Circular Steel Tubular Columns Research Articles

Ultra-high strength circular short CFST columns: Axisymmetric analysis, behaviour and design

A nonlinear axisymmetric simulation of axially loaded ultra-high strength circular short Concrete-Filled Steel Tubular (CFST) columns is reported in this paper. An efficient material law of Ultra-High Strength Concrete (UHSC) is employed in this axisymmetric simulation to consider the confining effects which increase the ultimate strain, stress and axial ductility. The peak loads and load-strain responses of short CFST columns predicted by the axisymmetric model are verified with the independent test data and those predicted by the three-dimensional (3D) model. The structural characteristics of circular short CFST columns having different material and geometric parameters are subsequently examined by the axisymmetric analysis. The numerical results indicate that the column size can approximately be reduced by 50% when UHSC is used in the composite construction instead of Normal Strength Concrete (NSC). Comparisons of the current test data are made with the current structural codes including AS/NZS 5100.6, Eurocode 4, AISC and GB 50936. The comparisons demonstrate that the Australian/New Zealand and European design codes provide consistent predictions for the ultimate axial strengths of ultra-high strength circular short CFST columns. On the other hand, the North American design code is conservative, whereas the Chinese code is unconservative.

Experimental and numerical investigation of circular double-tube concrete-filled stainless steel tubular columns under cyclic loading

This paper presents a cyclic loading investigation on double-tube concrete-filled stainless steel tubular (CFSST) columns with circular outer stainless steel tube and circular inner carbon steel tube. A total of eight specimens were tested under constant axial compressive load and lateral cyclic loading. The main variables explored in the test are: (a) axial load level (0.046–0.56); (b) diameter ratio of inner tube to outer tube (0.36, 0.57); and (c) presence of inner concrete or not. A finite element (FE) model was then developed and the prediction of lateral load (P)-lateral displacement (Δ) curves agree well with the test results. Furthermore, effects of various parameters on the P-Δ curves of the double-tube CFSST columns were analyzed in comparison to the double-tube concrete-filled steel tubular (CFST) columns.

Cyclic testing of Q690 circular high-strength concrete-filled thin-walled steel tubular columns

Under seismic action, the severe damage in critical regions of structures could be ascribed to the cumulative damage caused by cyclic loading. This article describes an investigation of the hysteresis behaviour of Q690 circular high-strength concrete-filled thin-walled steel tubular columns with out-of-code diameter-to-thickness ratios. A total of eight specimens were tested under constant axial compression and cyclic lateral loading. The study results of phase I testing consisting of a benchmark test were summarized to examine the seismic behaviour under standard loading, and those of the phase II testing that considered different fatigue loading modes and different concrete strengths were summarized to investigate the low-cycle fatigue behaviour. The load–displacement hysteretic curves, energy dissipation, strength and stiffness degradation were discussed in detail. A simplified method was proposed to predict the low-cycle fatigue life, which can be applied in the damage-based seismic design of circular concrete-filled steel tubular structures.

Creep behavior of thin-walled circular steel tubular columns filled with demolished concrete lumps and fresh concrete

Structural members containing large-scale (60–300 mm) demolished concrete lumps (DCLs), proposed previously by the authors, are new approaches for recycling demolished concrete to reduce the consumption of cement and the cost of labor during manufacturing of conventional small-scale recycled aggregates (≤31.5 mm) from existing buildings. The authors’ previous researches focused on the short-term mechanical behaviors of thin-walled circular steel tubular columns with compound concrete (referred to as compound CFST columns). In this paper, study is extended to experimental and theoretical studies on the long-term creep behaviors of compound CFST columns (4 specimens) and their cylindrical core counterparts (6 specimens), in which the effect of DCL replacement ratio and axial compression ratio on their creep behaviors were considered. Test results show that: (1) the basic creep of cylindrical compound concrete specimens was greater than those of the cylindrical FC or demolished concrete specimens, but increased with the rise of DCL replacement ratio; (2) the compound CFST specimens had nearly identical creep behaviors with the CFST specimens with FC only; (3) the experimental elastic modulus and basic creep were over- and under-estimated, respectively, by the Counto model, a two-phase composite model that regards the DCL and FC as the aggregate and matrix phases, respectively. A modified Counto model that considers the effect of micro-cracks within the DCLs and the DCL replacement ratio is proposed to predict the basic creep of the compound concrete with and without circular tube. Effectiveness of this approach is validated by experiments finally.

Compressive behavior of thin-walled circular steel tubular columns filled with steel stirrup-reinforced compound concrete

The reuse of coarsely crushed demolished concrete lumps (DCLs) with fresh concrete (FC) in compound concrete (i.e. concrete composed of DCLs and FC) provides a viable option to recycled concrete aggregates for recycling concrete waste. Compound concrete-filled steel tubular (CCFST) columns further improve the efficiency with which DCLs are used due to the advantages of concrete-filled steel tubular columns, such as improved strength and ductility. This paper presents an experimental study of the compressive behavior of thin-walled circular steel tubular columns filled with compound concrete with and without internal steel stirrups. Twenty CCFST columns were tested for experimental investigation of the effects of the replacement ratio of DCLs, the strength of the FC, the thickness of the steel tubes, and the distribution of steel stirrups. The test results show that steel stirrups can considerably enhance the load-carrying capacity of CCFST columns and significantly improve their ductility regardless of the strength of the FC, and a non-uniform layout (mainly in the middle height of the column) of steel stirrups can further enhance the performance of the CCFST columns without increasing the amount of steel. Based on the results, a simplified design method proposed for CCFST columns reinforced with internal steel stirrups compared well with the test results.

Residual Axial Bearing Capacity of Concrete-Filled Circular Steel Tubular Columns (CFCSTCs) after Transverse Impact

The purpose of this research is to study the effect of both transverse impact, and ratio of outer diameter to thickness of outer steel tube (D/t), on the residual axial bearing capacity of concrete-filled circular steel tubular columns (CFCSTCs). A total of sixteen samples, including four samples left untreated for comparison, are experimentally studied to investigate the effect of both drop-hammer transverse impact height (H), and D/t ratio, on the residual axial bearing capacity of CFCSTCs. The failure mode, load-displacement curves, load-strain curves, and residual axial bearing capacity of those samples are extensively investigated. A finite element analysis (FEA) model is established to predict the effect of D/t ratio on the residual axial bearing capacity of CFCSTCs. The results indicate that the H and the D/t ratio have noticeable effects on the axial compression performance of CFCSTCs. Failure mode of samples is commonly local buckling. In addition, maximum reduction of the axial bearing capacity of columns reaches about 35% compared with that of untreated columns. The results also show that the bearing capacity of the column increases with a decreasing D/t ratio of the same diameter (D).

Numerical simulation of high strength circular double-skin concrete-filled steel tubular slender columns

Circular double-skin concrete-filled steel tubular (DCFST) slender columns made of high-strength concrete are high performance structural members with wide applications in engineering structures. However, research studies on the behavior, load distributions in concrete and steel components and confinement characteristics of such composite columns under eccentric loading have been very limited. This paper describes a new mathematical model that computes the axial load-deflection performance of high-strength circular DCFST slender columns subjected to eccentric loading. The incremental nonlinear equilibrium equations of DCFST slender columns are solved by the developed efficient computational procedure and numerical solution algorithms accounting for initial geometric imperfections and second order effects. The mathematical model incorporates the accurate material constitutive laws of sandwiched concrete, which accurately predict the residual concrete strength and strain in the post-yield regime. The computer program implementing the mathematical model is utilized to quantify the influences of geometric and material properties and concrete confinements on the load-deflection behavior, column strength curves and load distributions in circular DCFST slender columns. It is shown that the mathematical model not only accurately predicts the experimental behavior of circular DCFST slender columns but also effectively monitors the load distributions in concrete and steel components of DCFST slender columns under deflection increments. The proposed mathematical model is an accurate and efficient computational and design technique for circular DCFST slender columns.

Axial compression behavior of circular recycled concrete-filled steel tubular short columns reinforced by silica fume and steel fiber

This paper presents an experimental work for short circular steel tube columns filled with normal concrete (NAC), recycled aggregate concrete (RAC), and RAC with silica fume and steel fiber. Ten specimens were tested under axial compression to research the effect of silica fume and steel fiber volume percentage on the behavior of recycled aggregate concrete-filled steel tube columns (RACFST). The failure modes, ultimate loads and axial load- strain relationships are presented. The test results indicate that silica fume and steel fiber would not change the failure mode of the RACFST column, but can increase the mechanical performances of the RACFST column because of the filling effect and pozzolanic action of silica fume and the confinement effect of steel fiber. The ultimate load, ductility and energy dissipation capacity of RACFST columns can exceed that of corresponding natural aggregate concrete-filled steel tube (NACFST) column. Design formulas EC4 for the load capacity NACFST and RACFST columns are proposed, and the predictions agree well with the experimental results from this study.

Composite action of concrete-filled double circular steel tubular stub columns

© 2018 Techno-Press, Ltd. This paper presents a combined numerical, experimental, and theoretical study on the behavior of the concrete-filled double circular steel tubular (CFDT) stub columns under axial compressive loading. Four groups of stub column specimens were tested in this study to find out the effects of the concrete strength, steel ratio and diameter ratio on the mechanical behavior of CFDT stub columns. Nonlinear finite element (FE) models were also established to study the stresses of different components in the CFDT stub columns. The change of axial and transverse stresses in the internal and external steel tubes, as well as the change of axial stress in the concrete sandwich and concrete core, respectively, was thoroughly investigated for different CFDT stub columns with the same steel ratio. The influence of inner-to-outer diameter ratio and steel ratio on the ultimate bearing capacity of CFDT stub columns was identified, and a reasonable section configuration with proper inner-to-outer diameter ratio and steel ratio was proposed. Furthermore, a practical formula for predicting the ultimate bearing capacity was proposed based on the ultimate equilibrium principle. The predicted results showed satisfactory agreement with both experimental and numerical results, indicating that the proposed formula is applicable for design purposes.

Study of recycled concrete–filled steel tubular columns on the compressive capacity and fire resistance

This study presents the analytical formulation of circular steel tubular column with hollow concrete section. This unified analytical formulation can evaluate the axial compression capacity and buc...

Analysis of axially loaded concrete filled circular hollow double steel tubular columns exposed to fire

A series of new unified design formulas for calculating the temperature field and fire resistance under axial compressive loading of a circular solid or hollow concrete filled double steel tubular (CFDST) short and slender columns exposed to fire are presented in this paper. The results of the experiments are firstly derived from exploring the fundamental behavior of the CFSDT slender columns under the ISO 834 standard fire and temperature distributions. Failure modes and axial deformation versus time curves are also obtained and discussed. It was realized that a solid or slender CFDST column has different temperature fields, stronger limiting temperature and better fire resistance, as compared to columns filled with plain concrete. Also, the load ratio and steel ratio have no evident difference between the results of the solid and hollow CFDST columns. A three-dimensional finite element analysis (FEA) model is developed to calculate the temperature field of CFDST columns. After calibration of the FE model, the influences of important parameters on the temperature field of the composite columns are investigated and a unified formula for calculating average temperatures of the columns’ cross-section is obtained. Combining the average temperature with the “Unified theory” under axial compression, a simplified design method is put forward, which provides a unified formulation for both the plain CFST and CFDST columns relating to the axial bearing capacity at room and elevated temperature. The proposed formulas are calibrated through comparisons with fire tests on the columns, and it was found that the method produces safe results on average.

Structural response of thin-walled circular steel tubular columns filled with demolished concrete lumps and fresh concrete

A straightforward use of coarsely-crushed demolished concrete lumps (DCLs) mixing with fresh concrete (FC) has recently been suggested by the authors and co-investigators, with a desire to provide another option for recycling concrete waste. Due to their being free of strong, costly crushing, the DCLs termed herein are characterized by larger size than conventional recycled aggregates. Bearing in mind this salient feature, the proposed recycling approach is easy to follow: a pre-determined percentage of DCLs, along with FC of complementary amount, can be placed in layers into a hollow steel tube, thereby forming a new structural member named steel tubular column filled with DCLs and FC. Field practice has demonstrated constructability of the proposed columns, as well as their advantages of being low-impact and cost-effective.In this research, several aspects pertaining to the structural response of said columns under concentric and eccentric loadings are addressed. An experimental program was first carried out, which comprised 24 intermediately slender thin-walled circular steel tubular columns filled with DCLs and FC, accompanied by 12 reference columns filled with FC alone. Primary test variables were the replacement ratio of FC by DCLs, the eccentricity of loading, and the thickness of steel wall. It was observed that, despite a noticeable reduction on ultimate strength, the overall structural performance of the proposed columns was not dramatically compromised, even though as much as 40% of FC was replaced by DCLs. Subsequently, a three-dimensional finite-element model is developed, attempting to understand the effect of random spatial distribution of DCLs on the ultimate strength of the columns, with the aid of Monte Carlo simulation technique. Stochastic simulations indicate that heterogeneous locations of DCLs lead to variations in the ultimate resistance, but such effect is generally limited in a probabilistic sense. This implies that when designing the columns concerned, a homogenization-based estimate of the resulting compressive strength of concrete infill may be reasonable and adequate, irrespective of the locations of DCLs. To examine this, lastly, a code-based design discussion is made, involving comparisons between analytical predictions using design provisions and experimental results of 111 pertinent column tests. A unified, simplified and more robust recommendation for determining the axial and axial-flexural capacities of the proposed columns is accordingly suggested, relying upon a strength-reduction factor of 0.9.

Large diameter concrete-filled high strength steel tubular stub columns under compression

Experimental and numerical investigations on three large diameter concrete-filled high strength steel tubular (CFHSST) stub columns under axial compression were performed. The three large size steel tubes had the same dimension in the test. The outer diameter was approximately 550mm, the length was approximately 1000mm, and the thickness was approximately 16mm. The steel tubes were made of high strength steel Q550 and filled with C30 concrete. A 40,000kN press machine was adopted to apply the required axial compression to the three specimens. It was found that the load-displacement curves of the three concrete-filled high strength circular steel tubular stub columns were notably close to each other, and the ultimate capacities were approximately 30,000kN. Finite element analysis (FEA) was performed to analyze the stub columns, and the FEA results are consistent with the experimental results. The formulas from three types of design codes were used to calculate the column loading capacity, and the calculation results were compared with the experimental results. The results were close to the experimental results. The EC4 design code gives the most accurate estimations, with discrepancy less than 4% being observed.

Numerical modeling on post-local buckling behavior of circular and square concrete-filled steel tubular beam columns

In concrete-filled steel tubular (CFST) beam-columns under cyclic loadings, local buckling of restrained steel tube, crushing and slipping of the confined concrete could have significant influences on strength and stiffness degradation. This paper presents a numerical model based on fiber element discretization for simulating the deterioration behaviour of both rectangular and circular CFST beam columns under axial load and cyclic loading. Uniaxial stress-strain relationships for steel and concrete in CFST beam columns are proposed by introducing unified parameters to control the extent of deterioration. Axial contraction caused by local buckling was accounted by defining an inelastic region that promises plasticity and strength degradation. The numerical model was validated by comparing the simulation results and the associated experimental results. The influences of diameter-to-thickness ratio, concrete and steel strength ranging from normal strength to high strength on the deterioration behavior of circular and rectangular CFST beam-columns were analyzed. Finally, through recognizing the limit state to trigger global strength degradation of a CFST frame, the developed numerical model is applicable for simulating global behavior of CFST frames under collapse-level deformations.

Analysis Theory of the Bearing Capacity and Deformation Process of Load-Bearing Column Subjected to Fire

The fire resistance ability of load-bearing column of building structure under fire is an important aspect affecting the safety of the structure. Although a large number of research results have been achieved in this respect, the researches on the numerical analysis of the bearing capacity and deformation process at high temperature are still not sufficient. The numerical simulation of the bearing capacity and deformation process at high temperature is hard to carry out and complex to operate, and not practical as well. Therefore, simplified analysis method is adopted to analyze the deformation and internal force of the controlling section of the load-bearing column subjected to fire. Besides, taking the concrete filled circular steel tubular column as example, the basic analysis theory of the fire resistance and the deformation performance of columns subjected to constant load is presented. The numerical calculation program which is developed on the basis of this theory can well simulate the process of deformation and the fire resistance of the columns subjected to fire. The simulation results are in good agreement with the experimental results.

Analysis for Pure Bending Performance of Circular Steel Tubular Columns Filled with Steel-Reinforced High-Strength Concrete

This paper is about a new steel tubular columns filled with concrete.

Experimental study on reinforced concrete filled circular steel tubular columns

Experimental results of 39 specimens including concrete columns, RC columns, hollow steel tube columns, concrete filled steel tubular (CFT) columns, and reinforced concrete filled steel tubular (RCFT) columns are presented. Based on the experimental results, the load-carrying capacity, confined effect, ductility, and failure mode of test columns are investigated. The effects of the main factors such as width-thickness ratio (the ratio of external diameter and wall thickness for steel tubes), concrete strength, steel tube with or without rib, and arrangement of reinforcing bars on the mechanical characteristics of columns are discussed as well. The differences between CFT and RCFT are compared. As a result, it is thought that strength, rigidity and ductility of RCFT are improved; especially strength and ductility are improved after the peak of load-displacement curve.

Finite Element Analysis of Recycled Concrete Filled Circular Steel Tubular Stub Columns under Compressive Loading

The paper achieved the nonlinear analysis of bearing capacity of recycled concrete filled steel tubular short columns by using finite element analysis software ABAQUS. In order to meet the finite element analysis the writer put forward the modified formula of recycled concrete constitutive relationship of core, and elaborate d the contact at the interface of steel tube and the core concrete and related modeling points. Finally the load-deformation curves of the finite element analysis and test results coincide well. It indicates that the modified formula of recycled concrete constitutive relationship can better meet the requirements of analyzing bearing capacity of recycled concrete filled circular steel tubular columns under compressive Loading by using ABAQUS. Through the simulation experiment, it is useful for us to obtain the ultimate reliable bearing capacity of the similar structure member.

Experimental Behavior of Circular Steel Tubular Columns Filled with Self-Compacting Concrete under Concentric Load

Experimental Behavior of Circular Steel Tubular Columns Filled with Self-Compacting Concrete under Concentric Load

Stability Bearing Capacity of Concrete Filled Thin-Walled Circular Steel Tubular Column under Axial Compression

The bearing capacity formula of concrete filled thin-walled steel tubular (CFTST) short column was established based on limit equilibrium method, and the reasonable value fork1in Richart Strength Model was regression introduced adapted with concrete stress-strain relations. According to the elasticity modulus theory, the calculation formulas of stability bearing capacity of CFTST slender column were deduced, reasonable considering the interactions between steel tube and concrete. And the calculation process is relatively simple which avoiding complicated iterations used in the conventional calculation method. Finally, the comparative evaluation on calculation formula was done based on 79 groups of test results of concrete filled steel tubular column at home and abroad. Results of calculation formula agree well with the test results in safe range.