Tubular Beam-columns Research Articles

Simplified design formula of slender concrete filled steel tubular beam-columns

The objective of this paper is to develop a simplified method that could predict the strength of concrete filled steel tube (CFT) columns applicable to high strength material under combined axial compression and flexure. The simplified method for determining the strength of CFT columns is based on the interaction curve of the section approached by a polygonal connection of the points. These points are determined by using symmetrical properties of the CFT section. For each point, a simple equation is proposed to determine the strength of the slender columns under compression and flexure. The simple equation was adjusted with results of elasto-plastic analysis results. Validation of the simplified method is undertaken by comparison with data from the test conducted at Kyushu University. These results confirm the fact that the simplified method could accurately and reliably predict the strength of CFT columns under combined axial compression and flexure.

一定軸力と変動水平力を受ける円形鋼管柱の弾塑性性状

This paper presents the results of an experimental work carried out to study the strength and behavior of circular steel tubular beam-columns under constant vertical and varying horizontal loads. Diameter-to-thickness ratios and axial load ratios are selected as main test parameters. From the test results, the effects of local buckling and the existence of vertical load on the strength and behavior of the beam-columns are discussed. Moreover, the column strength formula for the plastic design is compared with the test results to check the validity for tubular beamcolumns.

Inelastic large deflection analysis of structural steel members under cyclic loading

The present paper is concerned with the cyclic inelastic large deflection analysis of structural steel members, such as pin-ended columns and fixed-ended tubular beam-columns of strut type. An elastoplastic finite element formulation for beam-columns, accounting for both the material and geometrical nonlinearities, was developed and implemented in the computer program FEAP used in the analysis. The geometrical nonlinearity is considered using the modified approximate updated Lagrangian description of motion. The two-surface plasticity model, recently developed by the authors, is employed for material nonlinearity. The model accounts for the important cyclic characteristics of structural steel, even within the yield plateau, such as, the decrease and disappearance of the yield plateau, reduction of the elastic range and cyclic strain hardening. The cyclic elastoplastic performance of the formulation was found to be good when compared with the experimental results as well as the results obtained from other material models.

Tubular Members. I: Stability Analysis and Preliminary Results

This paper presents a finite-element technique for the analysis of tubular member stability under combined external pressure and structural loads. A tube element is developed for the purposes of this research. While polynomial (quadratic) interpolation is used in the longitudinal direction, Fourier series expansions of the displacement components are adopted at the nodal cross sections. The formulation accounts for large inelastic deformation and recognizes initial imperfections and residual stresses. To trace unstable equilibrium paths, arc-length procedures are implemented. A simple, yet effective estimate of the contribution of external pressure to the tube element stiffness matrix, particularly significant in the analysis of slender tubes, is included. Preliminary results regarding the behavior of tubular members subjected to pressure and bending are reported and discussed. The effects of initial imperfections and residual stresses on the response to pressure along with bending are summarized. Finally, the influence of residual stresses on thrust-moment interaction in tubular beam-columns is examined briefly.

Effects of External Pressure on Capacity of Tubular Beam-Columns

The study reported in this paper has been motivated by the need for accurate estimation of tube capacity under combined loads due to axial force, bending, and external pressure. Unstiffened and ring-stiffened tubular members for offshore applications are analyzed using a rigorous finite-element technique, developed for the purposes of this research. The technique accounts for changes in the geometry of the tube, elastoplastic material behavior, longitudinal and cross-sectional imperfections, and residual stresses from the tube-manufacturing process. The computational results are compared with available experimental data as well as design equations, toward better understanding of tubular-member behavior. Of particular interest is the axial capacity reduction in the presence of pressure. For the unstiffened tubes considered, the ultimate thrust is nearly unaffected by pressure. However, stiffened tubes can be subjected to high levels of pressure that will, in turn, affect the maximum axial compression. The ...

Three-Dimensional Nonlinear Dynamics of Nonintegral Riser Bundle

The dynamic behavior of a nonintegral riser bundle is studied parametrically. The dynamics of each component-riser is analyzed by a three-dimensional, nonlinear, large deflection, small strain model with coupled bending and torsion. Component-risers are slender, thin-walled, extensible or inextensible tubular beam-columns, subject to response and deformation dependent hydrodynamic loads. The con-nector equations of equilibrium are used to derive the connector forces and moments. Substructuring can thus be achieved even though in three dimensions connectors do not impose linearly dependent deflections at substructure interfaces. The developed time incremental and iterative finite-element computer code is used to analyze the effects of water depth, distribution of connectors, distance between component risers and number of finite elements in the numerical model. The problem of total CPU (central processor unit) time and the advantages of substructuring are discussed by running cases of up to 1094 degrees of freedom.

Hysteretic behaviour of thin tubular beam-columns with round corners

Abstract The hysteretic behavior of thin steel tubular beam-columns under cyclic bending and an axial compressive force is investigated experimentally, where the over-all load-deformation characteristics concerning the local instability of thin plate/shell elements are discussed. Special attention is paid to the effect of the presence of the axial compressive force and the use of round corners on the ductility after its ultimate state in view of the aseismic design consideration. From this study, it is found that the axial compressive force may reduce the strength and ductility considerably and also that round corners may be preferred to sharp edges for improving ductility without significant loss of strength and for their good appearance.

Design Interaction Equations for Cylindrical Tubular Beam Columns

The aim of the work described in this paper is to provide an improved interaction equation for the design of braced-steel, cylindrical tubular beam columns. It is found that the current American Institute of Steel Construction (AISC) linear interaction equations generally give a very conservative result for cylindrical tubular members, especially for shorter members and members bent in double curvature, because these equations were developed and refined on the basis of the test results and the exact analyses of wide-flange members. In this paper, a unified design interaction equation for wide-flange members under uniaxial bending recently proposed by the writers is extended to the design of cylindrical tubular beam columns. The effects of local buckling and external hydrostatic pressure on the strength of these members are also considered. Extensive evaluations of the proposed equation have been made by comparing with the results of exact inelastic solutions and more than 100 full-scale tubular column tests, providing final confirmation of the validity of the proposed equation.

曲げと圧縮を受ける冷間成形円形鋼管部材の終局耐力の統計的評価

This paper presents results of an analysis of ultimate behavior of tubular beam-columns based on statistical data for cold-formed circular tubes under combined bending and axial loads. The conclusions drawn are summarized as follows : (1) The hardening exponent included in a stress-strain model for tubular sections after cold-forming was found to be represented by a simple function of yield ratio. Statistics of the yield ratio were determined by using statistical data on compressive yield stresses and ultimate tensile strengths. (2) Mean values and coefficients of variation of the column buckling strengths were obtained by using a semi-probabilistic numerical approach. These values were found to agree well with exact values. (3) A simple theoretical approach based on a proposed stress-strain model was found to be capable of interpreting ultimate strengths of tubular beam-columns in the existing data base. Numerical analysis according to the first order probabilistic approximation was carried out to determine mean values and coefficients of variation of resistances. of tubular beam-columns. (4) On the basis of these numerical results, recommendations were given for the design of tubular beamcolumns.

Effect of pressure on tubular beam-column capacity

Abstract External hydrostatic pressure influences the elastic-plastic response of tubular beam-columns. This paper discusses the effects of pressure on beam-column capacities and proposes a set of interaction equations for analyzing/designing tubular members under combined axial, bending and pressure loads. These formulae are obtained by modifying the standard AISC formulae. Pressure reduces the axial and bending capacities of a member, and thus makes the member more susceptible to failure. Pressure more quickly affects members with high diameter-to-thickness ratios than members with low diameter-to-thickness ratios. A contemporary deep-water drilling platform was checked to determine the effects of pressure on typical designs. Unity checks increased up to 30% for the 1200-foot platform.

鋼管構造部材の弾塑性接線剛性行列

Plastic hinge models based on the concept of flow rule and a yield surface represented by generalized stresses are often used for elastic-plastic analysis of steel space frames. However, since the plastic deformations in plastic hinge are obtained directly by flow rule in those models, it is impossible to introduce distinctly the generalized strain hardening modulus which relates the infinitesimal generalized stress increment to the infinitesimal generalized strain increment as the strain hardening modulus in the finite element analysis of a continuum. This is a main factor that reduces the accuracy of the analitical results. A procedure to form an elastic-plastic tangent stiffness matrix of tubular members is presented in this paper. The generalized strain hardening modulus can be used directly to estimate the behavior of plastic hinge in the procedure and the effect of finite deformations of a frame are taken into account also. Numerical examples are made for two kind of tubular beam-columns and the results are compared with available theoretical and experimental results to verify the proposed method.

Inelastic post-buckling analysis of tubular beam-columns and frames

A numerical procedure for tracing the load-deflection path of tubular beam-columns and frames is presented. Nonlinearities arising from both the change of geometry and material yielding are included, incorporating the effects of arbitrarily large rotations and strain unloading. This numerical scheme is based on a compatible relationship between the incremental and the total equilibrium equations, as opposed to the generally available methods. An updated Lagrangian formulation, coupled with the numerical minimum residual displacement method, is employed for the solution of the nonlinear simultaneous equations. The proposed scheme is validated against a number of examples of which the results by other methods are available. The present method is capable of tracing the equilibrium paths of tubular struts with complex loading and boundary conditions using the incremental-iterative method throughout; suppression of iterations as required in other methods is not needed. This leads to a significant improvement in efficiency and accuracy because of the non-existence of the drift-off numerical error.

Improved convergence of the influence coefficient method

In recent years offshore oil production structures have been posing new problems for designers. The tendency to design lighter and more slender tubular members and structures, revealing greater efficiency in the use of steel, makes buckling an important failure mode. An efficient, theoretical model of cylindrical steel tubular members subjected to the biaxial bending moments combined with axial compression is presented. The model is based on the influence coefficient method, as used for the analysis of the space behaviour and strength of long and intermediate length beam-columns. A more rigorous estimation of the buckling state of end-restrained imperfect tubular spatial beam-columns is achieved, using the constrained displacement length method. Within the requirements of engineering accuracy the load-deflection paths of tubular beam-columns, under no-sway conditions, are determined permitting the examination of their maximum strength and behaviour. The validity of the analytical model is established by comparison with the results of an experimental study. The present method is suitable for use in the calculation of the effective length factors of tubular beam-columns with end-restraints, initial imperfections, eccentricities of the loading and residual stresses.

Multi-surface model application to beam-columns subjected to cyclic loads

This paper deals with an analytical study of the cyclic behaviour of structural members by employing a multi-surface model for material nonlinearity. Extensive numerical studies of tubular beam-columns have been performed with the special stress-strain relationship of cold-formed material. These numerical results are compared with test results by Sherman. It can be concluded from the present study that (i) the multi-surface model based on a special stress-strain relation for the cold-formed material gives excellent agreement with the experimental results by Sherman, for investigation of the cyclic behaviour of tubular beam-columns and (ii) the multi-surface model is suitable for analyses of structural members in general and cold-formed tubular beam-columns in particular, under cyclic loading conditions.

Moment-curvature-axial-compression-pressure relationship of structural tubes

Abstract For tubular members in deepwater offshore platforms which are sealed from the water, the high external hydrostatic pressure introduces an additional compressive hoop stress to the tube. In this paper, the effect of this external hydrostatic pressure on axial load and moment carrying capacity of imperfect inelastic tubular beam-columns is investigated parametrically from the standpoint of beam-column theory. Against the background of this information, modified AISC beam-column interaction equations and sectional-capacity interaction equations are proposed for practical use.

Buckling and cyclic inelastic analysis of steel tubular beam-columns

An numerical procedure combining the Finite Segment Method (FSM) with the Influence Coefficient Method (ICM) is presented for estimating the inelastic behaviour of steel tubular beam-columns under post-buckling and cyclic loading conditions. This combination takes the advantages of FSM and ICM, overcoming the difficulties encountered in numerical analysis at the stages of buckling and post-buckling. The effects of initial imperfections, residual stresses, and end-restraints are taken into account. Generalized stress-strain relationships are used in the analysis. Complete results obtained for a pin-ended beam-column are discussed and compared with available theoretical results.

Behaviour of portal and strut types of beam-columns

A numerical procedure combining the finite segment method with the influence coefficient method has been developed for the cyclic inelastic analysis of steel tubular beam-columns. In this paper, extensive numerical studies of the behaviour of portal and strut-types of beam-columns under monotonic and cyclic loadings are made, using the computer model developed. These studies confirmed the suitability of the numerical procedure proposed. Comparisons have also been made with the results of tests on actual members, providing the needed confirmation of the validity of the method.

Cyclic Analysis of Fix-Ended Steel Beam-Columns

The paper describes an analytical model for theoretically predicting the inelastic cyclic behavior of fix-ended steel beam-columns subjected to one cycle of axial loading. The analysis is based on the hinge-by-hinge method used widely in the study of elastic-plastic behavior of steel structures. In this analysis, the solution of an elastic-plastic beam-column under cyclic and reversed loading is obtained as a sequence of elastic column solutions which follow the history of loading. Using this analytical procedure, closed form expressions are derived for axially loaded beam-columns with constant lateral loads. With these expressions, extensive numerical solutions are presented. Some of the results are compared with available tests on actual tubular beam-columns, providing the needed confirmation of the validity of the simple analytical model for practical use.

Design Interaction Curves for Tubular Steel Beam-Columns

This paper describes a general-purpose computer program developed to determine ultimate load capacities in tubular steel beam-columns. An analytical model and a computer method are presented also. Analytical results are compared with published test data and the experimental data obtained in this investigation. Introduction Previous investigators have shown that tubular members Previous investigators have shown that tubular members of annular shapes exhibit structural characteristics markedly different from wide-flange shapes when subjected to loads that cause stresses above first yield. Methods for calculating failure loads and developing interaction diagrams for wide-flange members used as beam-columns have been developed and are used in design practice currently. Because the same type of technique practice currently. Because the same type of technique for tubular members is not available now, an investigation as launched to develop an analytical tool. This took the form of a computer program that could be used to generate load displacement histories and to calculate failure loads of circular steel tubes subjected to the combined effects of axial force and flexure. This study briefly documents the development of the mathematical model and presents experimental data verifying the results of this computer program. The computer program can account for the effects of residual stresses during the generation of moment-thrust-curvature (MP) data, the first phase in calculating beam-column failure loads. Any configuration of stress-strain relationships may be included by providing appropriate data in tabular form. However, while this investigation includes the determination of MP data, those provided by other investigators also may be put directly into the computer program. Failure loads are calculated by a numerical technique that increases the load in increments until no further load can be supported, when the beam-column is considered to have failed. A testing program was conducted to obtain experimental data. This program comprised four model tests of circular tubes loaded eccentrically to failure. These tests and those of other investigators verified the mathematical model presented. Computer Model The computer model has two major components:generation of MP data anddetermination of failure loads. Details of each are described below. The MP data characterize the behavior of column stubs. This information fundamentally defines the required stress distribution and magnitude necessary for equilibrium of a given strain condition. An open-form solution technique to determine MP relationships for circular tubes by dividing a cross-section into horizontal sectors has been developed previously. The method presented here divides the cross-section into layers of presented here divides the cross-section into layers of elements surrounding the circumference (Fig. 1a) and is more accurate and complete for element idealization. The number of layers and elements is limited only by the size of the specified arrays in the computer program. As developed, the open-form technique permits any configuration of sums-strain relationship and selected residual-stress distribution patterns (Fig. 1b) to be included directly into the solution. JPT P. 367

Plastic Behavior of Tubular Beams Columns

The elastic and plastic behavior of ASTM A-36 tubular beam columns is studied. Experimental results for three tests of tubular beam columns are presented. These tests show that the tubular section is appreciably stronger than a similar wide flange section. This is especially apparent when the beam column is subjected to a relatively large axial load. A theoretical investigation of the tubular shape of a beam column is also conducted. Theoretical moment-axial load-curvature ratio curves are derived for the tubular section with no residual stresses. Values of curvature are numerically integrated to obtain the theoretical beam column buckling load. These data are compared to current analysis equations for beam columns.