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CONTENTS
Volume 61, Number 1, January10 2017
 

Abstract
The effectiveness of the repair scheme for the damaged captive-columns with CFRPs (Carbon Fiber Reinforced Polymer) was investigated in terms of response quantities such as strength, ductility, dissipated energy and stiffness degradation. Two 1/3 scale, one-story one-bay RC (Reinforced Concrete) frames were designed to represent the substandard RC buildings in Turkish building stock. The first one, which is the reference specimen, is the bare frame without infill wall. Partial infill wall with opening was constructed between the columns of the second frame and this caused captive column defect. Severe damage was observed with the concentration of shear cracks in the second specimen columns. Then, the damaged members were repaired by CFRP wrapping and retested. For the three test series, similar reversed cyclic lateral displacement under combined effect of axial load was applied to the top of the columns. Overall response of the bare frame was dominated by flexural cracks. Brittle type of shear failure in the column top ends was observed in the specimen with partial infill wall. It was observed that former capacity of damaged members of the second frame was recovered by the applied repair scheme. Moreover, ultimate displacement capacity of the damaged frame was improved considerably by CFRP wrapping.

Key Words
repair; reinforced concrete; captive-column; CFRP; seismic

Address
Onur Tunaboyu and Özgür Avşar: Department of Civil Engineering, Anadolu University, 2 Eylul Campus, Eskisehir, Turkey

Abstract
The recently introduced index Ratio Of Torsion (ROT) quantifies the base shear amplification due to torsional effects on shear cantilever types of building structures. In this work, a theoretical proof based on the theory of elasticity is provided, depicting that the ratio of torsion (ROT) is independent of the forces acting on the structure, although its definition stems from the shear forces. This is a particular attribute of other design and evaluation criteria against torsion such as center of rigidity and center of strength. In the case of ROT, this evidence could be considered as inconsistent, as ROT is a function solely of the forces acting on structural members, nevertheless it is proven to be independent of them. As ROT is the amplification of the shear forces due to in-plan irregularities, this work depicts that this increase of internal shear forces rely only on the structural topology. Moreover, a numerical verification of this theoretical finding was accomplished, using linear statistics interpretation and nonlinear neural networks simulation for an adequate database of structures.

Key Words
torsional coupling; shear center; center of rigidity; center of twist; strength center; ratio of torsion; linear statistics; neural networks; solid mechanics

Address
Nikolaos Bakas: School of Architecture, Engineering, Land and Environmental Sciences, Neapolis University Pafos, 2 Danais Avenue, 8042 Paphos

Abstract
As a relatively new type of multi-layered rubber-based seismic isolators, fiber-reinforced elastomeric isolators (FREIs) are composed of several thin rubber layers reinforced with flexible fiber sheets. Limited analytical studies in literature have pointed out that \"warping\" (distortion) of reinforcing sheets has significant influence on buckling behavior of FREIs. However, none of these studies, to the best knowledge of authors, has investigated their warping behavior, thoroughly. This study aims to investigate, in detail, the warping behavior of strip-shaped FREIs by deriving advanced analytical solutions without utilizing the commonly used \"pressure\", incompressibility, inextensibility and the \"linear axial displacement variation through the thickness\" assumptions. Studies show that the warping behavior of FREIs mainly depends on the (i) aspect ratio (shape factor) of the interior elastomer layers, (ii) Poisson\'s ratio of the elastomer and (iii) extensibility of the fiber sheets. The basic assumptions of the \"pressure\" method as well as the commonly used incompressibility assumption are valid only for isolators with relatively large shape factors, strictly incompressible elastomeric material and nearly inextensible fiber reinforcement.

Key Words
bearing; buckling; distortion; elastomeric isolator; fiber-reinforced isolator; rubber; seismic isolation; warping

Address
Seval Pinarbasi: Department of Civil Engineering, Kocaeli University, Kocaeli 41380, Turkey
Yalcin Mengi: Department of Engineering Sciences, Middle East Technical University, Ankara 06531, Turkey

Abstract
This paper presents an original hyperbolic (first present model) and parabolic (second present model) shear and normal deformation theory for the bending analysis to account for the effect of thickness stretching in functionally graded sandwich plates. Indeed, the number of unknown functions involved in these presents theories is only five, as opposed to six or even greater numbers in the case of other shear and normal deformation theories. The present theory accounts for both shear deformation and thickness stretching effects by a hyperbolic variation of ail displacements across the thickness and satisfies the stress-free boundary conditions on the upper and lower surfaces of the plate without requiring any shear correction factor. It is evident from the present analyses; the thickness stretching effect is more pronounced for thick plates and it needs to be taken into consideration in more physically realistic simulations. The numerical results are compared with 3D exact solution, quasi-3-dimensional solutions and with other higher-order shear deformation theories, and the superiority of the present theory can be noticed.

Key Words
higher-order theories; shear deformation theory of sandwich plates; functionally graded material

Address
Tahar Hassaine Daouadji and Belkacem Adim: Département de Génie Civil, Université Ibn Khaldoun Tiaret, BP 78 Zaaroura, 14000 Tiaret, Algérie; Laboratoire de Géomatique et Développement Durable, Université Ibn Khaldoun de Tiaret, Algérie

Abstract
Prediction of the characteristics of both in-plane and out-of-plane elastic waves within conducting nanoplates in the presence of bidirectionally in-plane magnetic fields is of interest. Using Lorentz\'s formulas and nonlocal continuum theory of Eringen, the nonlocal elastic version of the equations of motion is obtained. The frequencies as well as the corresponding phase and group velocities pertinent to the in-plane and out-of-plane waves are analytically evaluated. The roles of the strength of in-plane magnetic field, wavenumber, wave direction, nanoplate\'s thickness, and small-scale parameter on characteristics of waves are discussed. The obtained results show that the in-plane frequencies commonly grow with the in-plane magnetic field. However, the transmissibility of the out-of-plane waves rigorously depends on the magnetic field strength, direction of the propagated transverse waves, small-scale parameter, and thickness of the nanoplate. The criterion for safe transferring of the out-of-plane waves through the conducting nanoplate immersed in a bidirectional magnetic field is also explained and discussed.

Key Words
conducting nanoplate; in-plane and out-of-plane waves; bidirectional magnetic field; Nonlocal Kirchhoff plate theory

Address
Keivan Kiani, Saeed Asil Gharebaghi: Department of Civil Engineering, K.N. Toosi University of Technology, Tehran, Iran
Bahman Mehri: Department of Mathematical Sciences, Sharif University of Technology, Tehran, Iran

Abstract
Glazed curtain walls are façade systems frequently chosen in modern architecture for mid and high-rise buildings. From recent earthquakes surveys it is observed the large occurrence of non-structural components failure, such as storefronts and curtain walls, which causes sensitive economic losses and represents an hazard for occupants and pedestrians safety. In the present study, the behavior of curtain wall stick systems under seismic actions has been investigated through experimental in-plane racking tests conducted at the laboratory of the Construction Technologies Institute (ITC) of the Italian National Research Council (CNR) on two full-scale aluminium/glass curtain wall test units. A finite element model has been calibrated according to experimental results in order to simulate the behavior of such components under seismic excitation. The numerical model investigates the influence of the interaction between glass panels and aluminium frame, the gasket friction and the stiffness degradation of aluminium-to-glass connections due to the high deformation level on the curtain walls behavior. This study aims to give a practical support to researchers and/or professionals who intend to numerically predict the lateral behavior of similar façade systems, so as to avoid or reduce the need of performing expensive experimental tests.

Key Words
non-structural elements; curtain walls; stick-wall systems; seismic behavior; in-plane test

Address
Nicola Caterino and Antonio Occhiuzzi: Department of Engineering, University of Naples \"Parthenope\", Naples, Italy; Construction Technologies Institute, Italian National Research Council (CNR), San Giuliano Milanese, Milan, Italy
Marta Del Zoppo: Department of Engineering, University of Naples \"Parthenope\", Naples, Italy
Giuseppe Maddaloni: Department of Engineering, University of Benevento \"Sannio\", Benevento, Italy; Construction Technologies Institute, Italian National Research Council (CNR), San Giuliano Milanese, Milan, Italy
Antonio Bonati and Giovanni Cavanna: Construction Technologies Institute, Italian National Research Council (CNR), San Giuliano Milanese, Milan, Italy

Abstract
This paper analyzes the dynamic behavior of the deck of pergola bridges affected by moving loads, specifically high-speed trains. Due to their characteristic advantages, pergola bridges have become a widely used structural typology on high-speed railways. In spite of such wide-spread use, there are few technical bibliographies published in this field. The first part of this paper develops a simple analytical methodology to study the complex dynamic behavior of these double dimensional structures. The second part compares the results obtained by the proposed formulae and the dynamic response obtained with different and gradually more complex FE models. The results obtained by the analytical model are in close agreement with those obtained by the FE models, demonstrating its potential application in the early design stages of this kind of structure.

Key Words
pergola bridge; high-speed rail; dynamic analysis; railway bridge; two dimensional structures; skew angle

Address
Jokin Ugarte: IDEAM S.A. 19 Jorge Juan St. 28001, Madrid, Spain
Antonio Carnerero: Universidad Politécnica de Madrid. E.T.S. de Ingenieros de Caminos, Canales y Puertos,Department of Continuum Mechanics and Structures, 3 Profesor Aranguren St. 28040, Madrid, Spain
Francisco Millanes: IDEAM S.A. 19 Jorge Juan St. 28001, Madrid, Spain; Universidad Politécnica de Madrid. E.T.S. de Ingenieros de Caminos, Canales y Puertos,Department of Continuum Mechanics and Structures, 3 Profesor Aranguren St. 28040, Madrid, Spain

Abstract
In this paper, the optimal extended homotopy analysis method (OEHAM) is introduced to deal with the damped Duffing resonator driven by a van der Pol oscillator, which can be described as a complex Multi-Degree-of-Freedom (MDOF) nonlinear coupling system. Ecumenically, the exact solutions of the MDOF nonlinear coupling systems are difficult to be obtained, thus the development of analytical approximation becomes an effective and meaningful approach to analyze these systems. Compared with traditional perturbation methods, HAM is more valid and available, and has been widely used for nonlinear problems in recent years. Hence, the method will be chosen to study the system in this article. In order to acquire more suitable solutions, we put forward HAM to the OEHAM. For the sake of verifying the accuracy of the above method, a series of comparisons are introduced between the results received by the OEHAM and the numerical integration method. The results in this article demonstrate that the OEHAM is an effective and robust technique for MDOF nonlinear coupling systems. Besides, the presented methods can also be broadly used for various strongly nonlinear MDOF dynamical systems.

Key Words
optimal extended homotopy analysis method; Duffing resonator; van der Pol oscillator; coupling stiffness; Multi-Degree-of-Freedom

Address
Y.H. Qian and Y.F. Zhang: College of Mathematics, Physics and Information Engineering, Zhejiang Normal University, Jinhua, Zhejiang 321004, P.R. China

Abstract
Load testing is one of the important tests to determine if the structural elements can be used at the intended locations for which they have been designed. It is nothing but gradually applying the loads and measuring the deflections and other parameters. It is usually carried out to determine the behaviour of the system under service/ultimate loads. It helps to identify the maximum load that the structural element can withstand without much deflection/deformation. It will also help find out which part of the element causes failure first. The load-deflection behaviour of the road bridge girder has been studied by carrying out the load test after simulating the field conditions to the extent possible. The actual vertical displacement of the beam at mid span due to the imposed load was compared with the theoretical deflection of the beam. Further, the recovery of deflection at mid span was also observed on removal of the test load. Finally, the beam was checked for any cracks to assert if the beam was capable of carrying the intended live loads and that it could be used with confidence.

Key Words
pre-stressed concrete; road bridge girder; load test; composite girder; mid span; deflection; recovery

Address
K. Gurunaathan: Anna University, Chennai-600025, Tamilnadu, India
S. Christian Johnson: Excel Engineering College, Komarapalayam-637303, Tamilnadu, India
G.S. Thirugnanam: Department of Civil Engineering, Institute of Road and Transport Technology, Erode-638316, Tamilnadu, India

Abstract
Extensive research work has been performed on shear strengthening of reinforced concrete (RC) beams retrofitted with externally bonded carbon fiber reinforced polymer (CFRP) in form of strips. However, most of this research work is experimental and very scarce studies are available on numerical modelling of such beams due to truly challenging nature of modelling concrete shear cracking and interfacial interaction between components of such beams. This paper presents an appropriate model for RC beam and to simulate its cracking without numerical computational difficulties, convergence and solution degradation problems. Modelling of steel and CFRP and their interfacial interaction with concrete are discussed. Finally, commercially available non-linear finite element software ABAQUS is used to validate the developed finite element model with key tests performed on full scale T-beams with and without CFRP retrofitting, taken from previous extensive research work. The modelling parameters for bonding behavior of CFRP with special anchors are also proposed. The results presented in this research work illustrate that appropriate modelling of bond behavior of all the three types of interfaces is important in order to correctly simulate the shear behavior of RC beams strengthened with CFRP.

Key Words
reinforced concrete beams; CFRP; shear behavior; bond behavior; finite element method

Address
Umais Khan, Mohammed A. Al-Osta: Civil and Environmental Engineering Department, King Fahd University of Petroleum and Minerals (KFUPM), Dhahran, Saudi Arabia
A. Ibrahim: Department of Civil Engineering, University of Idaho, Moscow, Idaho, 83844, USA; Structural Engineering Department, Faculty of Engineering, Zagazig University, Egypt

Abstract
The paper studies the attenuation of the axisymmetric longitudinal waves propagating in the bi-layered hollow cylinder made of linear viscoelastic materials. Investigations are made by utilizing the exact equations of motion of the theory of viscoelasticity. The dispersion equation is obtained for an arbitrary type of hereditary operator of the materials of the constituents and a solution algorithm is developed for obtaining numerical results on the attenuation of the waves under consideration. Specific numerical results are presented and discussed for the case where the viscoelasticity of the materials is described through fractional-exponential operators by Rabotnov. In particular, how the rheological parameters influence the attenuation of the axisymmetric longitudinal waves propagating in the cylinder under consideration, is established.

Key Words
wave attenuation; wave dispersion; viscoelastic material; characteristic creep time; long-term elastic constants

Address
Tarik Kocal: Department of Marine Engineering Operations, Yildiz Campus, 34349 Besiktas, Istanbul, Turkey
Surkay D. Akbarov: Department of Mechanical Engineering, Yildiz Technical University, Yildiz Campus, 34349, Besiktas, Istanbul, Turkey; Institute of Mathematics and Mechanics of the National Academy of Sciences of Azerbaijan, 37041, Baku, Azerbaijan

Abstract
This study aimed to develop a simple and effective method to facilitate the experimental research on mechanical properties of masonry under biaxial compressive stress. A series of tests on full-scale brick masonry panels under biaxial compression have been performed in limited principal stress ratios oriented at various angles to the bed joints. Failure modes of tested panels were observed and failure features were analyzed to reveal the mechanical behavior of masonry under biaxial compression. Based on the experimental data, the failure curve in terms of two orthotropic principal stresses has been presented and the failure criterion of brick masonry in the form of the tensor polynomial has been established, which indicate that the anisotropy for masonry is closely related to the difference of applied stress as well as the orientation of bed joints. Further, compared with previous failure curves and criteria for masonry, it can be found that the relative strength of mortar and block has a considerable effect on the degree of anisotropy for masonry. The test results demonstrate the validity of the proposed experimental method for the approximation of masonry failure under biaxial compressive stress and provide valuable information used to establish experimentally based methodologies for the improvement of masonry failure criteria.

Key Words
biaxial compression; failure criterion; masonry panel; mechanical behavior; experimental study; anisotropy

Address
Ren Xin, Jitao Yao: School of Civil Engineering, Xi\'an University of Architecture and Technology, Xi\'an 710055, China
Yan Zhao: School of Civil Engineering, Harbin Institute of Technology, Harbin 150090, China

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