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CONTENTS
Volume 22, Number 3, September 2018
 

Abstract
This study contributes to evaluate multiphase topology optimization design of plate-like elastic structures with constant thickness and Reissner-Mindlin plate theory. Stiffness and adjoint sensitivity formulations linked to Reissner-Mindlin plate potential energy of bending and shear are derived in terms of multiphase design variables. Multiphase optimization problem is solved through alternative active-phase algorithm with Gauss-Seidel version as an optimization model of optimality criteria. Numerical examples verify efficiency and diversity of the present topology optimization method of Reissner-Mindlin elastic plates depending on multiphase and Poisson\' s ratio.

Key Words
topology optimization; multiplase; Reissner-Mindlin plate; Q4 element approximation, adjoint sensitivity; Poisson

Address
Thanh T. Banh, Dongkyu Lee and Jaehong Lee:Department of Architectural Engineering, Sejong University, Seoul 05006, Korea
Joowon Kang: Department of Architecture, Yeungnam University, Gyeongsan 38541, Korea
Soomi Shin: Research Institute of Industrial Technology, Pusan National University, Busan 46241, Korea

Abstract
This paper studies the energies and energy release rate (ERR) for the initially rotationally symmetric compressed (or stretched) in the inward (outward) radial direction of the PZT/Elastic/PZT sandwich circular plate with interface penny-shaped cracks. The investigations are made by utilizing the so-called three-dimensional linearized field equations and relations of electro-elasticity for piezoelectric materials. The quantities related to the initial stress state are determined within the scope of the classical linear theory of piezoelectricity. Mathematical formulation of the corresponding problem and determination of the quantities related to the stress-strain state which appear as a result of the action of the uniformly normal additional opening forces acting on the penny-shaped crack\' s edges are made within the scope of the aforementioned three-dimensional linearized field equations solution which is obtained with the use of the FEM modelling. Numerical results of the energies and ERR and the influence of the problem parameters on these quantities are presented and discussed for the PZT- 5H/Al/PZT-5H, PZT-4/Al/PZT-4, BaTiO3/Al/BaTiO3 and PZT-5H/StPZT-5H sandwich plates. In particular, it is established that the magnitude of the influence of the piezoelectricity and initial loading on the ERR increases with crack radius length.

Key Words
electro-mechanical energy; energy release rate; piezoelectric material; penny-shaped interface crack; sandwich circular plate

Address
Surkay D. Akbarov:Department of Mechanical Engineering, Yildiz Technical University 34349, Besiktas, Istanbul, Turkey;
Institute of mathematics and Mechanics of the National Academy of Sciences of Azerbaijan, AZ1141, Baku, Azerbaijan
Fazile I. Cafarova: Genje State University, Genje, Azerbaijan
Nazmiye Yahnioglu: Department of Mathematical Engineering, Yildiz Technical University, Davutpasa Campus, 34220, Esenler, Istanbul, Turkey

Abstract
In this paper, wavelet finite element model (WFEM) updating technique is employed to detect sub-element damage in thin plate structures progressively. The procedure of WFEM-based detection method, which can detect sub-element damage gradually, is established. This method involves the optimization of an objective function that combines frequencies and modal assurance criteria (MAC). During the damage detection process, the scales of wavelet elements in the concerned regions are adaptively enhanced or reduced to remain compatible with the gradually identified damage scenarios, while the modal properties from the tests remains the same, i.e., no measurement point replacement or addition are needed. Numerical and experimental examples were conducted to examine the effectiveness of the proposed method. A scanning Doppler laser vibrometer system was employed to measure the plate mode shapes in the experimental study. The results indicate that the proposed method can detect structural damage with satisfactory accuracy by using minimal degrees-of-freedoms (DOFs) in the model and minimal updating parameters in optimization.

Key Words
progressive damage detection; thin plate; wavelet finite element; model updating

Address
Wen-Yu He and Wei-Xin Ren: Department of Civil Engineering, Hefei University of Technology, Hefei, 230009, China
Songye Zhu: Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong

Abstract
This paper presents a flexibility based method for damage identification from static measurements in beam-type structures. The response of the beam at the Damaged State is decomposed into the response at the Reference State plus the response at an Incremental State, which represents the effect of damage. The damage is localized by detecting slope discontinuities in the deflection of the structure at the Incremental State. A denoising filtering technique is applied to reduce the effect of experimental noise. The extent of the damage is estimated through comparing the experimental flexural stiffness of the damaged cross-sections with the corresponding values provided by analytical models of cracked beams. The paper illustrates the method by showing a numerical example with two cracks and an experimental case study of a simply supported steel beam with one artificially introduced notch type crack at three damage levels. A Digital Image Correlation system was used to accurately measure the deflections of the beam at a dense measurement grid under a set of point loads. The results indicate that the method can successfully detect and quantify a small damage from the experimental data.

Key Words
damage identification; static deflection; beams; digital photogrammetry

Address
Qiaoyu Ma and Mario Solís: Department of Continuum Mechanics and Structural Analysis, Escuela Tecnica Superior de Ingenieria, Universidad de Sevilla, Camino de los Descubrimientos s/n, 41092 Sevilla, Spain


Abstract
An original quasi-3D hyperbolic shear deformation theory for simply supported functionally graded plates is proposed in this work. The theory considers both shear deformation and thickness-stretching influences by a hyperbolic distribution of all displacements within the thickness, and respects the stress-free boundary conditions on the upper and lower surfaces of the plate without using any shear correction coefficient. By expressing the shear parts of the in-plane displacements with the integral term, the number of unknowns and equations of motion of the proposed theory is reduced to four as against five in the first shear deformation theory (FSDT) and common quasi-3D theories. Equations of motion are obtained from the Hamilton principle. Analytical solutions for dynamic problems are determined for simply supported plates. Numerical results are presented to check the accuracy of the proposed theory.

Key Words
vibration; functionally graded plate; plate theory; thickness-stretching effect

Address
Imene Ait Sidhoum and Djilali Boutchicha: Laboratoire de mecanique applique, Universite des Sciences et Technologie d\'ORAN Mouhamed Boudiaf,BP 1505 Elmnouar 31000, ORAN, Algeria
Samir Benyoucef: Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology,
Civil Engineering Department, Algeria
Abdelouahed Tounsi:Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran, Eastern Province, Saudi Arabia




Abstract
This paper presents a novel time-domain method for the identification of plastic rotations and stiffness parameters of single-bay frames with nonlinear plastic hinges. Each plastic hinge is modelled as a pseudo-semi-rigid connection with nonlinear hysteretic moment-curvature characteristics at an element end. Through the comparison of the identified end rotations of members that are connected together, the plastic rotation that furnishes information of the locations and plasticity degrees of plastic hinges can be identified. The force consideration of the frame members may be used to relate the stiffness parameters to the elastic rotations and the excitation. The damped-least-squares method and damped-and-weighted-least-squares method are adopted to estimate the stiffness parameters of frames. A noise-removal strategy employing a de-noising technique based on wavelet packets with a smoothing process is used to filter out the noise for the parameter estimation. The numerical examples show that the proposed method can identify the plastic rotations and the stiffness parameters using measurements with reasonable level of noise. The unknown excitation can also be estimated with acceptable accuracy. The advantages and disadvantages of both parameter estimation methods are discussed.

Key Words
nonlinear single-bay frames; parameters estimation; plastic rotation; stiffness parameter; unknown excitation

Address
Francis T.K. Auand Z.H. Yan: Department of Civil Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong, P.R. China

Abstract
In this paper, dynamic buckling of the smart subjected to blast load subjected to electric field is studied. The sandwich structure is rested on Pasternak foundation with springs and shear elements. Applying piezoelasticity theory and hyperbolic shear deformation beam theory (HSDBT), the motion equations are derived by energy method. For calculating the dynamic instability region (DIR) of the sandwich structure, differential quadrature method (DQM) along with Bolotin method is used. The aim of this study is to investigate the effects of applied voltage, geometrical parameters of structure and boundary conditions on the DIR of the structure. The results show that applying negative voltage, the DIR will be happened at higher excitation frequencies. In addition, the clamped-clamped beam leads to higher excitation frequency with respect to simply supported boundary condition.

Key Words
dynamic buckling; electric field; HSDBT; DQM; piezoelasticity theory

Address
Maryam Shokravi: Buein Zahra Technical University, Buein Zahra, Qazvin, Iran

Abstract
The behavior of concrete slabs in composite beam with C and L shaped angle shear connectors has been studied in this paper. These two types of angle shear connectors\' instalment have been commonly utilized. In this study, the finite element (FE) analysis and soft computing method have been used both to present the shear connectors\' push out tests and providing data results used later in soft computing method. The current study has been performed to present the aforementioned shear connectors\' behavior based on the variable factors aiming the study of diverse factors\' effects on C and L shaped angle in shear connectors. ANFIS (Adaptive Neuro Fuzzy Inference System), has been manipulated in providing the effective parameters in shear strength forecasting by providing input-data comprising: height, length, thickness of shear connectors together with concrete strength and the respective slip of shear connectors. ANFIS has been also used to identify the predominant parameters influencing the shear strength forecast in C and L formed angle shear connectors.

Key Words
ANFIS; forecasting; cmposite beams; shear connector ; C-formed angle; L-formed angle; psh-out test; Monotonic loading

Address
Yadollah Sedghi and Ebrahim Ahmadi: Department of Civil Engineering, Qeshm International Branch, Islamic Azad University, Qeshm, Iran
Yousef Zandi: Department of Civil Engineering, Tabriz Branch, Islamic Azad University, Tabriz, Iran
Mahdi Shariati: Faculty of Civil Engineering, University of Tabriz, Tabriz, Iran;
Department of Civil Engineering, University of Malaya, Kuala Lumpur, Malaysia;
Malaysia-Japan International Institute of Technology, Universiti Teknologi Malaysia, Kuala Lumpur
Vahid Moghimi Azar: Sofian Branch, Islamic Azad University, Sofian, Iran
Ali Toghroli and Maryam Safa: Department of Civil Engineering, University of Malaya, Kuala Lumpur, Malaysia
Edy Tonnizam Mohamad: Centre of Tropical Geoengineering (GEOTROPIK), Faculty of Civil Engineering, Universiti Teknologi Malaysia, Johor Bahru, Malaysia
Majid Khorami: Facultad de Arquitectura y Urbanismo, Universidad Tecnológica Equinoccial, Calle Rumipamba s/n y Bourgeois, Quito, Ecuador 9University of Human Development, Iraq
Karzan Wakil: University of Human Development, Iraq;
Information Technology Department, Technical College of Informatics, Sulaimani Polytechnic University, Iraq






Abstract
This present study investigates Love-type wave propagation in composite structure consists of a loosely bonded functionally graded piezoelectric material (FGPM) stratum lying over a functionally graded initially-stressed fibre-reinforced material (FGIFM) substrate. The closed-form expressions of the dispersion relation have been obtained analytically for both the cases of electrically open and electrically short conditions. Some special cases of the problem have also been studied and the obtained results are found in well-agreement with the classical Love wave equation. The emphatic influence of wave number, bonding parameter associated with bonding of stratum with substrate of the composite structure, piezoelectric coefficient as well as dielectric constant of the piezoelectric stratum, horizontal initial stresses, and functional gradedness of the composite structure on the phase velocity of Love-type wave has been reported and illustrated through numerical computation along with graphical demonstration in both the cases of electrically open and electrically short condition for the reinforced and reinforced-free composite structure. Comparative study has been carried out to analyze the distinct cases associated with functional gradedness of the composite structure and also various cases which reveals the influence of piezoelectricity, reinforcement and horizontal initial stress acting in the composite structure, and bonding of the stratum and substrate of the composite structure in context of the present problem which serves as one of the major highlights of the study.

Key Words
functionally graded; piezoelectric; loose bonding; reinforced; Love-type wave; initial stress; electrically open and short

Address
Abhishek K. Singh, Zeenat Parween, Mriganka S. Chaki and Shruti Mahto: Department of Applied Mathematics, Indian Institute of Technology (Indian School of Mines), Dhanbad, Jharkhand-826004, India

Abstract
A method is proposed for the identification of instantaneous frequencies (IFs) in time-varying structures. The proposed method combines a maximum gradient algorithm and a smoothing operation. The maximum gradient algorithm is designed to extract the wavelet ridges of response signals. The smoothing operation, based on a polynomial curve fitting algorithm and a threshold method, is employed to reduce the effects of random noises. To verify the effectiveness and accuracy of the proposed method, a numerical example of a signal with two frequency modulated components is investigated and an experimental test on a steel cable with time-varying tensions is also conducted. The results demonstrate that the proposed method can extract IFs from the noisy multi-component signals and practical response signals successfully. In addition, the proposed method can provide a better IF identification results than the standard synchrosqueezing wavelet transform.

Key Words
instantaneous frequency; time-varying structures; maximum gradient; wavelet transform; wavelet ridge

Address
Jing-liang Liu, Ren-Hui Qiu and Jin-Yang Zheng: College of Transportation and Civil Engineering, Fujian Agriculture and Forestry University, Fuzhou, China
Xiaojun Wei,Yan-Jie Zhu and Irwanda Laory: School of Engineering, University of Warwick, Coventry, United Kingdom


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