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CONTENTS
Volume 71, Number 1, July10 2019
 

Abstract
This study investigates optimum designs of steel space truss towers under seismic loading by using Jaya optimization algorithm. Turkish Earthquake Code (2007) specifications are applied on optimum designs of steel space truss towers under the seismic loading for different local site classes depending on different soil groups. The proposed novel algorithm does not have any algorithm-specific control parameters and depends only a simple revision equation. Therefore, it provides a practical solution for structural optimization problems. Optimum solutions of the different steel truss examples are carried out by selecting suitable W sections taken from American Institute of Steel Construction (AISC). In order to obtain optimum solutions, a computer program is coded in MATLAB in corporated with SAP2000-OAPI (Open Application Programming Interface). The stress and displacement constraints are applied on the design problems according to AISC-ASD (Allowable Stress Design) specifications. Firstly, a benchmark truss problem is examined to see the efficiency of Jaya optimization algorithm. Then, two different multi-element truss towers previously solved with other methods without seismic loading in literature are designed by the proposed algorithm. The first space tower is a 582-member space truss with the height of 80 m and the second space tower is a 942-member space truss of about 95 m height. The minimum optimum designs obtained with this novel algorithm for the case without seismic loading are lighter than the ones previously attained in the literature studies. The results obtained in the study show that Jaya algorithm is a practical and robust optimization method for structural optimization problems. Moreover, incorporation of the seismic loading causes significant increase in the minimum design weight.

Key Words
Jaya algorithm; steel space truss tower; optimum design; seismic loading; MATLAB-SAP2000 OAPI

Address
Musa Artar: Institute of 1Department of Civil Engineering, Bayburt University, Bayburt 69000, Turkey
Ayşe T. Daloğlu: Department of Civil Engineering, Karadeniz Technical University, Trabzon 61000, Turkey

Abstract
In this paper, the static and dynamic responses of a tied-arch railway bridge under train load were studied through field tests. The deflection and stresses of the bridge were measured in different static loading scenarios. The dynamic load test of the bridge was carried out under the excitation of running train at different speeds. The dynamic properties of the bridge were investigated in terms of the free vibration characteristics, dynamic coefficients, accelerations, displacements and derailment coefficients. The results indicate that the tie of the measuring point has a significant effect on the vertical movement of the test section. The dynamic responses of arch bridge are insensitive to the number of trains. The derailment coefficients of locomotive and carriage increase with the train speed and symmetrically distributed double-line loads reduce the train derailment probability.

Key Words
tied arch bridge; train load; dynamic response; field test; vertical movement; derailment coefficient

Address
Hongye Gou, Biao Yang: Department of Bridge Engineering, School of Civil Engineering, Southwest Jiaotong University, Chengdu 610031, China
Hongye Gou: Key Laboratory of High-Speed Railway Engineering, Ministry of Education, Southwest Jiaotong University, Chengdu 610031, China
Wei Guo: School of Civil Engineering, Central South University, Changsha 410075, China; National Engineering Laboratory for High Speed Railway Construction, Changsha 410075, China
Yi Bao: Department of Civil, Environmental and Ocean Engineering, Stevens Institute of Technology, NJ 07030 Hoboken, USA

Abstract
In this study we derive the governing equations of a functionally graded piezoelectric disk, subjected to thermo-electro-mechanical loads. First order shear deformation theory is used for description of displacement field. Principles of minimum potential energy is used to derive governing equations in terms of components of the displacement field and the electric potential. The governing equations are derived for a disk with variable thickness. The numerical results are presented in terms of important parameters of the problem such as profile of variable thickness, in-homogeneous index and other related parameters.

Key Words
electro-elastic; functionally graded piezoelectric disk; variable thickness; first order shear deformation theory

Address
Faculty of Mechanical Engineering, Department of Solid Mechanics, University of Kashan, Kashan 87317-51167, Iran

Abstract
This paper studies application of modified couple stress theory and first order shear deformation theory to magneto-electro-mechanical vibration analysis of three-layered size-dependent curved beam. The curved beam is resting on Pasternak\'s foundation and is subjected to mechanical, magnetic and electrical loads. Size dependency is accounted by employing a small scale parameter based on modified couple stress theory. The magneto-electro-mechanical preloads are accounted in governing equations to obtain natural frequencies in terms of initial magneto-electro-mechanical loads. The analytical approach is applied to investigate the effect of some important parameters such as opening angle, initial electric and magnetic potentials, small scale parameter, and some geometric dimensionless parameters and direct and shear parameters of elastic foundation on the magneto-electro-elastic vibration responses.

Key Words
vibration Responses; modified couple stress; initial electric and magnetic potentials; length scale parameter

Address
Department of Solid Mechanic, Faculty of Mechanical Engineering, University of Kashan, Kashan 87317-51167, Iran

Abstract
A modified mechanical model of pre-pressed spring self-centering energy dissipation (PS-SCED) brace is proposed, and the hysteresis band is distinguished by the indication of relevant state variables. The MDOF frame system equipped with the braces is formulated in an incremental form of linear acceleration method. A multi-objective genetic algorithm (GA) based brace parameter optimization method is developed to obtain an optimal solution from the primary design scheme. Parameter sensitivities derived by the direct differentiation method are used to modify the change rate of parameters in the GA operator. A case study is conducted on a steel braced frame to illustrate the effect of brace parameters on node displacements, and validate the feasibility of the modified mechanical model. The optimization results and computational process information are compared among three cases of different strategies of parameter change as well. The accuracy is also verified by the calculation results of finite element model. This work can help the applications of PS-SCED brace optimization related to parameter sensitivity, and fulfill the systematic design procedure of PS-SCED brace-structure system with completed and prospective consequences.

Key Words
frame structure; genetic algorithm; parameter sensitivity analysis; structural optimization; self-centering brace

Address
Longhe Xu, Xingsi Xie, Xintong Yan: School of Civil Engineering, Beijing Jiaotong University, Beijing 100044, China
Zhongxian Li: Key Laboratory of Coast Civil Structure Safety of China Ministry of Education, Tianjin University, Tianjin 300072, China

Abstract
During the last two decades, much joint research regarding vibration based methods has been done, leading to developing various algorithms and techniques. These algorithms and techniques can be divided into modal methods and signal methods. Although modal methods have been widely used for health monitoring and damage detection, signal methods due to higher efficiency have received considerable attention in various fields, including aerospace, mechanical and civil engineering. Signal-based methods are derived directly from the recorded responses through signal processing algorithms to detect damage. According to different signal processing techniques, signal-based methods can be divided into three categories including time domain methods, frequency domain methods, and time-frequency domain methods. The frequency domain methods are well-known and interest in using them has increased in recent years. To determine dynamic behaviours, to identify systems and to detect damages of bridges, different methods and algorithms have been proposed by researchers. In this study, a new algorithm to detect seismic damage in the bridge\'s piers is suggested. To evaluate the algorithm, an analytical model of a bridge with simple spans is used. Based on the algorithm, before and after damage, the bridge is excited by a sine force, and the piers\' responses are measured. The dynamic specifications of the bridge are extracted by Power Spectral Density function. In addition, the Least Square Method is used to detect damage in the bridge\'s piers. The results indicate that the proposed algorithm can identify the seismic damage effectively. The algorithm is output-only method and measuring the excitation force is not needed. Moreover, the proposed approach does not need numerical models.

Key Words
moment-rotation; forecasting; extreme learning machine; precast beam-to-column connection; partly hidden corbel

Address
Mahmoud Bayat: Department of Civil Engineering, Roudehen Branch, Islamic Azad University, Roudehen, Iran
Hamid Reza Ahmadi: Department of Civil Engineering, Faculty of Engineering, University of Maragheh, Maragheh, P.O. Box 55136-553, Iran
Navideh Mahdavi: Department of Civil Engineering, Marand Branch, Islamic Azad University, Marand, Iran

Abstract
In this article, the dynamic fracture instability characteristics, including dynamic crack propagation and crack branching, in PMMA brittle solids under dynamic loading are investigated using the discrete element method (DEM) simulations. The microscopic parameters in DEM are first calibrated using the comparison with the previous experimental results not only in the field of qualitative analysis, but also in the field of quantitative analysis. The calibrating process illustrates that the selected microscopic parameters in DEM are suitable to effectively and accurately simulate dynamic fracture process in PMMA brittle solids subjected to dynamic loads. The typical dynamic fracture behaviors of solids under dynamic loading are then reproduced by DEM. Compared with the previous experimental and numerical results, the present numerical results are in good agreement with the existing ones not only in the field of qualitative analysis, but also in the field of quantitative analysis. Furthermore, effects of dynamic loading magnitude, offset distance of the initial crack and initial crack length on dynamic fracture behaviors are numerically discussed.

Key Words
dynamic fracture instability; crack propagation; crack branching; brittle solids; discrete element method

Address
Miaomiao Kou: School of Civil Engineering, Qingdao University of Technology, Qingdao, 266033, China
Dongchen Han: School of Civil Engineering, Qingdao University of Technology, Qingdao, 266033, China; Institute of Qingdao, Ernst & Young, Qingdao, 266000, China
Congcong Xiao: China Resources Land Ltd., Shanghai, 201206, China
Yunteng Wang:Cooperative Innovation Center of Engineering Construction and Safety in Shandong Blue Economic Zone, Qingdao, 266033, China

Abstract
In this paper, the interaction between two neighboring tunnel has been investigated using PFC2D. For this purpose, firstly calibration of PFC was performed using Brazilian experimental test. Secondly, various configuration of two neighboring tunnel was prepared and tested by biaxial test. The maximum and minimum principle stresses were 0.2 and 30 MPa respectively. The modeling results show that in most cases, the tensile cracks are dominant mode of cracks that occurred in the model. With increasing the diameter of internal circle, number of cracks decreases in rock pillar also number of total cracks decreases in the model. The rock pillar was heavily broken when its width was too small. In fixed quarter size of tunnel, the crack initiation stress decreases with increasing the central tunnel diameter. In fixed central tunnel size, the crack initiation stress decreases with increasing the quarter size of tunnel.

Key Words
PFC2D, tunnel, tensile crack

Address
V. Sarfarazi: Department of Mining Engineering, Hamedan University of Technology, Hamedan, Iran
Hadi Haeri: Department of Civil Engineering, Malard Branch, Islamic Azad University, Malard, Iran
Salman Safavi: Department of Civil Engineering, Malard Branch, Islamic Azad University, Malard, Iran
Mohammad Fatehi Marji:Mine Exploitation Engineering Department, Faculty of Mining and Metallurgy, Institution of Engineering, Yazd University, Yazd, Iran
Zheming Zhu: MOE Key Laboratory of Deep Underground Science and Engineering, School of Architecture and Environment, Sichuan University,Chengdu 610065, China

Abstract
In this study, the mechanical bending behaviors of functionally graded porous nanobeams are investigated. Four types of porosity which are, the classical power porosity function, the symmetric with mid-plane cosine function, bottom surface distribution and top surface distribution are proposed in analysis of nanobeam for the first time. A comparison between four types of porosity are illustrated. The effect of nano-scale is described by the differential nonlocal continuum theory of Eringen by adding the length scale into the constitutive equations as a material parameter comprising information about nanoscopic forces and its interactions. The graded material is designated by a power function through the thickness of nanobeam. The beam is simply-supported and is assumed to be thin, and hence, the kinematic assumptions of Euler-Bernoulli beam theory are held. The mathematical model is solved numerically using the finite element method. Numerical results show effects of porosity type, material graduation, and nanoscale parameters on the static deflection of nanobeam.

Key Words
porosity models; static bending; functionally graded beam; nonlocal elasticity; finite element method

Address
Mostafa A. Hamed, Ayman M. Sadoun and Mohamed A. Eltaher:Mechanical Engineering Dept., Faculty of Engineering, King Abdulaziz University, P.O. Box 80204, Jeddah, Saudi Arabia
Ayman M. Sadoun and Mohamed A.: Mechanical Design & Production Dept., Faculty of Engineering, Zagazig University, P.O. Box 44519, Zagazig, Egypt

Abstract
Wave propagation analysis of a porous graphene platelet reinforced (GPLR) nanocomposite shell is investigated for the first time. The homogenization of the utilized material is procured by extending the Halpin-Tsai relations for the porous nanocomposite. Both symmetric and asymmetric porosity distributions are regarded in this analysis. The equations of the shell\'s motion are derived according to Hamilton\'s principle coupled with the kinematic relations of the first-order shear deformation theory of the shells. The obtained governing equations are considered to be solved via an analytical solution which includes two longitudinal and circumferential wave numbers. The accuracy of the presented formulations is examined by comparing the results of this method with those reported by former authors. The simulations reveal a stiffness decrease in the cases which porosity influences are regarded. Also, one must pay attention to the effects of longitudinal wave number on the wave dispersion curves of the nanocomposite structure.

Key Words
wave propagation; porous nanocomposite; graphene platelet (GPL); first-order shear deformation shell theory

Address
Farzad Ebrahimi, Ali Seyfi:Department of Mechanical Engineering, Faculty of Engineering, Imam Khomeini International University, Qazvin, Iran
Ali Dabbagh: School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran
Francesco Tornabene: Department of Civil, Chemical, Environmental, and Materials Engineering, University of Bologna, Bologna, Italy

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