Bare Steel Columns Research Articles

Axial compressive performance of cruciform timber-encased steel composite columns: Experimental investigation and buckling analysis through 3D laser scanning

Timber-encased steel composite (TESC) columns have garnered increasing attention owing to their high mechanical performance. However, limited studies have focused on the compressive performance of cruciform TESC columns and accurate evaluations of the full-field deformation of embedded steel components. In this paper, a novel cruciform TESC column embedded with a thin-walled cruciform steel component was proposed. 22 specimens including TESC columns, bare steel columns and bare glulam columns were tested under axial compression. Parameters such as the width and thickness of the cruciform steel component were considered. 3D laser scanning technologies were applied to measure the full-field deformation of 20 steel members, thus quantitatively assessing the reduction in the deformation of steel components resulting from the lateral restraint of timber. Finally, a nonlinear fitting equation was established to predict the load-carrying capacity. The results showed that the TESC columns exhibited significant enhancements in stiffness and load-carrying capacity. The lateral restraint of timber caused the buckling modes of the steel to change from torsional buckling to mainly local buckling. Moreover, the high post-yield stiffness of the steel components before reaching the maximum load indicated that the timber offered sufficient lateral restraint to make full use of the steel strength. The 3D laser scanning method accurately measured the full-field deformation of the steel at the failure state. Compared to bare steel columns, the torsional rotation of the steel components decreased by up to 83.14 %, while the maximum absolute lateral deflection decreased by up to 80.89 %. The suggested strength formula offered sufficient accuracy in predicting the load-carrying capacity of short TESC columns, with ratios between the calculated and experimental values ranging from 0.908 to 1.120.

Behavior of light-gauge steel short columns filled with normal and lightweight aggregate concrete under concentric axial loading

This study aims to investigate experimentally and numerically the behavior of light-gauge steel tubes filled with normal and lightweight concrete under axial loading. A total of thirty-five specimens, including thirty-two composite columns, two bare steel columns, and one normal-weight plain concrete column, were considered. The main variables in the tests were the concrete infill type (normal-weight and lightweight), the column's length (1, 1.25, 1.5, 1.75-m), the steel tube thickness (2 and 2.4-mm), and the cross-section (100×100 and 150×150-mm). In addition, theoretical capacities were computed according to Eurocode 4, and a finite element analysis was conducted using ABAQUS software. The results showed that the behavior of lightweight filled steel tubes was similar to the normal weight filled tubes during the test; however, their capacities were lower compared to the normal weight filled tubes by a range of (1%-20%). Yet, lightweight filled steel tubes can achieve high axial loads. In addition, the axial capacity of all composite columns decreased with the increase of the column's height and increased with the increase of both the cross-section and the steel thickness. Current code specifications of EC4 and the numerical results obtained from ABAQUS overestimated the capacities of the composite concrete-filled tubes by 3% and 14%, respectively; however, the EC4 was found to present close estimations to the experimental results.

Local and post-local buckling of normal/high strength steel sections with concrete infill

Steel sections in steel-concrete composite columns have been proofed to be less susceptible to local buckling and have higher capacity than bare steel columns, attributed to the internal restraints provided by the infilled concrete. This article presents a theoretical study concerning the local and post-local buckling of fabricated normal and high strength steel sections filled with concrete, including concrete filled steel tubular (CFST) sections and partially encased composite (PEC) sections. A nonlinear finite element (FE) model was established and validated to simulate the behavior of steel plates in contact with concrete, with both geometric imperfections and residual stresses explicitly incorporated. This model was subsequently applied in a parametric study to investigate the effects of several critical factors on the local buckling behavior of box and I steel sections. Based on the available test and FE results, new design formulas were proposed to predict the local buckling and post-buckling ultimate strengths of concrete-restrained steel box and I sections, taking into consideration high material strengths, residual stresses and geometric imperfections. The enhancement of strength due to the presence of concrete infill was confirmed through a comparison with the post-buckling strength of bare steel sections. Recommendations were also made for design purpose based on the formulas proposed.

Analysis of the composite effect of partially concrete-encased H-shaped steel composite columns

To research the composite effect of partially concrete-encased composite columns, the axial compression analysis of three groups of 12 specimens (six H-shape steel partially concrete-encased composite columns and six H-shape steel columns) was conducted by using the commercial finite element software ANSYS. The results show that partially concrete-encased composite columns possess sound mechanical performance as demonstrated by higher ultimate strength, deformability, stability and lateral stiffness than bare steel columns. The total cross-section of concrete and steel of partially concrete-encased composite columns both yield when specimens are damaged, showing better compatibility for deformation. Partially concrete-encased composite provides good restraint for H-shaped steel to prevent local buckling, and the H-shaped steel confines the concrete, increasing its strength and ductility. Moreover, there is superior interaction effect between the concrete and the steel.

CONCRETE FILLED STEEL TUBES SUBJECTED TO AXIAL COMPRESSION

Concrete-filled steel tubular columns have excellent earth-quake resistant properties such as high strength and ductility and large energy absorption capacity. For concrete-filled steel tubes (CFST), local buckling commonly observed in bare steel columns is effectively prevented, giving a higher capacity. However if the concrete core and the steel tube are loaded simultaneously the steel tube expands more than the concrete core under moderate loads since Poisson’s ratio is higher for the steel section. The objective of this paper is To evaluate the accuracy of codal design approach by comparing experimental results with the analytical results obtained using EC4, ACI-318 and AISC-LRFD, for prediction of load carrying capacity of CFST columns under axial compression. Based on this the experimental programme is conducted on concrete filled steel tubes of length 300mm, thickness 1 to 3mm for circular, square and rectangular cross section with three different grades of concrete.200 T capacity Compression testing machine is used for experimental investigation.. The experimental results are compared with analytical results obtained by stated code of practices. From this it is concluded that EC4 gives conservative results. From which it is observed that EC4 gives conservative results with experimental results and it is concluded that EC4 provisions may be used for further analytical study to develop an expression to predict the section capacity CFST columns. As the grade of concrete increases the load carrying capacity is also increases. This paper presents the details of study carried out and the conclusions arrived.

Behavior of Unrestrained and Restrained Bare Steel Columns Subjected to Localized Fire

Real fires start from localized burning and will not develop to flashover in an open space or in large open-plan compartments. Temperatures of gas and exposed steel columns in localized fires are not uniform. Current structural fire design methods are based on uniform heating and, therefore, do not account for temperature gradients in real fires. This paper presents a numerical investigation of the behavior of bare steel columns subjected to a localized fire. The buckling behaviors of steel columns surrounded by and adjacent to a localized fire are investigated. Simple approaches are provided to calculate the temperatures of steel columns surrounded by and adjacent to a localized fire. Sequentially coupled thermal-mechanical simulations were conducted. Unrestrained, axially restrained, and rotationally restrained steel columns of various load ratios and dimensions subjected to different heating conditions were considered. The study found that the behavior of steel columns subjected to a localized fire may be completely different from that of columns subjected to a standard International Organization for Standardization (ISO) 834 fire. The steel columns surrounded by a localized fire fail by local buckling, while the same columns subjected to a standard ISO 834 fire fail by global buckling. The temperatures at which steel columns buckled (buckling temperature) when surrounded by a localized fire are higher than those of columns subjected to both a standard ISO 834 fire and an assumed uniform steel temperature condition. However, the buckling temperature of steel columns adjacent to a localized fire may be much lower than that of the columns subjected to both a standard ISO 834 fire and an assumed uniform steel temperature condition. The location of the localized fire relative to the column has a significant effect on the temperature and buckling behavior of steel columns. Structural fire design for steel columns based on a standard ISO 834 fire or a uniform steel temperature may be conservative if the potential real fires are localized fires surrounding the columns and may not be conservative if the potential real fires are localized fires adjacent to the columns.

Experimental Research on the Load-Bearing Capacity of Partially Encased Steel Columns Under Fire Conditions

The composite steel and concrete columns are known to have enhanced fire behaviour when compared with bare steel columns. However there are still aspects that must be clarified, as the influence of the building surrounding structure on the fire resistance of the columns. In this paper, the results of fire resistance tests on partially encased steel columns carried out with two different experimental systems are compared. In one of the experimental systems, the building surrounding structure is materialised by a steel restraining frame, and in the other is performed by the so-called substructuring method. Due to the concept of hybrid substructuring, the entire building is decomposed in two parts: one is represented by the building element under test, whereas the remaining building is simulated numerically in a computer. The main conclusion drawn from this work was that the surrounding structure has a major influence in the development of axial forces in the test columns. Moreover, it was observed that the higher the non-dimensional axial restraint ratio the lower the critical time of the columns.

Behavior of Slender Steel-Concrete Composite Columns Wrapped with FRP Jackets

This paper studies the influence of slenderness on the behavior of steel-concrete composite columns encased in fiber-reinforced polymer (FRP) jackets. The composite columns are composed of steel I-sections that are partially encased by concrete and fully wrapped with epoxy-saturated glass and carbon FRP sheets. A total of nine specimens were tested with different slenderness parameters and heights ranging between 500 and 3,000 mm. The confining pressure provided by the FRP jacket and the composite action between the constituent materials resulted in an enhanced compressive behavior of the composite columns. The compressive strength, elastic axial stiffness, and energy dissipation capacity of the composite columns increased by a ratio of up to 5.2, 2.5, and 14.0, respectively, compared with that of the bare steel columns counterparts. A capacity curve, which shows the compressive strength of the composite columns for various slenderness parameters, was developed based on the experimental results.

Rankine approach for steel columns in fire: numerical studies

A finite element model has been extensively applied to verify the accuracy of the proposed Rankine formula for determining the fire resistance of bare steel columns. The parameters involved include relative slenderness ratio, load eccentricity, steel grade, and initial imperfections of initial crookedness and residual stresses. Through these parametric studies, it is possible to establish the safety limits on the application of the proposed Rankine formula. It is realised that incorporating a deflection control criterion in the evaluation of column elastic-critical loads helps to improve the overall performance of the formula. The Rankine formula is then compared to a series of 68 eccentrically-loaded column tests from the literature. The comparison study shows good agreement with both test results and analytical predictions.

The influence of the thermal expansion of beams on the structural behaviour of columns in steel-framed structures during a fire

In the UK, new design guidance is currently being developed for the behaviour of steel-framed buildings when subjected to fire. This is primarily based on recent research that considers the structural behaviour of all horizontal members, without applied fire protection, acting as a complete entity within the building. This guidance assumes that columns designed to current design procedures will always be adequate when used within this new design philosophy. For bare steel columns these existing design methods usually consist of applying some form of passive fire protection. Presented in this paper is an analytical investigation of the structural behaviour of columns when subjected to various structural and fire scenarios. The results from this study do not endorse the view that current fire design methods for columns are adequate. These design methods will require revision if instability of columns during a fire is to be avoided. In most cases this will result in the need for additional passive fire protection to be applied to the steel columns.

Some Design Considerations for Composite-frame Structures

Over the past 25 years, numerous innovative structural systems have evolved in tall building design where structural steel and reinforced concrete have been combined to produce a building having the advantages of each material. The use of these so-called composite-frame structures has as its underlying principle the combination of these two distinctive and different building materials to benefit from the advantages of both—namely, the inherent stiffness and economy of reinforced concrete and the speed of construction, strength and light weight of structural steel. The term composite-frame structure has taken on numerous meanings in recent years in utilizing several different building materials. As used here, it is taken to mean a building employing a structural steel and composite metal deck floor system and concrete encased steel columns. The composite beams use headed studs (shear connectors) to achieve composite action between the steel and concrete. The bare steel columns carry the initial gravity, construction and lateral loads until such time as the concrete is cast around them to form composite columns capable of resisting the total gravity and lateral loads of the completed structure.