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CONTENTS
Volume 21, Number 6, August30 2016
 

Abstract
Viscoelastic sandwich structures (VSSs) are widely used in mechanical equipment, but in the service process, they always suffer from aging which affect the whole performance of equipment. Therefore, aging state recognition of VSSs is significant to monitor structural state and ensure the reliability of equipment. However, nonstationary vibration response signals and weak state change characteristics make this task challenging. This paper proposes a novel method for this task based on adaptive second generation wavelet packet transform (ASGWPT) and multiwavelet support vector machine (MWSVM). For obtaining sensitive feature parameters to different structural aging states, the ASGWPT, its wavelet function can adaptively match the frequency spectrum characteristics of inspected vibration response signal, is developed to process the vibration response signals for energy feature extraction. With the aim to improve the classification performance of SVM, based on the kernel method of SVM and multiwavelet theory, multiwavelet kernel functions are constructed, and then MWSVM is developed to classify the different aging states. In order to demonstrate the effectiveness of the proposed method, different aging states of a VSS are created through the hot oxygen accelerated aging of viscoelastic material. The application results show that the proposed method can accurately and automatically recognize the different structural aging states and act as a promising approach to aging state recognition of VSSs. Furthermore, the capability of ASGWPT in processing the vibration response signals for feature extraction is validated by the comparisons with conventional second generation wavelet packet transform, and the performance of MWSVM in classifying the structural aging states is validated by the comparisons with traditional wavelet support vector machine.

Key Words
viscoelastic sandwich structures; aging state recognition; vibration response signals; adaptive second generation wavelet packet transform; multiwavelet support vector machine

Address
(1) Jinxiu Qu, Zhousuo Zhang, Xue Luo, Bing Li:
State Key Laboratory for Manufacturing Systems Engineering, Xi'an Jiaotong University, Xi'an 710049, People's Republic of China;
(2) Jinpeng Wen:
Institute of Systems Engineering, China Academy of Engineering Physics, Mianyang 621999, Peopl's Republic of China.

Abstract
In this study, free vibration and damping characteristics of composite beams with holes are investigated, experimentally and numerically. Two types of samples with different fabrics are used: unidirectional and woven. The effects of diameter, number and location of circular holes on the vibration characteristics of composite beams are examined. The effects of rotation angle and minor to major diameter ratio of the elliptical hole are also investigated numerically. Moreover, the mode shapes of all types of beams are obtained numerically. According to the results, the natural frequency decreases with increasing hole diameter but increases very little with increasing the distance between the hole center and the clamped end. Damping ratio decreases by increasing the diameter of hole. But it fluctuates by increasing the diameters of holes of beam having three holes. Furthermore it decreases by increasing the distance between hole center and clamped end except for the range 50 mm to 100 mm.

Key Words
free vibration; damping; experimental analysis; finite element analysis; glass fibers

Address
Department of Mechatronics Engineering, Pamukkale University, Kinikli Campus, 20070 Denizli, Turkey.


Abstract
Most of the research work has been conducted on K-joints under static loading. Very limited information is available in consideration of fatigue strength of K-joints with concrete-filled chord. This paper aims to describe experimental and numerical investigations on stress concentration factors (SCFs) of concrete-filled circular chord and square braces K-joints under balanced axial loading. Experiment was conducted to study the hot spot stress distribution along the intersection of chord and braces in the two specimens with compacting concrete filled in the chord. The test results of stress distribution curves of two specimens were reported. SCFs of concrete-filled circular chord and square braces K-joints were lower than those of corresponding hollow circular chord and square brace K-joints. The corresponding finite element analysis was also conducted to simulate stress distribution along the brace and chord intersection region of joints. It was achieved that experimental and finite element analysis results had good agreement. Therefore, an extensive parametric study was carried out by using the calibrated finite element model to evaluate the effects of main geometric parameters and concrete strength on the behavior of concrete-filled circular chord and square braces K-joints under balanced axial loading. The SCFs at the hot spot locations obtained from ABAQUS were compared with those calculated by using design formula given in the CIDECT for hollow SHS-SHS K-joints. CIDECT Design Guide was generally quite conservative for predicting SCFs of braces and was dangerous for predicting SCFs of chord in concrete-filled circular chord and square braces K-joints. Finally SCF formulae were proposed for circular chord and square braces K-joints with concrete-filled in the chord under balanced axial loading. It is shown that the SCFs calculated from the proposed design equation are generally in agreement with the values derived from finite element analysis, which were proved to be reliable and accurate.

Key Words
experimental investigation; finite element analysis; parametric study; stress concentration factor; concrete-filled chord; circular chord and square braces K-joints

Address
School of Urban Construction, Yangtze University, Jingzhou, China.


Abstract
After observing relatively poor performance of bolted web-welded flange beam-to-column connections during 1994 Northridge earthquake, various types of connections based on two concepts of: (i) strengthening the connection; and (ii) weakening the beam ends were proposed. Among these modified or newly proposed connections, bolted T-stub connection follows the concept of strengthening. One of the connections with the idea of weakening the beam ends is reduced beam section (RBS). In this paper, finite element simulation is used to study the cyclic behavior of a new proposed connection developed by using a combination of both mentioned concepts. Investigated connections are exterior beam-to-column connections designed to comply with AISC provisions. The results show that moment capacity and dissipated energy of the new proposed connection is almost the same as those computed for a T-stub connection and higher than corresponding values for an RBS connection.

Key Words
cyclic behavior; steel moment connection; T-stub; beam-column connection; RBS

Address
Department of Civil and Environmental Engineering, Shiraz University, Shiraz, Iran.


Abstract
This paper presents experimental results of advanced investigation carried out on the beams reinforced with Glass Fiber Reinforced Polymer (GFRP) rebar and stirrups. Twelve beams reinforced with GFRP and one beam with steel reinforcement of size 230

Key Words
shear strength; reinforced concrete; glass fiber reinforced polymer; strain gauge; beams

Address
(1) Tarak P. Vora:
PhD Department, Gujarat Technological University, Nr. Visat Three Roads, Visat - Gandhinagar Highway, Chandkheda, Ahmedabad . 382424, Gujarat, India;
(2) Bharat J. Shah:
Applied Mechanics Department, L. D. College of Engineering, No. 120, Circular Road, University Area, Opp. Gujarat University, Navrangpura, Ahmedabad – 380015, Gujarat, India.

Abstract
The current research presents a buckling analysis of isotropic and orthotropic plates by proposing a new four variable refined plate theory. Contrary to the existing higher order shear deformation theories (HSDT) and the first shear deformation theory (FSDT), the proposed model uses a new displacement field which incorporates undetermined integral terms and involves only four variables. The governing equations for buckling analysis are deduced by utilizing the principle of virtual works. The analytical solution of a simply supported rectangular plate under the axial loading has been determined via the Navier method. Numerical investigations are performed by using the proposed model and the obtained results are compared with CPT solutions, FSDT solutions, and the existing exact solutions in the literature. It can be concluded that the developed four variable refined plate theory, which does not use shear correction coefficient, is not only simple but also comparable to the FSDT.

Key Words
refined plate theory; buckling analysis; isotropic plate; orthotropic plate

Address
(1) Fouad Bourada:
Laboratoire des Structures Intelligentes, Département de Génie Civil, Institut des Sciences et de la Technologie, Centre Universitaire de Ain Témouchent, Algeria;
(2) Khaled Amara, Abdelouahed Tounsi:
Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria;
(3) Khaled Amara:
Département de Génie Civil, Institut des Sciences et de la Technologie, Centre Universitaire de Ain Témouchent, Algeria.

Abstract
Nonlinear behavior of two-span, continuous composite steel-concrete girders strengthened with Carbon Fiber Reinforced Polymers (CFRP) bonded to the top of concrete slab over the negative moment region was evaluated using a non-linear Finite Element (FE) model in this paper. A three-dimensional FE model of continuous composite girder using commercial software ABAQUS simulated and validated with experimental results. The interfacial regions of the composite girder components were modeled using suitable interface elements. Validation of the proposed numerical model with experimental data confirmed the applicability of this model to predict the loading history, strain level for the different components and concrete-steel relative slip. The FE model captured the different modes of failure for the continuous composite girder either in the concrete slab or at the interfacial region between CFRP sheet and concrete slab. Through a parametric study, the thickness of CFRP sheet and shear connection required to develop full capacity of the continuous composite girder at negative moment zone have been investigated. The FE results showed that the proper thickness of CFRP sheet at negative moment region is a function of the adhesive strength and the positive moment capacity of the composite section. The shear connection required at the negative moment zone depends on CFRP sheet\'s tensile stress level at ultimate load.

Key Words
continuous span; steel-concrete composite girder; CFRP; Finite Element (FE); contact model

Address
(1) Mohammad A. Samaaneh:
An-Najah National University, Nablus, Palestine;
(2) Alfarabi M. Sharif, Mohammed H. Baluch, Abul K. Azad:
Department of Civil & Environmental Engineering, King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia.

Abstract
Al2O3/SiC particulate reinforced (Metal Matrix Composites) MMCs which were produced by using stir casting process, bending strength and hardening behaviour were obtained using an analysis of variance (ANOVA) technique that uses full factorial design. Factor variables and their ranges were: particle size 2-60 μm; the stirring speed 450 rpm, 500 rpm and the stirring temperature 620°C, 650°C. An empirical equation was derived from test results to describe the relationship between the test parameters. This model for the tensile strength of the hybrid composite materials with R2 adj = 80% for the bending strength R2 adj = 89% were generated from the data. The regression coefficients of this model quantify the tensile strength and bending strengths of the effects of each of the factors. The interactions of all three factors do not present significant percentage contributions on the tensile strength and bending strengths of hybrid composite materials. Analysis of the residuals versus was predicted the tensile strength and bending strengths show a normalized distribution and thereby confirms the suitability of this model. Particle size was found to have the strongest influence on the tensile strength and bending strength.

Key Words
hybrid particulate reinforced composites; the tensile strength; bending strengths; hardness; porosity; full factorial design; analysis of variance (ANOVA)

Address
Department of Machine and Metal Technologies Sakarya University, Hendek Vocational School, Hendek, Sakarya, Republic of Turkey.

Abstract
In this article, an exact analytical solution for mechanical buckling analysis of symmetrically cross-ply laminated plates including curvature effects is presented. The equilibrium equations are derived according to the refined nth-order shear deformation theory. The present refined nth-order shear deformation theory is based on assumption that the in-plane and transverse displacements consist of bending and shear components, in which the bending components do not contribute toward shear forces and, likewise, the shear components do not contribute toward bending moments The most interesting feature of this theory is that it accounts for a parabolic variation of the transverse shear strains across the thickness and satisfies the zero traction boundary conditions on the top and bottom surfaces of the plate without using shear correction factors. Buckling of orthotropic laminates subjected to biaxial inplane is investigated. Using the Navier solution method, the differential equations have been solved analytically and the critical buckling loads presented in closed-form solutions. The sensitivity of critical buckling loads to the effects of curvature terms and other factors has been examined. The analysis is validated by comparing results with those in the literature.

Key Words
symmetrically cross-ply laminated; refined nth-order shear deformation theory; buckling; curvature terms

Address
(1) Tawfiq Becheri, Mokhtar Bouazza:
Department of Civil Engineering, University of Bechar, Bechar 08000, Algeria;
(2) Khaled Amara:
Department of Civil Engineering, University centre of Ain Temouchent, Ain Temouchent 46000, Algeria;
(3) Khaled Amara, Mokhtar Bouazza:
Laboratory of Materials and Hydrology (LMH), University of Sidi Bel Abbes, Sidi Bel Abbes 2200, Algeria;
(4) Noureddine Benseddiq:
Mechanics Laboratory of Lille, CNRS UMR 8107, University of Lille 1, 59655 Villeneuve d

Abstract
This study is an effort to clearly recognize the seismic damages occurred in strap-braced cold formed steel frames. In order to serve this purpose, a detailed investigation was conducted on 9 full scale strap-braced CFS walls and the required data were derived from the results of the experiments. As a consequence, quantitative and qualitative damage indices have been proposed in three seismic performance levels. Moreover, in order to assess seismic performance of the strap- braced CFS frames, a total of 8 models categorized into three types are utilized. Based on the experimental results, structural characteristics are calculated and all frames have been modeled as single degree of freedom systems. Incremental dynamic analysis using OPENSEES software is utilized to calculate seismic demand of the strap-braced CFS walls. Finally, fragility curves are calculated based on three damage limit states proposed by this paper. The results showed that the use of cladding and other elements, which contribute positively to the lateral stiffness and strength, increase the efficiency of strap-braced CFS walls in seismic events.

Key Words
performance-based; cold formed steel frame; strap braced; seismic; incremental dynamic analysis (IDA); fragility curve

Address
Department of Civil Engineering, Yasouj University, Yasouj, Iran.


Abstract
This paper proposes a hybrid of topological derivative-based level set method (LSM) and isogeometric analysis (IGA) for structural topology optimization. In topology optimization a significant drawback of the conventional LSM is that it cannot create new holes in the design domain. In this study, the topological derivative approach is used to create new holes in appropriate places of the design domain, and alleviate the strong dependency of the optimal topology on the initial design. Furthermore, the values of the gradient vector in Hamilton-Jacobi equation in the conventional LSM are replaced with a Delta function. In the topology optimization procedure IGA based on Non-Uniform Rational B-Spline (NURBS) functions is utilized to overcome the drawbacks in the conventional finite element method (FEM) based topology optimization approaches. Several numerical examples are provided to confirm the computational efficiency and robustness of the proposed method in comparison with derivative-based LSM and FEM.

Key Words
topology optimization; level set method; topological derivative; isogeometric analysis

Address
Department of Civil Engineering, University of Birjand, Birjand, Republic Islamic of Iran.



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