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Volume 29, Number 3, November10 2018
 
select * from journal_scs where volume=29 and num=3 order by ordernum asc

Abstract
The purpose of this study is to investigate the effectiveness of damped cable systems (DCS) to mitigate the earthquake-induced responses of a building frame structure. The seismic performance of the DCS is investigated using the fragility analysis and life cycle cost evaluation of an existing building retrofitted with the DCS, and the results are compared with the structure retrofitted with conventional fluid viscous dampers. The comparison of the analysis results reveals that, due to the self-centering capability of the DCS, residual displacement approximately reaches to zero for the structure retrofitted with the DCS. The fragility analysis shows that the structure retrofitted with the DCS has the least probability of reaching the specific limit states compared to the bare structure and the structure with the conventional fluid viscous damper (VD), especially under the severe ground motions. It is also observed that both the initial and the life cycle costs of the DCS seismic retrofitting technique is lesser compare to the structure retrofitted with the VD.

Key Words
damped cable system; fragility analysis; life cycle cost; seismic retrofit; self-centering

Address
Department of Civil Engineering and Architectural Engineering, Sungkyunkwan University, Suwon, Republic of Korea.


Abstract
Properties of AFS vary with the changes in the face-sheet materials. Hence, the performance of AFS can be optimized by selecting face-sheet materials. In this work, three types of face-sheet materials representing elastic-perfectly plastic, elastic-plastic strain hardening and purely elastic materials were employed to study their effects on the flexural behavior and failure mechanism of AFS systematically. Result showed face-sheet materials affected the failure mechanism and energy absorption ability of AFS significantly. When the foam cores were sandwiched by aluminum alloy 6061, the AFS failed by facesheet yielding and crack without collapse of the foam core, there was no clear plastic platform in the Load-Displacement curve. When the foam cores were sandwiched by stainless steel 304 and carbon fiber fabric, there were no face-sheet crack and the sandwich structure failed by core shear and collapse, plastic platform appeared. Energy absorption abilities of steel and carbon fiber reinforced AFS were much higher than aluminum alloy reinforced one. Carbon fiber was suggested as the best choice for AFS for its light weight and high performance. The versus strength ratio of face sheet to core was suggested to be a significant value for AFS structure design which may determine the failure mechanism of a certain AFS structure.

Key Words
aluminum foam sandwich; composite structure; quasi-static bending; failure mechanism; energy absorption

Address
(1) Wei Xiao, Weiping Tian:
Key Laboratory for Special Area Highway Engineering of Ministry of Education, Chang\'an University, Shannxi 710064 Xi\'an China;
(2) Chang Yan, Weibo Tian, Xuding Song:
Key Laboratory of Road Construction Technology & Equipment of Chang\'an University, MOE, Xi\'an, Shaanxi 710064, China.

Abstract
Steel girders are the structural members often used for passing long spans. Mostly being subjected to patch loading, or concentrated loading, steel girders are likely to face sudden deformation or damage e.g., web breathing. Horizontal or vertical stiffeners are employed to overcome this phenomenon. This study aims at assessing the feasibility of a machine learning method, namely the support vector machines (SVM) in predicting the patch loading resistance of longitudinally stiffened webs. A database consisting of 162 test data is utilized to develop SVM models and the model with best performance is selected for further inspection. Existing formulations proposed by other researchers are also investigated for comparison. BS5400 and other existing models (model I, model II and model III) appear to yield underestimated predictions with a large scatter; i.e., mean experimental-to-predicted ratios of 1.517, 1.092, 1.155 and 1.256, respectively; whereas the selected SVM model has high prediction accuracy with significantly less scatter. Robust nature and accurate predictions of SVM confirms its feasibility of potential use in solving complex engineering problems.

Key Words
steel girders; patch loading; longitudinal stiffener; support vector machines; machine learning

Address
Department of Civil Engineering, Istanbul Gelisim University, Cihangir Mah. Şht. P. Onb. Murat Şengöz Sok. No: 8 34310 Avc

Abstract
This paper investigates the free vibration of geometrically imperfect functionally graded car-bon nanotube-reinforced composite (FG-CNTRC) beams that are integrated with two sur-face-bonded piezoelectric layers and subjected to a combined action of a uniform temperature rise, a constant actuator voltage and an in-plane force. The material properties of FG-CNTRCs are assumed to be temperature-dependent and vary continuously across the thick-ness. A generic imperfection function is employed to simulate various possible imperfections with different shapes and locations in the beam. The governing equations that account for the influence of initial geometric imperfection are derived based on the first-order shear deformation theory. The postbuckling configurations of FG-CNTRC hybrid beams are determined by the differential quadrature method combined with the modified Newton-Raphson technique, after which the fundamental frequencies of hybrid beams in the postbuckled state are obtained by a standard eigenvalue algorithm. The effects of CNT distribution pattern and volume fraction, geometric imperfection, thermo-electro-mechanical load, as well as boundary condition are examined in detail through parametric studies. The results show that the fundamental frequency of an imperfect beam is higher than that of its perfect counterpart. The influence of geometric imperfection tends to be much more pronounced around the critical buckling temperature.

Key Words
free vibration; postbuckling; functionally graded materials; carbon nanotube-reinforced composites; piezoelectric materials; thermo-electro-mechanical load

Address
(1) Helong Wu, Sritawat Kitipornchai:
School of Civil Engineering, the University of Queensland, Brisbane, St. Lucia 4072, Australia;
(2) Jie Yang:
School of Engineering, RMIT University, P.O. Box 71, Bundoora, VIC 3083, Australia.

Abstract
An analytical method is developed for analysing the contact buckling response of infinitely long, thin corrugated plates and flat plates restrained by a Winkler tensionless foundation and subjected to linearly varying in-plane loadings, where the corrugated plates are modelled as orthotropic plates and the flat plates are modelled as isotropic plates. The critical step in the presented method is the explicit expression for the lateral buckling mode function, which is derived through using the energy method. Simply supported and clamped edges conditions on the unloaded edges are considered in this study. The acquired lateral deflection function is applied to the governing buckling equations to eliminate the lateral variable. Considering the boundary conditions and continuity conditions at the border line between the contact and non-contact zones, the buckling coefficients and the corresponding buckling modes are found. The analytical solution to the buckling coefficients is also expressed through a fitted approximate formula in terms of foundation stiffness, which is verified through previous studies and finite element (FE) method.

Key Words
linearly varying in-plane loading; contact buckling; buckling coefficient; Winkler tensionless foundation; finite element analysis

Address
School of Natural and Built Environments, University of South Australia, Adelaide, SA 5095, Australia.


Abstract
Thermal buckling behavior of porous functionally graded nanobeam integrated with piezoelectric sensor and actuator based on the nonlocal higher-order shear deformation beam theory is investigated for the first time. Its material properties are assumed to be temperature-dependent and varying along the thickness direction according to the modified power-law rule. Note that the porosity with even type is considered herein. The equations of motion are obtained through Hamilton\'s principle. The influences of several parameters (such as type of temperature distribution, external electric voltage, material composition, porosity, small-scale effect, Ker foundation parameters, and beam thickness) on the thermal buckling of FG nanobeam are investigated in detail.

Key Words
thermal buckling; higher-order shear deformation beam theory; functionally graded nanobeam; nonlocal elasticity theory; Kerr elastic foundation

Address
(1) Behrouz Karami, Davood Shahsavari:
Department of Mechanical Engineering, Marvdasht Branch, Islamic Azad University, Marvdasht, Iran;
(2) Seyed Mohammad Reza Nazemosadat:
Sama Technical and Vocational Training College, Islamic Azad University, Shiraz Branch, Shiraz, Iran;
(3) Seyed Mohammad Reza Nazemosadat:
Department of Mechanical Engineering of Biosystems, Shahrekord University, Shahrekord, Iran;
(4) Li Li:
State Key Lab of Digital Manufacturing Equipment and Technology, School of Mechanical Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China;
(5) Arash Ebrahimi:
Faculty of Computer Science and Electrical Engineering, University of Rostock, Albert-Einstein-Stra

Abstract
An efficient and free of shear locking finite element model is developed and employed to study free vibration of tapered bidirectional functionally graded material (BFGM) beams. The beam material is assumed to be formed from four distinct constituent materials whose volume fraction continuously varies along the longitudinal and thickness directions by power-law functions. The finite element formulation based on the first-order shear deformation theory is derived by using hierarchical functions to interpolate the displacement field. In order to improve efficiency and accuracy of the formulation, the shear strain is constrained to constant and the exact variation of the cross-sectional profile is employed to compute the element stiffness and mass matrices. A comprehensive parametric study is carried out to highlight the influence of the material distribution, the taper and aspect ratios as well as the boundary conditions on the vibration characteristics. Numerical investigation reveals that the proposed model is efficient, and it is capable to evaluate the natural frequencies of BFGM beams by using a small number of the elements. It is also shown that the effect of the taper ratio on the fundamental frequency of the BFGM beams is significantly influenced by the boundary conditions. The present results are of benefit to optimum design of tapered FGM beam structures.

Key Words
bi-directional functionally graded material; tapered beams; first-order shear deformation theory; hierarchical functions; free vibration; finite element model

Address
(1) Institute of Mechanics, VAST, 18 Hoang Quoc Viet, Hanoi, Vietnam;
(2) Graduate University of Science and Technology, VAST, 18 Hoang Quoc Viet, Hanoi, Vietnam.

Abstract
In this research, the explicit closed-form local buckling solution of steel plates in contact with concrete, with both loaded and unloaded edges elastically restrained against rotation and subjected to eccentric compression is presented. The Rayleigh-Rize approach is applied to establish the eigenvalue problem for the local buckling performance. Buckling shape which combines trigonometric and biquadratic functions is introduced according to that used by Qin et al. (2017) on steel plate buckling under uniform compression. Explicit solutions for predicting the local buckling stress of steel plate are obtained in terms of the rotational stiffness. Based on different boundary conditions, simply yet explicit local buckling solutions are discussed in details. The proposed formulas are validated against previous research and finite element results. The influences of the loading stress gradient parameter, the aspect ratio, and the rotational stiffness on the local buckling stress resultants of steel plates with different boundary conditions were evaluated. This work can be considered as an alternative to apply a different buckling shape function to study the buckling problem of steel plate under eccentric compression comparing to the work by Qin et al. (2018), and the results are found to be in consistent with those in Qin et al. (2018).

Key Words
explicit analysis; local buckling; rotationally restrained; combined compression and bending; steel plate

Address
(1) Ying Qin, Gan-Ping Shu, Er-Feng Du, Rui-Hua Lu:
Key Laboratory of Concrete and Prestressed Concrete Structures of Ministry of Education, and National Prestress Engineering Research Center, School of Civil Engineering, Southeast University, Nanjing, China;
(2) Ying Qin:
State Key Laboratory of Subtropical Building Science, South China University of Technology, Guangzhou, China.

Abstract
Researchers have been long studying new building implementation methods to improve the quality of construction, reduce the time of assembly, and increase productivity. One of these methods is the use of modular pre-fabricated structural forms that are composed of a beam, column, short column, pyramidal end block, and connection plates. In this study, a new geometry for the pyramidal end block was proposed that helps facilitate the assembly procedure. Since the proposed configuration affects the performance of this form of connection, its behavior was evaluated using finite element method. For this purpose, the connection was modeled in ABAQUS and then validated by comparing the outputs with experimental results. The research proceeded through analyzing 16 specimens under monotonic and cyclic loading. The results indicated that using the pyramidal end block not only makes the assembly process easier but also reduces the out-of-plane displacement of the short column webs and the vertical displacement of beam end. By choosing appropriate section properties for column and beam, the connection can bear a rotation up to 0.01 radians within its inelastic region and a total of 0.04 radians without any significant reduction in its bearing capacity.

Key Words
cyclic loading; finite element method; modular pre-fabricated structural form; monotonic loading; pyramidal end block

Address
(1) Seyed Morteza Kazemi, Mohammad Reza Sohrabi:
Civil Engineering Department, University of Sistan and Baluchestan, Zahedan, Iran;
(2) Hasan Haji Kazemi:
Civil Engineering Department, Ferdowsi University, Mashhad, Iran.

Abstract
In this research, experimental tensile test and manufacturing of carbon nanotube reinforced composite beam (CNTRC) is presented. Also, bending, buckling, and vibration analysis of CNTRC based on various beam theories such as Euler-Bernoulli, Timoshenko and Reddy beams are considered. At first, the experimental tensile tests are carried out for CNTRC and composite beams in order to obtain mechanical properties and then using Hamilton\'s principle the governing equations of motion are derived for Euler Bernoulli, Timoshenko and Reddy theories. The results have a good agreement with the obtained results by similar researches and it is shown that adding just two percent of carbon nanotubes increases dimensionless fundamental frequency and critical buckling load as well as decreases transverse deflection of composite beams. Also, the influences of different manufacturing processes such as hand layup and industrial methods using vacuum pump on composite properties are investigated. In these composite beams, glass fibers used in an epoxy matrix and for producing CNTRC, CNTs are applied as reinforcement particles. Applying two percent of CNTs leads to increase the mechanical properties and increases natural frequencies and critical buckling load and decreases deflection. The obtained natural frequencies and critical buckling load by theoretical method are higher than other methods, because there are some inevitable errors in industrial and hand layup method. Also, the minimum deflection occurs for theoretical methods, in bending analysis. In this study, Young\'s and shear modulli as well as density are obtained by experimental test and have not been used from the results of other researches. Then the theoretical analysis such as bending, buckling and vibration are considered by using the obtained mechanical properties of this research.

Key Words
bending, buckling, vibration analysis; carbon nanotube reinforced composite beam; hand layup method; industrial method using vacuum pump

Address
(1) M. Mohammadimehr, A.A. Mohammadi-Dehabadi, S.M. Akhavan Alavi, K. Alambeigi, M. Bamdad, R. Yazdani, S. Hanifehlou:
Department of Solid Mechanics, Faculty of Mechanical Engineering, University of Kashan, Kashan, Iran;
(2) A.A. Mohammadi-Dehabadi:
Department of Mechanical Engineering, Iran University of Science and Technology, Narmak, Tehran, Iran.


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