Hollow Concrete-filled Steel Tube Research Articles

Experimental Investigation on the Axial Loading Performance of Grooving-Damaged Square Hollow Concrete-Filled Steel Tube Columns

Under the influence of material defects, structural grooving, environmental corrosion, and other factors in engineering, concrete-filled steel tubes incur local defects on their external surfaces that affect their structural integrity and service life. This work conducts axial compression tests on 10 grooving-damaged square hollow concrete-filled steel tube (SHCFST) columns to investigate the effect of grooving damage on their axial compressive ultimate bearing capacity and the effect of steel tubes on concrete confinement. It explores the effects of three parameters, namely, the length of grooves, presence of slots in internal and external steel tubes, and orientation of grooves, on structural static performance. This study analyzes the loading, failure mechanisms, and axial compressive ultimate bearing capacity of grooving-damaged SHCFST columns. Results indicate that grooving weakens the steel tube’s confinement effect on the concrete core, reducing the axial compressive ultimate bearing capacity of specimens. On the basis of this experimental research, a method for calculating the axial compressive ultimate bearing capacity and axial compressive stiffness of grooving-damaged SHCFST columns is proposed. The calculation results closely align with experimental outcomes, providing valuable insights for related scientific research and engineering applications.

Research on the Residual Bearing Capacity of Square Hollow Concrete-filled Steel Tube After Fire

In order to study the change of the residual bearing capacity of square hollow concrete-filled steel tube after fire, the finite element analysis software ABAQUS was used to establish the finite element model of square hollow concrete-filled steel tube under the ISO-834 standard fire heating condition, and the temperature distribution and deformation of the model were simulated and analyzed. Based on that, the influence of parameters such as the strength grade of concrete, the strength grade of steel, the calculated length of member and the hollow ratio of section on the residual bearing capacity of member after fire is simulated and analyzed. The results show that the temperature distribution of the component is mainly affected by the section size, concrete strength grade and steel yield strength, but is less affected by the calculated length. The temperature of the inner concrete and the inner steel tube decreases with the increase of the thickness of the member. The strength of steel and the size of section have more influence on the stress characteristics of the member after fire, but the strength grade of concrete and the length of the member have less influence. Among them, the increase of steel strength, concrete strength will enhance the fire-resistant limits of components. When the hollow ratio of the section increases, the fire resistance limit of the component increases first and then decreases. The increase of the calculated length will reduce the fire resistance limit of the member. The residual bearing capacity of the component decreases with the increase of fire time.

Performance of Prefabricated Hollow Concrete-Filled Steel Tube Bracings on Transverse Bending: Experimental and Numerical Analyses

Due to the complex hydrogeological conditions in coastal regions, the use of internal bracing systems is necessary for supporting coastal foundation pits. This paper introduces a novel prefabricated foundation pit bracing system based on Hollow Concrete-Filled Steel Tube (H-CFST) structures that can be reused, offering significant economic and societal benefits. However, there is a severe lack of research on the application of H-CFST bracing systems. Through model tests and finite element simulations, the load-displacement characteristics and failure modes of prefabricated H-CFST bracing under transverse bending were investigated. The study revealed that when a wall thickness of 1.5 d was chosen, the self-designed hoop effectively mitigated strength and stiffness reduction at the bracing connection point. When the load reached 150 kN, the outer steel tube of the H-CFST components experienced localized yielding, and when the load was increased to 300 kN, the end supports exhibited cracking. Finite element analysis provided a more accurate prediction of bracing failure at 147.18 kN, and it offered valuable insights for optimizing the bracing design. Based on the above research, theoretical methods for calculating the bearing capacity of each bracing component under transverse bending conditions have been proposed and validated against experimental results.

Performance of Hollow Concrete Filled Circular Steel Tube Column Subjected Axial Loading

To improve the behavior of hollow concrete filled steel tube, a novel type of reinforced hollow concrete circular steel tubular member (RHCFST) was put forward and its axial behavior was studied. The finite element analysis model of 12 RHCFST short columns under axial compression was established by using ABAQUS. The influence of steel tube’s strength and wall thickness, diameter of steel bar with normal strength, sandwich concrete’s thickness and strength on the mechanical properties of members were investigated. The results showed that the loading process can be defined as five stages: elastic, elastoplastic, descending, strengthen and gentle stage. The new composite structure has good cooperative performance. The ultimate bearing capacity increaseswith the increase of yield strength and wall thickness of steel tube, thickness and strength of sandwich concrete and diameter of steel bar with normal strength.

Experimental Study on Supporting Capacity of Hollow Reinforced Concrete Filled Steel Tube

Hollow reinforced concrete supported specimens with different slenderness ratio and steel content were designed and the load-displacement test was carried out. The load-displacement curve of hollow reinforced concrete filled steel tube supported showed no obvious decreasing section, and the curve remained almost unchanged or slightly decreased after reaching the ultimate load, with good ductility. The bearing capacity of the support increases with the decrease of hollow ratio. The heart rate decreases from 0.33 to 0.19, and the bearing capacity increases 2.037~2.28 times. The bearing capacity calculation formula of hollow reinforced concrete filled steel tube is derived, and the improved compressive strength calculation formula of hollow reinforced concrete filled steel tube is obtained by considering the stirrup action of the member and combining with the relevant test data. At the same time, using the stability coefficient formula obtained from the regression analysis, the stability bearing capacity calculation formula of hollow concrete filled steel tube axial compression medium long column is obtained.

Finite Element Analysis and Verification on Hollow Concrete Filled Double Steel Tube Short Columns Subjected to Axial Load

In order to study the axial compression behavior of hollow concrete filled double steel tube (HCFST) short columns, the finite element numerical simulation of five existing short columns under axial compression is carried out by ABAQUS. By choosing reasonable material constitutive model, the finite element model of this kind of short column is established, and the load-displacement curve of hollow concrete filled double steel tube short column is obtained by simulation analysis. Compared with the existing test results, the simulation data is in good agreement with the test results. The rationality and practicability of the finite element modeling method in this paper are verified. It also lays a theoretical foundation for the popularization and application of hollow concrete filled steel tube short columns in practical engineering.

A unified method for calculating fire resistance of solid and hollow concrete-filled steel tube columns based on average temperature

This paper presents a new method for calculating fire resistance of axially loaded Concrete-Filled Steel Tube (CFST) columns with different section profiles, including circular and polygonal sections that can be solid and hollow. The uniqueness of this new method is that the fire resistance is calculated on the basis of the average temperature of the columns’ cross-sections. This is done by taking the bearing capacity of a CFST column at room temperature as a special case of the bearing capacity of the same column at the start of a fire. The equivalent strength and equivalent elastic modulus in relation to the average temperature of steel and concrete are investigated, and a unified method of calculation is proposed, by which the calculation of fire resistance of a CFST column can be divided into two steps, i.e. (a) calculation of the equivalent strength and elastic modulus of steel and concrete at elevated temperature based on the average temperature, and (b) calculation of fire resistance using the formulas at room temperature by replacing the equivalent material strength and elastic modulus at elevated temperature. The two sets of formulas for calculating fire resistance of CFST columns are given by combining the unified method, respectively, with Eurocode 4 and the authors’ previous work. The proposed formulas and procedure are validated through comparisons with the experimental results of a number of solid and hollow CFST columns with circular and square sections.

A unified formulation for circle and polygon concrete-filled steel tube columns under axial compression

Current design practice of concrete-filled steel tube (CFST) columns uses different formulas for different section profiles to predict the axial load bearing capacity. It has always been a challenge and practically important issue for researchers and design engineers who want to find a unified formula that can be used in the design of the columns with various sections, including solid, hollow, circular and polygonal sections. This has been driven by modern design requirements for continuous optimization of structures in terms of not only the use of materials, but also the topology of structural components. This paper extends the authors’ previous work [1] on a unified formulation of the axial load bearing capacity for circular hollow and solid CFST columns to, now, including hollow and solid CFST columns with regular polygonal sections. This is done by taking a circular section as a special case of a polygonal one. Finally, a unified formula is proposed for calculating the axial load bearing capacity of solid and hollow CFST columns with either circular or polygonal sections. In addition, laboratory tests on hollow circular and square CFST long columns are reported. These results are useful addition to the very limited open literature on testing these columns, and are also as a part of the validation process of the proposed analytical formulas.

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...