Myung-Rag Jung

Deflection Theory for Self-Anchored Suspension Bridges under Live Load

AbstractFor self-anchored suspension bridges having the fabrication camber subjected to live loads, a new deflection theory is formulated after an optimized initial state solution is found under dead loads. Its analytical solution for three-span continuous suspension bridges is consistently derived by considering tower effects compared with that derived by the conventional deflection theory for earth-anchored bridges. On the other hand, the unstrained length method (ULM), which keeps all element lengths constant in the nonlinear iteration process, is extended and applied to the nonlinear finite-element analysis of suspension bridges under live loads. Finally, an earth-anchored and self-anchored bridge examples are analytically and numerically solved using the two methods. The numerical results are compared to verify the accuracy and effectiveness of both the proposed deflection theory and the ULM.

Dynamic Interaction Analysis of Maglev-Guideway System Based on a 3D Full Vehicle Model

The purpose of this paper is to develop a detailed 3D maglev vehicle and guideway model and investigate the dynamic response characteristics of the coupled system. For this, the maglev vehicle is modeled as one cabin and four bogies having eight electromagnetics, four sensors, and four secondary suspensions based on the Urban Transit Maglev (UTM) system in Korea. The 3D dynamic equilibrium equations of the cabin and bogies are derived by considering the actively controlled electromagnetic forces. Also, the equations of motion for the guideway are derived using the modal superposition method for vertical, lateral, and torsional modes. The resulting coupled equations of motion are then solved using a predictor–corrector iterative algorithm. Finally, through the numerical simulation of the developed system, the responses using the 3D maglev vehicle model are compared with those obtained by the corresponding 2D model. The effects of surface irregularity on the dynamic interaction behaviors are then evaluated for increasing vehicle speeds. Particularly, the 3D resonance conditions of the guideway girder and the maglev vehicle are presented considering the resonance conditions due to equidistant moving loads. In addition, some resonance phenomena are rigorously explored, including the lateral resonance by a series of vehicles running on a girder.

Simplified Analytical Method for Optimized Initial Shape Analysis of Self-Anchored Suspension Bridges and Its Verification

A simplified analytical method providing accurate unstrained lengths of all structural elements is proposed to find the optimized initial state of self-anchored suspension bridges under dead loads. For this, equilibrium equations of the main girder and the main cable system are derived and solved by evaluating the self-weights of cable members using unstrained cable lengths and iteratively updating both the horizontal tension component and the vertical profile of the main cable. Furthermore, to demonstrate the validity of the simplified analytical method, the unstrained element length method (ULM) is applied to suspension bridge models based on the unstressed lengths of both cable and frame members calculated from the analytical method. Through numerical examples, it is demonstrated that the proposed analytical method can indeed provide an optimized initial solution by showing that both the simplified method and the nonlinear FE procedure lead to practically identical initial configurations with only localized small bending moment distributions.

Dynamic Interaction Analysis of Low, Medium and Super-high Speed Maglev and Guideways

The purpose of this study is to examine the dynamic characteristics of low, medium and high speed Maglev trains and guideways through dynamic interaction analysis. The coupled dynamic equations of motion for a vehicle of 10-dof and the associated guideway girders are developed by superposing vibration modes of the girder itself. The controller used in the UTM-01 Maglev vehicle is adopted to control the air gap between the bogie and guideway in this study. The effect of roughness, the guideway deflection-ratio and vehicle speed on the dynamic response of the maglev vehicle and guideway are then investigated using the 4th Runge-Kutta method. From the numerical simulation, it is found that the air gap increases with an increase of vehicle speed and the roughness condition. In particular, the dynamic magnification factor of the guideway girder is small at low and medium speeds, but the factor is noticeable at super-high speeds.

Elastic Stability Behavior of Self-Anchored Suspension Bridges by the Deflection Theory

To investigate the elastic buckling behavior of self-anchored suspension bridges subjected to proportionally increasing dead loads, a new stability procedure is proposed based on the deflection theory. For this purpose, a finite element buckling analysis is performed using the initial state solution based on the unstrained length method (ULM) (Ref. 1). The finite element solutions are compared with those by the deflection theory. It is shown that both the main girder and tower of the self-anchored suspension bridge are under compression, but their fundamental buckling modes are tower-dominant. Importantly, it is observed that local buckling within the main girder supported by hangers occurs without any geometric change of the main cable, in the higher buckling modes of the self-anchored suspension bridge.

The Effect of Moving Mass on Resonance Phenomenon and Natural Frequency of a Simply Supported Beam

ABSTRACT The purpose of this study is to investigate the influence of moving mass on the vibration charac-teristics and the dynamic response of the simply supported beam. The three types of the moving mass(moving load, unsprung mass, and sprung mass) are applied to the vehicle-bridge interaction analysis. The numerical analyses are then conducted to evaluate the effect of the mass, spring and damper properties of the moving mass on natural frequencies and dynamic responses of the simply supported beam. Particularly, in the case of the sprung mass, variations of the natural frequency of simply supported beam are explored depending on the position of the moving mass and the fre-quency ratio of the moving mass and the beam. Finally the parametric studies on the resonance phe-nomena are performed with changing mass, spring and damper parameters through the dynamic inter-action analyses. * 1. 서 론 열차-교량의 상호작용 해석은 이동하중에 따른 교량의 진동특성 및 동적 충격계수의 증가, 그리고 교량의 사용성 및 열차의 주행 안정성 등을 파악하는 분야로 많은 연구가 수행된바 있다. Willis

Structural Responses of Composite-girder Bridges Due to Design Live Loads using Distribution Factor Method and Grillage Analysis

Abstract In this paper, the modified live-load and designed formula are studied according to the fact the highway bridge design specifications are recently revised. The two examples for composite steel plates and PSC girder bridges are studied. The envelope is analyzed with the finite element models and lateral load distribution method applying the existing highway bridge specification(2010), the newly revised highway bridge specification(2015) and AASHTO LRFD. In case of composite steel plates, length changes between spans are studied, and in case of PSC girder. changes of the number of cross-beams and spans, and span-lengths, are analyzed. Keywords :Live load, plane grillage model, lateral distribution factor method, finite element method † Corresponding author: Tel: +82-31-290-7514; E-mail: kmye@skku.ac.kr Received October 17 2014; Revised January 21 2015Accepted February 23 2015Ⓒ2015 by Computational Structural Engineering Institute of KoreaThis is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License(http://creativecommons. org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Lagrangian Formulation of a Geometrically Exact Nonlinear Frame-Cable Element

Two nonlinear frame elements taking into account geometric nonlinearity is presented and compared based on the Lagrangian co-rotational formulation. The first frame element is believed to be geometrically-exact because not only tangent stiffness matrices is exactly evaluated including stiffness matrices due to initial deformation but also total member forces are directly determined from total deformations in the deformed state. Particularly two exact tangent stiffness matrices based on total Lagrangian and updated Lagrangian formulation, respectively, are verified to be identical. In the second frame element, the deformed curved shape is regarded as the polygon and current flexural deformations in iteration process are neglected in evaluating tangent stiffness matrices and total member forces. Two numerical examples are given to demonstrate the accuracy and the good performance of the first frame element compared with the second element. Furthermore it is shown that the first frame element can be used in tracing nonlinear behaviors of cable members.