behavior of thin-walled circular and stiffened square steel tubed-reinforced-concrete columns

Steel tubed-reinforced-concrete (TRC) columns have been gradually used in the construction of high-rise buildings recently because of their high axial load-carrying capacities and excellent seismic behavior. Existing studies about their seismic behavior were focused on columns with relatively thick tubes, i.e., diameter-to-thickness/width-to-thickness ( D / t ) ratios were below 100, while little is known about thin-walled TRC columns, especially for square TRC columns. Considering the infilled concrete of square TRC columns is non-uniformly and non-effectively confined, accordingly, stiffened square TRC columns are usually adopted in practice. Thus, two thin-walled circular TRC columns ( D / t =120) and two stiffened square ones with diagonal stiffeners in plastic hinge regions ( D / t =106) were tested under a constant axial compression combined with cyclic lateral loading. Both the circular and stiffened square TRC columns had the same cross sectional area, tube thickness, reinforcing bar ratio and column height. Flexural failure occurred for all the four specimens. Test results showed the strengths of the stiffened square TRC columns were a little higher in comparison to their circular counterparts; the ductility and energy dissipation capacities were excellent for both the stiffened and circular TRC columns, indicating very good confinement was gained from the yielded steel tubes of the plastic hinge regions at the peak loads. And shear stresses (35–90 MPa) in the sheared plates showed their moderate contribution of carrying lateral loads. Finally, cross sectional capacity analysis results demonstrated the method for TRC columns is acceptable for the stiffened square TRC columns.

Cyclic testing of square tubed-reinforced-concrete column to RC beam joints

This paper aims to investigate the cyclic behavior of a steel and concrete composite joint system connecting reinforced concrete (RC) beams and square tubed-reinforced-concrete (TRC) columns. In the joint system, the discontinuous outer thin-walled steel tube of a TRC column can avoid the direct transfer of an axial load and thus provide better confinement to the core concrete. Six specimens, including five beam-column joints with internal diaphragms in the joint region and one reference specimen with closely spaced stirrups in the joint region, were tested up to a large drift ratio of 6.7% under combined constant axial compression and cyclic lateral loading at the TRC column tip. All the six specimens were designed according to the strong-column/weak-beam concept. The cross-sectional dimensions of the TRC columns were 300 mm × 300 mm that is about a 1/2 model of the prototype column. The dimensions of the beam cross section were 200 mm × 350 mm and high-strength steel reinforcing bars (600 MPa) were used in the RC beams. Three important parameters were studied, including the width-to-thickness ratio of the square joint tube, the thickness of the internal diaphragm, and the level of axial load applied to the column. Two types of failure modes, i.e., joint shear failure and beam flexural failure with bond failure, were observed. The both failure modes were ductile. The analysis of ductility, energy dissipation capacity and bond demonstrated that the joint system has good seismic performance.

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.

Behavior and design of slender square tubed-reinforced-concrete columns subjected to eccentric compression

This paper reports the studies on the behaviors of slender square tubed-reinforced-concrete (TRC) columns under eccentric loading. Eight specimens with the key parameters of length to width ratio (6, 10), load eccentricity (25mm, 50mm), and width to thickness ratio of the steel tube (133, 160) were tested. The test results indicate that the slender square TRC columns exhibit good ductile behavior during the eccentric loading with a global bending failure mode. A finite element (FE) analysis model was developed and the predicted results are in fine agreement with the test results. Parametric analyses were carried out to investigate the influence of the key parameters on the moment magnification factor of square TRC columns. Based on the test and parametric analyses, a regression formula of moment magnification factor is proposed to estimate the second order effect on the slender square TRC columns subjected to eccentric compression.