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CONTENTS
Volume 59, Number 1, July10 2016
 

Abstract
In this paper, an alternative analytical method is presented to evaluate the nonlinear vibration behavior of single and double tapered cantilever beams. The admissible lateral displacement function satisfying the geometric boundary conditions of a single or double tapered cantilever beam is derived by using Rayleigh-Ritz method. Based on the Lagrange method and the Newton Harmonic Balance (NHB) method, analytical approximate solutions in closed and explicit form are obtained. These approximate solutions show excellent agreement with those of numeric method for small as well as large amplitude. Moreover, due to brevity of expressions, the present analytical approximate solutions are convenient to investigate effects of various parameters on the large amplitude vibration response of tapered beams.

Key Words
Newton Harmonic Balance method; analytical approximation; nonlinear vibration; tapered beam

Address
Weipeng Sun: Department of Mechanics and Engineering Science, School of Mathematics, Jilin University, Changchun 130012, PR China
Youhong Sun, Yongping Yu and Shaopeng Zheng: College of Construction Engineering, Jilin University, Changchun 130026, P.R. China

Abstract
The components of the seismic behavior factor of RC frames are expected to change as structural redundancy increases. Most researches indicate that increasing redundancy is desirable in response to stochastic events such as earthquake loading. The present paper investigated the effect of redundancy on a fixed plan for seismic behavior factor components and the nonlinear behavior of RC frames. The 3D RC moment resistant frames with equal lateral resistance were designed to examine the role of redundancy in earthquake-resistant design and to distinguish it from total overstrength capacity. The seismic behavior factor and dynamic behavior of structures under natural strong ground motions were numerically evaluated as the judging criteria for structural seismic behavior. The results indicate that increasing redundancy alone in a fixed plan cannot be defined as a criterion for improving the structural seismic behavior.

Key Words
redundancy; overstrength capacity; ductility; seismic behavior factor; incremental dynamic analysis

Address
Ali Massumi and Ramin Mohammadi: Department of Civil Engineering, Faculty of Engineering, Kharazmi University, No. 43, Dr Moffateh Ave, Tehran 15719-14911, Iran

Abstract
Reservoir geomechanics can play an important role in hydrocarbon recovery mechanism. In CO2-EOR process, reservoir geomechanics analysis is concerned with the simultaneous study of fluid flow and the mechanical response of the reservoir under CO2 injection. Accurate prediction of geomechanical effects during CO2 injection will assist in modeling the Carbon dioxide recovery process and making a better design of process and production equipment. This paper deals with the implementation of a program (FORTRAN 90 interface code), which was developed to couple conventional reservoir (ECLIPSE) and geomechanical (ABAQUS) simulators, using a partial coupling algorithm. A geomechanics reservoir partially coupled approach is presented that allows to iteratively take the impact of geomechanics into account in the fluid flow calculations and therefore performs a better prediction of the process. The proposed approach is illustrated on a realistic field case. The reservoir geomechanics coupled models show that in the case of lower maximum bottom hole injection pressure, the cumulative oil production is more than other scenarios. Moreover at the high injection pressures, the production rates will not change with the injection bottom hole pressure variations. Also the FEM analysis of the reservoir showed that at CO2 injection pressure of 11000 Psi the plastic strain has been occurred in the some parts of the reservoir and the related stress path show a critical behavior.

Key Words
geomechanics; coupled; bottom hole pressure; FEM; plastic strain; stress path

Address
Ayub Elyasi, Kamran Goshtasbi: Department of Rock Mechanics, Tarbiat Modares University, Tehran, Iran
Hamid Hashemolhosseini: Department of Mining Engineering, Isfahan University of Technology, Isfahan, Iran
Sharif Barati: Faculty of mining, petroleum and geophysics, Shahrood University of technology, Shahrood, Iran

Abstract
Simplifier assumptions which are used in numerical studies of progressive collapse phenomenon in structures indicate inconsistency between the numerical and experimental full-scale results. Neglecting the effects of infill panels and two-dimensional simulation are some of these assumptions. In this study, an existing seismically code-designed steel building is analyzed with alternate path method (AP) to assess its resistance against progressive collapse. In the AP method, the critical columns be removed immediately and stability of the remaining structure is investigated. Analytical macro-model based on the equivalent strut approach is used to simulate the effective infill panels. The 3-dimentional nonlinear dynamic analysis results show that modeling the slabs and infill panels can increase catenary actions and stability of the structure to resist progressive collapse even if more than one column removed. Finally, a formula is proposed to determine potential of collapse of the structure based on the quantity and quality of the produced plastic hinges in the connections.

Key Words
progressive collapse; steel frame structures; column loss; alternate path method; infill panels; nonlinear dynamic analysis

Address
Mohammad Abbasi Zoghi and Masoud Mirtaheri: Department of Civil Engineering, K.N. Toosi University of Technology, Tehran, Iran

Abstract
In this paper, the problem of interfacial stresses in steel beams strengthened with a fiber reinforced polymer plates is analyzed using linear elastic theory. The analysis is based on the deformation compatibility approach developed by Tounsi (2006) where both the shear and normal stresses are assumed to be invariant across the adhesive layer thickness. The analysis provides efficient calculations for both shear and normal interfacial stresses in steel beams strengthened with composite plates, and accounts for various effects of Poisson

Key Words
composites plates; interlaminar stresses; steel beam; strengthening; adherend shear deformations; adhesive

Address
Tahar Hassaine Daouadji, Hadj Bekki: Departement de Genie Civil, Universite Ibn Khaldoun Tiaret, BP 78 Zaaroura, 14000 Tiaret, Algerie; Laboratoire de Geomatique et Développement Durable, Universite Ibn Khaldoun Tiaret, Algerie
Lazreg Hadji, Mohamed Ait Amar Meziane: Departement de Genie Civil, Universite Ibn Khaldoun Tiaret, BP 78 Zaaroura, 14000 Tiaret, Algerie

Abstract
Elasticity solutions for bi-directional functionally graded beams subjected to arbitrary lateral loads are conducted, with emphasis on the end effects. The material is considered macroscopically isotropic, with Young\'s modulus varying exponentially in both axial and thickness directions, while Poisson\'s ratio remaining constant. In order to obtain an exact analysis of stress and displacement fields, the symplectic analysis based on Hamiltonian state space approach is employed. The capability of the symplectic framework for exact analysis of bi-directional functionally graded beams has been validated by comparing numerical results with corresponding ones in open literature. Numerical results are provided to demonstrate the influences of the material gradations on localized stress distributions. Thus, the material properties of the bi-directional functionally graded beam can be tailored for the potential practical purpose by choosing suitable graded indices.

Key Words
bi-directional functionally graded materials; analytical elasticity solutions; symplectic approach; state space; eigenfunction

Address
Li Zhao: Department of Civil Engineering, Ningbo University of Technology, No. 89 Cuibai Road, Ningbo, P.R. China
Jun Zhu: College of Mechanical Engineering, Zhejiang University of Technology, Hangzhou 310014, P.R. China
Xiao D. Wen: College of Electrical and Information Engineering, Yunnan Minzu University, No. 121 YIERYI Avenue, Kunming, P.R. China

Abstract
Many military and commercial aging aircrafts flying beyond their design life may experience severe crack and corrosion damage, and thus lead to catastrophic failures. In this paper, were used in a finite element model to evaluate the effect of corrosion on the adhesive damage in bonded composite repair of aircraft structures. The damage zone theory was implemented in the finite element code in order to achieve this objective. In addition, the effect of the corrosion, on the repair efficiency. Four different patch shapes were chosen to analyze the adhesive damage: rectangular, trapezoidal, circular and elliptical. The modified damage zone theory was implemented in the FE code to evaluate the adhesive damage. The obtained results show that the adhesive damage localized on the level of corrosion and in the sides of patch, and the rectangular patch offers high safety it reduces considerably the risk of the adhesive failure.

Key Words
composite repair; corrosion; damage ratio; finite element method (FEM)

Address
Berrahou Mohamed and B. Bachir Bouiadjra: LMPM, Department of Mechanical Engineering, University of Sidi Bel Abbes, BP 89, Cité Ben M

Abstract
Self-Compacting Concrete (SCC) has been originally developed in Japan to offset a growing shortage of skilled labors, is a highly workable concrete, which is not needed to any vibration or impact during casting. The utilizing of fibers in SCC improves the mechanical properties and durability of hardened concrete such as impact strength, flexural strength, and vulnerability to cracking. The purpose of this investigation is to determine the effect of steel fibers on mechanical performance of traditionally reinforced Self-Competing Concrete beams. In this study, two mixes Mix 1% and Mix 2% containing 1% and 2% volume friction of superplasticizer are considered. For each type of mixture, four different volume percentages of 60/30 (length/diameter) fibers of 0.0%, 1.0%, 1.5% and 2% were used. The mechanical properties were determined through compressive and flexural tests. According to the experimental test results, an increase in the steel fibers volume fraction in Mix 1% and Mix 2% improves compressive strength slightly but decreases the workability and other rheological properties of SCC. On the other hand, results revealed that flexural strength, energy absorption capacity and toughness are increased by increasing the steel fiber volume fraction. The results clearly show that the use of fibers improves the post-cracking behavior. The average spacing of between cracks decrease by increasing the fiber volume fraction. Furthermore, fibers increase the tensile strength by bridging actions through the cracks. Therefore, steel fibers increase the ductility and energy absorption capacity of RC elements subjected to flexure.

Key Words
self-compacting concrete; steel fibers; flexural strength; mechanical performance; fracture energy

Address
Orod Zarrin: Faculty of Civil Engineering, Eastern Mediterranean University, Famagusta, Cyprus
Hamid Reza Khoshnoud: Department of Civil Engineering, Islamic Azad University, Langroud Branch, Langroud, Iran

Abstract
This paper addresses temperature-dependent nonlinear vibration and instability of embedded functionally graded (FG) pipes conveying viscous fluid-nanoparticle mixture. The surrounding elastic medium is modeled by temperature-dependent orthotropic Pasternak medium. Reddy third-order shear deformation theory (RSDT) of cylindrical shells are developed using the strain-displacement relations of Donnell theory. The well known Navier-Stokes equation is used for obtaining the applied force of fluid to pipe. Based on energy method and Hamilton\'s principal, the governing equations are derived. Generalized differential quadrature method (GDQM) is applied for obtaining the frequency and critical fluid velocity of system. The effects of different parameters such as mode numbers, nonlinearity, fluid velocity, volume percent of nanoparticle in fluid, gradient index, elastic medium, boundary condition and temperature gradient are discussed. Numerical results indicate that with increasing the stiffness of elastic medium and decreasing volume percent of nanoparticle in fluid, the frequency and critical fluid velocity increase. The presented results indicate that the material in-homogeneity has a significant influence on the vibration and instability behaviors of the FG pipes and should therefore be considered in its optimum design. In addition, fluid velocity leads to divergence and flutter instabilities.

Key Words
nonlinear vibration; temperature-dependent; orthotropic pasternak medium; FG pipe; fluidnanoparticle mixture

Address
M. Raminnea, H. Biglari and F. Vakili Tahami: Faculty of Mechanical Engineering, University of Tabriz, Tabriz, Iran

Abstract
Practical ambient excitations of engineering structures usually do not comply with the stationary-white-noise assumption in traditional operational modal analysis methods due to heavy traffic, wind guests, and other disturbances. In order to eliminate spurious modes induced by non-white noise inputs, the improved stochastic subspace identification based on a delay index is proposed in this paper for a representative kind of stationary non-white noise ambient excitations, which have nonzero autocorrelation values near the vertical axis. It relaxes the stationary-white-noise assumption of inputs by avoiding corresponding unqualified elements in the Hankel matrix. Details of the improved stochastic subspace identification algorithms and determination of the delay index are discussed. Numerical simulations on a four-story frame and laboratory vibration experiments on a simply supported beam have demonstrated the accuracy and reliability of the proposed method in eliminating spurious modes under non-white noise ambient excitations.

Key Words
operational modal analysis; non-white noise ambient excitations; stochastic subspace identification; delay index

Address
Dan Li: School of Civil Engineering, Hefei University of Technology, Hefei, 230009, China; Department of Civil and Environmental Engineering, National University of Singapore, 117576, Singapore
Wei-Xin Ren: School of Civil Engineering, Hefei University of Technology, Hefei, 230009, China
Yi-Ding Hu: School of Information Engineering, Wuyi University, Jiangmen, 529020, China
Dong Yang: School of Civil Engineering, Hefei University of Technology, Hefei, 230009, China


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