Composite Tubular Columns Research Articles

Bearing Behavior of Engineered Cementitious Composite and Ultra-High-Performance Concrete Filled-In Double Steel Tubular Composite Columns Subjected to Eccentrical Load

To study the eccentric compression mechanical properties of ECC and UHPC filled-in double steel tubular (EUFDST) composite columns, 35 full-scale EUCFDST composite column specimens were designed by ABAQUS software with the slenderness ratio (λ), UHPC cylinder compressive strength (fcu), inner and outer steel tubular strength (fy1, fy2), inner and outer steel tubular thickness (t1, t2), inner and outer steel tubular diameter ratio (Ω), eccentricity (e), and fiber content (γ) as the main parameters. By comparison with the simulation of the existing test, the correctness of the finite element modeling is verified. The parameter analysis of 35 full-scale EUFDST composite columns was carried out to obtain the eccentric load-mid-span deflection curve of the specimens. The failure mechanism, ductility coefficient, and stiffness degradation of the composite columns under different parameters were analyzed, and the section of the composite column was verified to satisfy the plane section assumption. The variation trend of maximum load-bearing capacity and the ductility of composite columns under different parameter conditions was obtained. By introducing the eccentricity correction coefficient and slenderness ratio correction coefficient, the calculation equation of the eccentric maximum load-bearing capacity of EUCFDST composite columns is statistically regressed, which provides a basis for the practical use of these columns.

Experimental and numerical investigation of the seismic performance of concrete-filled steel tubular composite columns with UHPC plates

To study the seismic performance of concrete-filled steel tubular composite columns with UHPC plates. The pseudo-static tests were carried out on five specimens with the longitudinal distance of the column limbs and thickness of the UHPC plates as test parameters. Subsequently, a nonlinear finite element model of such composite columns was established based on OpenSees, and the calculation method of lateral bearing capacity of the specimen under compression-bending load was proposed. The results showed that the longitudinal distance of the column limbs significantly influenced the lateral bearing capacity as well as the initial stiffness of the specimens. The longitudinal distance of column limbs was increased from 250 mm to 650 mm, and the lateral bearing capacity as well as the initial stiffness of the specimens were increased by 246.0 % and 488.5 %, respectively. The thickness of the UHPC plate was increased from 50 mm to 100 mm, the lateral bearing capacity of the specimen was increased by 32.2 %, while the cumulative hysteretic energy consumption was reduced by 45.05 %. Keeping the same axial pressure ratio, the initial stresses in the column limb steel tubes of the concrete-filled steel tubular composite columns with UHPC plates specimens were higher compared to those of the concrete-filled steel tubular composite columns with ordinary reinforced concrete plates specimens, resulting in poorer ductility. The established nonlinear numerical model accurately captured the hysteretic performance of the specimen. Moreover, the proposed lateral bearing capacity calculation method has high accuracy and can predict the lateral bearing capacity of such structures well.

Seismic performance of concrete-filled steel tubular composite columns with ultra high performance concrete plates

Two 1:8 scale specimens were designed and created to examine the seismic performance of concrete-filled steel tubular (CFST) composite columns with ultra high performance concrete (UHPC) plates. Ground motion characteristics, axial pressure ratio, plate material, and mainshock-aftershock sequences were used as parameters in the pseudo-dynamic test study. The results show that the ground motion characteristics have a significant effect on the seismic response of the specimen; The initial stiffness of the specimens is mostly unaffected by the axial pressure ratio. Furthermore, the larger the axial pressure ratio, the earlier the specimen enters yielding and the more severe the final failure phenomenon; After UHPC was used in place of the plate material, the specimen's initial stiffness rose by about 13.7%, the stiffness degradation of the specimen was somewhat delayed, and the hysteretic energy dissipation increased by about 41.2%.; The specimen undergoes elastic, elastoplastic, and plastic failure stages under the aftershocks of increasing intensity. Under the mainshock-aftershock sequences of the same intensity, the seismic response of the specimens under the aftershock was not much different compared to the mainshock, and the hysteretic energy dissipation was about 67.7% and 74.5% of the mainshock respectively. These structures can withstand multiple earthquakes and have demonstrated good seismic performance.

Optimum design of steel columns filled with concrete via genetic algorithm: environmental impact and cost analysis

The use of concrete-filled tubular columns as part of structural systems has steadily increased throughout the years. The growing demand for structural elements of this nature is a direct result of the possibility to use various cross-section shapes that have increased strength, along with resistance to fire and other corrosive agents. The main objective of this article is to present the formulation for optimizing the design of composite columns in accordance with prescriptions from ABNT NBR 16239: 2013, considering financial cost and CO2 emission during manufacturing as objective functions. A Genetic Algorithm was used to solve three examples of composite tubular columns subjected to combined bending and compression, considering major axis and unsymmetrical bending. The financial cost in Brazilian currency and the CO2 emission in kilograms attributed to manufacturing concrete-filled composite columns were calculated and the optimization procedure was implemented on composite columns featuring CHS, RHS and SHS steel members. This study also considers the different concrete strengths and the optional inclusion of longitudinal rebar. For the cases analyzed, the financially and environmentally optimum design corresponds to a CHS composite column with no longitudinal rebar and the highest concrete strength tested, except when unsymmetrical bending is applied, in which case the optimum solution includes longitudinal rebar. Furthermore, results indicate that structural steel has the highest impact on the CO2 emission of the optimal designs. For the column with longitudinal rebar, the reinforcement steel presents the second highest financial impact, while concrete is responsible for the highest influence on CO2 emission.

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.

Applicability of new regression model for determining axial load capacity of concrete filled double steel tubular composite columns

Using various composite materials and components as a replacement for conventional materials and components has various structural benefits in the construction field. Concrete Filled Double Steel Tubular Composite Columns (CFDST) are composite components consisting of two concentric metal (steel) tubes and a gap between them filled with concrete. These are composed of three constituent materials that exhibit higher structural performance than constituent materials. This study aims to propose a new regression model for determining the axial load capacity of CFDST columns. For this purpose, one twenty-four data collected from various experimental studies referred to literature. The model represented here was developed using the statistical tool Minitab. Length, yield strengths, diameters and thicknesses of both external and internal tubes of CFDST columns, compressive strength of in-filled concrete and experimental ultimate axial strength of CFDST columns are considered for model development. The model's applicability is confirmed when the developed model's results are compared to earlier researchers' models and the equations provided in the design guidelines. The suggested model achieves an R2 value close to one hundred percent and ultimate axial load capacity estimation with the least error.

Eccentric compression behavior of FRP-concrete-steel tubular composite columns

FRP-concrete-steel tubular (FCS) composite columns are composed of the external tube, the internal steel tube, and the concrete between both tubes. They have been attracting the attention of many researchers due to their high ductility, lightweight, resistance to corrosion, and easiness of construction. However, there are few studies on FRP-concrete-steel tubular composite columns under eccentric load. To investigate the behavior of composite columns under the eccentric compression, a non-linear analysis program for FCS composite columns was compiled. The program was verified by existing tests, and the influences of eccentricity, FRP tube wall thickness, steel tube wall thickness, steel tube radius, slenderness ratio, and concrete strength grade on the eccentric compression performance were systematically analyzed. The results showed that the calculated results were in good agreement with the experimental results. It showed that the program can accurately reflect the deformation of FCS composite columns under various loads and estimate the ultimate load of FCS composite columns under eccentric compression. The eccentric ultimate load increased with the decrease of eccentricity and slenderness ratio, and with the increase of FRP tube wall thickness, steel tube wall thickness, and concrete strength grade. The ultimate eccentric load decreased with the increase of steel tube radius, but when the steel tube wall thickness reached a certain thickness, the ultimate eccentric load of FCS composite columns increases with the increase of steel tube radius. The conclusion can provide reference for the practical application of the structure.

Research on concrete-filled stainless steel tubular composite columns

Concrete-filled stainless steel tubular composite columns are used in the structures. It is important to define the structural behaviour of this type of columns. This paper presents experimental and theoretical studies of eccentrically loaded concrete-filled stainless steel tubular composite columns. The column specimens were manufactured with high strength outer stainless steel tube, in-filled concrete and inner carbon structural steel. The tubular composite column specimens were designed with plain concrete and steel fiber reinforced concrete. The column specimens were tested and the experimental load–deflection curves of columns were presented in the study. In addition, the tested plain and steel fiber concrete-filled stainless steel tube composite columns were analysed based on a theoretical method for the prediction of strength and load–deflection behaviour. It was observed that the tested tubular column specimens behaved in a ductile manner. A good degree of agreement was obtained between the experimental and theoretical load–deflection curves of concrete-filled stainless steel tubular composite columns. In addition, a parametric study was carried out to examine the influences of loading eccentricity, slenderness, plate slenderness and the concrete compressive strength on concrete-filled stainless steel tubular composite column behaviour. It was concluded from the parametric study that the strength of columns increased by increasing stainless steel wall thickness and concrete compressive strength. However, column strength decreased when the eccentricity and column length were increased.

Experimental Verification on Finite Element Model of Composite Columns with Concrete Filled Steel Tube Flange

In order to study mechanical performance of composite columns with concrete-filled steel tube flange subjected to the eccentric compression, the finite element model of this kind of composite columns is established by using ABAQUS finite element software. In this paper, the reasonable material constitutive and finite element modelling method are selected to carry out numerical simulation analysis of concrete-filled steel tubular composite columns and concrete-filled square steel tubular columns. The load vertical displacement curves, load lateral deflection curves and failure modes are obtained, which are in good agreement with the existing test data. The rationality of material constitutive and finite element modelling is verified, which lays a foundation for further establishing the calculation formula of eccentric compression bearing capacity of this kind of column.

Flexural behavior of a novel high-strength RCFST column-to-column connection

Brittle fracture is one of the principal disincentives to limit the use of ultrahigh-strength steels in tall buildings. This paper proposes a novel column-to-column connection without full penetration welding in reinforced concrete-filled steel tubular composite columns. The paper describes an experimental investigation into the flexural behavior of the proposed RCFST column-to-column connection, in which the steel was manufactured using ultrahigh-strength steel grades H-SA700 and USD 685. Four specimens with varying configurations of reinforcing steel bars (separated type or gathered type) and column shapes (square or circular) were tested under four-point bending to evaluate the failure modes, flexural capacity, and deformation capacity. The results show that the gathered type of configuration of reinforcing steel bars can effectively improve the flexural capacities while having a negligible effect on the strain distribution of steel tubes or steel bars. Besides, the column type was found to significantly influence the strain distribution of the steel tube. The design formulae show accuracy and reliability and could be applied to assess the yield and ultimate strength of the proposed new connections.

Load transfer mechanism of an unwelded, unbolted, grouted connection for prefabricated square tubular columns under axial loads

This study develops a novel unwelded, unbolted, ultrahigh-performance fibre-reinforced concrete (UHPFRC) grouted connection for prefabricated square tubular composite columns. Herein, eight full-scale columns with UHPFRC grouted connections are tested to investigate their ultimate tensile and compressive resistance. The test results show that the novel connections exhibit good tensile and compressive resistance and structural stiffness. The primary failure modes are punching shear of the end plate, welding fracture at the inner tube, tube yielding and local buckling of the steel tube. The test specimens are simulated using finite element (FE) analysis in ABAQUS. The experimental and simulated results are in good agreement, indicating that the FE simulations can capture the observed failure modes and ultimate tensile and compressive resistance. Thereafter, existing analytical design formulas are evaluated to assess their suitability to predict the compressive and tensile resistance of prefabricated tubes with/without the novel grouted connections. A good agreement between the formula predictions and the test results are observed. These analytical formulas have the potential to be used in the design of the novel unwelded, unbolted, UHPFRC grouted connections for prefabricated steel, reinforced concrete and steel–concrete composite columns.

Concrete filled FRP–PVC tubular columns used in the construction sector: A review

In recent years, fber-reinforced polymer-polyvinyl chloride (FRP-PVC) tubular columns have been used increasingly in civil engineering applications. Concrete-flled RP-PVC tubes possess high durability, high strengthening performance, satisfactory bond strength, and compressive behavior. It has been observed that these cost-effective tubular columns are promising materials for enhancing strain capacities, strength, and stiffness of structures containing reinforced concrete (RC). These composite tubular columns are composed of FRP and PVC and are used for strengthening concrete. FRP enhances strength capacity while PVC improves the corrosion resistance of concrete piles in harsh environments. This review focuses on the properties of FRP-PVC tubular columns, their application in civil engineering, and the recent advancements in this feld.

An innovative concrete-steel structural system for long-span structure allowing a fast and simple erection

In achieving medium-to-long span slab, steel-concrete composite beams may offer an alternative over pre-stressed beams for the so-called disadvantages of the latter; for example the heavy weight of pre-stressed beams makes their handling expansive. However, the use of composite beams by concrete builders is still limited due to the lack of specific tools and skills for on-site erections and the need for a supplementary fire protection. This article presents an innovative steel-concrete moment resisting portal frame that overcomes these difficulties. It is composed of composite tubular columns, and a composite beam made of a U-shape steel profile used as permanent formwork to encase a concrete beam. The steel-concrete duality of the proposed beam allows an erection on site without any weld or bolt by a wise positioning of the construction joints. As only steel elements have to be handled on site, there is no need of heavy cranes. This system has been used to build a research center near Rennes, in France. As it is not covered in present norms, an experimental validation was required. In this paper, a series of full-scale experimental tests that have been performed in order to assess the global and the local behaviour of the frame and its connections are presented. A series of asymmetrical push-out tests were carried out in order to determine the ductility and resistance of shear connectors; one 4-point bending test was made to investigate the resistance under sagging bending moment; and, two tests of the beam-to-column joint were performed in order to validate a strut and tie design model of the joint. Finite element simulations have also been made in order to acquire more information for the development of the analytical models.

Seismic Behavior of Column-Beam Joints with Concrete-Filled Glass Fiber Reinforced Polymer Tubular Composite Columns

Seismic Behavior of Column-Beam Joints with Concrete-Filled Glass Fiber Reinforced Polymer Tubular Composite Columns

Structural performance of CFRP-strengthened concrete-filled stainless steel tubular short columns

The use of concrete-filled stainless steel tubular (CFSST) members is relatively innovative and new. CFSST columns can be used for bridge piers, multi-story buildings and other supporting structures. However, a common mode of failure with these type of tubular composite columns is inelastic outward local buckling occurring at the column ends. Therefore, this paper presents the results of experimental, numerical and analytical investigations into the behavior of circular CFSST columns strengthened by carbon fiber reinforced polymer (CFRP) wrap and subjected to axial compression loading. The experimental investigation comprised three series of tests. The main variables tested were the diameter to thickness ratio of the stainless steel tube and the thickness of the CFRP wrap. 3D finite element models (FEMs) were developed for CFRP-wrapped CFSST columns using the ABAQUS software and were validated with experimental results. An extensive parametric study was carried out by using the validated FEMs. It was shown from the experimental and FEMs results that CFRP jacketing was highly effective in improving the axial load carrying capacity and axial shortening capacity of the CFSST columns. Finally, an analytical model based on the FE parametric study results was proposed to predict the axial load carrying capacity of the CFRP-wrapped CFSST columns.

Experimental Comparison for Flexural Behavior of Concrete Filled Tubular and Double-Skinned Composite Tubular Columns

Experimental Comparison for Flexural Behavior of Concrete Filled Tubular and Double-Skinned Composite Tubular Columns

10.14: Fire design method for eccentrically loaded concrete‐filled steel tubular columns based on interaction diagrams

ABSTRACTIn this paper, a simplified design method for evaluating the fire resistance of eccentrically loaded concrete filled steel tubular (CFST) columns is presented. The developed method is based on the results of an extensive parametric analysis conducted in the framework of the RFCS European Project FRISCC (Fire resistance of innovative and slender concrete filled tubular composite columns) and is currently being evaluated by the Working Group SC4.T4 for its approval as the method to replace the current Annex H in EN1994‐1‐2, which was proved in previous investigations to be unsafe for slender columns.The method presented in this paper is based on the provisions of Clause 6.7.3.6 of EN 1994‐1‐1 for room temperature design, using bending moment – axial force interaction curves specially built up for the fire situation. These interaction curves are obtained by considering several possible positions of the plastic neutral axis within the cross‐section, and determining the internal forces and moments from the plastic stress blocks, which results particularly challenging for CFST sections subjected to elevated temperatures, given the thermal gradient that occurs within the cross‐section. For simplifying this process, equivalent temperatures are proposed, which allow using a single uniform temperature for representing each part of the composite section. Appropriate coefficients are also proposed for evaluating the effective flexural stiffness for second‐order analysis at elevated temperatures. The influence of the cross‐section shape, load eccentricity and percentage of reinforcement is accounted for in the proposal.

Fire response of restrained composite columns made with concrete filled hollow sections under different end-support conditions

The fire behaviour of composite columns made with concrete filled hollow sections under different structural boundary conditions was experimentally investigated and their results are presented and discussed in this paper. The main objectives of this research were therefore to investigate the influence of the section geometry, slenderness, section factor, boundary conditions, and stiffness of the surrounding structure to the thermal elongation of the columns on the structural performance of such columns exposed to fire. The critical time (fire resistance), the failure temperature distribution and the respective failure modes of the columns were then assessed. These experimental results were still compared with predictions from the currently European design rules (EN 1994-1-2:2005) in order to observe how unsafe they might be. Finally, results of this research study showed that circular composite tubular columns presented an enhanced fire performance, comparing to other sections (square and rectangular sections for instance). As the difference between the principal moments of inertia for the cross-section of a column increases, the effect of the boundary conditions in their fire resistance increases.

Evaluation on thermal behavior of concrete-filled steel tubular columns based on modified finite difference method

This article presents a modified finite difference method specific for predicting temperatures in concrete-filled steel tubular composite columns. The modifications were based on existing researches on heat transfer analyses of composite columns by finite difference method. The temperature predictions by the modified method were implemented via MATLAB. Validity was established by comparing the predicted temperatures with test results and those obtained from finite element analyses via ABAQUS. The comparisons showed reasonable predictions by the modified finite difference method. Sensitivity studies were also carried out on the effects of emissivity of fire, thermal contact resistance, thermal property model, and cavity ratio based on the modified method. Through the implementation with MATLAB, it is attractive to calculate fire resistance of the concrete-filled steel tubular columns by combining the modified method with the simple calculation models according to Eurocode 4.

Fire resistance of double-skinned composite tubular columns including concrete confinement

Double-skinned composite tubular (DSCT) columns consisting of concrete cast between outer and inner tubes have been developed to overcome certain limitations of other columns, such as the large self-weight of concrete-filled tubular columns and lack of concrete confinement of hollow concrete-filled tubular columns. The strength and ductility of the column are enhanced by the continuous confining stress provided by the inner tube. Their excellent structural performances make them particularly suitable for applications in high-rise buildings. However, if a high-rise building is damaged by fire, the economic costs associated with building repair can be high. It is very important to put the fire-damaged building back into service with the minimum post-fire repair. Thus, to predict the status of a structure under fire, its behavior should be evaluated based on the fire duration. Studies on the fire resistance of DSCT columns have been carried out for this purpose. However, they have involved the performance of the entire system without considering the effects of the DSCT column’s components on the fire resistance. In this paper, the behavior of a DSCT column is investigated under an ISO-834 standard fire using an analytical method. The evaluation method for the fire resistance of a DSCT column utilizes a thermal analysis and Eurocode. In addition, the relationship between the DSCT column’s components and the fire resistance is investigated, considering the confining effect. Moreover, the behavior of the DSCT column is evaluated through parametric studies of the hollow ratio, thickness of the outer tube, and thickness of the inner tube.