Young Jong Kang

Stability of continuous welded rail track

Abstract As the use of continuous welded rail (CWR) increases in track structures, derailing disasters associated with track buckling also increase in great numbers due to high compressive thermal stress. A three-dimensional CWR track model is developed in the present study to be used for extensive buckling analysis of CWR tracks subjected to temperature load. The analysis model is encoded into a special purpose program using the finite element method. The CWR track model consists of four elements: a mono-symmetric thin-walled open section beam element with 7 degrees of freedom per node to represent the rail; a solid beam-on-elastic-foundation element having 6 degrees of freedom per node to simulate the tie, including vertical and/or longitudinal ballast resistance; an elastic spring element with two nodes and zero length to stand for pad-fastener system; and spring elements for the lateral or longitudinal ballast resistances. Also, two types of significant nonlinearity are included in the track model: the geometric nonlinearity of the rail element, and the materially nonlinear resistance of the ballast. The validity of the present study is strictly verified through a series of comparative analyses with those by others. The nonlinear analysis results have shown that buckling of the track is a three-dimensional problem, and the 2-D rail–tie model and beam model overestimated the CWR track stability.

Summary Review of GPS Technology for Structural Health Monitoring

Over the last two decades, global positioning system (GPS) technology has been developed rapidly and recently applied to civil structures for appropriate monitoring of structural performance. Currently, the GPS technique can only be applied to flexible structures having lower modal frequency ranges, and it still has remaining issues when it comes to obtaining accurate measurements. However, the application of GPS is promising as a monitoring tool because it can measure dynamic characteristics and static displacements in real time, whereas the conventional monitoring system using accelerometers cannot measure static and quasi-static displacements. Furthermore, rapid advancements in GPS devices and algorithms can mitigate erroneous sources of GPS data, and integrated systems using GPS receivers with other supplement sensors are capable of providing accurate measurements. Therefore, GPS technology can provide accurate displacements of structures in real time, and stress and strain conditions of the structures can be computed using finite-element models and numerical analyses. It is also expected that damage localization and severity can be identified using the dynamic characteristics of structures obtained from GPS. This paper summarizes the use of GPS technology for structural health monitoring.

Elastic buckling of I-beams under linear moment gradient

Abstract This paper investigates the elastic lateral–torsional buckling of I-beams under linear moment gradient that very precisely incorporates the effects of moment gradient and various end restraints. The elastic critical buckling moments are obtained independently by using: (1) the Bubnov–Galerkin method and (2) the finite element method. The present formula of the moment gradient correction factor cannot satisfactorily predict the buckling capacities of doubly symmetric and monosymmetric I-beams with various end restraints. We propose alternative equations for evaluating the moment gradient correction factor, considering end restraint conditions.

A consideration on intermediate diaphragm spacing in steel box girder bridges with a doubly symmetric section

Abstract Diaphragms in box girder bridges are implemented primarily to prevent premature excessive distortional deformation under torsional loading condition. Distortional warping and transverse bending stresses, which are the major stress components resulting from distortion, should be appropriately limited to a specific level for efficient use of the cross-section by installing adequate intermediate diaphragms. The objectives of the present study are to develop a thin-walled box beam finite element and to propose tentative design charts for adequate spacing of intermediate diaphragms. The developed beam element possesses nine degrees of freedom per node and the validity was intensively verified from a series of comparative studies using a conventional shell element. Also, performed herein are extensive parametric studies for continuous box girder bridges of doubly symmetric steel box section. The design parameters taken into account were the desired ratio of the distortional warping normal stress to the bending normal stress, the number of spans, the span length, the aspect ratio of the box section, and the spacing of the intermediate diaphragms. The results were summarized into tentative design charts indicating efficient spacing of intermediate diaphragms for the various stress ratios.

A Study on Behavior Characteristics of Precast Coping Part under Axial Load

Recently, bridge construction technology has made great progress from development of high performance materials and new bridge types. However, most technology are based on methods of cast-in-place and material cost saving. The method of cast-in-place concrete causes environmental damages and costumer complaints. Especially, under bad weather conditions, the construction can not proceed. To overcome these disadvantages, new construction methods were developed to reduce construction time. These methods are called precast method. Most prefabricated methods have been applied to superstructure constructions of bridges, but very minutely applied to substructure constructions. The most important agendas on precast method are light weight and transportability of the precasted members, because very strict transporting specifications exist for road transportation of the precasted members. For example, the weight and length of coping members may be larger than the available transporting vehicles. Although column is constructed by precast method to save construction time, if coping member is constructed by cast-in-place method, then the column construction time reduction becomes meaningless. Therefore, in this study, a new precast coping member and a connecting system of column-coping member are proposed. The proposed method is verified by analyzing their ultimate performance through analysis and experimental study.

Behavior of Internally Confined Hollow RC Columns

Dept. of Civil Engineering, Sunmoon University, Asan 336-708, KoreaABSTRACT A nonlinear column model of an internally confined hollow (ICH) reinforced concrete (RC) column was suggestedand a parametric study was performed. The suggested column model considered the confining effect and the material nonlinearityof concrete. To verify the suggested column model, its analysis results were compared with the test results from previous research-ers and a quasi static test performed in this study. They showed that the suggested column model was reasonable and had accepta bleaccuracy. The results from parametric studies showed that the thickness of the internal tube, concrete strength, and the hollow ratioof the ICH RC column affected its behavior.Keywords : column, composite, nonlinear, hollow, confining effect

Performance Evaluation of the Column-Coping Joint for Prefabricated DSCT Pier

Recently, Technology of bridge construction has made great progress for reduction of construction period and Green Growth. The construction period of Pier had about 50% in construction period of entire bridge. Therefore, construction method of prefabricated piers have researched by many researchers, lately. In this paper, we suggested the joint of coping-column for prefabricated DSCT pier and verified by experimental study. To experimental study, the test methods had proposed for the performance characteristics evaluation of coping-column joint. Test methods were made up cyclic eccentricity loading test and static compressive loading test. We had produced the major parameters and suggested the standard model for joint of coping-column through the experimental study.

Flexural-torsional buckling of stepped beams subjected to pure bending

The cross sections of continuous multi-span beams are sometimes increased suddenly, or stepped, at interior supports of continuous beams to resist high negative moments. An investigation of the elastic flexural-torsional buckling (FTB) behavior of I-shaped stepped beams was conducted using finite element method (FEM) and resulted in the development of design equations for beams having singly or doubly stepped cross sections within a laterally unbraced length. The finite element models are subjected to pure bending moment in the entire beam span. Results from the design equations were demonstrated with comparisons between the proposed equations or the weighted average approach (WAA) and FEM results for doubly and singly stepped beam spans of existing highway bridges. The new equations proposed definitely improve current design methods for the FTB problem and increase efficiency in building and bridge design. The proposed solutions can be easily used to develop new design equation for FTB resistance of stepped beams subjected to general loading condition such as a concentrated load, a series of concentrated loads or uniformly distributed load.

A Study of the Effect of Imperfection on Buckling Strength in Thin Cylindrical Shells under Bending

The thin cylindrical shell structure under compression should be checked with buckling stability. Initial imperfection effects on buckling strength has been investigated by many researchers. Even though there have been a number of these studies, more studies of buckling strength with various initial imperfections are still necessary. In Eurocode, there is a design parameter that is applicable only on specific imperfection by section thickness rather than on various initial imperfection. In this study, structural analyses, using geometry and material nonlinear analysis, of cylindrical buckling strength with various initial imperfection were performed and compared with Eurocode design strength and Finite Element Method (FEM) analysis results. Moreover, the modified design parameter, which gives more exact prediction result of buckling strength under bending with initial imperfection, is proposed for various initial imperfections.

Evaluation of the Weak Part for Wave Dissipating Blocks under Various Conditions: Tetrapod

Super typhoons develop as a result of meteorological changes. In 2012, Typhoons Bolaven and Denba reached Korea. The maximum instantaneous wind speed of the typhoons reached 60 m/sec. Harbor structures including sofa block sustained damage and loss by the abnormally high waves. In Korea, tetrapod blocks were installed the most for wave dissipating. Nevertheless, a structural evaluation of the tetrapod block has not been performed. This study examined the structural mechanism and weakness part of the tetrapod block under a range of boundary conditions. The block has weakness against a tensile force because it is plain concrete. The joint part of the legs is the most vulnerable to tensile stress. The weakest part can be reduced if the joint part is reinforced as a hunch.