Concrete Encased Steel Composite Columns Research Articles

Optimization of Structural Steel Used in Concrete-Encased Steel Composite Columns via Topology Optimization

Concrete-encased steel composite columns are preferred for their exceptional ductility and strength, particularly in high-rise buildings. This research aims to enhance both the strength and ductility of these composite columns by increasing the height of the steel profile. Typically, hexagonal or circular openings, referred to as castellated elements, are incorporated into the steel profile to achieve this height increase. This study employed a topology optimization method to identify the ideal opening shape for the steel profile in concrete-encased steel composite columns. The analysis revealed a sinusoidal-like opening shape, which was then refined for manufacturing. The optimal opening shape was used to increase the height of the existing steel profile, and nonlinear analyses were conducted to evaluate the effectiveness of this new optimized steel profile in concrete-encased steel composite columns. Two concrete-encased steel composite columns were designed: one with the optimal steel profile and the other with a standard steel I profile. ANSYS APDL 19.0 software was used to simulate an experiment based on an existing concrete-encased steel column to validate the nonlinear analysis. The verification analysis demonstrated a remarkable similarity between the experimental and numerical load–displacement graphs, indicating that the numerical analysis was reliable. In the analysis of the composite columns, both axial and lateral forces were applied in the nonlinear analyses. The axial force was applied at 15% of the column’s capacity, while the lateral force was applied until the composite column reached a state of failure. The results of the nonlinear analyses allowed for a comparison of load–displacement curves and the performance of the composite columns. In comparison to the standard steel I profile, the steel profile with the optimal opening shape increased load-carrying capacity by approximately 19% and energy absorption capacity by approximately 24%.

Axial compressive strength of concrete encased extended T-shaped steel composite columns with less reinforcement

A novel concrete encased extended T-shaped steel composite stub (ET-CES) column with less reinforcement for the prefabricated structure is proposed. Eight ET-CES columns, including one covered by concrete fireproof boards and two bare extended T-shaped steel stub columns, were tested under axial compression. Finite element analysis was also conducted. The effects of stirrup spacing, stirrup form, steel ratio, and concrete compressive strength on the axial compressive behaviour were studied. Furthermore, the failure modes, axial load-displacement curves, axial load-strain curves, and post-peak deformability of ET-CES columns were also investigated. The results demonstrated that the concrete cover with less reinforcement and a thin concrete encasement for the ET-CES column could still prevent steel skeleton instability under axial compression. Premature spalling of concrete cover might be prevented by installing fireproof boards, reducing stirrup spacing, and using closed stirrups. The steel ratio in ET-CES columns increasing from 8.1% to 10.4% had no effect on the maximum normalized resistance but could enhance the post-peak ductility and residual strength. The reduction of the concrete compressive strength of ET-CES columns from C50 to C30 could improve the maximum normalized resistance and residual strength. ET-CES columns had excellent post-peak deformability. Finally, an axial strength formula for ET-CES columns was proposed and validated.

Axial stress-strain characteristics and confinement mechanism of concrete-encased steel composite columns: An analytical model

Axial stress-strain characteristics and confinement mechanism of concrete-encased steel composite columns: An analytical model

Structural performance of rigid shear connectors in concrete encased steel composite columns

Concrete encased steel (CES) composite columns possess a wide variety of advantages in constructing concrete-steel composite frames. In order to achieve the composite behaviour of these columns, it is necessary to transfer the force between steel and concrete, effectively. Therefore, shear connectors should be used on the contact surface between concrete and steel. In this research, behaviour of the rigid shear connectors in CES composite columns is numerically studied. The results – obtained from the finite element analysis – were validated against the experimental results. Afterwards, parametric studies were conducted to investigate the effective parameters on the behaviour of the rigid shear connectors. The results show that the length, the thickness and the penetration depth of the shear connector, the compressive strength of concrete and the thickness of concrete cover have a noticeable effect on the strength and stiffness of the shear connector. Moreover, increasing the length and the penetration depth of the shear connector, and the thickness of the concrete would increase the residual strength level. In general, the rigid shear connector is mobilized under a much smaller slippage (between concrete and steel), as compared to the stud shear connector, and provides greater stiffness and strength. Moreover, due to being encased in reinforced concrete, it can also provide sufficient ductility. Finally, based on the parametric studies, a formula is suggested to predict the ultimate shear capacity of the rigid shear connector in the CES composite columns.

Axial compressive behaviour of concrete encased extended I-shaped steel composite stub columns with less reinforcement

A novel concrete encased extended I-shaped steel composite (EI-CES) column with less reinforcement for prefabricated structures is proposed. Eight EI-CES stub columns with one covered by concrete fireproof board, and two bare extended I-shaped steel stub columns, are tested under axial compression loads. The effects of stirrup spacing, stirrup form, proportion of steel sectional area, and concrete compressive strength on the axial compressive behaviour of composite columns are studied by test and finite element analysis. According to the results, the concrete cover with less reinforcement can prevent internal steel instability under axial compression. 25 mm thickness of concrete cover can satisfy the load-carrying capacity and serviceability requirements for the composite column. The premature spalling of concrete cover can be prevented by installing fireproof board, reducing stirrup spacing, and using closed stirrups. The proportion of steel sectional area in composite columns increasing from 7.5 % to 9.6 % has no effect on the maximum material full-utilization coefficient, but can reduce premature concrete cracks and improve the residual strength of EI-CES columns. The concrete compressive strength in composite columns decreasing from C50 to C30 can improve the maximum material full-utilization coefficient and residual strength. The composite columns have excellent post-peak deformability. A formula for the axial resistance of EI-CES columns is proposed and validated.

A novel compatible truss-arch model to predict shear strength of concrete-encased steel composite columns

A novel compatible truss-arch model to predict shear strength of concrete-encased steel composite columns

Finite Element Analysis of Frames with Reinforced Concrete Encased Steel Composite Columns

Structural frame systems that consists of concrete-encased-steel-embedded composite columns and reinforced concrete beams are typically used in mid-rise to tall buildings. In order to understand their overall structural behavior, a total of 12 frame models with high and low ductility features were constructed and analyzed using LS-DYNA software. Two of these models were validated using the results of previously tested frames. The remaining 10 models were studied to predict the behavior of frames with varying concrete strengths, reinforcement configurations, and structural steel sections under vertical and lateral loads. The results were investigated in terms of cracks and failure patterns, load-deflection relationships, energy dissipation, and stiffness degradation. The analytical results indicated that the high ductile frame models showed slightly better lateral load carrying performances compared to low ductility frame models. Moreover, the analytical studies demonstrated that the existence of structural steel in a column, regardless of its cross-sectional shape, was the most important parameter in improving the lateral load carrying capacity of a frame.

Buckling resistance of steel fibre-reinforced concrete encased steel composite columns

Six steel fibre reinforced high strength concrete (SFRHSC) encased steel columns were tested to investigate their structural performance without the need of conventional longitudinal steel reinforcements and stirrups. The SFRHSC encased steel composite columns were tested until failure under eccentric compression load to determine their buckling resistance including the compression and moment strength interaction behaviour. Furthermore, two composite beams with similar cross-section were subject to four-point load to obtain the load-deflection behaviour and ultimate moment resistance. The experimental results showed that, without the presence of longitudinal steel bar reinforcements, the steel fibre-reinforced composite columns exhibited ductile behaviour and showed no evidence of debonding or early cover spalling. Test evidence showed that the hooked-end steel fibres were able to bridge the growing cracks effectively. Two analytical approaches were proposed to predict the compression and moment resistances of the tested columns. The first model was based on the fibre element analysis, while the second model provided a simplified analytical prediction. Both the models were developed accounting for second-order effects in slender columns. The models were able to predict the test results with reasonable accuracy. The test results also fitted well with the predicted axial force–moment strength interaction curves.

Development of analytical model for predicting compressive behavior of engineered cementitious composites‐concrete encased steel composite columns

AbstractAnalytical models which can reliably predict the load–deformation behaviors and the ultimate strength of columns are indispensable tools for the practical design. In this paper, an analytical model is developed to predict the compressive load–deformation behavior and the ultimate capacity of engineered cementitious composite confined concrete encased steel (ECC‐CES) composite columns. The proposed analytical model employs the effective material stress and strain compatibility approaches for the predictions of compressive load–deformation response of ECC‐CES columns. The material constitutive models for ECC, concrete, and steel are first established, and then used in the analytical model. The effect of ECC and steel confinement on the concrete core and the softening behavior of steel column due to compression buckling are also considered. Based on the experimental results, appropriate strength reduction factors are proposed so that the effective material stresses can be calculated. The strength predictions from the proposed analytical methods and different design codes are compared with the experimental and numerical results. It was found that the proposed analytical models using effective material stresses gave better predictions than many commonly used design codes.

Behavior of precast composite columns under axial and transverse forces

In this study, the effect of the steel core orientation to combined stresses behavior of a concrete encased steel (CES) composite column was studied. The various sectional configurations were used to define contributions to capacity under compression and flexural loading. CES composite sections were generally designed as column to resist axial compression and biaxial bending. This study would provide better understanding in case the section should carry flexural bending beside axial compression. The samples were tested under constant axial and repeated transverse forces, and a finite element analysis (FEA) model was developed to express flexural behavior of the composite column and to verify the experimental study. A total of four concrete encased steel composite columns with differently oriented I-shaped and circular tube steel sections and a reinforced concrete column were tested. Behavior of the columns were evaluated regarding failure modes, load versus displacement relationships and ultimate strength. Experimental results indicated that the specimen with steel section oriented regarding tension region exhibited better flexural response.

Numerical investigation for the design of rectangular concrete encased steel composite columns

AbstractAdvanced design methods are becoming more important for the structural analysis. However, their results depend strongly on the quality of the numerical model and its underlying assumptions. Current Eurocode 4 does not provide clear guidance for this analysis type.A literature review on the compression tests conducted on concrete encased steel composite columns is presented. It was found out that there is a lack in the literature when it comes to the testing of slender composite columns as opposed to numerous tests done on stub columns. A selection of existing specimen tests are then simulated using finite element analysis software ABAQUS. Nonlinearity in the model was defined through materials and geometry. The interface modelling between steel and concrete as well as the modelling of load introduction are discussed. The finite element model was intended to be as generic as possible so that it can be taken as a basis for future parameter studies. Moreover, the column resistance check using interaction curves was discussed. Different approaches to form interaction curves namely strain limitation and plastic section capacity were compared.

Prediction of fire resistance of concrete encased steel composite columns using artificial neural network

Concrete encased steel (CES) columns, also known as steel reinforced concrete (SRC) composite columns, exhibit superior fire resistance due to concrete acting as a protection layer for the embedded steel section. While modern design codes have provided design guides for the fire resistance of CES columns, they are only applicable to those made of normal strength concrete. For high strength CES columns, advanced analysis is needed to capture the brittleness of high strength concrete at elevated temperature. In this paper, two methods, namely the artificial neural network (ANN) and the analytical equations, are proposed to predict the fire resistance of axially-loaded CES columns made of high strength concrete. To train the ANN, a finite difference model is developed to compute the temperature field in CES columns and it is used to establish a database containing 15,200 specimens. The cross-sectional dimensions and materials grades of the specimens are carefully selected to cover a wide range of values including those commonly adopted in real-life applications. The inputs of the ANN are identified through an extensive parametric analysis. The selected ANN consists of 7 inputs, 3 outputs and 2 hidden layers and achieves a high determination coefficient R2 value of 0.999. For practical implementation, analytical equations are also derived and achieve high R2 values above 0.953. The predictive power of the ANN and the analytical equations are examined against the observations obtained from actual fire tests, showing reasonable accuracy of prediction. Both methods are simple, of high accuracy and have implicitly accounted for temperature-dependent material degradation, and hence do not require input of temperature-dependent material properties and advanced analysis software.

Parametric study on high strength ECC-CES composite columns under axial compression

This paper presents the results of a comprehensive numerical parametric study on axial compressive behaviours of recently introduced Engineered Cementitious Composites (ECC) confined concrete encased steel composite columns (ECC-CES). For that purpose, a criterion to calculate the effective material stresses for non-linear finite element (FE) modelling of ECC-CES columns is first established. The results of criteria-based FE analysis are validated against the experimental results in terms of failure mode, column strength and load-deformation response, and a good agreement is demonstrated. The validated FE model is then employed to conduct a detailed parametric study. The effects of extended range of material strengths, geometric dimensions and column scaling on the axial compressive performance of ECC-CES columns are investigated. Based on the finite element analysis (FEA) results, some important implication for practical design of ECC-CES columns are recommended. In addition, the applicability of a simple squash load formula to predict the ultimate capacity of ECC-CES columns is also evaluated and discussed against the results of comprehensive parametric study.

Fire performance of composite columns made of high strength steel and concrete

The use of high strength steel and concrete materials for composite column construction is partly impeded by the lack of research on their fire performance. In EN1994-1-1, the highest concrete grade allowed for designing composite columns is capped at C50. This paper investigates the behaviour of concrete encased steel (CES) composite columns made of C120 concrete and S500/690 steel section under ISO834 standard fire through a series of experimental and numerical analyses. Fire tests were carried out on five high strength CES column specimens subject to varying eccentricity of loading to study their behaviours in fire. Polypropylene fibres were added into the high strength concrete mix to prevent the explosive spalling so that explicit modelling of cover spalling phenomenon can be omitted in the numerical analysis. A unified method is proposed to determine the transient strain of high strength concrete at elevated temperatures, allowing the stress-strain curves in EN1992-1-2 to be extended to high strength concrete up to C120. A numerical model, which can capture the strain reversal of concrete caused by the flexural deformation of columns at elevated temperatures, is proposed to enable a good prediction of axial displacement responses of CES columns in comparison with the test results. Finally, based on the validated numerical model and parametric studies, a new tabulated data method is proposed for the fire resistance design of CES columns with concrete class up to C90 concrete and steel section grade up to S550.

Experimental investigation on fire resistance of high-strength concrete encased steel composite columns

This paper presents the experimental findings on fire resistance of concrete encased steel (CES) composite columns made of C120 concrete and S500/S690 high-strength steel section. Eight full-scale CES columns were tested under concentrated load and heated under the ISO834 fire until failure. The fire performance of each CES column specimen was evaluated by analysing the fire resistance time, axial displacement-time curve, temperature-time curve, rotational angle of end support, post-fire conditions of the concrete surface and failure mode. The experimental study showed that the addition of polypropylene fibre was effective in minimizing explosive concrete spalling in high-strength CES columns to achieve comparable fire resistance time as those of normal-strength CES columns. A database containing 40 CES specimens was established to assess the accuracy of the current design methods in predicting the fire resistance of CES columns. The limitations of each design method were discussed based on whether they can provide safe and accurate predictions of the fire resistance of tested CES column specimens. Finally, recommendations were provided to modify the current methods for fire resistant design of CES columns made of high-strength concrete.

Concrete Encased Steel Composite Columns: A Review

Concrete Encased Steel (CES) composite columns are those columns in which structural steel is encased inside reinforced concrete. By combining both materials, columns can handle a large amount of load with a lesser cross sectional area. Moreover they improves the overall rigidity of the building and provide significant resistance to lateral loads. These columns are widely used in high rise building construction. Main disadvantage of these columns are the construction difficulties. Since reinforcement bars and steel sections are encased, the concrete pouring becomes more difficult. Solution for these problems are the use of welding couplers or providing holes in steel flanges and steel web. Both the methods will increase the cost of construction and also it can affect the total bearing capacity and authenticity of the structure. An innovative method proposed to overcome these difficulties is the use of steel fibers and replacing the reinforcement bars. This paper discuss various studies conducted on concrete encased steel composite members.

Investigation on axial load-shorting behaviour of high strength concrete encased steel composite section

Experimental work on steel H-section fully encased by high strength concrete showed the occurrence of premature failure due to concrete cover spalling. This failure mode limits the utilization of full material strength and hence impedes the attainment of anticipated load-carrying capacity. This paper proposes an analytical model to predict the full range axial load-displacement behaviour of concrete encased steel composite section made from concrete grade up to C130 and steel section grade up to S690. The analytical model captures the compression behaviour of concrete encased steel composite section at the constitutive level including premature cover spalling, concrete confinement from stirrups and steel section. Concrete fracture energy is used to estimate the cover spalling strain, and a confinement model is proposed to evaluate the confining pressure provided by the steel section. Good agreement is observed between the analytical predictions and test results in terms of initial stiffness, peak load, residual strength, and the full range of load-displacement response. Based on the findings, recommendations are put forward for practical design of high strength concrete encased steel composite columns.

Axial-moment interaction of high strength concrete encased steel composite columns: Experimental investigation

This paper investigates the failure mechanism and structural behavior of high strength Concrete Encased Steel (CES) composite columns subject to compression and bending. Twelve composite column specimens with C90 concrete and S500 steel section were tested under concentric compression, eccentric compression and four-point bending. All specimens had the same geometry and were reinforced with the same steel section and same amount of reinforcing bars. In some specimens, micro steel fiber was added into concrete mix with 0.5% or 1.0% dosage to delay or prevent the potential premature cover spalling. The load-carrying capacity, load-deformation response, post-peak ductility, flexural stiffness, as well as damage pattern are comprehensively analyzed. Comparison is made between the experimental results and analytical predictions using modern design codes such as EN 1994-1-1 and AISC 360–16. From the four-point bending test, the flexural stiffness obtained from the test seems to be smaller than the codes' predicted values, indicating that modification is needed to achieve better prediction of structural response of composite beams at the service load level. As for the axial force (N)-bending moment (M) strength interaction diagram, it is found AISC 360–16 gives overall more conservative prediction than EN 1994-1-1 method for high strength CES columns with C90 concrete and S500 steel. However, both methods overestimate the axial compression capacity although they can predict their flexural capacity well.

Axial-moment interaction of high strength concrete encased steel composite columns: Design recommendation

This paper investigates the axial force-moment (N-M) interaction behaviour of high strength concrete encased steel (CES) composite columns. A numerical method is developed to simulate the nonlinear inelastic behaviour of CES composite beam-columns, which includes concrete cover spalling, concrete confinement effect, buckling of longitudinal reinforcing bars, and stain-hardening of the encased steel section. The numerical model is implemented in a self-developed computer program to generate the load-deflection response, moment-curvature relation, as well as the N-M strength interaction diagrams. The accuracy of the proposed analysis method is validated by comparison with the experimental results report in the companion paper and the test data available in literatures. To further understand the resistance of CES columns consisting of high strength concrete and high strength steel, parametric study is performed to evaluate the effect of concrete compressive strength, steel yield strength, load eccentricity, as well as steel area ratio. Finally, a simplified method is proposed to construct the N-M strength interaction curve of CES composite columns. The proposed method can be used to design CES beam columns for concrete grade up to C100 and steel grade up to S960.

Numerical modelling of engineered cementitious composites-concrete encased steel composite columns

Recently, a new section form of concrete encased steel composite columns with Engineered Cementitious Composites (ECC) confinement (ECC-CES), which outperforms conventional CES columns in terms of failure behaviour, ductility and toughness has been introduced. Numerical modelling of the post-peak behaviours of such encased composite columns is a challenging task due to brittle failure of concrete, interface bond failure and buckling of steel section. This study presents a finite element modelling procedure for the ECC-CES columns. Both material and geometric nonlinearities are incorporated in the model and inelastic behaviour of ECC, concrete and steel were described by using appropriate material constitutive laws. Moreover, effects of initial geometric imperfections, contact interactions and confinement by steel and ECC encasement on concrete core were considered. Concrete damaged plasticity model was employed to describe the failure of ECC and concrete. The FE model was validated against experimental results and found to give good predictions of compressive behaviour of ECC-CES columns compared with the test results. Finally, a small scale parametric study was conducted using the validated numerical model to study the effect of the materials' strength on the column compressive behaviour.