Buckling Of Steel Tube Research Articles

Seismic performance of special-shaped hexagonal concrete filled steel tubes with inner diaphragm plates and shear studs

With the development of the high-rise buildings, the columns with special cross-sectional shapes are frequently adopted for architectural and aesthetic purposes. The concrete filled steel tube (CFST) is a reasonable choice for such requirement due to the characteristics of excellent seismic performances, construction efficiency and strong adaptability to special shapes. This paper focuses on the seismic performance of a special-shaped hexagonal CFST column with an inner diaphragm plate and shear studs adopted in a super high-rise building. Experiments were conducted on five column specimens under axial compressive force and lateral cyclic loading to investigate the influence of various parameters including loading angle, axial compression ratio, shear studs and the type of in-filled concrete. In one of the specimens, the ultra-high performance concrete (UHPC) was used as the in-filled concrete to substitute the conventional normal strength concrete, and the effects on the capacity and ductility of the column were revealed. Then the failure mode, the load-deflection curves, seismic performance indexes and the strain distribution were analyzed. The flexural capacities of the columns were evaluated by the fiber section model, where the failure criterion considering the buckling of steel tube was proposed and the effects of studs were included. Finally, the contribution to axial force and bending moment from outer steel tubes, inner diaphragm plate and in-filled concrete were calculated and compared based on the proposed model. It is found that the fiber section model considering the steel plate buckling and strengthening effects of studs precisely predicted the moment-curvature curves and the flexural capacity of the test specimens. The contribution of the inner diaphragm plate was considerable which could not be neglected.

Experimental and numerical investigation on concrete filled steel tube columns reinforced with diagonal stiffeners under axial loading

In modern construction use of composite sections such as CFST columns was improved because of their numerous benefits in construction processes. However, some disadvantages like buckling of steel tube, poor corrosion and fire resistance necessitates the stiffening measures to be adopted. In this study, a novel stiffening scheme was proposed to use with unstiffened CFST column. The stiffening scheme is named as diagonal stiffeners which comprises diagonal stiffeners attached at diagonally opposite ends of steel tube. The stiffeners can be provided in three formats viz, binary, tertiary, and quaternary arrangement. In this paper the response of diagonal stiffeners CFST columns under axial compression was investigated through experimental program. The findings of the analysis were collected with regard to ultimate capacity, load vs strain response, and load vs deformation behavior. Further, to explore the performance of suggested stiffener arrangement, a FE model was developed in ABAQUS and validated through experimental findings. A parametric examination was conducted to evaluate the influence of diameter of stiffeners, number of stiffeners and its yield strength on the ultimate load capacity, load vs strain behavior, axial stress distribution in concrete, lateral deformation of column, and Poisson’s ratio of outer steel casing. Results of the analysis showed that CFST columns strengthened with proposed stiffening arrangements showed approximately 15–25 % higher ultimate load capacity than unstiffened CFST section. Also, using the diagonal stiffeners improved the pre-peak and post-peak behavior of column section. The local buckling of outer steel casing was eliminated and ductility of column section improved. It was deduced that stiffened CFST columns had better confining pressure on concrete infill and composite interaction between outer steel casing and infill concrete was enhanced. The prediction formula to anticipate axial load capacity was also established and can be employed to design of CFST with diagonal stiffeners.

Experimental Study on the Behavior of a Novel Stiffened Hexagonal CFDST Stub Column under Axial Load

A concrete-filled double skin tube (CFDST) consists of an outer steel tube, an inner steel tube, and the space between them filled with concrete. Existing studies have shown that the buckling of steel tubes can be significant in noncircular CFDST for nonuniform confinement or a large width-thickness ratio. Stiffening of the steel tubes is necessary to fully utilize the strength and improve the load-carrying capacity of CFDST. Against this background, the author proposed a novel stiffened hexagonal CFDST column with steel strips welded on both the inner tube and outer tube to form several closed cavities. This paper presents an experimental study on the axial compressive behavior of this new type of CFDST column. The experimental program consisted of five stiffened hexagonal CFDST specimens and two reference specimens for comparison, and the test variables were the hollow ratio and rib width. The test results showed that the ultimate bearing capacity and ductility of the CFDST specimens were greatly enhanced by the steel strips and ribs. Moreover, the finite-element (FE) method was used to develop a three-dimensional model of the CFDST column subjected to axial loading and validated against the experiment. The average error of the FE analysis when predicting the column bearing capacity was 0.029 compared with experimental results. Based on the FE model, a parametric study was conducted to analyze further the effect of each parameter on the axial behavior. Furthermore, a strength design formula was developed to estimate the compressive strength of the novel hexagonal CFDST column.

Experimental study on seismic behavior of full scale square concrete filled steel tubular stocky columns

This study mainly presented a pseudo-static experiment on two full-scale square CFST short columns with the cross-sectional width of 600 mm under combined constant axial load and cyclic lateral load. The seismic performance of the two full-scale CFST columns were investigated. Meanwhile, the plastic hinge length of the specimens was discussed. The test results presented that the specimens suffered bend-shear failure. The local buckling of steel tube occurred at the end of the specimens and the core concrete crushed. The safety redundancy of lateral bearing capacity decreased in full-scale specimen. By the method of physical observation, the plastic hinge length Lp1 was determined mainly according to the range of the local buckling of steel tube. There had a great difference between the prediction of plastic hinge lengths by the existing calculation model and the plastic hinge lengths obtained by the test.

A Study on Effect of Steel Tube in Axial Behavior of CFST Stubs

Concrete filled steel tubular (CFST) columns are becoming popular due to its advantages from both steel and concrete in resisting loads. CFST members are made up of steel hollow section of rectangular or circular sections filled with plain or reinforced concrete. CFST columns can be used effectively in high raised structures and in bridges. The reduced cross sections of columns can be achieved by the composite action of steel and concrete. The steel tube provides confinement to the concrete and helps to improve load carrying capacity. The concrete core offers higher resistance to axial compression. The inward buckling of steel tube will be avoided due to concrete and the out buckling resistance may be improved due to higher stiffness of the column due to higher gross moment inertia with combined effect of steel and concrete. This experimental work made an attempt to understand the effect of thickness of steel tube in behavior of CFST stubs.In the present experimental study, a total of 24 cylindrical concrete filled steel tube specimens were prepared to evaluate the uniaxial compressive behavior and to understand the effect of thickness and aspect ratio (h/D) on the compressive strength. Two different thickness of steel tubes 3 mm and 5 mm and four aspect ratios (h/D) 1, 2, 3 and 4 are considered in the present study. M30 grade of concrete is used. From this study, as the aspect ratio increases the buckling loads decreases. The decrement is up to 37% in aspect ratio 4 when compared to aspect ratio1.

Damage Evolutions and AE Characteristics for Square Concrete-Filled Steel Tubular Columns Under Axial Load

The damage evolutions of square concrete-filled steel tubular (CFT) columns were experimentally studied by the axial compression cyclic loading test and the acoustic emission (AE) monitoring technique. Based on the mechanical analysis and damage observations, the limit damage states, i.e. inner concrete cracking, confinement of steel tube, yielding and buckling of steel tube, weld seam splitting and inner concrete spalling were verified. The released strain energy due to the damage of CFT column was monitored by the AE technique and analyzed by the peak frequency classification method. The results show that the buckling of steel tube is the damage state with the maximum load carrying capacity for CFT columns. Most of the released strain energy were detected by the AE signals with the peak frequency between 30 and 75 kHZ and most of the strain energy were released after the buckling of the steel tube.

RESEARCH ON THE DAMAGE CONDITION OF REINFORCED CONCRETE FILLED STEEL TUBES UNDER AXIAL LOAD USING ULTRASONIC TESTING

The ultrasonic technique was used to evaluate the damage conditions of plain concrete, reinforced concrete, concrete filled steel tubes (CFST) and reinforced concrete filled steel tubes (RCFST) subjected to axial load. The ultrasonic waveforms passing through the middle section of a column were obtained under different loads. The root mean square (RMS) amplitude and RMS amplitude ratio of waveforms are defined for analyzing the development of concrete cracks. The waveforms were transformed into the frequency domain by fast Fourier transform (FFT). According to the principle that the solid medium cracking absorbs high frequency sound wave energy that makes the ultrasonic main frequency shift from high to low frequency, the first main frequency and its amplitude variation were selected to investigate the damage condition of concrete and reinforced concrete in steel tubes. The experimental results show that the crack variation of concrete and reinforced concrete in steel tubes can be effectively reflected by the RMS amplitude, RMS amplitude ratio and the first main frequency and its amplitude. The damage condition of reinforced concrete under axial load can be divided into five stages, that is, the concrete crack generation and extension, concrete compaction resulted from steel tubular constraint, concrete crack rapid expansion, strengthening due to the steel tubular hoop effect and loss of component strength after the buckling of steel tubes. It is found that the constraint stage of steel tube to core concrete obtained from the strain analysis of steel tube is consistent with the damage evolution obtained from ultrasonic testing. Therefore, the ultrasonic testing method is an accurate tool to evaluate the damage of reinforced concrete inside steel tubes under axial load and to determine the hoop effect of steel tubes.

Evaluation of Full Interaction Composite Columns Subjected to Static and Dynamic Loading

Composite column such as other columns made from two or more materials worked as partially or fully. The composite column consists of hot steel section with filled reinforced concrete behaving as compression member and mainly to resisting axial force and moments. The high strength capacity of composite columns with a reduction in cross-sectional area as compared with the reinforced concrete columns gave benefits to adopt this type of construction in building, especially in high-rise and complex buildings. In this paper, an evaluation of composite columns under the effects of static and dynamic loadings to check the adequacy of such composite column that analyzed and designed under static load and then after subjected to dynamic load. Theoretical analysis and numerical solution by finite element approach through ANSYS software program are adopted and assumed that full interactions between reinforced concrete and steel section to check out the performance of composite column taking into account parameters such as loading type as static and dynamic loading, concrete type and method of analysis as modal and harmonic dynamic loading. The results showed that the increasing of core concrete strength delayed the occurrence of local buckling of steel tube. Therefore, the harmonic analysis must be taken into account to check out in the analysis and adopted in the design of composite column in case of the presence of this type of dynamic loading because of the performance of the column is different under this type of loading.

Concrete Filled Square Steel Tubular Deep Beam subjected to Bending-shear

This study aims to investigate experimentally mechanical characteristics of S-CFT deep beam under bending-shear through symmetrically three-point loading test method with a constant axial load. Selected test parameters are shear span and the width-to-thickness ratios, which are ranging from 1.0 to 1.5 and 62.5 to 200, respectively. As the results, observed failure modes of the specimens with width-to-thickness ratio being 200 were local buckling of steel tube associated with shear failure of in-filled concrete between two supports. No effect of the constant axial load on bending-shear capacities can be found. The experimental strength of the specimens with shear span ratio between 1.0 and 1.5 can be predicted by the accumulative strength being composed of RC deep beam and web steel plate.

Seismic Behaviors of Concrete-Filled T-Shaped Steel Tube Columns

Concrete-filled special-shaped (L-shaped, T-shaped, and cross-shaped, and etc.) steel tube column is a type of member in which concrete is poured into special-shaped steel tube so that steel and concrete support loads together. It improves the seismic behaviors of reinforced concrete special-shaped columns due to the better confining effects provided by the steel tube. A test research on the seismic behaviors of one concrete-filled T-shaped steel tube column with pseudo static method is presented and the load-displacement curve and skeleton curve are provided. Series of steel bar stiffeners were welded onto the steel tube in order to postpone the buckling of steel tube and to enhance confining effects. A numerical analysis program was developed using a fiber-based method. The constitutive model of concrete employed the modified Mander model, and that of steel employed a bi-linear model considering the Bausinger effect. The numerical analysis program was verified by the test results and parametric analysis was carried out, in which the influences of the ratio of axial compression stress to strength, steel tube thickness and concrete strength were mainly discussed. The following conclusions are obtained: with the increase of the ratio of axial compression stress to strength, the bearing capacity of member increases and the energy dissipation capacity improve, while the ductility deteriorates. With the increase of steel tube thickness, the initial rigidity, bearing capacity, ductility and energy dissipation capacity improves simultaneously. With the increase of concrete strength, the bearing capacity increases, the energy dissipation capacity improves, while the ductility deteriorates.