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CONTENTS
Volume 67, Number 5, September10 2018
 

Abstract
Structural pounding is commonly observed phenomenon during major ground motion, which can cause both structural and architectural damages. To reduce the amount of damage from pounding, the best and effective way is to increase the separation distance. Generally, existing design procedures for determining the separation distance between adjacent buildings subjected to structural pounding are based on approximations of the buildings\' peak relative displacement. These procedures are based on unknown safety levels. The aim of this research is to estimate probabilistic separation distance between adjacent structures by considering the variability in the system and uncertainties in the earthquakes characteristics through comprehensive numerical simulations. A large number of models were generated using a robust Monte-Carlo simulation. In total, 6.54 million time-history analyses were performed over the adopted models using an ensemble of 25 ground motions as seismic input within OpenSees software. The results show that a gap size of 50%, 70% and 100% of the considered design code for the structural periods in the range of 0.1-0.5 s, leads to have the probability of pounding about 41.5%, 18% and 5.8%, respectively. Finally, based on the results, two equations are developed for probabilistic determination of needed structural separation distance.

Key Words
structural pounding; separation distance; probabilistic analysis; Monte-Carlo simulation; time-history analyses

Address
Mojtaba Naeej and Javad Vaseghi Amiri: Department of Civil Engineering, Babol Noshirvani University of Technology, Babol, Iran
Sayyed Ghasem Jalali: Department of Civil Engineering, Qaemshahr Branch, Islamic Azad University, Qaemshahr, Iran

Abstract
Within a probabilistic framework, this paper addresses the determination of the static structural response of beams and frames with partially restrained (semi-rigid) connections. The flexibility of the nodal connections is incorporated via an idealized linear-elastic behavior of the beam constraints through the use of rotational springs, which are here considered uncertain for taking into account the largely scattered results observed in experimental findings. The analysis is conducted via the Probabilistic Transformation Method, by modelling the spring stiffness terms (or equivalently, the fixity factors of the beam) as uniformly distributed random variables. The limit values of the Eurocode 3 fixity factors for steel semi-rigid connections are assumed. The exact probability density function of a few indicators of the structural response is derived and discussed in order to identify to what extent the uncertainty of the beam constraints affects the resulting beam response. Some design considerations arise which point out the paramount importance of probability-based approaches whenever a comprehensive experimental background regarding the stiffness of the beam connection is lacking, for example in steel frames with semi-rigid connections or in precast reinforced concrete framed structures. Indeed, it is demonstrated that resorting to deterministic approaches may lead to misleading (and in some cases non-conservative) outcomes from a design viewpoint.

Key Words
probability transformation method; probability density function; semi-rigid connections; partially restrained beams; probability-based design

Address
Dario De Domenico, Giovanni Falsone and Rossella Laudani: Department of Engineering, University of Messina, Contrada Di Dio, 98166 Sant

Abstract
This paper presents a method for detecting damage in irregular 2D and 3D continuum structures based on combination of wavelet transform (WT) with fuzzy inference system (FIS) and particle swarm optimization (PSO). Many damage detection methods study regular structures. This method studies irregular structures and doesn\'t need response of healthy structures. First the damaged structure is analyzed with finite element methods, and damage response is obtained at the finite element points that have irregular distance, secondly the FIS, which is optimized by PSO is used to obtain responses at points, having equal distance by response at those points that previously obtained by the finite element methods. Then a 2D (for 2D continuum structures) or a 3D (for 3D continuum structures) matrix is performed by equal distance point response. Thirdly, by applying 2D or 3D wavelet transform on 2D or 3D matrix that previously obtained by FIS detail matrix coefficient of WT is obtained. It is shown that detail matrix coefficient can determine the damage zone of the structure by perturbation in the damaged area. In order to illustrate the capability of proposed method some examples are considered.

Key Words
discrete wavelet transform; damage detection; fuzzy inference system; particle swarm optimization

Address
Davood Hamidian, Eysa Salajegheh and Javad Salajegheh: Department of Civil Engineering, Shahid Bahonar University of Kerman, Kerman, 7618868366, Iran

Abstract
In a previous study, design charts where proposed to help the torsional design of axially restricted reinforced concrete (RC) beams with squared cross section. In this article, new design charts are proposed to cover RC beams with rectangular cross section. The influence of the height to width ratio of the cross section on the behavior of RC beams under torsion is firstly shown by using theoretical and experimental results. Next, the effective torsional strength of a reference RC beam is computed for several values and combinations of the study variables, namely: height to width ratio of the cross section, concrete compressive strength, torsional reinforcement ratio and level of the axial restraint. To compute the torsional strength, the modified Variable Angle Truss Model for axially restricted RC beams is used. Then, an extensive parametric analysis based on multivariable and nonlinear correlation analysis is performed to obtain nonlinear regression equations which allow to build the new design charts. These charts allow to correct the torsional strength in order to consider the favourable influence of the compressive axial stress that arises from the axial restraint.

Key Words
reinforced concrete; beams; torsion; axial restraint; torsional design; charts

Address
Catia S.B. Taborda and Luis F.A. Bernardo: Department of Civil Engineering and Architecture, Centre of Materials and Building Technologies (C-Made), University of Beira Interior, Covilha, Portugal
Jorge M.R. Gama: Department of Mathematics, Center of Mathematics and Applications, University of Beira Interior, Covilha, Portugal

Abstract
The current experimental study is the reinforcement of the simple curvature vault masonry structures. In this study, we discuss complex structure include vault and rib cover with two radii and actual dimensions under a vertical load. The unreinforced structure data were compared with analysis data. The analysis data are in good agreement with experimental data. In the first experiment, a structure without reinforcement is tested and according to the test results, the second structure was reinforced using the carbon polymer fibers and the same test is done to see the effects of reinforcement. Based on the test results of the first structure, the first cracks are created in the vault. Moreover, the reinforcement with carbon fibers will increase the loading capacity of the structure around 35%.

Key Words
brick masonry arches; experimental tests; FRP; structural reinforcements; vault and rib cover

Address
Majid Reza Takbash, Abbas Ali Akbarzadeh Morshedi and Seyyed Ali Sabet: Department of Civil Engineering, Kashan Branch, Islamic Azad University, Kashan, Iran

Abstract
In this paper, the tensile failure behaviour of transversally bedding layers was numerically simulated by using particle flow code in two dimensions. Firstly, numerical model was calibrated by uniaxial, Brazilian and triaxial experimental results to ensure the conformity of the simulated numerical model\'s response. Secondly, 21 circular models with diameter of 54 mm were built. Each model contains two transversely bedding layers. The first bedding layer has low mechanical properties, less than mechanical properties of intact material, and second bedding layer has high mechanical properties, more than mechanical properties of intact material. The angle of first bedding layer, with weak mechanical properties, related to loading direction was 0o, 15o, 30o, 45o, 60o, 75o and 90o while the angle of second layer, with high mechanical properties, related to loading direction was 90o, 105o, 120o, 135o, 150o,160o and 180o. Is to be note that the angle between bedding layer was 90o in all bedding configurations. Also, three different pairs of the thickness was chosen in models; i.e., 5 mm/10 mm, 10 mm/10 mm and 20 mm/10 mm. The result shows that In all configurations, shear cracks develop between the weaker bedding layers. Shear cracks angel related to normal load change from 0o to 90o with increment of 15o. Numbers of shear cracks are constant by increasing the bedding thickness. It\'s to be note that in some configuration, tensile cracks develop through the intact area of material model. There is not any failure in direction of bedding plane interface with higher strength.

Key Words
bedding layer; intersection; Brazilian tensile strength; PFC2D

Address
Hadi Haeri and Zheming Zhu: College of Architecture and Environment, Sichuan University, Chengdu 610065, China
Vahab Sarfarazi: Department of Mining Engineering, Hamedan University of Technology, Hamedan, Iran
Mohammad Fatehi Marji: Department of Mining Engineering, Yazd University, Yazd, Iran

Abstract
In this paper, the effects of particle size and model scale of concrete has been investigated on the failure mechanism of PFC2D numerical models under uniaxial compressive test. For this purpose, rectangular models with same particle sizes and different model dimensions, i.e., 3 mmx6 mm, 6 mmx12 mm, 12 mmx24 mm, 25 mmx50 mm and 54 mmx108 mm, were prepared. Also rectangular models with dimension of 54 mmx108 mm and different particle sizes, i.e., 0.27 mm, 0.47 mm, 0.67 mm, 0.87 mm, 1.07 mm, 1.87 mm and 2.27 mm were simulated using PFC2D and tested under uniaxial compressive test. Concurrent with uniaxial test, direct shear test was performed on the numerical models. Dimension of the models were 75x100 mm. Two narrow bands of particles with dimension of 37.5 mmx20 mm were removed from upper and lower of the model to supply the shear test condition. The particle sizes in the models were 0.47 mm, 0.57 mm, 0.67 mm and 0.77 mm. The result shows that failure pattern was affected by model scale and particle size. The uniaxial compressive strength and shear strength were increased by increasing the model scale and particle size.

Key Words
model scale; particle size; uniaxial compression test; direct shear test; PFC2D

Address
Hadi Haeri and Zheming Zhu: College of Architecture and Environment, Sichuan University, Chengdu 610065, China
Vahab Sarfarazi: Department of Mining Engineering, Hamedan University of Technology, Hamedan, Iran
Hossein Ali Lazemi: Department of Mining Engineering, Bafgh Branch, Islamic Azad University, Bafgh, Iran

Abstract
In this study, we investigate the vibration of single-walled carbon nanotubes embedded in a polymeric matrix using nonlocal elasticity theories with account arbitrary boundary conditions effects. A Winkler type elastic foundation is employed to model the interaction of nanobeam and the surrounding elastic medium. Influence of all parameters such as nonlocal small-scale effects, Winkler modulus parameter, vibration mode and aspect ratio of nanobeam on the vibration frequency are analyzed and discussed. The mechanical properties of carbon nanotubes and polymer matrix are treated and an analytical solution is derived using the governing equations of the nonlocal Euler-Bernoulli beam models. Solutions have been compared with those obtained in the literature and The results obtained show that the non-dimensional natural frequency is significantly affected by the small-scale coefficient, the vibrational mode number and the elastic medium.

Key Words
non-local; frequency; Winkler; boundary conditions; nanobeam

Address
Samir Belmahi:
1) University of Ibn Khaldoun,PB 78 Zaaroura, 14000 Tiaret, Algeria
2) Laboratory of Materials and Hydrology, University of Sidi Bel Abbes, Sidi Bel Abbes, Algeria
Mohamed Zidour and Tayeb Bensattalah:
1) University of Ibn Khaldoun,PB 78 Zaaroura, 14000 Tiaret, Algeria
2) Laboratory of Geomatics and Sustainable Development, University of Ibn Khaldoun Tiaret, Algeria
Mustapha Meradjah and Ahmed Dihaj: Laboratory of Materials and Hydrology, University of Sidi Bel Abbes, Sidi Bel Abbes, Algeria

Abstract
In this paper, the effect of homogenization models on stress analysis is presented for functionally graded plates (FGMs). The derivation of the effective elastic proprieties of the FGMs, which are a combination of both ceramic and metallic phase materials, is of most of importance. The majority of studies in the last decade, the Voigt homogenization model explored to derive the effective elastic proprieties of FGMs at macroscopic-scale in order to study their mechanical responses. In this work, various homogenization models were used to derive the effective elastic proprieties of FGMs. The effect of these models on the stress analysis have also been presented and discussed through a comparative study. So as to show this effect, a refined plate theory is formulated and evaluated. The number of unknowns and governing equations were reduced by dividing the transverse displacement into both bending and shear parts. Based on sinusoidal variation of displacement field trough the thickness, the shear stresses on top and bottom surfaces of plate were vanished and the shear correction factor was avoided. Governing equations of equilibrium were derived from the principle of virtual displacements. Analytical solutions of the stress analysis were obtained for simply supported FGM plates. The obtained results of the displacements and stresses were compared with those predicted by other plate theories available in the literature. This study demonstrates the sensitivity of the obtained results to different homogenization models and that the results generated may vary considerably from one theory to another. Finally, this study offers benchmark results for the multi-scale analysis of functionally graded plates.

Key Words
bending; stresses; FGM; plate theory; homogenization models

Address
Sihame Ait Yahia:
1) Departement de Genie Civil, Faculte des Sciences Appliquees, Universite Ibn Khaldoun, Tiaret, Algerie
2) Material and Hydrology Laboratory, Faculty of Technology, Civil Engineering Department, University of Sidi Bel Abbes, Algeria
Lemya Hanifi Hachemi Amar: Laboratoire des Ressources Hydriques et Environnement, Universite Dr Tahar Moulay, BP 138 Cite En-Nasr 20000 Saida, Algerie
Zakaria Belabed:
1) Material and Hydrology Laboratory, Faculty of Technology, Civil Engineering Department, University of Sidi Bel Abbes, Algeria
2) Department of Technology, Institute of Science and Technology, Center University of Naama, Algeria
Abdelouahed Tounsi:
1) Material and Hydrology Laboratory, Faculty of Technology, Civil Engineering Department, University of Sidi Bel Abbes, Algeria
2) Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals,
31261 Dhahran, Eastern Province, Saudi Arabia

Abstract
Mode II delamination propagation is an important damage mode in laminated composites and this paper aims to investigate the behavior of this damage in laminated composite materials using acoustic emission (AE) technique. Three different lay-ups of glass/epoxy composites were subjected to mode II delamination propagation and generated AE signals were recorded. In order to investigate the propagation of delamination behavior of these specimens, AE signals were analyzed using Wavelet Packet Transforms (WPT) and Fast Fourier Transform (FFT). In addition, conventional AE analyses were used to enhance understanding of the propagation of delamination damage. The results indicate that different fracture mechanisms were the main cause of the AE signals. The dominant mechanisms in all the specimens were matrix cracking, fiber/matrix debonding and fiber breakage, with varying percentage of the damage mechanisms for each lay-up. Scanning Electron Microscopy (SEM) observations were in accordance to the AE results.

Key Words
composite material; glass/epoxy; acoustic emission; wavelet packet transform; delamination

Address
Parinaz Belalpour Dastjerdi and Mehdi Ahmadi: Non-Destructive Testing Lab, Department of Mechanical Engineering, Amirkabir University of Technology,
424 Hafez Ave, 15914, Tehran, Iran



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