Techno Press
Tp_Editing System.E (TES.E)
Login Search


sem
 
CONTENTS
Volume 30, Number 2, September30 2008
 

Abstract
This study utilizes the fine-tuning and small-digit characteristics of the successive zooming genetic algorithm (SZGA) to propose a method of structural damage detection in a continuum structure, where the differences in the natural frequencies of a structure obtained by experiment and FEM are compared and minimized using an assumed location and extent of structural damage. The final methodology applied to the structural damage detection is a kind of pseudo-discrete-variable-algorithm that counts the soundness variables as one (perfectly sound) if they are above a certain standard, such as 0.99. This methodology is based on the fact that most well-designed structures exhibit failures at some critical point due to manufacturing error, while the remaining region is free of damage. Thus, damage of 1% (depending on the given standard) or less can be neglected, and the search concentrated on finding more serious failures. It is shown that the proposed method can find out the exact structural damage of the monitored structure and reduce the time and amount of computation.

Key Words
damage detection; structure; successive zooming genetic algorithm (SZGA); natural frequency; optimization.

Address
Young-Doo Kwon: School of Mechanical Engineering, Kyungpook National University, Daegu 702-701, Korea
Hyun-Wook Kwon: Ubiquitous Fusion Research Department, Research Institute of Industrial Science & Technology, Korea
Whajung Kim: School of Architecture and Civil Engineering, Kyungpook National University, Korea
Sim-Dong Yeo: Graduate School, Mechanical Engineering Department, Kyungpook National University, Korea

Abstract
Recently, many researches have been done to examine the behavior of fiber reinforced concrete (FRC) subjected to the static loading. However, a few studies have been devoted to cyclic behaviors of FRC. A main objective of this paper is to investigate the cyclic behavior of FRC through theoretical method. A new cyclic bridging model was proposed for the analysis of fiber reinforced cementitious composites under cyclic loading. In the model, non-uniform degradation of interfacial bonding under cyclic tension was considered. Fatigue test results for FRC were numerically simulated using proposed models and the proposed model is achieving better agreement than the previous model. Consequently, the model can establish a basis for analyzing cyclic behavior of fiber reinforced composites.

Key Words
cyclic fiber bridging relation; cyclic constitutive relation; fiber reinforced cementitious composites; numerical modeling.

Address
Kyung-Joon Shin: Dept. of Civil Engineering Seoul National University, Shillim-dong, Gwanak-gu, Seoul 151-744, Korea
Kwang-Myong Lee: Dept. of Civil and Environmental Engineering SungKyunKwan University, 300 Cheoncheon-dong, Jangan-gu, Suwon 440-746, Korea
Sung-Pil Chang: Dept. of Civil Engineering Seoul National University, Shillim-dong, Gwanak-gu, Seoul 151-744, Korea

Abstract
In this paper, a new iterative method for solving vehicle-bridge interaction problems is proposed. Iterative methods have advantages over the non-iterative methods in that it is not necessary to
update the system matrix for a given wheel location, and the method can be applied for a new type of car or bridge with few or no modifications. In the proposed method, the necessity of system matrices update is eliminated using the equivalent interaction force acting on the bridge, which is obtained iteratively. Ballast stiffness is included in the interaction forces and the geometric compatibility at the contact points are used as convergence criteria. The bridge is considered as an elastic Bernoulli-Euler beam with surface irregularity and ballast stiffness. The moving vehicle is modeled as a multi-axle mass-spring-damper system having many degrees of freedom depending on the number of axles. The pitching effect, which is the interaction effect between the rear and front wheels when a vehicle begins to enter or leave the bridge, is also considered in the formulation including extended ground boundaries having surface irregularity and ballast stiffness. The applicability of the proposed method is illustrated in the numerical studies.

Key Words
vehicle-bridge interaction; moving vehicle; finite element method; iteration method.

Address
Ji-Seong Jo: POSCO E&C Technical Research Institute, 79-5 Youngcheon, Dongtan, Hwaseong, Gyeonggi-do, Korea
Hyung-Jo Jung: Dept. of Civil and Environmental Engineering, KAIST, 335, Gwahangno, Yuseong-gu, Daejeon 305-701, Korea
Hongjin Kim: School of Architecture & Civil Engineering, Kyungpook National University, 1370 Sangyeok-dong, Buk-gu, Daegu 702-701, Korea

Abstract
Material failure behavior is generally dependent on loading rate. Especially in brittle and quasi-brittle materials, rate dependent material behavior can be significant. Empirical formulations are often used to predict the rate dependency, but such methods depend on extensive experimental works and are limited by practical constraints of physical testing. Numerical simulation can be an effective means for extracting knowledge about rate dependent behavior and for complementing the results obtained by testing. In this paper, the failure behavior of a brittle material under different loading rates is simulated by
molecular dynamics analysis. A notched specimen is modeled by sub-million particles with a normalization scheme. Lennard.Jones potential is used to describe the interparticle force. Numerical simulations are performed with six different loading rates in a direct tensile test, where the loading velocity is normalized to the ratio of the pseudo-sonic speed. As a consequence, dynamic features are achieved from the numerical experiments. Remarkable failure characteristics, such as crack surface interaction/crack arrest, branching, and void nucleation, vary in case of the six loading cases. These characteristics are interpreted by the energy concept approach. This study provides insight into the change in dynamic failure mechanism under different loading rates.

Key Words
dynamic fracture mechanics; rate dependency; molecular dynamics; energy concept approach.

Address
Kunhwi Kim, Jihoon Lim, Juwhan Kim and Yun Mook Lim:
School of Civil and Environmental Engineering, College of Engineering, Yonsei University 134, Sinchon-dong, Seodaemun-gu, Seoul 120-749, Korea

Abstract
A structural monitoring system based on cheap and wireless monitoring system is investigated in this paper. Due to low-cost and low power consumption, micro-electro-mechanical system (MEMS) is suitable for wireless monitoring and the use of MEMS and wireless communication can reduce system cost and simplify the installation for structural health monitoring. For system identification using wireless
MEMS, a finite element (FE) model updating method through correlation with the initial analytical model of the structure to the measured one is used. The system identification using wireless MEMS is evaluated
experimentally using a three storey frame model. Identification results are compared to ones using data measured from traditional accelerometers and results indicate that the system identification using wireless MEMS estimates system parameters with reasonable accuracy. Another smart sensor considered in this paper for structural health monitoring is Lead Zirconate Titanate (PZT) which is a type of piezoelectric material. PZT patches have been applied for the health monitoring of structures owing to their simultaneous sensing/actuating capability. In this paper, the system identification for building structures by using PZT patches functioning as sensor only is presented. The FE model updating method is applied with the experimental data obtained using PZT patches, and the results are compared to ones obtained using wireless MEMS system. Results indicate that sensing by PZT patches yields reliable system identification results even though limited information is available.

Key Words
MEMS; PZT; health monitoring; system identification; FE model updating.

Address
Hongjin Kim, Whajung Kim and Boung-Yong Kim: School of Architecture & Civil Engineering, Kyungpook National University, Korea
Jae-Seung Hwang: School of Architecture, Chonnam National University, Gwangju, Korea

Abstract
A number of studies have suggested that the use of high ductile and high shear materials, such as Engineered Cementitious Composites (ECC) and High Performance Fiber Reinforced Cementitious Composites (HPFRCC), significantly enhances the shear capacity of structural elements, even with/without shear reinforcements. The present study emphasizes the development of a nonlinear model of shear behaviour of a HPFRCC panel for application to the seismic retrofit of reinforced concrete buildings. To model the shear behaviour of HPFRCC panels, the original Modified Compression Field Theory (MCFT) for conventional reinforced concrete panels has been newly revised for reinforced HPFRCC panels, and is referred to here as the HPFRCC-MCFT model. A series of experiments was conducted to assess the shear behaviour of HPFRCC panels subjected to pure shear, and the proposed shear model has been verified through an experiment involving panel elements under pure shear. The proposed shear model of a HPFRCC panel has been applied to the prediction of seismic retrofitted reinforced concrete buildings with in-filled HPFRCC panels. In retrofitted structures, the in-filled HPFRCC element is regarded as a shear spring element of a low-rise shear wall ignoring the flexural response, and reinforced concrete elements for beam or beam-column member are modelled by a finite plastic hinge zone model. An experimental study of reinforced concrete frames with in-filled HPFRCC panels was also carried out and the analysis model was verified with correlation studies of experimental results.

Key Words
HPFRCC panel; in-plane shear; MCFT; seismic retrofit.

Address
Chang-Geun Cho: Hanwha Research Institute of Technology, Hanwha E&C, Korea
Gee-Joo Ha: Dept. of Architectural Engineering, Kyungil University, Korea
Yun-Yong Kim: Dept. of Civil Engineering, Chungnam National University, Korea

Abstract
T-splines are recently proposed mathematical tools for geometric modeling, which are generalizations of B-splines. Local refinement can be performed effectively using T-splines while it is not the case when B-splines or NURBS are used. Using T-splines, patches with unmatched boundaries can be combined easily without special techniques. In the present study, an analysis framework using T-splines is
proposed. In this framework, T-splines are used both for description of geometries and for approximation of solution spaces. This analysis framework can be a basis of a CAD/CAE integrated approach. In this
approach, CAD models are directly imported as the analysis models without additional finite element modeling. Some numerical examples are presented to illustrate the effectiveness of the current analysis
framework.

Key Words
Non-Uniform Rational B-Splines (NURBS); T-splines; isogeometric analysis; finite element method; Computer-Aided Design (CAD); Computer-Aided Engineering (CAE).

Address
Tae-Kyoung Uhm: Dept. of Mechanical Engineering, KAIST, 373-1, Guseong-dong, Yuseong-gu, Daejeon 305-701, Korea
Ki-Seung Kim: Mechanical Engineering R&D Center, LIG Nex1, 148-1, Mabuk-dong, Giheung-gu, Yongin-si, Gyeonggi-do 449-910, Korea
Yu-Deok Seo and Sung-Kie Youn: Dept. of Mechanical Engineering, KAIST, 373-1, Guseong-dong, Yuseong-gu, Daejeon 305-701, Korea

Abstract
Performance of shear-deficient reinforced concrete (RC) beams strengthened with carbon fiber-reinforced polymer (CFRP) strips/sheets is analyzed through numerical simulations on four-point bending tests. The numerical simulations are carried out using the finite element (FE) program ABAQUS. A micromechanics-based constitutive model (Liang et al. 2006) is implemented into the FE program ABAQUS to model CFRP strips/sheets. The predicted results are compared with experiment data (Khalifa and Nanni 2002) to assess the accuracy of the proposed FE analysis approach. A series of numerical tests are conducted to investigate the influence of stirrup lay-ups on the shear strengthening performance of the CFRP strips/sheets, to illustrate the influence of the damage parameters on the microcrack density
evolution in concrete, and to investigate the shear and flexural strengthening performance of CFRP strips/sheets. It has been shown that the proposed FE analysis approach is suitable for the performance
prediction of RC beams strengthened with CFRP strips/sheets.

Key Words
finite element analysis; performance prediction; CFRP strips/sheets; micromechanics-based constitutive model; load-deflection curve.

Address
H. K. Lee, S. K. Ha and M. Afzal: Dept. of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology, Guseong-dong, Yuseong-gu, Daejeon 305-701, Korea


Techno-Press: Publishers of international journals and conference proceedings.       Copyright © 2017 Techno-Press
P.O. Box 33, Yuseong, Daejeon 34186 Korea, Tel: +82-42-828-7996, Fax : +82-42-828-7997, Email: info@techno-press.com