Steel Tube-reinforced Concrete Research Articles

Seismic Performance of Steel Tube-Reinforced Concrete Columns after Exposure to Fire on Two Adjacent Sides

A nonlinear finite element model has been developed to numerically simulate the hysteretic behavior of steel tube-reinforced concrete columns after exposure to fire on two adjacent faces under reciprocating loads. This model considers various parameters, including fire duration, slenderness ratio, section size, core area ratio, external concrete strength, and reinforcement ratio. The study systematically investigates and analyzes characteristics such as the skeleton curve, ductility coefficient, stiffness degradation, and hysteretic energy dissipation of columns post-fire. Results indicate that member stiffness decreases with increasing displacement loading, and the equivalent viscous damping coefficient of the member escalates with increased horizontal displacement. Moreover, as fire duration and slenderness ratio increase, there is a corresponding decrease in member stiffness, leading to a reduction in the equivalent viscous damping coefficient. In contrast, increases in section size and core area ratio enhance member stiffness and decrease the equivalent viscous damping coefficient. Furthermore, enhancements in external concrete strength and reinforcement ratio elevate member stiffness, which subsequently increases the equivalent viscous damping coefficient.

Shear bearing capacity prediction of STRC shear walls using data‐augmented fusion model

AbstractMachine learning (ML) accurately predicts the shear bearing capacity of steel tube‐reinforced concrete (STRC) shear walls, aiding optimization design. However, creating a database for STRC shear walls experimentally is time‐consuming and costly. The aim of this study is to propose a method for high‐accuracy prediction of STRC shear wall shear bearing capacity using a small‐sample dataset. This study employs generative adversarial network (GAN) data augmentation techniques to address the issues of insufficient ML model training and low prediction accuracy in small‐sample databases. Based on the stacking framework, a fusion model (Stacking‐XRL) combining extreme gradient boosting (XGBoost), random forest (RF), and least absolute shrinkage and selection operator (LASSO) is established to predict the shear bearing capacity of STRC shear walls. Results show that after augmenting the training set with GAN, the prediction performance of K‐nearest neighbors (KNN), backpropagation neural network (BPNN), RF, light gradient boosting machine (LightGBM), XGBoost, and stacking‐XRL models significantly improve, with average increases of 10% in R2 and average decreases of 30% and 25% in MAE and RMSE, respectively. The proposed stacking‐XRL fusion model outperforms tested models, existing formulas, and Abaqus numerical simulations for the shear bearing capacity of STRC shear walls. Model interpretation reveals that the shear span ratios as the most important factors in predicting shear bearing capacity, followed by axial force ratio and whole section configuration steel tubular index.

Prediction of Failure Modes of Steel Tube-Reinforced Concrete Shear Walls Using Blending Fusion Model Based on Generative Adversarial Networks Data Augmentation

The steel tube-reinforced concrete (STRC) shear wall plays an important role in the seismic design of high-rise building structures. Due to the synergistic collaboration between steel tubes and concrete, they effectively enhance the ductility and energy dissipation capacity of conventional shear walls. To identify vulnerable areas prone to brittle failure and optimize the design, it is essential to develop a rapid method for identifying the failure mode of STRC shear walls. In this study, a fast identification method of STCR shear wall failure modes based on a Blending fusion model with Generative Adversarial Network (GAN) augmented data is proposed. The GAN is employed to address the issue of inadequate experimental data by generating new samples. This method combines classification boosting (Catboost), Random Forest (RF), K-Nearest Neighbors (KNN), and Least Absolute Shrinkage and Selection Operator (LASSO) to establish the Blending-CRKL fusion model to improve the prediction accuracy of the failure mode of STRC shear walls. The results reveal a significant improvement in the prediction performance of KNN, Backpropagation Neural Network (BPNN), RF, Light Gradient Boosting Machine (LightGBM), Catboost, and Blending-CRKL models after augmenting the training set with GAN. On average, the accuracy increased by 13%, precision increased by 81%, recall increased by 48%, and F1 score increased by 67%. The proposed Blending-CRKL fusion model outperforms the tested KNN, BPNN, RF, LightGBM, and Catboost models, achieving an accuracy rate of 97% in predicting the failure mode of STRC shear walls. Additionally, the stability and robustness of the Blending-CRKL model were validated, while the important features and value ranges of different failure modes were analyzed. This study provides a reference for the rapid identification of the failure mode of STRC shear walls.

Axial compression behaviour and design of square tubed steel reinforced-concrete stub columns after fire exposure

The tubed steel reinforced-concrete (TSRC) column is an innovative type of steel-concrete composite column, the steel tube of which mainly provides confinement to concrete core without sustaining axial load directly. This paper presents the axial compressive behaviour of square TSRC stub columns after ISO 834 standard fire exposure, experimentally and numerically. Eighteen square TSRC stub columns were heated and cooled and subsequently loaded to failure under axial compression. The influences of heating time, concrete compressive strength and steel tube area ratio on the load vs. displacement response, failure mode, residual capacity and stiffness of the tested columns were investigated. Finite element analysis (FEA) models were then developed and validated against test results. The working mechanism, e.g. confinement effect and axial force distribution within the composite section, was studied via parametric studies. Both the residual ultimate capacity and axial stiffness of square TSRC stub columns decrease significantly with the increase in heating time. The negative effect of fire exposure on residual stiffness is more significant than on the residual capacity. Finally, practical equations for determining the residual ultimate capacity and residual compressive stiffness of square TSRC stub column were proposed, which remain consistent with the ambient-temperature methods given in current design standard.

Behavior and design of eccentrically-loaded slender tubed steel-reinforced high-strength concrete columns

This study experimentally and numerically investigated the behavior of eccentrically-loaded slender circular tubed steel-reinforced concrete (CTSRC) columns filled with high-strength concrete (HSC). Six specimens with the HSC of 81.4 MPa were tested considering the length-to-diameter ratio and load eccentricity; and their effects on the failure phenomenon, bearing capacity, and ductility were evaluated. A three-dimensional finite element model was established and validated for further investigating the column behavior. The study results indicate that all specimens fail in a flexural failure mode and show good ductility; and the shear studs and circular steel tube are found to ensure the composite behavior of CTSRC columns. Besides, increasing the tube thickness contributes more to the improvement of column ductility than the load capacity and the steel shape yields before the peak load, indicating the full utilization of steel strength. Based on the parametric study, a design method considering the second-order effect and the influence of unequal load eccentricities at both column ends is proposed to assist designers to determine the load capacity of slender CTSRC columns.

Behavior of eccentrically loaded circular tubed steel-reinforced concrete short columns using high-strength concrete

The tubed steel reinforced-concrete (TSRC) column is a compression member composed of a thin-walled steel tube filled with the structural steel shape-reinforced concrete, in which the steel tube is disconnected at the beam-column connections while providing a strong lateral restraint to the core concrete. To access the structural behavior of circular TSRC (referred as “CTRSC”) column using the HSC, a total of 11 short column specimens with the cubic concrete strength of 81.4 MPa were tested under the eccentric compression. The load eccentricity and the diameter-to-thickness ratio of steel tubes were considered as the key parameters; and their influences on the failure mode, load-bearing capacity, and deformation characteristics were investigated. The experimental results indicate that the failure sections of the test specimens strongly depend on the load eccentricity and the use of steel tube improves the ductility of HSC and ensures the composite action between the concrete and the structural steel shape. A simplified calculation method for the resistance of eccentrically loaded CTSRC columns is proposed, which gives satisfactory predictions when compared with the test results and the theoretical model.

Behavior comparison of seven-types of steel–concrete composite stub columns under axial compression

Steel-concrete composite columns are widely used in civil engineering structures for superior structural performance and economical cost. In response to the varying construction conditions, extensive types of composite columns have been developed nowadays, including concrete-filled steel tubes (CFST), CFST with steel bar (CFST-B) or steel section embedded (CFST-S), steel tubed concrete (T-C), steel tubed reinforced concrete (T-RC), steel tubed steel-reinforced concrete (T-SRC), and the newly proposed steel-tube-confined CFST (T-CFST), etc. A systematic and comparative experimental study was conducted for the seven types of steel–concrete composite stub columns with the same steel ratio, aiming to clarify their differences and facilitate an appropriate selection. Experimental results showed that all the conventional composite columns suffered from brittle failure, which was changed to ductile failure for T-CFST. Moreover, the employment of internal rebar or structural steel led to a variation of 13.3% in the ultimate load of CFST members; setting steel gap at the column ends for T-C columns increased the ultimate load by about 10% further; the addition of outer steel tube and sandwich material in T-CFST achieved up to 42.4% higher ultimate load. The enhanced mechanical properties of T-C and T-CFST were resulted from the increasing concrete confinement by the outer steel tube. The current design codes for different types of composite columns were examined by the experimental results, and a more suitable design method is needed for T-CFST.

Seismic Behavior Experimental Study on the Joint of Circular Tubed Steel-Reinforced Concrete Columns

A new type joint of Circular Tubed Steel-Reinforced Concrete (CTSRC) columns was designed in this paper. The structural characteristics, manufacturing process, and mechanical properties of raw materials of the new joint were introduced. In order to simulate the earthquake action, two joint specimens were subjected to low-cycle cyclic loading at the end of the column. Based on the in-depth study of the failure characteristics, load-displacement hysteretic curve, skeleton curve, ductility index, load-strain hysteretic curve in the core area of the joint, energy dissipation performance, strength and stiffness degradation performance, and shear deformation in the core area of the joint during the whole loading process, the seismic behavior of this new type of joint was investigated. The results show that the new joint has reasonable failure characteristics, high bearing capacity, good ductility, excellent seismic energy dissipation performance, and strong resistance to strength and stiffness degradation, which meets the seismic design principle of “strong joint and weak component” and is suitable for the results with special requirements for seismic performance. In addition, preliminary design recommendations were put forward. The research results of this paper can provide a theoretical basis for the application of this kind of new structure.

Restoring Force Model Research on Joint of Circular Tubed Steel-Reinforced Concrete Column

In this paper, two joints of circular tubed steel-reinforced concrete (CTSRC) column were designed. The load-displacement hysteretic curve and skeleton curve of this new type of joint are obtained by the pseudostatic test under low cycle cyclic load on the top of the column. The results show that this new type of joint has good seismic energy dissipation performance. On the basis of the test, a three-fold skeleton curve model considering three characteristic points of yield, limit, and failure is proposed, and the expression of skeleton curve model is given. The load and unload stiffness degradation law of specimens under reciprocating load is studied, and the expression of stiffness degradation law is given. The hysteresis law of the new type joint specimens is described in detail. The validity of the model is verified by comparing the experimental curve with the model curve. The model can be used in the elastic-plastic seismic time-history analysis on the joint of circular tubed steel-reinforced concrete (CTSRC) column.

Numerical Study on Shear Studded Tubed Steel Reinforced Concrete Columns Under Impact Loads

Tubed steel reinforced concrete (TSRC) columns are the advanced version of steel reinforced concrete column (SRC) which consists of inner and outer confinement along with the concrete core. In this composite member, a structural steel member and the outer confinement provides inner confinement as well as outer confinement. During recent years, TSRC sections got wide attention mainly because of its advantages over common CFST sections. Main advantage is that it simplifies the construction of beam-column joints and spalling of concrete during an event of earthquake can be avoided as outer steel confinement is provided. Many studies are done to check the performance of these TSRC columns in different loading scenarios. During the initial stages behavior under axial and eccentric loading was done on this section by different researchers and tried to develop analytic formulas and equations for TSRC columns. In this era of time it is necessary to check the ability of structures under impact loads. This study aims to investigate the performance of TSRC columns under impact loading condition and concluded. For the finite element analysis LS-Dyna software is adopted and for modelling purpose Hypermesh software is used. In this study, first validation is done by applying axial load vertically to the tubed steel reinforced concrete column. For the application of axial load rigid impactor plate is used. Impact force is applied to the TSRC short column in two directions: vertical, horizontal. For providing vertical impact a rigid plate impactor is used and for horizontal impact a dogde neon vehicle is used. Here in this analysis shear studs are incorporated on the surface of flanges of the inside steel section.

Effect of Steel Casing on Vertical Bearing Characteristics of Steel Tube-Reinforced Concrete Piles in Loess Area

This study aims at investigating the effect of steel casing on vertical bearing characteristics of steel tube-reinforced concrete piles in loess area by centrifugal model test. Five piles were selected, one of them was a conventional reinforced concrete pile which was 35 cm in length and 2.5 cm in diameter as a contrast pile, and the length of steel casing for the remaining four steel tube-reinforced concrete piles was 8 cm, 12 cm, 16 cm, and 20 cm respectively. The results show that the axial force, unit skin friction, tip resistance, and shaft resistance of steel tube-reinforced concrete piles with different steel casing lengths were different from conventional reinforced concrete pile. Additionally, the ultimate bearing capacity of steel tube-reinforced concrete piles was compared with a conventional reinforced concrete pile. Moreover, advantages of steel casing in pile foundation engineering were summarized. The results of this study can provide reference for vertical bearing characteristics of steel tube-reinforced concrete piles in loess area.

Compressive Behavior of Circular Tubed Steel-Reinforced High-Strength Concrete Short Columns

AbstractIn this paper, a total of 12 circular tubed steel-reinforced concrete (CTSRC) short columns with high-strength concrete are constructed and tested under axial compressive load. The main var...

Investigations on the Shear Mechanism of Steel-Tube-Reinforced Concrete Shear Walls with a Low Shear-Span Ratio

This paper describes the study of steel tube reinforced concrete (STRC) shear walls with a low shear-span ratio, in which steel tubes are embedded in the web of the shear wall. The addition of these steel tubes can significantly improve the shear behavior of ordinary RC shear walls. A series of cyclic loading tests allow us to examine the failure mode, hysteretic behavior, deformability, and energy dissipation capacity of the STRC shear walls. The investigation indicate the STRC shear walls transform from entire section walls to walls with vertical slits under loading. This prevents brittle shear failure and improves the deformation and energy dissipation capacity of the specimens. A softened strut-and-slip model is applied to analyze the shear mechanism of STRC shear walls, and is shown to predict the shear capacity accurately.

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.

Cyclic behavior of steel tube-reinforced high-strength concrete composite columns with high-strength steel bars

To study the cyclic behavior of steel tube-reinforced, high-strength concrete columns with high-strength steel bars, a cyclic loading test of six full-sized square columns was carried out, including one traditional reinforced concrete (RC) column and five steel tube-reinforced concrete (STRC) composite columns. The cross-sectional shape of the inner steel tube, the strength matching of the outer concrete and the core concrete, and the presence of steel fiber in outer concrete were the major parameters of the test. The research shows that steel fiber-reinforced high-strength STRC composite columns had better seismic behavior compared to RC columns. The strength matching method, where the C90 core concrete was combined with the C70 outer concrete, resulted in a better composite effect in comparison to the method of using C80 concrete in both core concrete and outer concrete. Moreover, the addition of steel fibers in outer concrete effectively reduced the damage degree and improved the ductility, resilient capacity, and energy dissipation capacity of the specimens. Finally, based on the test research and theoretical analysis, a calculation model for predicting the maximum load-carrying capacity was proposed. The model was then verified by comparing its predictions with test results.

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.

Shear behavior of short square tubed steel reinforced concrete columns with high-strength concrete

Six shear-critical square tubed steel reinforced concrete (TSRC) columns using the high-strength concrete (fcu,150 = 86.6 MPa) were tested under constant axial and lateral cyclic loads. The height-to-depth ratio of the short column specimens was specified as 2.6, and the axial load ratio and the number of shear studs on the steel shape were considered as two main parameters. The shear failure mode of short square TSRC columns was observed from the test. The steel tube with diagonal stiffener plates provided effective confinement to the concrete core, while welding shear studs on the steel section appeared not significantly enhancing the seismic behavior of short square TRSC columns. Specimens with higher axial load ratio showed higher lateral stiffness and shear strength but worse ductility. A modified ACI design method is proposed to calculate the nominal shear strength, which agrees well with the test database containing ten short square TSRC columns with shear failure mode from this study and other related literature.

Influence of slenderness on axially loaded square tubed steel-reinforced concrete columns

This paper aims to investigate the axial load behavior and stability strength of square tubed steel-reinforced concrete (TSRC) columns. Unlike concrete filled steel tubular (CFST) column, the outer steel tube of a TSRC column is mainly used to provide confinement to the core concrete. Ten specimens were tested under axial compression, and the main test variables included length-to-width ratio (L/B) of the specimens, width-to-thickness ratio (B/t) of the steel tubes, and with or without stud shear connectors on the steel sections. The failure mode, ultimate strength and load-tube stress response of each specimen were summarized and analyzed. The test results indicated that the axial load carried by square tube due to friction and bond of the interface increased with the increase of L/B ratio, while the confinement effect of tube was just the opposite. Parametric studies were performed through ABAQUS based on the test results, and the feasibility of current design codes has also been examined. Finally, a method for calculating the ultimate strength of this composite column was proposed, in which the slenderness effect on the tube confinement was considered.

Seismic behavior of circular tubed steel-reinforced concrete column to steel beam connections

The tubed steel-reinforced concrete (TSRC) column is a special type of SRC columns where the longitudinal reinforcement and reinforcement cage in the SRC column are replaced by a thin-walled steel tube. Without any traditional reinforcement, concrete pouring becomes easier in a TSRC member. Although the TSRC columns possess high load-carrying capacity and good ductility performance in seismic zones, the seismic behavior of TSRC column to beam connections has not received much attention, which limits the application of TSRC columns. This paper aims to investigate the seismic behavior of circular TSRC column to steel beam connections with cross diaphragms. Four such connection specimens were tested under cyclic loading, considering the thickness of joint tube, the height of extended tube, and the axial compression ratio of columns. Based on experimental results, the failure progression, load-displacement curves, and stresses for the circular TSRC column to steel beam connections are discussed. The favorable seismic performance for such connections is demonstrated and a design model for determining the joint strength is proposed in this paper.

Seismic behavior of shear-critical circular TSRC columns with a shear span-to-depth ratio of 1.3

Beam-column connections of steel reinforced concrete (SRC) structures are complicated and difficult to be constructed due to the densely arranged longitudinal reinforcements and stirrups. One good alternative is to use the composite construction where the reinforcing cage in the SRC column is replaced by an outer thin-walled steel tube, known as tubed steel reinforced concrete (TSRC). This paper presents and discusses the results of an experimental study on the seismic behavior of short circular TSRC columns with a shear span-to-depth ratio of 1.3. A total of 6 specimens using the high strength concrete with fcu,150 = 86.6 MPa were tested under simulated earthquake loading conditions, considering the two main parameters of axial load ratio and the number of shear studs on the steel shape. The short TSRC columns that failed in shear failure mode still showed good ductile behavior due to the effective confinement from the steel tube. Increasing the axial load ratio resulted in an increase of the lateral load resistance and energy dissipation capacity but decreased the ductility and deformation ability of the specimens. The shear studs welded on the steel shape had little effect on improving the seismic behavior of shear-critical circular TSRC columns. A modified ACI design method is proposed to predict the nominal shear strength of circular TSRC columns.