Load Bearing Capacity Of Columns Research Articles

Experimental and analytical investigation of square-shaped concrete-filled steel tube columns

Square-shaped concrete-filled steel tube (CFST) columns inherit the advantages of conventional steel and concrete columns, and have been used in several super high-rise buildings. This paper presents a calculation model for square-shaped CFST columns. Based on the experimental results of a square-shaped CFST column and the application of a super high-rise building, numerical models are established to simulate the force–displacement curves of the CFST column and the stress–strain curves of square steel tubes and stiffeners, which show consistency with the experimental data. Meanwhile, the load-bearing capacity and ductility of CFST columns can be effectively increased by incorporating tensile plates, diaphragms, shear studs, and stiffeners. Considering the steel ratio, axial compression ratio, and concrete strength, nine finite element models are developed to evaluate the ductility and load-bearing capacity of the columns under the reversed-cyclic lateral load. The seismic and wind resistance properties of the structures are analyzed using a CFST column application.

An analytical study on nano-alumina modified concrete in-filled lightgauge steel fluted columns

Cold-formed steel sections are widely practiced cutting-edge of steel sections. A wide range of advantages prevails over the functioning of structural elements while cold-formed steel is been used along with the concrete in combination. Cold-formed steel in-filled columns filled with concrete have gained significance in the construction industry in recent times. Columns are built to withstand most of the axial load by the use of a thin-walled cold-formed steel tube by encasing the concrete. Far-reaching research regarding the behaviour, stress and strain characteristics of the columns using Cold-formed steel in-filled columns and the columns are stiffened using flutes which are provided along the length of the column as an integral part of the section of the column. The so-provided flutes will be triangular and rectangular in shape across the cross-section of columns. In this study, the behaviour of eighteen specimens with various types of flutes and thicknesses was examined. Analytical work was done using software for Finite Element Analysis. In this investigation, three cases with three, four, and five flutes each with a steel sheet thickness of one millimetre were taken into consideration. By the analytical investigation, the behavioural patterns of Cold-formed steel in-filled columns with flutes were carried out. From the analytical investigation implies that the load-bearing capacity of columns and the flute shape are directly related to the number of flutes in columns has an influential effect on resistance to higher loads.

Experimental study on axial compressive behavior of full-scale masonry columns strengthened with reinforced high ductile concrete (RHDC)

The present paper demonstrates the results of an experimental study on full-scale masonry columns strengthened with reinforced high ductile concrete (RHDC) system. This technique can be applied for existing masonry structures as a strengthening technique or for new construction as RHDC-masonry composite columns. Three unreinforced masonry (URM) columns and nine RHDC-strengthened columns were prepared and subjected to concentric axial loads. Each column had a rectangular cross-section and a heigh of 2400 mm. The variables considered in the tests were different configurations of RHDC system. The axial behavior of full-scale columns was discussed and analyzed including modes of failure, axial load-deformation response, peak load, and deformation capacity. Overall, the failure mode of columns was improved by RHDC system, preventing masonry from seriously crushing. Moreover, RHDC system increased both axial capacity and corresponding displacement of full-scale masonry columns, with maximum increases of 168% and 34%, respectively. Due to the enhanced stiffness and cross-sectional area of columns, the results from the current investigation allowed using a stability coefficient higher than that of URM structures for the prediction of the axial capacity of RHDC-strengthened columns. Finally, the effect of initial masonry strength and vertical stress on the load-bearing capacity of columns was analyzed theoretically. The strength reduction coefficient of HDC obtained from analysis can be used in engineering.

Experimental study on flexural properties of timber columns with interior notches in traditional Japanese timber structures

In this study, the columns with interior notches in traditional Japanese timber frames were selected as the research object, and static bending tests were performed to investigate the effect of interior notches on the flexural properties of columns. First, the bending behaviors of columns under three-point and four-point load configurations were compared to obtain a suitable referenced strength of a column without notches. The reduction in the load-bearing capacity of columns with different types of interior notches in traditional Japanese timber structures was determined through experimental tests and statistical analysis. The results indicated that the mean bending strength of columns with three different notch types was consistent with those without notches, the continuous timber on both sides of the notch had a beneficial effect on maintaining a higher strength and reducing the stress intensity around the notch. The fracture position and the standard deviation of the bending strength were affected not only by the notch depth, but also by the notch width on the tensile side of the column.

Postfire reliability analysis of axial load bearing capacity of CFRP retrofitted concrete columns

A reliability analysis of the axial compressive load bearing capacity of postfire reinforced concrete (RC) columns strengthened with carbon fiber reinforced polymer (CFRP) sheets was presented. A 3D finite element (FE) model was built for heat transfer analysis using software ABAQUS. Based on the temperature distribution obtained from the FE analysis, the residual axial compressive load bearing capacity of RC columns was worked out using the section method. Formulas for calculating the residual axial compressive load bearing capacity of the columns after fire exposure and the axial compressive load bearing capacity of postfire columns retrofitted with CFRP sheets were developed. Then the Monte Carlo method was used to analyze the reliability of the axial compressive load bearing capacity of the RC columns retrofitted with CFRP sheets using a code developed in MATLAB. The effects of fire exposure time, load ratio, number of CFRP layers, concrete cover thickness, and longitudinal reinforcement ratio on the reliability of the axial compressive load bearing capacity of the columns after fire were investigated. The results show that within 60 minutes of fire exposure time, the reliability index of the RC columns after retrofitting with two layers of CFRPs can meet the requirements of Chinese code GB 50068 (GB 2001) for safety level II. This method is effective and accurate for the reliability analysis of the axial load bearing capacity of postfire reinforced concrete columns retrofitted with CFRP.

Axial behaviour of CFST stub columns strengthened with steel tube and sandwiched concrete jackets

This study addresses some key concerns on using steel tube and sandwiched concrete jackets to strengthen intact concrete-filled steel tubular (CFST) columns. The research background lies in engineering cases, in which the functional purpose changes when the structure remains intact. Within the parameters investigated, the load-bearing capacity of columns was enhanced by 114%–199% after being jacketed with steel tube and sandwiched concrete. The observable enhancement depended on section enlargement and the confinement effects of the outer steel tube, the latter of which could account for as large as 19% of the nominal load-bearing capacity. A finite element (FE) model was developed and verified, and the load distribution on components of the strengthened columns was presented. The radial stress between the inner concrete and inner steel tube was validated to increase substantially after the CFST column is jacketed with steel tube and sandwiched concrete. The decrease in the diameter-to-thickness ratio of the outer steel tube contributes to the synchronisation of the inner and sandwiched concrete in reaching peak load and benefits the load increase. A parametric study based on the FE model was conducted, and the effects of estimation error with respect to the properties of existing CFST columns were evaluated. A reasonable match between the outer steel tube grade and sandwiched concrete class was advised.

Axial behavior of ultra-high performance concrete (UHPC) filled stocky steel tubes with square sections

This paper presents an experimental investigation on the axial behavior of square ultra-high performance concrete (UHPC) filled steel tube columns (SUHPCFSTs). To this end, 32 short specimens are fabricated and tested in the presence of uniaxial compression. The confinement index is considered as a variable by changing the steel tube thickness and the UHPC strength. The roles of failure modes, load-deformation curves, ultimate load bearing capacity, and post-peak ductility of specimens are examined in some detail. The results indicate that the axial load-deformation curves can be classified into three distinct types with three stages based on the confinement index. Good ductility is observed for all specimens with the confinement index in the range of 1.41 to 5.27. The ductility and strength indexes grow by increasing of the confinement index, in spite that the increase of the strength index is insensitive. Additionally, the interaction between the UHPC and the steel tube is mainly treated in the ductility, not the load bearing capacity of columns. Finally, a revised calculation method for predicting the ultimate bearing capacity of SUHPCFSTs is proposed, and then, it is validated by the experimental results.

Progressive collapse analysis of 3D steel frames with concrete slabs exposed to localized fire

This paper numerically investigates progressive collapse resistance of three-dimensional steel frames with reinforced concrete slabs exposed to localized fire using LS-DYNA. An explicit dynamic analysis is carried out and the real fire time is scaled down to save the computational cost. The prototype of the model is based on the eight-storey building in Cardington tests. The scenario of heating individual columns on the ground floor is first studied followed by a sever case of simultaneously heating four columns in one compartment. The collapse modes and load redistribution scheme of the frame subjected to different load ratios and fire locations are investigated. The modelling parameters such as mesh size, initial imperfection, timescale are first studied by validating against the fire test data. It is found that the mesh size has little influence on the responses of members at elevated temperature. The initial imperfection has significant effect on the load-bearing capacity of columns. The quasi-static behaviour of structures under a fire duration of hours can be simulated in a dynamic analysis by being scaled to seconds without causing oscillation of responses. The numerical results of the 3D frame show that the frame does not collapse in the case of single column heated for a fire design load (load ratio of 0.25 for columns). By increasing the load ratio to 0.5 as for the ambient design, progressive collapse occurs. For a fire of four columns heated, the frame collapses for the corner bay fire and long edge bay fire but withstands for the internal and short edge bay fires. The collapse modes are dominated by the uneven load redistribution in the two horizontal directions and the fire location, which cannot be simulated by a 2D model. The loads previously sustained by the buckled heated column are transferred more along the short span than the long span. The critical temperature of a column in a frame is significantly lower than that given in EC3, due to the fact that the translational and rotational restraint increase its load ratio and reduce its effective length, respectively. The critical temperature for the global collapse of the frame is about 50–100°C higher than that of individual heated columns.

Analysis on Load Bearing Capacity of Column with Different Diameters of Steel Tube under Horizontal Displacement

In order to analyze load bearing capacity of column with different steel tube diameters under horizontal displacement, and provide reference for further study about seismic performance of column which is called CFRP steel reinforced concrete filled with steel tube concrete column, this paper makes the nonlinear finite element analysis on this column by using ABAQUS. The load–displacement curves of the specimens with different steel tube diameters are acquired by establishing model, choosing constitutive relationship, making unit types and mesh settings, and then analyze the influence of different steel tube diameters on load bearing capacity of specimens. The curves show that with the increasing of steel tube diameters, the slope of curves in the elastic stage increases, besides, maximum point of load–displacement curves in the elastic stage is increasing. The results show that only with horizontal displacement, the slope of curves and the bearing capacity in the elastic stage is increasing with the increasing of diameters, it is clearer when the horizontal displacement is small.

Experimental Investigation on the Effect of Reinforcement Ratio to Capacity of RC Column to Resist Lateral Impact Loading

The influence of lateral impact loading rate, longitudinal reinforcement ratio and stirrup ratio on the failure mode, lateral load bearing capacity etc. was investigated. It was carried out with experimental research on the dynamic response of RC columns under lateral impact loading. Results show that increasing in longitudinal reinforcement ratio can enhance ultimate load bearing capacity of columns. The greater the loading rate, the greater the increased amplitude. It is also demonstrated that he main influence factor on the failure mode of RC columns is stirrup spacing. The column is prone to shear failure when the stirrup spacing is large otherwise to flexural failure.

The effectiveness of CFRP materials strengthening of eccentrically compressed reinforced concrete columns

In the paper the investigations of load-bearing capacity of eccentrically compressed reinforced concrete columns strengthened with CFRP strips and sheets are presented. The aim of the conducted researches was to estimate the influence of changeable longitudinal CFRP reinforcement intensity on load-bearing capacity of columns. In the experimental investigations three longitudinal CFRP strengthening intensities were applied – 2.10%, 1.68% and 1.26%. The experimental tests were performed on columns models with cross-section of 200×200 mm and height of 1 500 mm. The investigative members were loaded axially or eccentrically. The eccentric force was exerted in the area of cross-section core (h/12 and h/6 from neutral axis). In the paper the results of experimental studies on load-bearing capacity depending on longitudinal strengthening intensity were presented and discussed. The failure mechanisms were described. The values of failure force and maximum longitudinal strain were given. The application of longitudinal CFRP strips (as external composite strengthening) causes the increase of column rigidity. Additional transverse strengthening implies delay in debonding the strips from concrete. The interaction of both CFRP materials entails the reduction of strains increase velocity which transfers to the increase of load-bearing capacity.

Evaluation of the load bearing capacity of columns of a hall building during a fire

Evaluation of the load bearing capacity of columns of a hall building during a fire