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CONTENTS
Volume 64, Number 3, November10 2017
 

Abstract
Modal expansion technique (MET) is a method to estimate the vibration fields of flexible structures by using eigenmodes of the structure and the signals of sensors. It is the useful method to estimate the vibration fields but has the truncation error since it only uses the limit number of the eigenmodes in the frequency of interest. Even though block-wise MET performed frequency block by block with different valid eigenmodes was developed, it still has the truncation error due to the absence of other eigenmodes. Thus, this paper suggested an improved block-wise modal expansion technique. The technique recovers the truncation errors in one frequency block by utilizing other eigenmodes existed in the other frequency blocks. It was applied for estimating the vibration fields of a cylindrical shell. The estimated results were compared to the vibration fields of the forced vibration analysis by using two indices: the root mean square error and parallelism between two vectors. These indices showed that the estimated vibration fields of the improved block-wise MET more accurately than those of the established METs. Especially, this method was outstanding for frequencies near the natural frequency of the highest eigenmode of each block. In other words, the suggested technique can estimate vibration fields more accurately by recovering the truncation errors of the established METs.

Key Words
modal expansion technique; vibration field; truncation error; modal assurance criterion; sensor placement optimization

Address
Byung Kyoo Jung and Weui Bong Jeong : School of Mechanical Engineering, Pusan National University, 2, Busan 46241, Republic of Korea
Jinrae Cho : Department of Naval Architecture and Ocean Engineering, Hongik University, Sejong 339-710, Korea

Abstract
In the present research, an available flexural stiffness degradation model was modified and a new comprehensive model called \"X-NFSD\" was developed. The X-NFSD model is capable of predicting the flexural stiffness degradation of composite specimen at different states of stresses and at room temperature. The model was verified by means of different experimental data for chopped strand mat/epoxy composites under displacement controlled bending loading condition at different displacements and states of stresses. The obtained results provided by the present model are impressively in very good agreement with the experimental data and the mean value of error of 5.4% was achieved.

Key Words
flexural fatigue; displacement controlled loading; chopped strand mat/epoxy composites; degradation; composites

Address
M.M. Shokrieh, A.R. Haghighatkhah and M. Esmkhan : Composites Research Laboratory, Center of Excellence in Experimental Solid Mechanics and Dynamics,
School of Mechanical Engineering, Iran University of Science and Technology, Narmak, 16846-13114 Tehran, Iran

Abstract
Submarine collisions is one of the major hazardous factor for Submerged Floating Railway Tunnel (SFRT) and this study presents the safety evaluation for submarine collision to SFRT by using theoretical approach. Simplified method to evaluate the collision safety of SFRT was proposed based on the beam on elastic foundation theory. Firstly, the time history load function for submarine collision was obtained by using one-degree-of-freedom vibration model. Then, the equivalent mass and stiffness of the structure were calculated, and the collision responses of SFRT were evaluated. Finite element analysis was conducted to verify the proposed equations, and it can be found that the collision responses, such as deflection, and acceleration, agreed well with the proposed equations. Finally, derailment condition for high speed train in SFRT due to submarine collision was proposed.

Key Words
Submerged Floating Railway Tunnel (SFRT); submarine collision; collision analysis

Address
Sung-il Seo and Hyung-Suk Mun : New Transportation Research Center, Korea Railroad Research Institute(KRRI), Uiwang-Si, Gyeonggi-do, 437-757, South Korea
Jiho Moon : Department of Civil Engineering, Kangwon National University, Chuncheon-si, Gangwon-do 24341, South Korea

Abstract
For further development of passive control systems to dissipate larger seismic energy and prevent the structures from earthquake losses, this paper proposes an innovative two-level control system to improve behavior of chevron braced steel frames. Combining two Knee Braces, KB, and a Vertical Link Beam, VLB, in a chevron braced frame, this system can reliably sustain main shock and aftershocks in steel structures. The performance of this two-level system is examined through a finite element analysis and quasi-static cyclic loading test. The cyclic performances of VLB and KBs alone in chevron braced frames are compared with that of the presented two-level control system. The results show appropriate performance of the proposed system in terms of ductility and energy dissipation in two different excitation levels. The maximum load capacity of the presented system is about 30% and 17% higher than those of the chevron braced frames with KB and VLB alone, respectively. In addition, the maximum energy dissipation of the proposed system is about 78% and 150% higher than those of chevron braced frames with VLB and KB respectively under two separate levels of lateral forces caused by different probable seismic excitations. Finally, high performance under different earthquake levels with competitive cost and quick installation work for the control system can be found as main advantages of the presented system.

Key Words
two-level control system; chevron braced steel frame; knee brace; vertical link beam; energy dissipation; cyclic testing

Address
Ali Mohammad Rousta : School of Civil Engineering, College of Engineering, The University of Tehran, Iran
Seyed Mehdi Zahrai : Center of Excellence for Engineering and Management of Civil Infrastructures, School of Civil Engineering,College of Engineering, The University of Tehran, P.O. Box 11155-4563, Tehran, Iran

Abstract
This paper presents the details of analytical studies carried out towards the prediction of flexural capacity and loaddeflection behaviour of Laced Steel-Concrete Composite (LSCC) beams. Analytical expressions for flexural capacity of the beams are derived in accordance with the basic principles of conventional Reinforced Concrete (RC) beams, but incorporated with relevant modifications to account for the composite nature of the cross-section. The ultimate flexural capacity of the two LSCC beams predicted using the derived expressions is found to be approximately 20% lower than those obtained due to measurement from experiments. Further to these, two simple methods are also proposed on the basis of unit load method and equivalent steel beam method to determine the non-linear load-deflection response of the LSCC beams for monotonic loading. Upon validation of the proposed methods by comparing the predicted responses with those of experiments and finite element analysis, it is found that the methods are useful to find nonlinear response of such composite beams.

Key Words
steel-concrete composite construction; flexural capacity; equivalent steel beam method; unit load method

Address
A. Thirumalaiselvi, N. Anandavalli and J. Rajasankar : Academy of Scientific and Innovative Research, CSIR-Structural Engineering Research Centre, CSIR Campus,
CSIR Road, Taramani (P.O.), Chennai, 600 113, India

Abstract
This paper presents a three-dimensional finite element method analysis of repairing plate with bonded composite patch subjected to tensile load. The effect of the corrosion on the damage of the adhesive (FM73) in the length of two horizontal cracks on the both sides is presented. The obtained results show that the crack on the left side creates a very extensive area of the damaged zone and gives values of the stress intensity factor (SIF) higher than that on the right side. We can conclude that the left crack is more harmful (dangerous) than that on the right side.

Key Words
repairing plate; composite; FEM; fracture mechanics; corrosion

Address
Mohamed Berrahou, Mokadem Salem, B. Mechab and B. Bachir Bouiadjra : LMPM, Department of Mechanical Engineering, University of Sidi Bel Abbes, BP 89 Cite Ben M\'hidi 22000, Sidi Bel Abbes, Algeria

Abstract
This study concerns the vibrational behavior of multi-walled nested silicon-carbide and carbon nanotubes using the finite element method. The beam elements are used to model the carbon-carbon and silicon-carbon bonds. Besides, spring elements are employed to simulate the van der Waals interactions between walls. The effects of nanotube arrangement, number of walls, geometrical parameters and boundary conditions on the frequencies of nested silicon-carbide and carbon nanotubes are investigated. It is shown that the double-walled nanotubes have larger frequencies than triple-walled nanotubes. Besides, replacing silicon carbide layers with carbon layers leads to increasing the frequencies of nested silicon-carbide and carbon nanotubes. Comparing the first ten mode shapes of nested nanotubes, it is observed that the mode shapes of armchair and zigzag nanotubes are almost the same.

Key Words
dynamic analysis; finite element method; numerical methods; size effect; nanostructures/nanotubes

Address
Abed Nikkar and Reza Ansari : Department of Mechanical Engineering, University of Guilan, P.O. Box 3756, Rasht, Iran
Saeed Rouhi : Young Researchers and Elite Club, Langarud Branch, Islamic Azad University,Langarud , Guilan, Iran

Abstract
Slabs prevent harmful effects of fire that may occur in any floor. However, it is necessary to protect the slabs from fire. Insulation materials may be appropriate to protect reinforced concrete (RC) slab from elevated temperature. In the present study, a model has been developed in artificial neural network (ANN) to predict the moment capacity (Mr) of RC slabs exposed to fire with insulation material. 672 data were obtained for ANN model through author\'s prepared program. Input layer in model consisted of seven input parameters; such as effective depth (d), ratio of d\'/d, thermal conductivity coefficient (kinsulation), insulation materials thickness (Linsulation), reinforcement area (Ast), fire exposure time (texp), and concrete compressive strength (fc). The predicted Mr by ANN was consistent with the obtained Mr by author. It is proposed to ease computational complexity in determining Mr using ANN. The effects of using insulation material on the moment capacity in RC slabs were also investigated. Insulating material with low thermal conductivity has been found to be more effective for durability to high temperature.

Key Words
insulation material; fire; slab; reinforced concrete; moment capacity; artificial neural network

Address
Hakan Erdem : Civil Engineering Department, Niğde Ömer Halisdemir University, Nigde, 51240, Turkey

Abstract
The poor maintenance practice increases the possibility of system failure. Subsequently, the consequences of failure fall on the aspects of output, safety and healthy, environmental integrity, system quality, and customer satisfaction. Conditionbased maintenance is seen as a potential strategy to improve performance. Whereby, the key success factor of this maintenance strategy is identified as the system inspection. This study aims to investigate the association between system breakdown rate and frequency of inspection. A mixed method approach is implemented by distributing questionnaire and interviewing for data collection. Subsequently, descriptive analysis, correlation analysis and regression are adopted to analyse the collected data from 100 respondents and the results are validated with interview data of 10 interviewees. The research result establishes significant relationship between the system breakdown rate and the frequency of inspection. Additionally, the result of regression analysis confirms that the frequency of inspection is the significant predictor of system breakdown rate. Planning of accurate inspection frequency is crucial to secure the system performance. Hence, the research signifies the importance to carry out regular inspection towards the building systems and components. As a recommendation, the maintenance personnel should assess the risk criticality of the building systems. Then, continuously monitor the condition of critical building systems; regularly inspect the condition of non-critical building systems and randomly inspect all of them.

Key Words
inspection; preventive maintenance; condition-based maintenance; system failure; maintenance performance

Address
Cheong Peng Au-Yong, Azlan Shah Ali, Faizah Ahmad and Shirley Jin Lin Chua : Centre for Building, Construction & Tropical Architecture (BuCTA), Faculty of Built Environment, University of Malaya,50603 Kuala Lumpur, Malaysia

Abstract
This study presents the Big Bang and Big Crunch (BB-BC) optimization algorithm for detection of structure damage in large severity. Local damage is represented by a perturbation in the elemental stiffness parameter of the structural finite element model. A nonlinear objective function is established by minimizing the discrepancies between the measured and calculated acceleration responses (AR) of the structure. The BB-BC algorithm is utilized to solve the objective function, which can localize the damage position and obtain the severity of the damage efficiently. Numerical simulations have been conducted to identify both single and multiple structural damages for beam, plate and European Space Agency Structures. The present approach gives accurate identification results with artificial measurement noise.

Key Words
damage detection; time domain; BB-BC algorithm; optimization

Address
J.L. Huang and Z.R. Lu : Department of Applied Mechanics, Sun Yat-sen University, Guangzhou, Guangdong Province, 510006, P.R. China

Abstract
In this article, the vibration behavior of double-bonded sandwich microplates with homogeneous core and nanocomposite facesheets reinforced by carbon nanotube and boron nitride nanotube under multi physical fields such as 2D magnetic and electric fields is investigated. Symmetric and un-symmetric distributions of nanotubes are considered for facesheets of sandwich microplates such as uniform distribution and various functionally graded distributions. The doublebonded sandwich microplates rest on visco-Pasternak foundation. Material properties of sandwich microplates are obtained by the extended rule of mixture. The sinusoidal shear deformation theory (SSDT) is employed to describe displacement fields of sandwich microplates. Also, the dimensionless natural frequency is obtained by classical plate theory (CPT) and compared with the obtained results by SSDT. It can be seen that the obtained dimensionless natural frequencies by CPT are higher than SSDT. In order to study the material length scale parameters, modified strain gradient theory at micro scale is utilized and then, the equations of motion are derived using Hamilton\'s principle. The effects of different parameters such as foundation parameters including Winkler, shear layer and damping coefficients, various distributions and volume fraction of nanotubes, core to facesheet thickness ratio, aspect and side ratios on the dimensionless natural frequencies are discussed in details. The results of present work can be used to optimum design and control of similar systems such as micro-electro-mechanical and nano-electromechanical devices.

Key Words
vibration analysis; double-bonded sandwich microplates; nanocomposite facesheets; symmetric and unsymmetric distributions of nanotubes; 2D magnetic and electric fields

Address
Mehdi Mohammadimehr, Hassan BabaAkbar Zarei, Ali Parakandeh and Ali Ghorbanpour Arani : Department of Solid Mechanics, Faculty of Mechanical Engineering, University of Kashan, P.O. Box: 87317-53153, Kashan, Iran

Abstract
Present paper deals with the large amplitude flexural vibration of carbon nanotube reinforced composite (CNTRC) plates. Distribution of CNTs as reinforcements may be uniform or functionally graded (FG). The equivalent material properties of the composite media are obtained according to a refined rule of mixtures which contains efficiency parameters. To account for the large deformations, von Kármán type of geometrical nonlinearity is included into the formulation. The matrix representation of the governing equations is obtained according to the Ritz method where the basic shape functions are written in terms of the Chebyshev polynomials. Time dependency of the problem is eliminated by means of the Galerkin method and the resulting nonlinear eigenvalue problem is solved employing a direct displacement control approach. Results are obtained for completely clamped and completely simply supported plates. Results are first validated for the especial cases of FG-CNTRC and cross-ply laminated plates. Afterwards, parametric studies are given for FG-CNTRC plates with different boundary conditions. It is shown that, nonlinear frequencies are highly dependent to the volume fraction and dispersion profiles of CNTs. Furthermore, mode redistribution is observed in both simply supported and clamped FG-CNTRC plates.

Key Words
functionally graded; nonlinear free vibration; CNTRC; rectangular plate; Ritz method

Address
Mostafa Mirzaei : Department of Mechanical Engineering, Faculty of Engineering, University of Qom, Qom, Iran
Yaser Kiani : Faculty of Engineering, Shahrekord University, Shahrekord, Iran


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