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CONTENTS
Volume 51, Number 4, August25 2014
 

Abstract
In this paper the extension of a recently established energy-based pushover procedure in order to include the higher mode contributions to the seismic response of structures is presented and preliminary evaluated. The steps of the proposed methodology in its new formulation are quite similar to those of the well-known Modal Pushover Analysis. However, the determination of the properties of the „modal‟ equivalent single-degree-of-freedom systems is achieved by a rationally founded energy-based concept. Firstly, the theoretical background and the assumptions of the proposed methodology are presented and briefly discussed. Secondly, the sequence of steps to be followed for its implementation along with the necessary equations is systematically presented. The accuracy of the methodology is evaluated by an extensive parametric study which shows that, in general, it provides better results compared to those produced by other similar procedures. In addition, the main shortcoming of the initial version of the methodology now seems to be mitigated to a large extent.

Key Words
inelastic seismic response; advanced pushover procedures; energy based procedures; equivalent single-degree-of-freedom system; higher mode effects; multimodal pushover analysis; planar frames

Address
Grigorios E. Manoukas, Asimina M. Athanatopoulou and Ioannis E. Avramidis : Department of Civil Engineering, Aristotle University, University Campus, 54124, Thessaloniki, Greece

Abstract
This study focuses on the application of an active tuned mass damper (ATMD) for controlling the seismic response of an 11-story building. The control action is achieved by combination of a fuzzy logic controller (FLC) and Particle Swarm Optimization (PSO) method. FLC is used to handle the uncertain and nonlinear phenomena while PSO is used for optimization of FLC parameters. The FLC system optimized by PSO is called PSFLC. The optimization process of the FLC system has been performed for an 11-story building under the earthquake excitations recommended by International Association of Structural Control (IASC) committee. Minimization of the top floor displacement has been used as the optimization criteria. The results obtained by the PSFLC method are compared with those obtained from ATMD with GFLC system which is proposed by Pourzeynali et al. and non-optimum FLC system. Based on the parameters obtained from PSFLC system, a global controller as PSFLCG is introduced. Performance of the designed PSFLCG has been checked for different disturbances of far-field and near-field ground motions. It is found that the ATMD system, driven by FLC with the help of PSO significantly reduces the peak displacement of the example building. The results show that the PSFLCG decreases the peak displacement of the top floor by about 10%-30% more than that of the FLC system. To show the efficiency and superiority of the adopted optimization method (PSO), a comparison is also made between PSO and GA algorithms in terms of success rate and computational processing time. GA is used by Pourzeynali et al for optimization of the similar system.

Key Words
active tuned mass damper (ATMD); fuzzy logic controller (FLC); particle swarm optimization (PSO) method; PSFLCG; displacement reduction; earthquake excitations

Address
Hashem Shariatmadar and Hessamoddin Meshkat Razavi : Department of Civil Engineering, Ferdowsi University of Mashhad, Azadi Square, Mashhad, Islamic Republic of Iran

Abstract
The pullout capacity of plate anchors has been studied extensively over the past 40 years. However, very few studies have attempted to calculate the pullout capacity of anchors in sandy slopes. In this paper, three upper bound approaches are used to study the effect of a sloping ground surface and friction angle on pullout capacity and failure of plate anchors. This includes the use of; simple upper bound mechanisms; the block set mechanism approach; and finite element upper bound limit analysis. The aim of this research is to better understand the various failure mechanisms and to develop a simple methodology for estimating the pullout capacity of anchors in sandy slopes.

Key Words
anchors; sand; slope; failure surface; pullout capacity; limit analysis

Address
S.B. Yu, R.S. Merifield, A.V. Lyamin : Centre for Geotechnical and Materials Modelling, The University of Newcastle, Australia
X.D. Fu : School of Civil Engineering, Wuhan University, Wuhan 430072, China

Abstract
In this paper the overall dynamic response of simple railway bridges subjected to high-speed trains is investigated numerically based on the mechanical models of simply supported single-span and continuous two-span Bernoulli-Euler beams. Each axle of the train, which is composed of rail cars and passenger cars, is considered as moving concentrated load. Distance, magnitude, and maximum speed of the moving loads are adjusted to real high-speed trains and to load models according to Eurocode 1. Nondimensional characteristic parameters of the train-bridge interaction system are identified. These parameters permit a spectral representation of the dynamic peak response. Response spectra assist the practicing engineers in evaluating the expected dynamic peak response in the design process of railway bridges without performing time-consuming time history analyses.

Key Words
dynamic peak response; high-speed train; response spectra; train-bridge interaction

Address
Christoph Adam and Patrick Salcher : Department of Civil Engineering Science, Unit of Applied Mechanics, University of Innsbruck, 6020 Innsbruck, Technikerstra

Abstract
Based on continuum mechanics and the principle of virtual displacements, incremental total Lagrangian formulation (T.L.) and incremental updated Lagrangian formulation (U.L.) were presented. Both T.L. and U.L. considered the large displacement stiffness matrix, which was modified to be symmetrical matrix. According to the incremental updated Lagrangian formulation, small strain, large displacement, finite rotation of three dimensional Timoshenko fiber beam element tangent stiffness matrix was developed. Considering large displacement and finite rotation, a new type of tangent stiffness matrix of the beam element was developed. According to the basic assumption of plane section, the displacement field of an arbitrary fiber was presented in terms of nodal displacement of centroid of cross-area. In addition, shear deformation effect was taken account. Furthermore, a nonlinear finite element method program has been developed and several examples were tested to demonstrate the accuracy and generality of the three dimensional beam element.

Key Words
3D Timoshenko fiber beam element; large displacement matrix; finite rotation; total Lagrangian formulation and updated Lagrangian formulation; incremental nonlinear finite element method

Address
Zhengzhou Hu and Minger Wu : Department of Building Engineering, Tongji University, Shanghai 200092, P.R. China

Abstract
Functionally graded steels (FGSs) are a family of functionally graded materials (FGMs) consisting of ferrite (a), austenite (v), bainite (B) and martensite (M) phases placed on each other in different configurations and produced via electroslag remelting (ESR). In this research, the flow stress of dual layer austenitic-martensitic functionally graded steels under hot deformation loading has been modeled considering the constitutive equations which describe the continuous effect of temperature and strain rate on the flow stress. The mechanism-based strain gradient plasticity theory is used here to determine the position of each layer considering the relationship between the hardness of the layer and the composite dislocation density profile. Then, the released energy of each layer under a specified loading condition (temperature and strain rate) is related to the dislocation density utilizing the mechanism-based strain gradient plasticity theory. The flow stress of the considered FGS is obtained by using the appropriate coefficients in the constitutive equations of each layer. Finally, the theoretical model is compared with the experimental results measured in the temperature range 1000-1200\'C and strain rate 0.01-1 s-1 and a sound agreement is found.

Key Words
hot deformation; functionally graded steel; dual-layer; mechanism-based strain gradient plasticity theory

Address
Hadi Salavati, Yoness Alizadeh : Department of Mechanical Engineering, Amirkabir University of Technology, Hafez Ave. 424, Tehran, Iran
Filippo Berto : Department of Management and Engineering, University of Padova, Stradella S. Nicola, 3, 36100 Vicenza, Italy

Abstract
A chaotic vibration isolation system is designed according to the chaotic vibration theory in this paper. The strong nonlinearity is generated by the system. Line spectra in the radiated noise maybe easily detected caused by marine vessels. It is Important to reduce the line spectra by improving the acoustic stealth of marine vessels. A multi-degree-freedom (MDF) nonlinear vibration isolation system (NVIS) system is setup by the experiment and finite element method. The model is established with finite element method. The results show that the behavior of the device gradually varies from period bifurcation into chaotic state and the line spectrum is changed from single spectral structure into broadband spectral structure. It is concluded that chaotic vibration isolation is preferable contrasted on line spectra isolation.

Key Words
chaos; nonlinear system; vibration isolation; multi-degree-freedom

Address
Guoping Jiang and Weijun Tao : School of Engineering, Fujian Jiangxia University, Fuzhou, Fujian 350108, China

Abstract
The main goal of this study is to extend the domain of influence result to cover the micropolar thermoelastic diffusion. So, we prove that for a finite time t>0 the displacement field ui, the microrotation vector oi, the temperature e and the chemical potential P generate no disturbance outside a bounded domain Bt.

Key Words
thermoelastic; micropolar; diffusion; domain of influence

Address
Marin Marin : Department of Mathematics, Transilvania University of Brasov, Romania
Ibrahim Abbas : Department of Mathematics, King Abdulaziz University, Jeddah, Saudi Arabia, Department of Mathematics, Faculty of Science, Sohag University, Egypt
Rajneesh Kumar : Department of Mathematics, Kurukshetra University, India

Abstract
In order to study the dynamic failure mechanism and aseismic measure for high concrete gravity dam under earthquake, the comparative models experiment on the shaking table was conducted to investigate the dynamic damage response of concrete gravity dam with and without the presence of reinforcement and evaluate the effectiveness of the strengthening measure. A new model concrete was proposed and applied for maintaining similitude with the prototype. A kind of extra fine wires as a substitute for rebar was embedded in four-points bending specimens of the model concrete to make of reinforced model concrete. The simulation of reinforcement concrete of the weak zones of high dam by the reinforced model concrete meets the similitude requirements. A tank filled with water is mounted at the upstream of the dam models to simulate the reservoir. The Peak Ground Acceleration (PGA) that induces the first tensile crack at the head of dam is applied as the basic index for estimating the overload capacity of high concrete dams. For the two model dams with and without strengthening tested, vulnerable parts of them are the necks near the crests. The results also indicate that the reinforcement is beneficial for improving the seismicresistant capacity of the gravity dam.

Key Words
similitude relationship; seismic measure; model test; reinforced bar; shaking table

Address
Mingming Wang : Faculty of Electric Power Engineering, Kunming University of Science and Technology, No. 727 South Jingming Road, Chenggong District, Kunming, P.R. China
Jianyun Chen, Shuli Fan and Shaolan Lv : State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, No. 2 Linggong Road, Ganjingzi District, Dalian, Liaoning Province, P.R. China

Abstract
This paper presents a new formulation for forward scalar wave simulations in semi-infinite media. Perfectly-Matched-Layers (PMLs) are used as a wave absorbing boundary layer to surround a finite computational domain truncated from the semi-infinite domain. In this work, a hybrid formulation was developed for the simulation of scalar wave motion in two-dimensional PML-truncated domains. In this formulation, displacements and stresses are considered as unknowns in the PML domain, while only displacements are considered to be unknowns in the interior domain. This formulation reduces computational cost compared to fully-mixed formulations. To obtain governing wave equations in the PML region, complex coordinate stretching transformation was introduced to equilibrium, constitutive, and compatibility equations in the frequency domain. Then, equations were converted back to the time-domain using the inverse Fourier transform. The resulting equations are mixed (contain both displacements and stresses), and are coupled with the displacement-only equation in the regular domain. The Newmark method was used for the time integration of the semi-discrete equations.

Key Words
perfectly-matched-layers; hybrid formulation; scalar elastic waves; PML-truncated domain; complex coordinate stretching

Address
Alireza Pakravan, Craig M. Newtson : Department of Civil Engineering, New Mexico State University, Las Cruces, NM 88003, USA
Jun Won Kang : Department of Civil Engineering, Hongik University, 94 Wausan-ro, Mapo-gu, Seoul 121-791, Korea
Loukas F. Kallivokas : Department of Civil, Architectural and Environmental Engineering, The University of Texas at Austin, Austin, TX 78712, USA


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