TEM investigation of hydrogen-implanted and annealed single-crystal SrTiO3

G.K.H. Pang,C.W. Tai,Y. Wang,W.L. Liu,Z.T. Song,S.L. Feng,H.L.W. Chan,C.L. Choy 한국물리학회 2006 Current Applied Physics Vol.6 No.3

In this study, the structural properties of single-crystal SrTiO3 implanted with H+ have been investigated by transmission electronmicrocopy (TEM). The investigation was carried out on an as-implanted sample and samples after annealing at 500.C and 700 .Cfrom the implanted energy similar to the process in the case of silicon. The as-implanted sample shows large out-of-plane strain alsosimilar to the report in silicon. The microcavities are lled with amorphous material as the result of complicated interaction of the defectsduring the annealing.

Buffeting-induced stresses in a long suspension bridge: structural health monitoring oriented stress analysis

T.T. Liu,Y.L. Xu,W.S. Zhang,K.Y. Wong,H.J. Zhou,K.W.Y. Chan 한국풍공학회 2009 Wind and Structures, An International Journal (WAS Vol.12 No.6

Structural health monitoring (SHM) systems have been recently embraced in long span cablesupported bridges, in which buffeting-induced stress monitoring is one of the tasks to ensure the safety of the bridge under strong winds. In line with this task, this paper presents a SHM-oriented finite element model (FEM) for the Tsing Ma suspension bridge in Hong Kong so that stresses/strains in important bridge components can be directly computed and compared with measured ones. A numerical procedure for buffeting induced stress analysis of the bridge based on the established FEM is then presented. Significant improvements of the present procedure are that the effects of the spatial distribution of both buffeting forces and self-excited forces on the bridge deck structure are taken into account and the local structural behaviour linked to strain/stress, which is prone to cause local damage, are estimated directly. The field measurement data including wind, acceleration and stress recorded by the wind and structural health monitoring system (WASHMS) installed on the bridge during Typhoon York are analyzed and compared with the numerical results. The results show that the proposed procedure has advantages over the typical equivalent beam finite element models.

Evaluation of typhoon induced fatigue damage using health monitoring data for the Tsing Ma Bridge

Chan, Tommy H.T.,Li, Z.X.,Ko, J.M. Techno-Press 2004 Structural Engineering and Mechanics, An Int'l Jou Vol.17 No.5

This paper aims to evaluate the effect of typhoons on fatigue damage accumulation in steel decks of long-span suspension bridges. The strain-time histories at critical locations of deck sections of long-span bridges during different typhoons passing the bridge area are investigated by using on-line strain data acquired from the structural health monitoring system installed on the bridge. The fatigue damage models based on Miner's Law and Continuum Damage Mechanics (CDM) are applied to calculate the increment of fatigue damage due to the action of a typhoon. Accumulated fatigue damage during the typhoon is also calculated and compared between Miner's Law and the CDM method. It is found that for the Tsing Ma Bridge case, the stress spectrum generated by a typhoon is significantly different than that generated by normal traffic and its histogram shapes can be described approximately as a Rayleigh distribution. The influence of typhoon loading on accumulative fatigue damage is more significant than that due to normal traffic loading. The increment of fatigue damage generated by hourly stress spectrum for the maximum typhoon loading may be much greater than those for normal traffic loading. It is, therefore, concluded that it is necessary to evaluate typhoon induced fatigue damage for the purpose of accurately evaluating accumulative fatigue damage for long-span bridges located within typhoon prone regions.

A new bridge-vehicle system part II: Parametric study

Chan, Tommy H.T.,Yu, Ling,Yung, T.H.,Chan, Jeffrey H.F. Techno-Press 2003 Structural Engineering and Mechanics, An Int'l Jou Vol.15 No.1

The formulation of a new bridge-vehicle system using shell with eccentric beam elements has been introduced in a companion paper (Part I). The new system takes into account of the contribution of the twisting and pitching modes of vehicles to the bridge responses. It can also be used to study the dynamic transverse load distribution of a bridge. This paper presents a parametric study on the impact induced by one vehicle or multi-vehicle running across a bridge using the proposed model. Several parameters were considered as variables including the mass ratio, the speed parameter, the frequency ratio and the axle spacing parameter to investigate their effects on the impact factor. A total number of 189 cases were carried out in this parametric study. Within the realistic range of vehicle considered, the maximum impact factors could be 2.24, 1.78 and 1.49 for bridges with spans 10 m, 20 m and 30 m respectively.

Damage detection in truss bridges using vibration based multi-criteria approach

H.W. Shih,D.P. Thambiratnam,T.H.T. Chan 국제구조공학회 2011 Structural Engineering and Mechanics, An Int'l Jou Vol.39 No.2

This paper uses dynamic computer simulation techniques to develop and apply a multicriteria procedure using non-destructive vibration-based parameters for damage assessment in truss bridges. In addition to changes in natural frequencies, this procedure incorporates two parameters, namely the modal flexibility and the modal strain energy. Using the numerically simulated modal data obtained through finite element analysis of the healthy and damaged bridge models, algorithms based on modal flexibility and modal strain energy changes before and after damage are obtained and used as the indices for the assessment of structural health state. The application of the two proposed parameters to truss-type structures is limited in the literature. The proposed multi-criteria based damage assessment procedure is therefore developed and applied to truss bridges. The application of the approach is demonstrated through numerical simulation studies of a single-span simply supported truss bridge with eight damage scenarios corresponding to different types of deck and truss damage. Results show that the proposed multi-criteria method is effective in damage assessment in this type of bridge superstructure.

Statistical models from weigh-in-motion data

Chan, Tommy H.T.,Miao, T.J.,Ashebo, Demeke B. Techno-Press 2005 Structural Engineering and Mechanics, An Int'l Jou Vol.20 No.1

This paper aims at formulating various statistical models for the study of a ten year Weigh-in-Motion (WIM) data collected from various WIM stations in Hong Kong. In order to study the bridge live load model it is important to determine the mathematical distributions of different load affecting parameters such as gross vehicle weights, axle weights, axle spacings, average daily number of trucks etc. Each of the above parameters is analyzed by various stochastic processes in order to obtain the mathematical distributions and the Maximum Likelihood Estimation (MLE) method is adopted to calculate the statistical parameters, expected values and standard deviations from the given samples of data. The Kolmogorov-Smirnov (K-S) method of approach is used to check the suitability of the statistical model selected for the particular parameter and the Monte Carlo method is used to simulate the distributions of maximum value stochastic processes of a series of given stochastic processes. Using the statistical analysis approach the maximum value of gross vehicle weight and axle weight in bridge design life has been determined and the distribution functions of these parameters are obtained under both free-flowing traffic and dense traffic status. The maximum value of bending moments and shears for wide range of simple spans are obtained by extrapolation. It has been observed that the obtained maximum values of the gross vehicle weight and axle weight from this study are very close to their legal limitations of Hong Kong which are 42 tonnes for gross weight and 10 tonnes for axle weight.

The use of eccentric beam elements in the analysis of slab-on-girder bridges

Chan, Tommy H.T.,Chan, Jeffrey H.F. Techno-Press 1999 Structural Engineering and Mechanics, An Int'l Jou Vol.8 No.1

With the advent of computer, the finite element method has become a most powerful numerical method for structural analysis. However, bridge designers are reluctant to use it in their designs because of its complex nature and its being time consuming in the preparation of the input data and analyzing the results. This paper describes the development of a computer based finite element model using the idea of eccentric beam elements for the analysis of slab-on-girder bridges. The proposed method is supported by a laboratory test using a reinforced concrete bridge model. Other bridge analytical schemes are also introduced and compared with the proposed method. The main aim of the comparison is to prove the effectiveness of the shell and eccentric beam modelling in the studies of lateral load distribution of slab-on-girder bridges. It is concluded that the proposed finite element method gives a closer to real idealization and its developed computer program, SHECAN, is also very simple to use. It is highly recommended to use it as an analytical tool for the design of slab-on-girder bridges.

A new bridge-vehicle system part I: Formulation and validation

Chan, Tommy H.T.,Yu, Ling,Yung, T.H.,Chan, Jeffrey H.F. Techno-Press 2003 Structural Engineering and Mechanics, An Int'l Jou Vol.15 No.1

This paper presents the formulation of a new bridge-vehicle system with validation using the field data. Both pitching and twisting modes of the vehicle are considered in the contribution of the dynamic effects in the bridge responses. A heavy vehicle was hired as a control vehicle with known axle weight, axle spacing and spring coefficients. The measured responses were generated from the control vehicle running at a particular speed at a test span at Ma Tau Wai Flyover. The measured responses were acquired using strain gauges installed beneath the girder beams of the test bridge. The simulated responses were generated using BRVEAN that is a self-developed program based on the proposed bridge-vehicle system. The validation shows that the bridge model is valid for representing the test bridge and the governing equations are valid for representing the motion of moving vehicles.

Micro-ultrasonic welding using thermoplastic-elastomeric composite film

Chan, W.X.,Ng, S.H.,Li, K.H.H.,Park, W.T.,Yoon, Y.J. Elsevier 2016 Journal of materials processing technology Vol. No.

<P>A composite film of PMMA microspheres in PDMS is used as the fusion layer to avoid trapped air and to restrict the flow of the melted polymer during welding. The matrix material selection and distribution of PMMA microspheres is determined by the 1-D theoretical model. The theoretical work reveals that the difference in dynamic modulus between the matrix material and PMMA is the most significant contribution to the viability of this composite ultrasonic welding film. The experiment is conducted with PDMS as the matrix material to determine effect of the concentration of PMMA microspheres as micro energy directors on the welding strength and quality of the proposed methodology with the chosen composite. While there are no visible signs of trapped air in all specimens, the resultant welding strength in this methodology is limited by the particle size range of the PMMA microspheres. For ultrasonic energy input of 1 kJ on a 32 mm x 32 mm sample, the optimum concentration of PMMA microspheres is found to be 0.24. (C) 2016 Elsevier B.V. All rights reserved.</P>

Hot spot stress approach for Tsing Ma Bridge fatigue evaluation under traffic using finite element method

T. H. T. Chan,T. Q. Zhou,Z. X. Li,L. Guo 국제구조공학회 2005 Structural Engineering and Mechanics, An Int'l Jou Vol.19 No.3