Concrete-filled Steel Columns Research Articles

Prediction of the Strength of the Concrete-Filled Tubular Steel Columns Using the Artificial Intelligence

Introduction. The machine learning algorithms are highly promising for predicting the load-bearing capacity of the building structures. The paper aims at building the predictive models for calculating the strength of the concrete-filled steel tubular (CFST) columns to enable a highly accurate prediction of the ultimate loads for the entire possible range of parameters affecting the load-bearing capacity of the eccentrically compressed columns.Materials and Methods. The article studies the eccentrically compressed short concrete-filled steel tubular (CFST) columns of circular cross-section. Model input parameters: column outer diameter, pipe wall thickness, yield strength of steel, compressive strength of concrete, relative eccentricity. Output parameters: the ultimate loads without taking into account and taking into account the random eccentricities. The models were trained on synthetic data generated based on the theoretical principles of the limit equilibrium method. Two machine learning models were built. When training the first model, the ultimate loads were determined at a given eccentricity of the longitudinal force without taking into account the additional random eccentricity. When training the second model, the additional random eccentricity was taken into account. The effect of the features on the model predictions was assessed using the Feature Importance function. The Optuna method was used to select the hyperparameters. The machine learning models were implemented in the Jupiter Notebook environment using the Gradient Boosting learning method. The total volume of the training sample was 179 025 samples.Results. The importance of the features most affecting the predictive values of the model have been determined. For both models, the outer diameter of the column and the relative eccentricity have proved to be the most important features, which is consistent with the existing experience of designing and calculating such structures. Optimisation of the hyperparameters using the Grid Search method enabled getting the improved results. The high accuracy of prediction has been ascertained by the low values of the regression metrics: MSE = 9.024; MAE = 9.250; MAPE = 0.004 — for the model built without taking into account the additional random eccentricity; MSE = 8.673; MAE = 8.673; MAPE = 0.004 — for the model built taking into account the additional random eccentricity.Discussion and Conclusion. The developed Gradient Boosting models for predicting the ultimate loads of the eccentrically compressed short concrete-filled steel tubular (CFST) columns of circular cross-section, both without taking into account and taking into account the additional random eccentricities, have demonstrated high accuracy and stability of prediction, they can be applied for assessing the strength of the columns during design and construction, which will reduce the time and resources involved in physical testing. In the future, it is planned to expand the data range by including other materials, different cross-section geometries of the columns and a slenderness parameter, which may improve the generalization ability of the model.

Effect of Preload on Box-Section Steel Columns Filled with Concrete under Axial Load: A Numerical Study

External loads applied to a box-section steel column before it is filled with concrete to increase its efficiency due to modifications in structural systems or design errors may reduce its ultimate capacity and change its structural behavior. To examine this effect, finite element modeling (FEM) has been used to simulate these columns under preloading at different ratios with many variables in the geometric dimensions of the columns. The FEM results have been investigated using 38 experimental specimens obtained from previous studies without preloading. The results demonstrated high accuracy in modeling these columns in structural behavior and ultimate load capacity. After verifying the results, 84 Concrete-Filled Steel Columns (CFSC) were modeled under different preload ratios. The results indicated that some variables have directly affected the value of the decrease in column capacity in terms of its height, wall thickness, yield stress, and preload ratios, while others were inversely proportional in terms of the cross-section dimensions and concrete strength. The preload effect ratio had two separate limits, where when it reached 70%, the maximum value of the decrease in column capacity was 10.90%. The value increased sharply reaching 19.90% when there was a preload equal to 80%. New equations have been proposed to predict the ultimate capacity of CFSC under preloading with suitable accuracy with a correlation coefficient of no less than 0.949.

Fire resistance of square double-skin concrete-filled steel tubular columns and concrete-filled double steel tubular columns

Square double-skin concrete-filled steel tubular (DSCFST) columns and concrete-filled double steel (CFDST) columns possess excellent load-carrying capacity and ductility. However, there has been limited research on the responses of DSCFST and square CFDST columns exposed to fire. This paper presents a series of tests on such columns loaded concentrically to determine the effects of the steel tube thickness, the strength of materials, load ratio, and boundary conditions on their fire resistance. Additionally, finite element (FE) models are established using ABAQUS, in which the concrete’s transient creep strain is considered through the development of the user-subroutine UEXPAN. A parametric study is undertaken by simulating 156 FE models to further study the behavior of DSCFST and CFDST columns under fire exposure. The fire test and numerical results suggest that both the load ratio and strengths of the internal tube and concrete core play significant roles in determining the fire resistance of DSCFST and CFDST columns. The developed FE models are demonstrated to capture well the fire behavior of loaded DSCFST and CFDST columns. The proposed design model predicts the ultimate loads of DSCFST columns with good accuracy; therefore, it can be employed in the practical design of DSCFST columns.

A STUDY ON BEHAVIOUR OF CONCRETE FILLED STEEL COLUMN IN FRAMED STRUCTURE

A STUDY ON BEHAVIOUR OF CONCRETE FILLED STEEL COLUMN IN FRAMED STRUCTURE

Comparative study on the impact behaviors of CFWST columns reinforced with steel spiral and tube

To obtain superior corrosion resistance and impact resistance, as well as good economic benefits, two new types of composite structure called as steel tube internally-reinforced concrete-filled weathering steel tube (STRCFWST) and steel spiral internally-reinforced concrete-filled weathering steel (SSRCFWST) columns are proposed and compared in terms of their impact resistance in this paper. Eleven impact tests were conducted and three parameters comprising steel spiral diameter, wall thicknesses of outer and inner steel tube were considered to evaluate their influences on the lateral impact behaviors. Results show the presence of inner steel tube and reinforcement cage significantly enhances the impact resistance while slightly decreases the energy absorption capacity. Increasing inner steel tube wall thickness helps to improve the impact resistance, however the contribution is not so good as that produced by increasing the outer steel tube wall thickness, whilst varying steel spiral diameter almost has no impact. Numerical models were developed by ABAQUS/Explicit and verified via the test, based on which the full-range behaviors of STRCFWST, SSRCFWST and unreinforced concrete-filled weathering steel tube (CFWST) columns under impact loading were compared and discussed. It is demonstrated that steel tube and reinforcement cage provide little confinement on concrete infill under impact. With the same internal steel ratio, inner steel tube makes a greater contribution to sectional bending moment resistance and energy absorption as compared to the reinforcement cage.

A Critical Review of Cold-Formed Steel Built-Up Composite Columns with Geopolymer Concrete Infill

Concrete-filled built-up cold-formed steel (CFS) columns offer enhanced load-carrying capacity, improved strength-to-weight ratios, and delayed buckling through providing internal resistance and stiffness due to the concrete infill. Integrating sustainable alternatives like self-compacting geopolymer concrete (SCGC) with low carbon emissions is increasingly favoured for addressing environmental concerns in construction. This review aims to explore the current knowledge regarding CFS built-up composite columns and the performance of SCGC within them. While research on geopolymer concrete-filled steel tubes (GPCFSTs) under various loads has demonstrated high strength and ductility, investigations into built-up sections remain limited. The literature suggests that geopolymer concrete’s superior compressive strength, fire resistance, and minimal shrinkage render it highly compatible with steel tubular columns, providing robust load-bearing capacity and gradual post-ultimate strength, attributed to the confinement effect of the outer steel tubes, thereby preventing brittle failure. Additionally, in built-up sections, connector penetration depth and spacing, particularly at the ends, enhances structural performance through composite action in CFS structures. Consequently, understanding the importance of using a sustainable and superior infill like SCGC, the cross-sectional efficiency of CFS sections, and optimal shear connections in built-up CFS columns is crucial. Moreover, there is a potential for developing environmentally sustainable built-up CFS composite columns using SCGC cured at ambient temperatures as infill.

Investigation of effective parameters on seismic performance of steel frames with CFST columns

The seismic performance of steel frames with composite columns is evaluated by the seismic performance factors. Despite the essentiality of appropriate coefficient values, there are limitations in the building code regarding seismic performance factors of composite structures. These values have been presented in the regulations based on engineering judgment and comparison with similar steel and concrete structures. However, limited research exists on the determination of seismic performance factors for composite structures, where these coefficients are affected by numerous parameters. This article aims to cover the existing gaps and examine the parameters that have received inadequate attention in regulations and articles, despite their significance in the seismic design of composite structures. The present study conducts a nonlinear static pushover analysis of steel structures with concrete-filled tubular steel columns (CFST) to investigate the influential parameters in seismic performance factors. The variables studied in this research encompass the height of the structure, soil type, lateral force-resisting system, and structural irregularity. The findings demonstrate that changes in structural height influence the value of the response modification factor in all examined soil types for IMFs and SMFs. Also, the response modification factors provided in ASCE 7 prove to be conservative for the studied lateral force-resisting systems excluding SMFs in composite structures. In addition, the seismic performance of the studied models has dropped due to the geometric irregularity of the plan and the irregularity of non-parallel systems. Besides, the response modification factor values for composite structures surpass those specified for similar steel structures, while Eurocode 8 and ASCE 7 consider these values to be equal and similar to steel structures, respectively.

Study of recycled aggregate concrete-filled circular steel columns with H-shaped steel reinforcement

In this study, the prediction formula of the axial compressive bearing capacity of recycled aggregate concrete-filled (RAC) circular steel columns with H-shaped steel reinforcement was theoretically studied with the limit analysis method. To differentiate the restraining effect due to H-shaped steel and steel tube, the bearing capacity of the concrete is divided into two parts, i.e., recycled aggregate concrete in the H-shaped steel confined area and the recycled aggregate concrete in the steel-tube confined area. Second, the effect of inner diameter-thickness ratio of steel tube, H-shaped steel and recycled coarse aggregate replacement rate on the axial compressive bearing capacity of the column is studied. Finally, a set of calculation formulas for the axial load bearing capacity of recycled aggregate concrete stub columns with steel tubes with H-shaped steel reinforcement is proposed. The validity and accuracy of the calculation formula of the bearing capacity was assessed by comparing with test results. The error between the theoretically formula and test results was within 10%. It demonstrates the feasibility of the proposed formula and accuracy of the limit analysis method.

Investigation of intumescent coating on the fire endurance of concrete-filled steel columns with varied characteristics

Concrete-filled steel columns (CFSC) are becoming increasingly popular in contemporary construction, particularly for the construction of tall buildings and structures with large spans. These columns offer superior fire protection compared to concrete or steel-only columns. Furthermore, CFSCs offer significant structural benefits by enhancing properties such as high tensile and compressive strength, ductility, capacity for energy absorption, improved fire resistance, and thermal insulation. However, there remains a notable research gap pertaining to the comprehensive analysis of the temperature distribution in CFSC sections that are protected by intumescent fire coating (IFC). Particularly, there is a need to investigate the specific effects of various heating rates, intumescent coating thickness, and steel thickness on the temperature distribution within these sections. The current research involved the creation of a finite element model for analyzing heat transfer and fire resistance in columns. This model was used to examine how the columns would perform under different fire conditions, including Standard (ISO-834), Fast, Slow, and Smouldering fires. The model has been verified with the available literature. Core concrete, dry film thickness (DFT) of intumescent coating, and steel section thickness are the primary determinants of the temperature rise of the protected CFSC section under fire considered in the developed models. This study adds large-scale column specimens to the corresponding numerical database. The numerical results provide additional proof that a CFSCs coated with an intumescent fire coating can achieve high fire resistance. With efficient IFC insulation and core concrete heat absorption, the temperature increase of a CFSC can be greatly retarded.

CONVERGENCE PROBLEMS WITH ANSYS'S SOLID 65 FINITE ELEMENT IN CONCRETE-FILLED TUBULAR (CFT) COLUMNS AS A CASE STUDY

<p>Using limited materials for numerical modeling of structural samples and comparing the behavior of samples with each other in order to reduce the number of straw test samples in order to reduce laboratory costs is one of the best methods today. ANSYS is one of the finite element software that is used for modeling reinforced concrete elements by Solid65 element. As a case study, a concrete-filled steel column under cyclic loading is examined and the best value for the Crushed Stiffness Factor (CSTIF) parameter that is one of Solid65 element parameters is suggested to confirm the modeling. By investigating the results, it can be concluded that this parameter is one of the most important factors that plays a significant role in convergence in ANSYS software for modeling CFT columns.</p>

Influence of waste foundry sand on microstructural and mechanical behavior of self consolidated concrete filled steel columns

The impacts of leftover foundry sand on steel sections filled with high strength Self-Consolidated Concrete (SCC) were investigated and addressed in this study. 24 steel sections were examined under progressive axial pressure to establish the optimal proportion of leftover foundry sand, a byproduct. 24 samples were divided into 12 columns with eight circular cross sections of 50 mm in radius and 500 mm in length, and eight additional specimens with square sections of 500 mm in length and 100 mm on each side. Additional 12 columns with eight circular specimens measuring 50 mm in radius and 1000 mm in height and eight square specimens measuring 100 mm on each side and 1000 mm in length. The twelve sections can be divided into hollow steel sections and SCC filled sections. The predicted outcome from the studies show that the capability of carrying axial loads and ductility of the SCC-filled steel sections are affected by the use of leftover foundry sand. Additionally, the steel section parts serve as external reinforcement to promote lateral stability and decrease local buckling. The square sections use 25% less steel than the circular sections. By substituting leftover foundry sand for some of the cement, SCC mixes are made. In this project, steel sections filled with self-consolidated concrete were made using varying amounts of leftover foundry sand, including 0%, 4%, 8%, 12%, 16% and 20%. According to the analysis, steel columns with leftover foundry sand have a higher ultimate load than standard concrete, which results in a 12% reduction in construction costs. The work offers a remedy for efficient byproduct management that lessens environmental risk and creates an atmosphere that is eco-friendly.

Behavior of concrete-filled cold-formed steel built-up section stub columns

This paper presents a test campaign concerning the behavior of concrete-filled cold-formed steel built-up section stub columns. The test program consisted of five types of cold-formed steel built-up sections infilled with concrete of three different grades (C40, C80 and C120). A pair of identical open sections were built-up to form a closed section by discrete self-tapping screws and connected using steel strips where necessary. A total of 42 stub columns, including 32 concrete-filled specimens and 10 hollow counterparts, was axially compressed between fixed-ends. Details of material properties tests and stub column tests are described in this paper. The stub column compressive strengths, full range axial load-shortening histories as well as load–strain responses and failure modes are presented and discussed. The test strengths were compared with the design predictions by the current American Specification ACI318, despite that this design rule was originally developed for concrete-filled steel columns with conventional tubular sections rather than built-up sections. The comparison demonstrated that the American Specification ACI318 provides generally unconservative and unreliable compressive strength predictions for the concrete-filled cold-formed steel built-up section stub columns. Necessary improvements shall be made in order to yield accurate compressive strength predictions.

Axial compression behaviour of concrete-filled auxetic tubular short columns

Concrete-filled steel columns (CFSCs) are of great interest in the literature as they are capable of carrying higher loads by combining the exceptional qualities of steel and concrete. With auxetic materials being introduced to civil engineering applications, the influence of these materials on CFSCs remains a matter of curiosity. The current study implements a nonlinear finite element analysis to evaluate the performance of circular CFSCs with six auxetic tubes under axial compression and the proposed numerical model was validated using published experimental data. The effect of the auxetic steel tube’s porosity and Poisson’s ratio on CFSCs was examined parametrically in terms of ultimate strength using the confined concrete model. Moreover, the stress distributions of the concrete and the auxetic steel tubes were also thoroughly examined. Based on the findings of the analysis, the ultimate load of CFSCs, utilising auxetic tubes with the same density and porosity but different Poisson’s ratio, increased proportionally with the increase of auxetic behaviour. When it comes to auxetic tubes with different densities and porosities, the influence of the Poisson’s ratio of the tubes diminished and the stiffness of tubes became more dominant over the mechanical characteristics of columns as the density of the auxetic steel tubes increased or decreased. The stiffness of the auxetic tubes reduced as porosity increased, as did the ultimate load of the columns. Additionally, the ultimate loads of the auxetic steel tube columns are found to be lower than those of bare steel tube columns filled with concrete due to perforations.

Damage analysis of concrete-filled square stainless steel columns based on acoustic emission and Markov chain methods

A test of concrete-filled square stainless steel (CFSST) columns with different eccentricities under compression was conducted to evaluate their failure and damage characteristics. Acoustic emission (AE) analysis was used to assess the damage process, and a damage prediction model based on the Markov chain was established. The monitoring results showed that the outward buckling was the dominant damage mode. As the eccentricity increased, the damage location changed from both sides of the column to the compressed side. The AE characteristic energy and b-value accurately described the damage process, which was divided into three stages: initial stability, cracking and buckling, and approaching failure. An analysis of the rise time/peak amplitude ratio (RA) and AE count/duration ratio (AF) indicated that tensile cracking was dominant in the three stages. A prediction model based on Markov chain was proposed to reflect state of CFSST columns, which could provide effective guidance in practical engineering.

Finite element, analytical, artificial neural network models for carbon fibre reinforced polymer confined concrete filled steel columns with elliptical cross sections

In the present era of architecture, different cross-sectional shapes of structural concrete elements have been utilized. However, this change in shape has a significant effect on load-carrying capacity. To restore this, the use of column confinements with elliptical sections has gained attention. This paper aim to investigate the effect of elliptical shape sections of confined concrete reinforced with Carbon Fiber Reinforced Polymer (CFRP) and steel tube on axial load-carrying capacity. This study is achieved using following tools Finite Element (FE) in Abaqus and Artificial Neural Networks (ANN) modeling. The study involved a 500-mm-high column with three sets of aspect ratios: 1.0, 1.5, and 2.0. In each aspect ratio, three different layers of CFRP were used, i.e., .167, .334, and .501-mm. Analytical results showed that with the increase in aspect ratio from 1 to 2, there is a decrease in ultimate axial load of about 23.2% on average. In addition, the combined confining pressure of steel tube and CFRP increases with a decrease in dilation angle as the number of CFRP layers increases. The failure mode for the column with a large aspect ratio is local buckling at its mid-height along the minor axis. The result showed a good correlation between FE and experimental results of ultimate stress and strains, with a mean squared error of 2.27 and .001, respectively. Moreover, ANN and analytical models showed a delightful correlation of R2 of .97 for stress models and .88 for strain models, respectively. The elliptical concrete section of the column confined with steel tubes can be adopted for a new architectural type of construction; however, with more than three aspect ratios, the wrapping of the section with CFRP jackets is highly recommended.

Innovative compressive design resistance and behaviour of concrete-filled short columns with stiffened square steel sections

The concrete-filled tubular steel columns with stiffened steel sections, abbreviated as CFSST, have lower sensitivity to local buckling and higher confinement of the concrete core than standard concrete-filled tubes. Herein, available test results for CFSST short columns with a single stiffener or multiple stiffeners are collected from the literature. They are analysed and then a new power law formula for the lateral confining pressure (frp) is proposed. After that, the results provided by the formula are verified by simulating the behaviour of the available test specimens using ABAQUS finite element (FE) software. The results of the test and FE analyses reveal that the proposed frp formula performs well and it is used further in the parametric studies on the strength and behaviour of CFSST columns, namely the effect of (i) the plate slenderness ratio, (ii) the steel yield strength, (iii) the concrete cylindrical strength and (iv) the number of stiffeners and their depth. Increasing the concrete cylindrical strength is found to provide the largest increase in the strength of the columns compared to other parameters, although it reduces the ductility of the columns. In addition, the resistance values for the CFSST columns are calculated on the basis of Japanese, British, European and Chinese structural standards for comparison with the values obtained numerically. Because these standards provide conservative predictions, an innovative design formula is suggested for CFSST columns based on the analytical expression developed for the lateral confining pressure. The new design formula yields much better predictions than the formulae in the existing structural standards.

Seismic performance of a ring–beam connecting concrete-filled steel columns with RC frames

The seismic performance of a ring–beam connection system to integrate concrete-filled steel tubular columns and reinforced concrete (RC) frames was studied. Physical experiments on two specimens were conducted under monotonic and cyclic loading. The results showed the connection system had a displacement ductility ratio of 4.68 and an energy dissipation coefficient over 2.0. A finite-element model was established and the numerical and experimental results were compared in terms of skeleton curves and stiffness degradation trends. Parametric studies were then performed to evaluate the effects of the axial compressive force ratio, concrete strength and reinforcement ratio of the ring–beam joint (RBJ) and the reinforcement ratio of the frame beam on the seismic performance of the proposed RBJ connection system. The results showed that an increase in the axial compression ratio or strength of the concrete material improved the initial stiffness and strength of the connection system. The effects of the RBJ reinforcement ratio and the frame beam reinforcement ratio on seismic performance were negligible.

Analysis of Concrete-filled Lean Duplex Stainless Steel Columns Using ANSYS

Abstract: The Lean Duplex Stainless Steel (LDSS) which is a category of stainless steel is becoming popular as a structural member because of its increased corrosion resistance and durability compared with that of steel. LDSS offers relatively cheaper cost (as compared to austenitic stainless steel), higher strength, acceptable weld ability, and fracture toughness properties, etc. When concrete is filled inside the stainless steel hollow section the load-carrying capacity of this section increases. The aim of this study is to understand the buckling behaviour of concrete-filled stainless steel columns of L, T, and + shaped cross-sections using ANSYS. The LDSS columns having equal material cross-sectional areas with varying thickness are analysed in the current study. This paper gains an understanding of different cross-sectional shape effects under varying thickness.

Experimental behavior of circular composite columns with different weld arrangements

Eighteen (18) circular short composite columns including 9 concrete-filled steel columns and 9 concrete-filled stainless steel columns, were experimentally studied in this paper. All composite columns have the same dimensions: D= 160 mm, H= 300 mm and t= 2 mm. The objective of this study is to shed light on the effect of the number and arrangement of lateral and longitudinal welds on the resistance and behavior of concrete-filled composite columns. Based on the results obtained, it was confirmed that weld joints have slight effect on the bearing capacity and instability modes of the studied composite columns. Lateral and longitudinal welds were very successful in conveying compression and bending efforts. The experimentally measured load-bearing capacities of the composite columns were compared to those predicted by Eurocode 4, AISC 360–16 and the equation proposed by Giakoumelis and Lam. All the results predicted by the AISC 360–16 code showed a good concordance with the experimental test results. However, the predictions calculated by the EC4 and the equation proposed by Giakoumelis and Lam were not conservative. This investigation shows that the use of lateral and longitudinal welds in composite columns applications would result in a reliable and economical design. This encourages designers to build their confidence in the use of this type of waste metal plates as structural components of locally produced materials.

Performance of rubberized concrete-filled hollow steel column under monotonic and cyclic loadings

Performance of rubberized concrete-filled hollow steel column under monotonic and cyclic loadings