Byung H. Choi

Bending Stiffness Requirement for Closed-Section Longitudinal Stiffeners of Isotropic Material Plates under Uniaxial Compression

AbstractLongitudinally stiffened plates with closed-section ribs are supposed to be an effective system for axially compressed members. However, current design specifications on closed-section ribs, particularly for the minimum required stiffness, are not sufficient, and thus, excessive designs are quite common because of the absence of suitable design guides. In this paper, simple closed-form formulas for the minimum required stiffness of compressively loaded isotropic plates braced by U-shaped longitudinal stiffeners (U-ribs) are derived. The effects of the sectional stiffness of U-ribs on the buckling modes and strengths of stiffened plates are examined by numerical analyses. Three-dimensional finite-element models of U-rib stiffened plates were obtained, and a series of eigenvalue analyses was conducted. By parametric study, thresholds of the sectional stiffness of U-ribs that may be adopted as the minimum requirement were collected, and these were used for regression analysis to obtain a simple and p...

Local Buckling Strength of Modular Hexagon-section Shell Wind-Turbine Towers

Since dimensions and height of wind-turbine towers keep growing, new modular construction methods using polygonal-section shell columns are strongly required in order to enhance the economical construction during fabrication, transportation and erection of those. This study examines the local buckling strength of newly proposed 3-module type and 6-module type hexagon-section shell towers by using the finite element method. Initial imperfections due to newly proposed fabrication processes were considered for numerical evaluation of local buckling strenngth of hexagonal section modular towers. The strength equations suggested by AASHTO LRFD, DIN codes and previous research results were compared with the analytically evaluated strengths from this study. From the comparative study, it could be identified that design equations show statistically better correlation with the analysis results. Experimental studies to verify initial imperfections existed in the modular hexagonal-section shell towers are required for future study.

Compressive Strength Evaluation of Longitudinally Stiffened Octangular-Section Modular Shell Towers

This paper examined the uniaxial compressive strength of longitudinally-stiffened octangular modular section towers. Through a series of comparative studies, the 3-dimensional finite element analysis results were considerably larger than the nominal strength values based on Eurocode. Therefore, the design strength equations are simply applicable to the design of the octangular-section tower module, but a more rational method will be needed to properly predict the capacity.

Numerical Analysis on Bending Strength and Ductility of Compact Section I-Girders with HSB800 Steels

New high performance steel HSB800 have been developed in South Korea, the yield strength of which is equal to 690MPa. High strength steels typically show a lower ductility and a larger yield ratio than conventional steels. Since the inelastic design procedure of current AASHTO specifications is not permitted to the flanges and webs of nominal yield stress exceeding 485 MPa, this study is intended to present an assessment result of the compactness requirements for I-section girders by performing 3D nonlinear finite element analyses. On the hypothetical specimens designed to be compact-section girders, the numerical analysis was performed using the finite element code ABAQUS. From the analysis results, it is found that the compact section limits speculated in the 2007 AASHTO LRFD could be applicable to the design of HSB800 steel I-girders to reach the plastic moment. However, the inelastic design procedure does not surely confirm a sufficient flexural ductility. More extensive studies of HSB800 I-girders are still in need.

Flexural Ductility of High Strength Steel Girder in Negative Moment Region

For I-girder with high strength steel, it is known that the flexural ductility is considerably decreased by increasing the yield strength of material. Thus, it is necessary to conduct a study for guaranteeing proper flexural ductility of I-girder with high-strength steel. In this study, the evaluation of flexural ductility of negative moment region of I-girder with high strength steel where yield stress of steel is 690Mpa is presented based on the results of finite element analysis and experiment. From the results, it is found that the flexural ductility of the I-girder is significantly reduced due to the increase of elastic deformation and the decrease of plastic deformation ability of the material when the yield strength increases. This study proposed equation predicted flexural ductility of high strength steel in negative moment region. It is also proposed the method to improve the flexural ductility by an unequal installation of cross beam and an optimal position of cross beam. Finally, the effects of the unequal installation of cross beam on the flexural ductility are discussed based on the finite element results and the experimental results.