Seung-Eock Kim

Direct design of three-dimensional frames using practical advanced analysis

A new design method of three-dimensional frames using practical advanced analysis is presented. In this method separate member capacity checks encompassed by the code specifications are not required, because the stability of separate members and the structure as a whole can be rigorously treated in determining the maximum strength of the structures. To capture second-order effects associated with P-δ and P-Δ effects, stability functions are used to minimize modeling and solution time. Generally, only one or two elements are needed per member. The Column Research Council (CRC) tangent modulus concept is used to account for gradual yielding due to residual stresses. A softening plastic hinge model is used to represent the transition from elastic to zero stiffness associated with a developing hinge. The load-displacements predicted by the proposed analysis compare well with those given by other approaches. A design example has been presented for a 22-story frame. The analysis results show that the proposed method is suitable for adoption in practice.

Flexural–torsional buckling of thin-walled I-section composites

Abstract Buckling of an axially loaded thin-walled laminated composite is studied. A general analytical model applicable to the flexural, torsional and flexural–torsional buckling of a thin-walled I-section composite subjected to axial load is developed. This model is based on the classical lamination theory, and accounts for the coupling of flexural and torsional modes for arbitrary laminate stacking sequence configuration, i.e. unsymmetric as well as symmetric, and various boundary conditions. A displacement-based one-dimensional finite element model is developed to predict critical loads and corresponding buckling modes for a thin-walled composite bar. Governing buckling equations are derived from the principle of the stationary value of total potential energy. Numerical results are obtained for axially loaded thin-walled composites addressing the effects of fiber angle, anisotropy, and boundary conditions on the critical buckling loads and mode shapes of the composites.

Buckling strength of the cylindrical shell and tank subjected to axially compressive loads

This paper aims to develop practical design equations and charts estimating the buckling strength of the cylindrical shell and tank subjected to axially compressive loads. Both geometrically perfect and imperfect shells and tanks are studied. Numerical analysis is used to evaluate buckling strength. The modeling method, appropriate element type and necessary number of elements to use in numerical analysis are recommended. According to the results of the parametric study of the perfect shell, the buckling strength decreases significantly as the diameter-to-thickness ratio increases, while it decreases slightly as the height-to-diameter ratio increases. These results are different from those in the case of columns. The buckling strength of the perfect tank placed on an extremely soft foundation and a stiff foundation increases by up to 1.6% and 5.6%, respectively, compared with that of the perfect shell. The buckling strength of the shell and tank decreases significantly as the amplitude of initial geometric imperfection increases. Convenient and sufficiently accurate design equations and charts used for estimating buckling strength are provided.

Second-order distributed plasticity analysis of space steel frames

This paper provides benchmark solutions of space steel frames using second-order distributed plasticity analysis. The majority of available benchmark solutions of steel frames in the past were only of two-dimensional frames. Therefore, three-dimensional benchmark solutions are needed to extend the knowledge of this field. Details of the modeling including element type, mesh discretization, material model, residual stresses, initial geometric imperfections, boundary conditions, and load applications are presented. Case studies of Vogels portal frame and space steel frames are performed. The ultimate loads obtained from the proposed analysis and Vogel agree well within 1% error. The ultimate loads of the space steel frames obtained from the proposed analysis and experiment compare well within 3∼5% error. The benchmark solutions of the space steel frames are useful for the verification of various simplified second-order inelastic analyses. It is observed that the load carrying capacities calculated by the AISC-LRFD method are 25∼31% conservative when compared with those of the proposed analysis. This difference is attributed to the fact that the AISC-LRFD approach does not consider the inelastic moment redistribution, but the analysis includes the inelastic redistribution effect.

Flexural–torsional coupled vibration of thin-walled composite beams with channel sections

Free vibration of a thin-walled laminated composite beam is studied. A general analytical model applicable to the dynamic behavior of a thin-walled channel section composite is developed. This model is based on the classical lamination theory, and accounts for the coupling of flexural and torsional modes for arbitrary laminate stacking sequence configuration, i.e. unsymmetric as well as symmetric, and various boundary conditions. A displacement-based one-dimensional finite element model is developed to predict natural frequencies and corresponding vibration modes for a thin-walled composite beam. Equations of motion are derived from the Hamiltons principle. Numerical results are obtained for thin-walled composites addressing the effects of fiber angle, modulus ratio, and boundary conditions on the vibration frequencies and mode shapes of the composites.

Lateral buckling analysis of thin-walled laminated channel-section beams

The lateral buckling of a laminated composite beam with channel section is studied. A general analytical model applicable to the lateral buckling of a channel-section composite beam subjected to various types of loadings is derived. This model is based on the classical lamination theory, and accounts for the material coupling for arbitrary laminate stacking sequence configuration and various boundary conditions. The effects of the location of applied loading on the buckling capacity are also included in the analysis. A displacement-based one-dimensional finite element model is developed to predict critical loads and corresponding buckling modes for a thin-walled composite beam with arbitrary boundary conditions. Numerical results are obtained for thin-walled composites under central point load, uniformly distributed load, and pure bending with angle-ply and laminates. The effects of fiber orientation, location of applied load, and types of loads on the critical buckling loads are parametrically studied.

Free vibration of thin-walled composite beams with I-shaped cross-sections

Abstract A general analytical model applicable to the dynamic behavior of a thin-walled I-section composite is developed. This model is based on the classical lamination theory, and accounts for the coupling of flexural and torsional modes for arbitrary laminate stacking sequence configuration, i.e. unsymmetric as well as symmetric, and various boundary conditions. A displacement-based one-dimensional finite element model is developed to predict natural frequencies and corresponding vibration modes for a thin-walled composite beam. Equations of motion are derived from Hamiltons principle. Numerical results are obtained for thin-walled composites addressing the effects of fiber angle, modulus ratio, height-to-thickness ratio, and boundary conditions on the vibration frequencies and mode shapes of the composites.

Practical advanced analysis software for nonlinear inelastic analysis of space steel structures

This paper presents a practical advanced analysis software which can be used for nonlinear inelastic analysis of space steel structures. The software employs the stability functions and the refined plastic hinge model to minimize modeling and computational time. The generalized displacement control method is adopted to solve the nonlinear equilibrium equations. This algorithm can accurately trace the equilibrium path of the nonlinear problem with multiple limit points and snap-back points. A user-friendly graphic interface of the software is developed to facilitate the modeling process and result interpretation of the problem. Several numerical examples are presented to verify the accuracy and computational efficiency of the proposed software by comparing the results predicted by the present software with those given by the ABAQUS and other available results.

3-D second-order plastic-hinge analysis accounting for local buckling

Abstract In this paper, 3-D second-order plastic-hinge analysis accounting for local buckling is developed. This analysis accounts for material and geometric non-linearities of the structural system and its component members. The problem associated with conventional second-order plastic-hinge analyses, which do not consider the degradation of the flexural strength caused by local buckling, is overcome. Efficient ways of assessing steel frame behavior including gradual yielding associated with residual stresses and flexure, second-order effect, and geometric imperfections are presented. In this study, a model containing the width–thickness ratio is used to account for local buckling. The proposed analysis is verified by the comparison with other analyses and Load Resistance Factor Design results. A case study shows that local buckling is a very crucial element to be considered in second-order plastic-hinge analysis. The proposed analysis is shown to be an efficient, reliable tool ready to be implemented into design practice.

Practical advanced analysis for semi-rigid space frames

A practical advanced analysis of semi-rigid space frame is developed. Herein, the nonlinear behavior of beam-to-column connections is discussed, and practical modeling of these connections is introduced. The proposed analysis can predict accurately the combined nonlinear effects of connection, geometry, and material on the behavior and strength of semi-rigid frames. Kishi–Chen power model is used to describe the nonlinear behavior of semi-rigid connections. Stability functions are used to capture second-order effects associated with P-δ and P-Δ effects. The column research council tangent modulus and a parabolic function for gradual yielding are used to represent material nonlinearity. The load–displacements predicted by the proposed analysis compare well with those available experiments. A case study has been performed for a four story semi-rigid frame.