Concrete Filled Steel Tube Elements Research Articles

Modelling and experimental studies of the stress-strain state of compressed concrete filled steel tube elements of a continuous section

Modern building structures must meet the requirements of efficiency and resource-saving. The main direction for implementing these requirements is to reduce the consumption of steel (14–16%) and save cement (10–12%). These tasks can be solved through the rational combination of concrete and steel when they work together and the use of high-strength materials. One embodiment of this task is the use of Concrete Filled Steel Tube (CFST) structures. The purpose of this study is to identify the possibility of using the Drucker-Prager model by comparing the results of test studies on short compressed Concrete Filled Steel Tube (CFST) elements with different strength and deformation characteristics of the concrete core to the results from finite element analysis (FEA) modelling of corresponding CFST elements. Additionally, the behaviour of a steel pipe without a concrete core was investigated. The results show that the FEA method used in this work is sufficiently accurate for studying the behaviours of short CFST elements. The modelling technique adopted in the study made it possible to consider the redistribution of stresses in the concrete and pipe dynamically. The stress distribution patterns inside the concrete during both linear and non-linear deformations of CFST elements, as well as the characteristics of the interaction between the concrete and pipe in the contact zone, have been revealed.

Hybrid simulation of bridges constructed with concrete-filled steel tube columns subjected to horizontal and vertical ground motions

This paper presents the application of multi-axis hybrid simulation for evaluating the seismic response of a rigid-frame bridge structure constructed with concrete-filled steel tube (CFST) columns subjected to combined horizontal and vertical ground motions. These types of bridges are believed to have superior seismic performance and better ability to withstand collapse when subjected to extreme multi-directional seismic loads. The case-study hybrid model was a 1:3 scaled bridge structure with three spans and double-column bents. The experimental element consisted of one CFST column while the rest of the bridge elements were modelled numerically in the computer. Two popular cross-section shapes of circular and square CFST columns were tested and compared. The structure was subjected to the horizontal (longitudinal) and vertical components of the Northridge ground motion with five increasing intensity levels to cover all scenarios ranging from frequent to very rare events during the lifecycle of the structure. A state-of-the-art hybrid testing facility, referred to as the multi axis substructure testing system, was used to simulate complex boundary effects on the physical specimen using mixed load/deformation modes. The bridge columns showed great levels of ductility and no sign of severe damage or loss of stability, while they were subjected to large axial force variations and lateral deformation demands during hybrid simulations. The superior seismic performance of CFST elements highlights their benefit in construction of more resilient bridges, particularly those with the vital roles in post-disaster operations.

Compressed Concrete Filled Steel Tube Elements with Confinement Reinforcement of Concrete Core

The purpose of this paper is to study the main features of power resistance of compressed concrete filled steel tube elements (CFSTE) with spiral reinforcement. The spiral reinforcement of a concrete core makes it possible to increase the load-bearing capacity of such structures significantly. Based on the results of performed experiments, the coefficient of indirect reinforcement efficiency among CFSTE with spiral reinforcement made 1.48 to 1.62, depending on initial concrete class. This coefficient was in the range from 1.23 to 1.33 in similar samples without spiral reinforcement. The experiments showed that a high efficiency of these structures is maintained when high-strength concrete is used in them.

Accounting for the Scale Factor in Determining the Compressed Concrete Strength of Concrete-Filled Steel Tube Elements

The published experimental data on the influence of the concrete samples dimensions on their strength under axial compression had been analyzed in the article. The mechanism of this influence is revealed from the positions of strength statistical theories. The known dependences are given and a new formula is proposed for taking into account the scale factor in determining the strength of compressed concrete. An algorithm for calculating the strength of centrally compressed concrete-filled steel tube elements (CFSTE) with a circular cross-section taking into account the scale factor is shown.

Strength of compressed concrete filled steel tube elements of circular and square cross- section

Strength of compressed concrete filled steel tube elements of circular and square cross- section

Strength of Axially Loaded Concrete Filled Steel Tube Elements of Self-Stressing Concrete

This work is dedicated to an experimental research of strength and resistance characteristics of axially loaded concrete filled steel tube elements of self-stressing concrete, including high-performance concrete. Labcrete specimens of circular section 112 mm in diameter and 1000 mm in length were used in experiments. The research shows that the use of self-stressing concrete increased the strength of the specimens by approximately 10%, and enhanced elastic behavior limit by 20-33%. In the course of testing self-stressing concrete specimens, registered longitudinal deformations were within 0.52-0.75%. Analysis of the obtained results indicates a significantly greater case effect in the pre-stressed specimens. This effect is somewhat less pronounced in high-performance concrete specimens, yet still prominent.

Compressed Concrete-Filled Steel Tube Elements with Indirect Reinforcement of the Concrete Core

The purpose hereof is to study the specifics of the force resistance and to experimentally identify the reinforcement effect of short square-section concrete-filled steel tube elements (CFSTE) with spiral reinforcement. Analysis of the laboratory samples of concrete-filled steel tube columns shows that spiral reinforcement makes them stronger by 18÷43% depending on the source concrete class. Maximum recorded longitudinal deformation in spiral-reinforced samples is 1.7÷2 times larger. Using a relatively small amount of spiral reinforcement (about 1%) has resulted in a mean 23% stronger reinforcement effect in the studied structures. Such structures remain efficient when using high-strength concrete.

Strength of compressed concrete filled steel tube elements of circular and square cross- section

The purpose of the research is to determine the values of compressive force eccentricities at which the strength of square-sectioned compressed concrete filled steel tube elements (CCSTEs) is not lower than that of circular-sectioned elements that are similar in materials consumption. Strength calculations are carried out using a specially developed “CFST” computer program. The reliability of calculations, obtained with this program, is pre- verified basing on the calculation data, related to 203 circular-sectioned CCSTEs and 264 square-sectioned elements. The results of the calculations demonstrate that, given eccentric compression, where eccentricities are slightly outside the bounds of the core of section, the CCSTE strength criterion should not significantly influence the selection of their geometric shape. Based on this criterion, when relative eccentricities exceed 0.2-0.25, the preference should be given to the elements with a square cross-section. Moreover, the area of rational use of square-sectioned CCSTEs is extended with the increase in structural flexibility.

Compressed Concrete Filled Steel Tube Elements of Annular Cross-Section

The problem of determining the strength of a short centrally compressed concrete-filled steel tube element of annular cross-section is considered. The corresponding calculation procedure is proposed. The procedure is based on the theoretical positions of the mechanics of solids and it implements the method of limiting forces. It considers the complex stress state of the concrete core and steel shell as well as nonuniform distribution of transversal stresses over the cross-section of the calculated element. If there is high-strength reinforcement in the concrete, the stress in it is calculated considering the increased deformability of the concrete. The dependences for determining the initial modulus of elasticity of concrete as well as ultimate relative strains of uniaxially compressed and volumetrically compressed concrete are presented. The proposed procedure is applicable to structures made of different concrete types and steel classes.

Experimental Performance Studies of Improving Compressed Concrete Filled Steel Tube Elements of Square Section

Abstract The objective of the present work is improving compressed concrete filled steel tube elements of square section by means of helical reinforcement of a concrete core. Conducted experimental studies of centrically and eccentrically compressed laboratory samples of such elements have shown that in comparison with similar samples without helical reinforcement their durability ha increased by 31÷42%. Values of longitudinal sample deformation fixed at maximum with helical reinforcement made of C25 concrete class have increased almost 3 times. Maximum longitudinal sample deformation made of C50 concrete class were inferior by 20%. Increase in durability and deformability of improved samples is explained by increase in performance of placing of shear reinforcement that is ensured by helical reinforcement. Confining element ration at central compression was equal to 1.36÷1.9, at eccentrical compression with eccentricity ratio of 0.107 it was 1.28÷1.35, and at eccentricity ratio of 0.214 -1.15÷1.26. High durability and deformability ensure greater tenacity of such structure that makes them attractive for usage in buildings and constructions in areas with increased seismic activity. The revealed features of strength resistance of concrete filled steel tube elements with square section will be used when developing an algorithm and a computer program for the automated calculation of their bearing capacity.

Seismic performance of composite moment-resisting frames achieved with sustainable CFST members

The main objective of the research presented in this paper is to study the bending behaviour of Concrete Filled Steel Tube (CFST) columns made with Rubberized Concrete (RuC), and to assess the seismic performance of moment-resisting frames with these structural members. The paper describes an experimental campaign where a total of 36 specimens were tested, resorting to a novel testing setup, aimed at reducing both the preparation time and cost of the test specimens. Different geometrical and material parameters were considered, namely cross-section type, cross-section slenderness, aggregate replacement ratio, axial load level and lateral loading type. The members were tested under both monotonic and cyclic lateral loading, with different levels of applied axial loading. The test results show that the bending behaviour of CFST elements is highly dependent on the steel tube properties and that the type of infill does not have a significant influence on the flexural behaviour of the member. It is also found that Eurocode 4 is conservative in predicting the flexural capacity of the tested specimens. Additionally, it was found that the seismic design of composite momentresisting frames with CFST columns, according to Eurocode 8, not only leads to lighter design solutions but also to enhanced seismic performance in comparison to steel frames.

Limit Wind Loads of a Concrete Filled Steel-Tube Transmission Tower

Limit wind loads of a Concrete Filled Steel-Tube (CFST) transmission tower in a long-span tower-line system is computed. Firstly, fine Finite Element Method (FEM) model of the tower and its Multiple-Degrees-Of-Freedom (MDOF) model are built and the material nonlinear models including steel-tube and CFST are also modeled. Secondly, based on MDOF model, mean displacements under mean wind force are evaluated and the Root Mean Square Displacement (RMSD) under fluctuating wind force is also evaluated by random vibration theory. Then, Equivalent Static Wind Loads (ESWL) are computed considering the first three order modes. Finally, based on FEM model, the nodes are loaded by the ESWL and the nodal loads increase step by step in order to impel materials into plastic status until calculation can not converge. Plastic analysis shows the tower’s failure is caused by steel-tube element failure and the CFST elements have enough strength reserve. The tower’s three kinds of limit wind loads are computed based on different references and it is suggested to select the limit wind loads, whose corresponding wind velocity is 69.7m/s, as the design limit wind loads of the tower.

BEHAVIOUR OF HOLLOW CONCRETE‐FILLED STEEL TUBULAR COMPOSITE ELEMENTS

Behaviour of composite steel‐concrete elements in various loading stages is quite well analysed by theoretical investigations and experiments. Concrete‐Filled Steel Tube (CFST) is one of many composite elements used at present in civil engineering. Different approaches and design philosophies were adopted in different design codes for it. But for hollow CFST elements, which are more effective than ordinary CFST, any code does not provide information about how to design these elements. Further investigations of hollow composite CFST elements are needed. In loading stage, when a particular level of stresses exists, an interaction between steel tube and concrete core appears and therefore a complex stress state of element takes place, which increases the load‐bearing capacity of the whole composite element. This interaction between components of CFST elements is reached because of different material properties, such as Poisson's ratio, elasticity modulus etc. In this article reasons of the above‐mentioned complex stress state appearance and behaviour of hollow CFST element components in different load stages of compressed stub structural member are analysed. The test results are presented in diagrams, tables. Previous researches of other investigators are summarised. Differences and similarities in behaviour of solid concrete and composite elements and hollow members with different number of concrete core layers are discussed.

Behaviour of hollow concrete‐filled steel tubular composite elements

Abstract Behaviour of composite steel‐concrete elements in various loading stages is quite well analysed by theoretical investigations and experiments. Concrete‐Filled Steel Tube (CFST) is one of many composite elements used at present in civil engineering. Different approaches and design philosophies were adopted in different design codes for it. But for hollow CFST elements, which are more effective than ordinary CFST, any code does not provide information about how to design these elements. Further investigations of hollow composite CFST elements are needed. In loading stage, when a particular level of stresses exists, an interaction between steel tube and concrete core appears and therefore a complex stress state of element takes place, which increases the load‐bearing capacity of the whole composite element. This interaction between components of CFST elements is reached because of different material properties, such as Poisson's ratio, elasticity modulus etc. In this article reasons of the above‐men...