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CONTENTS
Volume 72, Number 5, December10 2019
 

Abstract
Wind induced dynamic responses on hyperbolic cooling tower (HCT) shells are complicated functions of structure and wind properties, such as the fundamental frequency fmin, damping ratio zeta wind velocity V, correlationship in meridian direction and so on, but comprehensions on the sensitivities of the dynamic responses to these four factors are still limited and disagree from each other. Following the dynamic calculation in time domain, features of dynamic effects were elaborated, focusing on the background and resonant components SigmaB and SigmaR, and their contributions to the total rms value SigmaT. The SigmaR is always less than SigmaB when only the maximum SigmaT along latitude is concerned and the contribution of SigmaR to SigmaT varies with responses and locations, but the SigmaR couldn\'t be neglected for structural design. Then, parameters of the above four factors were artificially adjusted respectively and their influences on the gust responses were illustrated. The relationships of SigmaR and the former three factors were expressed by fitted equations which shows certain differences from the existing equations. Moreover, a new strategy for wind tunnel tests aiming at surface pressures and the following dynamic calculations, which demands less experiment equipment, was proposed according to the influence from meridian correlationship.

Key Words
hyperbolic cooling towers; wind induced dynamic responses; background component; resonance component; gust response factor; fundamental frequency; damping ratio; wind velocity; meridian correlationship

Address
Jun-Feng Zhang, Qing-Shuai Liu: School of Civil Engineering, Zhengzhou University, Zhengzhou 450001, China
Yao-Jun Ge and Lin Zhao: State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China

Abstract
Accurate modeling of contact interface in bolted joints is crucial in predicting the dynamic behavior for bolted assemblies under external load. This paper presents a contact pressure distribution based non-uniform virtual material method to describe the joint interface of assembly structure, which is connected by sparsely distributed multi-bolts. Firstly, the contact pressure distribution of bolted joints is obtained by the nonlinear static analysis in the finite element software ANSYS. The contact surface around bolt hole is divided into several sub-layers, and contact pressure in each sub-layer is thought to be evenly. Then, considering multi-asperity contact at the micro perspective, the relationship between contact pressure and interfacial virtual material parameters for each sub-layer is established by using the fractal contact theory. Finally, an experimental platform for the dynamic characteristics testing of a beam lap structure with double-bolted joint is constructed to validate the efficiency of proposed method. It is found that the theoretical results are in good agreement with experimental results by impact response in both time- and frequency-domain, and the relative errors of the first four natural frequencies are less than 1%. Furthermore, the presented model is used to examine the effect of rough contact surface on dynamic characteristics of bolted joint.

Key Words
bolted joints; rough contact surface; fractal contact theory; non-uniform virtual material

Address
1 School of Mechanical Engineering, Xi\'an Jiaotong University, Xi\'an 710049, PR China
2 State Key Laboratory for Manufacturing and Systems Engineering, Xi\'an Jiaotong University,
Xi\'an 710049, PR China

Abstract
Tubular steel sections are widespread all over the world because of their strength and aesthetic appearance. Tubular steel members may exhibit local buckling such as elephant foot or overall buckling under extreme compression load. Recently, external bonding of fiber reinforced polymers (FRP) sheets for strengthening these members has been explored through experimental research. This paper presents three-dimensional nonlinear finite element analysis (FEA) to investigate the structural behavior of strengthening tubular steel members with FRP against local and overall buckling phenomena. Out-of-roundness and out-of-straightness imperfections were introduced to the numerical models to simulate the elephant foot and overall buckling, respectively. The nonlinear analysis preferences such as the integration scheme of the shell elements, the algorithm for solution of nonlinear equations, the loading procedure, the bisection limits for the load increments, and the convergence criteria were set, appropriately enough, to successfully track the sophisticated buckling deformations. The agreement between the results of both the presented FEA and the experimental research was evident. The FEA results demonstrated the power of the presented rigorous FEA in monitoring the plastic strain distribution and the buckling phenomena (initiation and propagation). Consequently, the buckling process was interpreted for each mode (elephant foot and overall) into three sequential stages. Furthermore, the influence of FRP layers on the nonlinear analysis preferences and the results was presented.

Key Words
tubular steel compression member, FRP strengthening, nonlinear FEA, elephant foot buckling, overall buckling, imperfection

Address
Ahmed M. El-Kholy, Ayman A. Shaheen and Yomna A. Mohamed: Department of Civil Engineering, Faculty of Engineering, Fayoum University, Kiman Fares, El-Fayoum, 63541, Egypt
Sherif A. Mourad: Department of Structural Engineering, Faculty of Engineering, Cairo University, Giza, 12613, Egypt

Abstract
Foundations are a vital part of structures. Over time, the foundations can deteriorate due to unforeseen overloads and/or settlements, resulting in the appearance of cracks in the concrete. These cracks produce changes in the static and dynamic behavior of the affected foundation, which alter its load carrying capacity. In this work, non-destructive techniques of relative simplicity of application are presented for the detection, location, and quantification of damage, using numerical models, solved with the finite element method and Power Series. For this, two types of parameters are used: static (displacement and elastic curvature) and dynamics (natural frequencies). In the static analysis, the damage detection is done by means of a finite elements model representing a beam supported on an elastic foundation with a discrete crack that varies in length and location. With regard to dynamic analysis, the governing equations of the model are presented and a method based on Power Series is used to obtain the solution for a data set, which could be the Winkler coefficient, the location of the crack or the frequency. In order to validate the proposed methodologies, these techniques are applied to data obtained from laboratory tests.

Key Words
foundation beam; failure detection; reinforced concrete; structural dynamics

Address
Claudio J. Orbanich, Néstor F. Ortega, Sandra I. Robles and Marta B. Rosales: Engineering Department, Universidad Nacional del Sur, Bahía Blanca, Buenos Aires, Argentina
Néstor F. Ortega, Sandra I. Robles: Engineering Institute, CIC, Universidad Nacional del Sur, Bahía Blanca, Buenos Aires, Argentina
Marta B. Rosales: IFISUR, CONICET, Avenida Alem 1253, 8000 Bahía Blanca, Buenos Aires, Argentina

Abstract
The paper studies the dispersion of the axisymmetric longitudinal wave propagating in the \"hollow cylinder + surrounding medium\" system with inhomogeneous initial stresses caused by the uniformly distributed radial compressional forces acting at infinity. Up to now in the world literature, there exist only a few investigations related to the wave dispersion in a hollow cylinder with inhomogeneous initial stresses. Therefore, this paper is one of the first attempts in this field in the sense of the development of investigations for the case where the cylinder is surrounded with an infinite medium. The three-dimensional linearized theory of elastic waves is used for describing the considered wave propagation problem and, for a solution to the corresponding mathematical problem, the discrete-analytical solution method is developed and employed. The corresponding dispersion equation is obtained and this equation is solved numerically and, as a result of this solution, the dispersion curves are constructed for the first and second modes. By analyzing these curves, the character of the influence of the inhomogeneous initial stresses on the dispersion curves is established. In particular, it is established that as a result of the inhomogeneity of the initial stresses both new dispersion curves and the \"band gap\" for the wave frequencies can appear.

Key Words
inhomogeneous initial stresses; \"hollow cylinder + surrounding medium\" system; discrete-analytical method; wave dispersion; dispersion curves; band gap

Address
Surkay D. Akbarov and Emin T. Bagirov: Yildiz Technical University, Faculty of Mechanical Engineering, Department of Mechanical Engineering,
Yildiz Campus, 3349, Besiktas, Istanbul-Turkey
Emin T. Bagirov: Institute of Mathematics and Mechanics of National Academy of Sciences of Azerbaijan, Az141, Baku, Azerbaijan

Abstract
Based on the finite element method of traditional straight Euler-Bernoulli beams and the coupled relations between linear displacement and angular displacement of a pre-twisted Euler-Bernoulli beam, the shape functions and stiffness matrix are deduced. Firstly, the stiffness of pre-twisted Euler-Bernoulli beam is developed based on the traditional straight Euler-Bernoulli beam. Then, a new finite element model is proposed based on the displacement general solution of a pre-twisted Euler-Bernoulli beam. Finally, comparison analyses are made among the proposed Euler-Bernoulli model, the new numerical model based on displacement general solution and the ANSYS solution by Beam188 element based on infinite approach. The results show that developed numerical models are available for the pre-twisted Euler-Bernoulli beam, and which provide more accurate finite element model for the numerical analysis. The effects of pre-twisted angle and flexural stiffness ratio on the mechanical property are investigated.

Key Words
Pre-twisted; Euler-Bernoulli beam; Stiffness matrix; Parametric analysis

Address
Ying Huang: 1School of Civil Engineering, Xi\'an University of Architecture and Technology, Xi\'an, China, 710055, China
2Key Lab of Structural Engineering and Earthquake Resistance, Ministry of Education

Abstract
The objective of the present study is to examine the flexural behavior of two-span post-tensioned lightweight aggregate concrete (LWAC) beams using unbonded tendons and the reliability of the design provisions of ACI 318-14 for such beams. The parameters investigated were the effective prestress and loading type, including the symmetrical top one-point, two third-point, and analogous uniform loading systems. The unbonded prestressing three-wire strands were arranged with a harped profile of variable eccentricity. The total length of the beam, measured between both strand anchorages, was 11000 mm. The test results were compared with those compiled from simply supported LWAC one-way members, wherever possible. The ultimate load capacity of the present beam specimens was evaluated by the collapse mechanism of the plasticity theorem and the nominal section moment strength calculated following the provision of the ACI 318-14. The test results showed that the two-span post-tensioned LWAC beams had lower stress increase (Deltafps) in the unbonded tendons than the simply supported LWAC beams with a similar reinforcement index. The effect of the loading type on Deltafps and displacement ductility was less significant for two-span beams than for the comparable simply supported beams. The design equations for Deltafps and Deltafps proposed by ACI 318-14 and Harajli are conservative for the present two-span post-tensioned LWAC beams, although the safety decreases for the two-span beam, compared to the ratios between experiments and predictions obtained from simply supported beams.

Key Words
lightweight concrete, post-tension, two-span beams, load capacity, ductility, ACI 318-14

Address
Keun-Hyeok Yang: Department of Architectural Engineering, Kyonggi University, Suwon, Kyonggi-do, Korea
Kyung-Ho Lee and Hyun-Sub Yoon: Department of Architectural Engineering, Kyonggi University Graduate School, Seoul, Kyonggi-do, Korea

Abstract
Protection of cultural heritage and carrying it to the future are at the top of the significant topics of research and implementation in engineering in the 21st century. There are several historical structures in the district of Ahlat located in the east of Turkey on the Lake Van Basin that has harbored many civilizations. Some of such works are the gravestones that are found in the Ahlat Seljuk Cemetery, which is the oldest and largest cemetery in the district. This study firstly provides information about the Ahlat Seljuk Cemetery and the gravestones found in it. Observation-based structural analyses were carried out on these gravestones that are found in this area that are known to have belonged to different civilizations based on their physical and constructional characteristics. These stones were built out of Ahlat stone as single pieces. Information is provided on the damages that have occurred on the gravestones in time and their causes. In general, losses of mass, abrasions, separations, collapses and calcifications due to natural conditions, as well as vegetative formations, were observed in the gravestones. To provide an example of other gravestones within the context of the study, the gravestone that is known to belong to the person named Nureddin Ebu Hasan was selected. As a result of the modeling that was carried out for this gravestone by using the finite elements method, modal analyses were carried out. With these analyses, for the gravestone, period, effective mass participation rates and stress values were calculated. The stress values that were obtained in this study were compared to the material safety stress values that were obtained in previous studies. Additionally, QR code application was created for the gravestone that was selected as an example in the study, and information on this gravestone was transferred to an electronic environment. The QR code application includes different language options, visuals of the gravestone and information on the gravestone. The QR application was also supported with a video of the cemetery where the gravestone is located. With this application, access to information about gravestones will be possible by using tablets and smartphones. With a QR code to be created for each gravestone, these gravestones will obtain identity cards.

Key Words
Gravestone; cultural heritage; seismic behavior; QR code; monitoring

Address
Ercan IsIk,AydIn Buyuksarac: Department of Civil Engineering, Faculty of Engineering and Architecture, Bitlis Eren University, TR-13100, Bitlis, Turkey
BarIs Antep: Civil Engineer, TR-13100, Bitlis, Turkey
Mehmet Fatih IsIk: Department of Electric-Electronics Engineering, Faculty of Engineering, Hitit University, TR-19030, Corum, Turkey

Abstract
This work investigates a novel quasi-3D hyperbolic shear deformation theory is presented to discuss the buckling of new type of sandwich plates. This theory accounts for both shear deformation and thickness stretching effects by a hyperbolic variation of all displacements through the thickness. The enhancement of this formulation is due to the use of only five unknowns by including undetermined integral terms, contrary to other theories where we find six or more unknowns. It does not require shear correction factors and transverse shear stresses vary parabolically across the thickness. A new type of FGM sandwich plates, namely, both FGM face sheets and FGM hard core are considered. The governing equations and boundary conditions are derived using the principle of virtual displacements. Analytical solutions are obtained for a simply supported plate. The accuracy of the present theory is verified by comparing the obtained results with quasi-3D solutions and those predicted by higher-order shear deformation theories. The comparison studies show that the obtained results are not only more accurate than those obtained by higher-order shear deformation theories, but also comparable with those predicted by quasi-3D theories with a greater number of unknowns.

Key Words
buckling analysis; functionally graded plate; new type of sandwich plate; refined plate theory; novel quasi-3D theory

Address
Sara Chelahi Chikr, Abdelhakim Kaci, Redha Yeghnem: Université Dr Tahar Moulay, Faculté de Technologie, Département de Génie Civil et Hydraulique,
BP 138 Cité En-Nasr 20000 Saida, Algérie
Sara Chelahi Chikr: Laboratoire des Ressources Hydriques et Environnement, Université Dr Tahar Moulay, BP 138 Cité En-Nasr20000 Saida, Algérie
Redha Yeghnem and Abdelouahed Tounsi: Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria
Abdelouahed Tounsi: Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran,
Eastern Province, Saudi Arabia


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