Behavior Of Beam-columns Research Articles

Experimental study of steel single unequal-leg angles under eccentric compression

A total of 26 steel unequal-leg angle specimens were tested under eccentric compression with respect to either major or minor principal axis of the cross-section to study the steel single angle beam–column behavior. Results suggested that for angles subjected to major principal axis bending causing the angle short leg in compression, the presence of moment, in some cases, resulted in the angle ultimate load higher than its concentric compressive capacity. In the case of the major axis bending causing the long leg in compression and minor axis bending, an increase in eccentricity resulted in a reduction in the angle ultimate load but the extent of the reduction was more pronounced for specimens under minor axis bending. Overall, the effect of eccentricity on the ultimate load decreased as the slenderness increased. The design of angle beam–columns as proposed in AISC Specification 2005 and the Direct Strength Method was evaluated using the test results.

Experimental and code based study of beam–column behaviour of equal leg single-angles

This study intends to establish the behaviour of equal leg single-angles under bi-axial bending and compression experimentally and analytically using nonlinear finite element analysis techniques. In the experimental system, 100×100×10 nominally sized equal leg single-angles were tested. The legs of angles were placed in a flange-down position, and their axes were restrained laterally as a simply supported beam. These simply supported beams were loaded with a concentrated vertical load applied at the middle of the length and an axial load parallel to the beam axis until failure was reached. The FEM model of the experimental system was generated with ABAQUS software. Suitable finite element mesh configurations, boundary conditions and nonlinear analysis solution techniques were determined to identify the system behaviour. The test and ABAQUS software results were interpreted using some code specifications and one design procedure.

Large-deflection and post-buckling behavior of slender beam-columns with non-linear end-restraints

The large-deflection analysis and post-buckling behavior of laterally braced or unbraced slender beam-columns of symmetrical cross section subjected to end loads (forces and moments) with both ends partially restrained against rotation, including the effects of out-of-plumbness, are developed in a classical manner. The classical theory of the “Elastica” and the corresponding elliptical functions utilized herein are those presented previously by Aristizabal-Ochoa [1]. The proposed method can be used in the large-deflection analysis and post-buckling behavior of elastic slender beam-columns with rigid, semi-rigid, and simple flexural connections at both ends including linear and non-linear inelastic connections like those that suffer from flexural degradation (such as flexural cracking and elasto-plastic connections) or flexural stiffening. Only bending strains are considered in the proposed analysis. Results from the proposed method are theoretically exact from small to very large curvatures and transverse and longitudinal displacements for laterally braced or unbraced slender beam-columns under bending caused by end loads. The large-deflection analysis and post-buckling behavior of slender beam-columns with both supports partially restrained against rotation and with sway inhibited or uninhibited are complex problems requiring the simultaneous solution of two coupled non-linear equations with elliptical integrals whose unknowns are the limits of the integrals. The validity of the proposed method and equations are verified against solutions available in the technical literature. Three comprehensive examples are included that show the effects of linear and non-linear connections at both ends on the large-deflection analysis and post-buckling behavior of slender beam-columns.

Linear and non-linear stability analyses of thin-walled beams with monosymmetric I sections

The paper investigates beam lateral buckling stability according to linear and non-linear models. First, the classical linear stability solutions are derived from the stability equation in the case of monosymmetric cross-sections. Bending distribution, load height parameter and Wagner's coefficient effects are taken into account. In the second step, they are extended to non-linear stability by considering pre-buckling deformation and improved solutions are then obtained. Based on a finite element model developed for large torsion of thin-walled beams with open sections, the stability of beams under gradient moments ( M 0, ψM 0, −1≤ ψ≤1) is particularly investigated. It is then concluded that beam lateral buckling resistance depends not only on pre-buckling deformation but also on section shape and load distribution. For bisymmetric I beam, closed form solutions are possible and pre-buckling deformations have an incidence. In the case of beams with monosymmetric I and Tee sections, effects of pre-buckling deflections are important only when the largest flange is in compression under M 0 and positive gradient moment. Analytical solutions are possible. For negative gradient moments all available solutions fail and numerical solutions are more powerful. Effect of gradient moments on stability of redundant beams is investigated at the end. Under such boundary conditions, important axial forces are present due to non-linear beam deformation. These forces, omitted in literature, have an incidence on stability. The element is then concerned with beam-column behaviour rather than beam stability.

Predicting Fire Behavior of Composite CFT Columns Using Fundamental Section Behavior

Abstract This paper presents the development and verification of a fiber-based analytical approach for predicting the behavior of concrete filled steel tube (CFT) columns subjected to constant axial load and standard fire loading. The approach consists of three parts: (1) Two-dimensional heat transfer analysis, (2) section moment-curvature analysis, and (3) column inelastic buckling analysis using modified Newmark’s method. The analytical approach was verified by using it to predict (1) the thermal and structural behavior of CFT column specimens subjected to standard fire tests by different researchers and (2) the fundamental moment-curvature behavior of CFT beam-column specimens subjected to special (non-standard) fire tests conducted by the authors. The analytical approach predicts the fundamental moment-curvature behavior of CFT beam-column specimens and the standard fire behavior of CFT column specimens with reasonable accuracy. The analytical results also compare favorably with the overall behavior and stress states predicted by three-dimensional finite element analyses conducted earlier by the authors. The fiber-based analytical approach is recommended for modeling and predicting the standard, non-standard, or realistic fire behavior of CFT columns and beam-columns under various loading, heating, and boundary conditions.

Post-critical behavior of damped beam columns with variable cross section subjected to distributed follower forces

In this paper the post-critical behavior of beam columns with variable mass and stiffness proper- ties subjected to follower forces arbitrarily distributed along their length in the presence of damping (both in- ternal and external) is investigated using a complete nonlinear dynamic analysis. Although the static non- linear analysis is more economical in computational cost, it is associated only with the loss of local stability via flutter or divergence. Thus, the nonlinear dynamic analysis is adopted in order to examine the global sta- bility of the system. The governing equations of hyper- bolic type are derived in terms of the displacements by considering (a) nonlinear response including the axial deformation, (b) nonlinear response excluding the axial deformation and (c) linear response. More- over, as the cross-sectional properties of the beam vary along its axis, the resulting coupled nonlinear differ- ential equations have variable coefficients. Their so- lution is achieved using the analog equation method (AEM) of Katsikadelis. Besides its accuracy and ef- fectiveness, this method overcomes the shortcoming of a possible FEM solution which may experience a lack of convergence. The problems treated in this in-

Experimental study of beam–column behaviour of steel single angles

Twenty-eight rolled steel single angle specimens were tested to investigate their response when required to carry axial compressive loading at various end eccentricities. Results suggested that when eccentrically loaded with respect to the major principal axis, there is a critical eccentricity below which any consequent reduction in the ultimate load is marginal. In contrast, as eccentricity of loading with respect to the minor principal axis is increased, reduction of the ultimate load is more pronounced and no similar critical eccentricity can be identified. Test results, when compared with the corresponding values as determined from the design equations suggested by Adluri and Madugula (1992), in AISC Specification 2000 and AISC Specification 2005, indicated that the former two methods give a conservative estimate of the ultimate compressive capacity of single angles. This conservatism is more pronounced for specimens subjected to eccentric loading with respect to the major principal axis than that resulting from eccentric loading with respect to the minor principal axis. Although intended for doubly symmetric sections, the third method provides improved capacity estimates of single angles.

Large-Deflection Stability of Slender Beam-Columns with Both Ends Partially Restrained against Rotation

The large-deflection analysis and postbuckling behavior of laterally braced or unbraced slender beam columns of symmetrical cross section subjected to end loads (forces and moments) with both ends partially restrained against rotation including the effects of out-of-plumbness is developed in a classical manner. The classical theory of the “Elastica” and the corresponding elliptical functions utilized herein are those presented previously by the senior writer. The proposed method can be used in the large-deflection elastic analysis and postbuckling behavior of slender beam columns with rigid, semirigid, and simple flexural connections and both ends. Only bending strains are considered, i.e., the effects of axial and shear strains are neglected. An example is included that shows the effects of flexible connections at both ends on the large-deflection analysis and postbuckling behavior of slender beam columns.

Static and dynamic stability of uniform shear beam-columns under generalized boundary conditions

The stability and dynamic analyses (i.e., the buckling loads, natural frequencies and the corresponding modes of buckling and vibration) of a 2D shear beam-column with generalized boundary conditions (i.e., with rotational restraints and lateral bracings as well as lumped masses at both ends) and subjected to linearly distributed axial load along its span are presented in a classic manner. The two governing equations of dynamic equilibrium, that is, the classical shear-wave equation and the bending moment equation are sufficient to determine the modes of vibration and buckling, and the corresponding natural frequencies and buckling loads, respectively. The proposed model includes the simultaneous effects of shear deformations, translational and rotational inertias of all masses considered, the linearly applied axial load along the span, and the end restraints (rotational and lateral bracings at both ends). These effects are particularly important in members with limited end rotational restraints and lateral bracings. Analytical results indicate that except for members with perfectly clamped ends, the stability and dynamic behavior of shear beams and shear beam columns are governed by the bending moment equation, rather than the second-order differential equation of transverse equilibrium (or shear-wave equation). This equation is formulated in the technical literature by simple applying transverse equilibrium at both ends of the member “ignoring” the bending moment equilibrium equation. This causes erroneous results in the stability and dynamic analyses of such members with supports that are not perfectly clamped. The proposed equations reproduce as special cases: (1) the non-classical vibration modes of shear beam-columns including the inversion of modes of vibration (i.e. higher modes crossing lower modes) in members with soft end conditions, and the phenomena of double frequencies at certain values of beam slenderness ( L/ r) and (2) the phenomena of tension buckling in shear beam-columns.

Behaviour of fire-exposed concrete-filled steel tubular beam columns repaired with CFRP wraps

This paper presents the test results of fire-exposed concrete-filled steel tubular (CFST) beam columns repaired by unidirectional carbon fibre reinforced polymer (CFRP) composites. Both circular and square specimens were tested to investigate the repair effects of CFRP composites on them. The test results showed that the load-bearing capacity of the fire-exposed CFST beam columns was enhanced by the CFRP jackets to some extent, while the influence of CFRP repair on stiffness was not apparent. The strength enhancement from CFRP confinement decreased with the increasing of eccentricity or slenderness ratio. Ductility enhancement was also observed except those axially loaded shorter specimens with rupture of CFRP jackets at the mid-height, occurred near the peak loads. However, the strengths of all repaired specimens have not been fully restored due to the long exposure time of them in fire. From the test results, it is recommended that, in repairing severely fire-damaged CFST members, slender members or those members subjected to comparatively large bending moments, other appropriate repair measures should be taken.

Shape sensitivities in the reliability analysis of nonlinear frame structures

A unified and comprehensive treatment of shape sensitivity that includes variations in the nodal coordinates, member cross-section properties, and global shape parameters of inelastic frame structures is presented. A novelty is the consideration of geometric uncertainty in both the displacement- and force-based finite element formulations of nonlinear beam-column behavior. The shape sensitivity equations enable a comprehensive investigation of the relative influence of uncertain geometrical imperfections on structural reliability assessments. For this purpose, finite element reliability analyses are employed with sophisticated structural models, from which importance measures are available. The unified approach presented herein is based on the direct differentiation method and includes variations in the equilibrium and compatibility relationships of frame finite elements, as well as the member cross-section geometry, in order to obtain complete shape sensitivity equations. The analytical shape sensitivity equations are implemented in the OpenSees software framework. Numerical examples involving a steel structure and a reinforced concrete structure confirm that geometrical imperfections may have a significant impact on structural reliability assessments.

Behaviour of concrete-filled double skin (CHS inner and CHS outer) steel tubular stub columns and beam-columns

A series of tests on concrete filled double skin steel tubular (CFDST) stub columns (14) and beam-columns (12) were carried out. Both outer and inner tubes were circular hollow sections (CHS). The main experimental parameters for stub columns were the diameter-to-thickness ratio and hollow section ratio, while those for beam-columns were slenderness ratio and load eccentricity. A theoretical model is developed in this paper for CFDST stub columns and beam-columns. A unified theory is described where a confinement factor (ξ) is introduced to describe the composite action between the outer steel tube and the sandwiched concrete. The predicted load versus deformation relationships are in good agreement with stub column and beam-column test results. Simplified models are derived to predict the load-carrying capacities of the composite members.

Behavior of Concrete-Filled Steel Tube Beam Columns

The behavior of concrete-filled circular and square steel tubular (CFT) beam columns with a variety of material strengths was investigated experimentally. The main test parameters are steel strength (400, 590, and 780 MPa), diameter- (width-) to-thickness ratio of steel tube, and concrete strength (40 and 90 MPa). The interior beam-column models were tested under constant axial compression and cyclic horizontal load with incrementally increasing lateral deformation to clarify the effects of the test parameters on the behavior. The exterior beam-column models were laterally loaded under variable axial load, including axial tension. The behavior of square beam columns subjected to biaxial bending was also investigated. The test results show that higher strength and thicker steel tubes give better overall behavior of the beam column, while higher strength concrete has an adverse effect on the behavior. Furthermore, computer simulations for the hysteretic behavior of CFT beam-column specimens are presented here. The analytical results show excellent agreement with the test results except for a few cases.

Recent Findings from Phase V of the United States–Japan Cooperative Earthquake Research Program

Recent Findings from Phase V of the United States–Japan Cooperative Earthquake Research Program

Seismic Behavior and Design of High-Strength Square Concrete-Filled Steel Tube Beam Columns

The behavior of high strength square concrete filled steel tube (CFT) beam columns subjected to constant axial load and cyclically varying flexural loading was investigated experimentally. The effe...

BUCKLING AND STRESS SOFTENING OF BEAM-COLUMNS UNDER COMPLEX THREE-DIMENSIONAL LOADING

This paper is concerned with buckling and stress softening of beam-columns under axial compression, biaxial bending and torsion. Members with no warping whose cross sections vary along the axis in a uniform manner with respect to the principal directions are also considered. The basic four coupled differential equations governing the behavior of three-dimensional beam columns are reformulated to include varying cross sections. A 12 × 12 stiffness matrix is assembled by solving the equations 6 times (which is sufficient to describe 3D behavior) for a sequence of appropriate discontinuities using the finite difference method. Two sets of curves are then computed. One set displays interaction diagrams that highlight the stress softening of beam stiffnesses. The other set of curves displays the buckling compressive load of a rectangular cantilevered beam under a variety of tri-directional moments (two bending moments and one twisting moment).

THREE-DIMENSIONAL NON-PRISMATIC BEAM-COLUMNS

This paper is concerned with three-dimensional straight beam-columns with no warping whose cross sections vary along the axis in a uniform manner with respect to the principal directions. The basic four coupled differential equations governing the behavior of 3D beam-columns are first rederived using the method of perturbations. These equations are reformulated to include varying cross sections. Finally, a 6 × 6 stiffness matrix (which is sufficient to describe 3D behavior) is computed by solving the equations 6 times for a sequence of appropriate discontinuities. The finite difference method is employed for that purpose. Timoshenko's closed form solution for the buckling load of a tapered column is chosen for comparison with that obtained by the proposed formulation. Effects of twist are also presented.

Beam-column behavior of concrete filled steel tubes

In the present investigation the experimental and theoretical flexural and compressive behavior of short tubular steel columns filled with plain concrete and fiber-reinforced concrete (FRC) was examined. For a given length of the members, the effects of different geometry and dimensions of the transverse cross-section (square and circular) were investigated. Constituent materials were characterized through direct tensile tests on steel coupons and through compressive and split tension tests on concrete cylinders. Load-axial shortening and load-deflection curves were recorded for unfilled and composite members. Finally, simplified expressions for the calculus of the load-deflection curves based on the cross-section analysis were given and the ultimate load of short columns was predicted.

Nonlinear Analysis of Mixed Steel-Concrete Frames. II: Implementation and Verification

This is the second of two companion papers that describe the formulation of analysis models for simulating the inelastic seismic response of three-dimensional mixed frame structures comprised of steel, reinforced-concrete, and/or composite members. Described in a companion paper is the flexibility-based formulation of a three-dimensional beam-column element to model the inelastic cyclic behavior of beam-columns under combined axial load and biaxial bending. This paper describes the development of yield surface equations and stiffness parameter calibration for bisymmetric steel, reinforced concrete, and encased composite beam-columns. Accuracy of the model is verified through comparisons to data from previously published tests and detailed analyses.

鉄筋で補強した円形コンクリート充填鋼管柱の耐火性能

This study deals with the elasto-plastic beam-column behavior of circular steel tube columns infilled with reinforced concrete subjected to fire. Based upon the stress-strain characteristics of materials at high temperatures and the mechanics of column deflection curves, a numerical analysis method has been developed to simulate the time historical response. This method can provide a fairly good estimation for the fire resistant performance of the column. It is found that, comparing a proposed simpler superposed strength theory with the above refined numerical solution, the theory gives a satisfactory approximation to predict reinforcement effects of both steel bars and hoops on the ultimate strength of such columns.