Naoki Kawanishi

Nonlinear Finite-Element Analysis for Hysteretic Behavior of Thin-Walled Circular Steel Columns with In-Filled Concrete

The strength and ductility of thin-walled steel columns under cyclic loads are considerably upgraded by filling concrete into hollow spaces surrounded by steel tube and diaphragms. The above thin-walled steel columns filled with concrete are referred here to as thin-walled CFT columns. Up to the present, no sufficient and precise research has been conducted on the versatile finite-element model (FE model) analysis that can take into account the upgrading mechanism of thin-walled CFT columns in a direct manner. Herein, an accurate FE model is investigated in order to fully include the important factors such as cyclic local buckling of steel tube, nonlinear behavior of confined concrete, and interface action between steel tube and in-filled concrete. The validity of the proposed models is examined by comparing with the results of cyclic loading experiments on CFT columns. With the proposed model, the effect of in-filled concrete on the upgrading mechanism of thin-walled CFT columns is discussed in detail.

Dynamic Stress Amplification Caused by Sudden Failure of Tension Members in Steel Truss Bridges

The property of dynamic stress amplification resulting from the sudden failure of a tension member in a truss bridge is investigated by a precise dynamic response analysis. The primary sources of the dynamic stress amplification are from two types of impacts. The primary impact is attributable to longitudinal strain wave propagation from a failure point. The secondary impact is a result of the dynamic transition of equilibrium from a prefailure to a postfailure state. However, the effect of the primary impact is so small that it can be ignored in evaluating the impact coefficients used for the structural redundancy analysis. The impact coefficients for critical members in a structure take almost a constant value that ranges from 1.4 to 1.8, for which 5% structural damping is assumed, following the single degree of freedom model employed to evaluate the existing impact coefficient of 1.854. To avoid a cumbersome dynamic response analysis, the root mean square mode combination method is applied to calculate approximately the impact coefficients. The impact coefficients so calculated are moderately accurate for practical purposes.

A unified analysis method to predict long-term mechanical performance of steel structures considering corrosion, repair and earthquake

The paper presents a unified structural analysis method in order to take into account the histories of corrosion loss of material and repair on their long term mechanical performance of steel structures in addition to their histories of the damages caused by excessive external loads, e.g. big seismic loads. The analysis method is characterized by the point that the volume change of material due to corrosion or repair is adopted as a new controlling parameter in addition to the conventional parameters such as load and displacement. With this new parameter, the residual stress and residual deformations of structures that are determined by the histories of corrosion loss of material, past repair and seismic damage can be accurately predicted as an arbitrary point of their lifetime.

Transition of Plastic Buckling Modes in Cylindrical Shells

Publisher Summary This chapter analyzes the plastic buckling behavior of cylindrical shells under axial compression, as well as that under alternate transverse loading. It also discusses the characteristics of buckling behavior with a special emphasis on the buckling mode. Thick cylindrical shells under axial compression buckle axisymmetrically to show an elephant-foot bulge, whereas thin-cylindrical shells commonly exhibit a nonaxisymmetric buckling mode, referred to as a diamond-buckling mode. Moderately thick cylindrical shells under axial compression initially exhibit an axisymmetric buckling mode in the plastic range, but this buckling mode develops into a diamond-buckling mode under subsequent loading. The cylindrical shell first exhibits an axisymmetric deformation mode with two symmetric slight bulges near the upper and lower ends of the cylinder. Without the change of this deformation mode, the equilibrium curve reaches the maximum load point. However, if the loading by displacement control is continued after the maximum load point is reached, a localization of buckling patterns occurs at either bulge of the shell. This phenomenon, referred to as an elephant-foot buckling, is caused by a plastic bifurcation on the decreasing equilibrium path, subsequent to the maximum load point. When the localization develops to some extent, the transition from the axisymmetric mode to a nonaxisymmetric mode may occur due to the next bifurcation.