Concrete-filled Steel Columns Research Articles

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

A study on self-curing self-compacting concrete filled steel columns subjected to axial compression

For vehicle parking areas, in multi-storey buildings and bridge piers, composite tubular columns have been considered as a better solution. The cold-formed steel and concrete combination is notable, because of the benefits of inherent material properties of both the materials. Concrete filled tubular (CFT) columns is in-filled with concrete having single tubes or concentric double tubes leaving the core as hollow. Moreover, for the design of such composite columns a specific design code is yet to be released in India. Henceforth, this experimental research intends to study the structural behaviour of CFT columns, consisting steel tube in terms of load- deflection graph, ultimate load carrying capacity, confinement of concrete and ductility. The structural use of a unique Self-Curing and Self-Compacting Concrete (SCSCC) using 10% granite saw dust waste and 25% fly ash as partial replacement to cement was confirmed. The experimental results are compared with computer modelling analysis done using ABAQUS for a better understanding of the column specimen's behaviour. Based on experimental studies percentage of super plasticizer and Super Absorbent Polymer (SAP) is determined as 1.3% & 0.3% respectively. The variation between experimental and analytical results is minimum and is due to minor material defects in steel sections. In this present experimental study three different cross sections namely: (i) cylindrical (ii) rectangular and (iii) square cross sections with 500 mm length and 2 mm thickness was used. Secondly a parametric study was conducted for 3 different lengths and 3 thickness which also showed that the performance of square cross sections was effective irrespective of the lengths. The load carrying capability of columns with increased steel section thickness is seen to be greater for the same length of column. When compared to cylindrical sections, rectangular and square sections show a significant reduction in load carrying capability as the thickness of the steel section is reduced. These changes in load carrying capacity are mainly due to the shape factor. The main advantage of the CFST column is that it has a better ultimate strength than a regular column due to the concrete confinement. This increased strength due to confinement is higher in cylindrical specimens.

Optimized design of concrete-filled steel columns

Abstract The objective of this paper is to present the formulation of the optimization problem and its application to the design of concrete-filled composite columns with and without reinforcement steel bars, according to recommendations from NBR 8800:2008, NBR 16239:2013 and EN 1994-1-1:2004. A comparative analysis between the aforementioned standards is performed for various geometries considering cost, efficiency and materials in order to verify which parameters influence the solution of the composite column that satisfies the proposed problems. The solution of the optimization problem is obtained by using the genetic algorithm method featured in MATLAB’s guide toolbox. For the examples analyzed, results show that concretes with compressive strength greater than 50MPa directly influence the solution of the problem regarding cost and resistance to normal forces.

Short columns composed of concrete-filled steel tubes in a fire situation – Numerical model and the “air-gap” effect

Abstract The increase in temperature reduces the strength of steel and concrete, in such a way that it is essential to verify concrete-filled steel tube columns in fire situations. Numerical simulations, with lower costs than laboratory tests, have great importance in checking resistance and defining simplified methods for design practice. However, peculiarities of the thermal and mechanical behavior of heated confined concrete and the air-gap effect (a phenomenon inherent to concrete-filled steel columns) must still be better understood. Therefore, this study presents the development of a numerical model performed in the ABAQUS software (Dassault Systemes SIMULIA Corp., 2014) for the thermomechanical analysis of short columns composed of circular and square concrete-filled steel tubes considering the air-gap effect. The air-gap phenomenon is presented and analyzed according to possibilities of implementation to the numerical model and, finally, the proposed numerical model is validated with experimental results presented in the literature. According to the study results, the numerical model can be used to define and adjust simplified methods for verification of composite columns in fire situation. The importance of considering the air-gap effect in numerical modeling was confirmed, taking into account that disregarding its effect may result in overestimated responses of the steel tube resistance in fire situations. Moreover, it was suggested thermomechanical joint analysis and the use of the explicit solver as a strategy to minimize processing time.

Lateral Impact Response of Elliptical Hollow and Partially Concrete-Filled Cold-Formed Steel Columns Under Static Axial Compression Load

In recent years, the use of partially concrete-filled steel tubular (PCFST) columns has been considered due to their cost-effectiveness and reduction of structural weight in bridge piers and building columns. One of the critical discussions about these columns is their impact resistance. In this article, the dynamic response of hollow and PCFST columns with elliptical cross-section under simultaneous loading of static axial compressive load and lateral impact load is presented using finite element modeling in ABAQUS software (FEA). To ensure the accuracy of the numerical modeling, the analysis results are compared with the results of previous works. The effects of different parameters such as impact velocity, the height of the impact location, the impact direction, the impact block mass, the size and shape of the impact block are investigated in this paper. The results of the numerical analysis showed that the partially filled specimens had better performance than the hollow specimens. The changes in impact direction and impact block mass parameters have a significant effect on the failure of the columns, especially when they are under high impact velocity. Changing the impact velocity significantly affects the impact resistance of specimens. However, the size and shape of the impact block did not have a significant effect on the displacement of the column against the impact loading.

Impact behavior of concrete-filled steel tube with cruciform reinforcing steel under lateral impact load

The objectives of this research are to investigate the behavior of cruciform steel-reinforced concrete-filled steel columns under impact load through experimental and numerical studies. The effects of impact velocity/height, axial pressure, thickness of steel tube and boundary conditions on the impact resistance of composite columns are studied through the tests of 16 specimens. The detailed progressive responses were recorded, including deformation mode, impact force-time history, deflection-time history and axial force-time history. Based on the test results, the impact resistances of steel-reinforced concrete-filled steel tubular columns and concrete-filled square steel tubular (CFST) columns are compared. In addition, FE models of the composite column are established using ABAQUS and validated based on experimental data. The strain rate effect of steel and concrete is considered in the model. The results show that the outer square steel tube effectively protects the internal steel-reinforced concrete. In the impact energy range of 17.02–51.08 kJ, the specimens only suffer minor bending deformation, which shows their excellent impact resistance. The ultimate plastic strain energy of square steel tube (EPT), cruciform steel section (EPS) and concrete (EPC) accounts for 56.4%, 18.2% and 25.4% of the total energy dissipation, which suggests that the steel tube (EPT) is the main energy dissipation mechanism of concrete-filled square steel tube columns.

Impact of Temperature Rise on the Seismic Performance of Concrete-Filled Double Skin Steel Columns with Prismatic Geometry

Abstract This paper studies the impact of temperature rise on the performance of Concrete-Filled Double Skin Tubular Steel Columns with prismatic geometry. In doing so, several columns whose interior cores were square, diamond, and circularly shaped and whose exterior cores were prismatic with a square cross-sectional area that increases with the slope of 2.1 degrees from top to the bottom, were constructed and exposed to the temperatures of 25°C, 250°C, 500°C, and 700°C. Afterward, all column specimens were subjected to cyclic loads adopted from the Applied Technology Council (ATC)-24 loading protocol, which proceeded until the specimens failed to further carry loads. The results indicate that although the failure modes of the columns with an interior core of a square or diamond shape are similar to each other, the columns whose interior cores were circularly shaped experienced more intensive damages compared to the others. The base of the columns was fractured diagonally with a degree of 45 by the temperature of 500°C, but at 700°C, the damages have occurred horizontally at the height of 10 cm from the column base. Moreover, the initial stiffness and ductility ratio of the columns with a diamond-shaped interior core was approximately two times greater than the other columns.