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CONTENTS
Volume 57, Number 5, March10 2016
 

Abstract
An innovative Reduced Beam Section (RBS) connection, called Tubular Web RBS connection (TW-RBS), has been recently introduced and its performance has been numerically investigated in some earlier studies. The TW-RBS connection is a kind of accordion-web RBS connection in which part of the flat web of the beam is replaced by a steel tube at the expected region of the plastic hinge. This paper presents experimental results of three TW-RBS connections under cyclic loading. Obtained results indicated that TW-RBS reduces contribution of the beam web to the whole moment strength and creates a ductile fuse far from components of the beam-to-column connection. Besides, TW-RBS connection can increase story drift capacity up to 9% in the case of shallow beams which is much more than those stipulated by the current seismic codes. Based on the experimental results, the tubular web in the plastic hinge region improves lateral-torsional buckling stability of the beam such that only local buckling of the beam flange at the center of the reduced section was observed during the tests. In order to achieve a better understanding, behavior of all TW-RBS specimens are also numerically investigated and compared with those of experimental results.

Key Words
cyclic testing; special moment frame; reduced beam section; tubular web RBS (TW-RBS); test specimens; shallow beams

Address
Aboozar Saleh, Seyed M. Zahrai and Seyed R. Mirghaderi:School of Civil Engineering, the University of Tehran, Iran

Abstract
Concentric-tube continuum robots have formed an active field of research in robotics because of their manipulative exquisiteness essential to facilitate delicate surgical procedures. A set of concentric tubes with designed initial curvatures comprises a robot whose workspace can be controlled by relative translations and rotations of the tubes. Kinematic models have been widely used to predict the movement of the robot, but they are incapable of describing its time-dependent hysteretic behaviors accurately particularly when snapping occurs. To overcome this limitation, here we present a finite element modeling approach to investigating the dynamics of concentric-tube continuum robots. In our model, each tube is discretized using MITC shell elements and its transient responses are computed implicitly using the Bathe time integration method. Inter-tube contacts, the key actuation mechanism of this robot, are modeled using the constraint function method with contact damping to capture the hysteresis in robot trajectories. Performance of the proposed method is demonstrated by analyzing three specifications of two-tube robots including the one exhibiting snapping phenomena while the method can be applied to multiple-tube robots as well.

Key Words
concentric-tube continuum robot; finite element; hysteresis; contact

Address
Changyeob Baek and Do-Nyun Kim: Department of Mechanical and Aerospace Engineering, Seoul National University, Gwanak-ro 1, Gwanak-gu, Seoul 08826, Republic of Korea
Kyungho Yoon: Institute of Advanced Machines and Design, Seoul National University, Gwanak-ro 1, Gwanak-gu, Seoul 08826, Republic of Korea

Abstract
Using the Complementary Functions Method (CFM), a general solution for the one-dimensional steady-state thermal and mechanical stresses in a hollow thick sphere made of functionally graded material (FGM) is presented. The mechanical properties are assumed to obey the exponential variations in the radial direction, and the Poisson\'s ratio is assumed to be constant, with general thermal and mechanical boundary conditions on the inside and outside surfaces of the sphere. In the present paper, a semi-analytical iterative technique, one of the most efficient unified method, is employed to solve the heat conduction equation and the Navier equation. For different values of inhomogeneity constant, distributions of radial displacement, radial stress, circumferential stress, and effective stress, as a function of radial direction, are obtained. Various material models from the literature are used and corresponding temperature distributions and stress distributions are computed. Verification of the proposed method is done using benchmark solutions available in the literature for some special cases and virtually exact results are obtained.

Key Words
complementary functions method; thick sphere; functionally graded materials (FGMs); exponentially varying properties

Address
Kerimcan Celebi: Department of Mechanical Engineering, Adana Science and Technology University, Adana,Turkey
Durmus Yarimpabuc: Department of Mathematics, Osmaniye Korkut Ata University, Osmaniye, Turkey
Ibrahim Keles: Department of Mechanical Engineering, Ondokuz Mayis University, Samsun, Turkey

Abstract
An efficient shear deformation theory is developed for wave propagation analysis of an infinite functionally graded plate in the presence of thermal environments. By dividing the transverse displacement into bending and shear parts, the number of unknowns and governing equations of the present theory is reduced, and hence, makes it simple to use. The thermal effects and temperature-dependent material properties are both taken into account. The temperature field is assumed to be a uniform distribution over the plate surface and varied in the thickness direction only. Material properties are assumed to be temperature-dependent, and graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents. The governing equations of the wave propagation in the functionally graded plate are derived by employing the Hamilton\'s principle and the physical neutral surface concept. There is no stretching–bending coupling effect in the neutral surface-based formulation, and consequently, the governing equations and boundary conditions of functionally graded plates based on neutral surface have the simple forms as those of isotropic plates. The analytic dispersion relation of the functionally graded plate is obtained by solving an eigenvalue problem. The effects of the volume fraction distributions and temperature on wave propagation of functionally graded plate are discussed in detail. It can be concluded that the present theory is not only accurate but also simple in predicting the wave propagation characteristics in the functionally graded plate. The results carried out can be used in the ultrasonic inspection techniques and structural health monitoring.

Key Words
wave propagation; functionally graded plate; thermal effects; efficient shear deformation theory; neutral surface position

Address
Ahmed Boukhari, Hassen Ait Atmane, Abdelouahed Tounsi, E.A. Adda Bedia: Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria
S.R. Mahmoud: Department of Mathematics, Faculty of Science, King Abdulaziz University, Saudi Arabia

Abstract
The determination of the critical buckling load of multistory structures is important since this load is used in second order analysis. It is more realistic to determine the critical buckling load of multistory structures using the whole system instead of independent elements. In this study, a method is proposed for designating the system critical buckling load of torsion-free structures of which the load-bearing system consists of frames and shear walls. In the method presented, the multistory structure is modeled in accordance with the continuous system calculation model and the differential equation governing the stability case is solved using the differential transform method (DTM). At the end of the study, an example problem is solved to show the conformity of the presented method with the finite elements method (FEM).

Key Words
stability; differential transform method; continuous system; multistory structure; wall-frame

Address
Kanat Burak Bozdogan: Department of Civil Engineering, Kirklareli University, Kirklareli, Turkey
Suleyman Aydin: Vocational School, Kirklareli University, Kirklareli, Turkey

Abstract
This paper is concerned with the analytical derivation of natural sloshing frequencies of liquid in annular cylindrical tank and its verification by experiment. The whole liquid domain is divided into three simple sub-regions, and the region-wise linearized velocity potentials are derived by the separation of variables. Two sets of matrix equations for solving the natural sloshing frequencies are derived by enforcing the boundary conditions and the continuity conditions at the interfaces between sub-regions. In addition, the natural sloshing frequencies are measured by experiment and the numerical accuracy of the proposed analytical method is verified through the comparison between the analytical and experimental results. It is confirmed that the present analytical method provides the fundamental sloshing frequencies which are in an excellent agreement with the experiment. As well, the effects of the tank radial gap, the bottom flow gap and the liquid fill height on the fundamental sloshing frequency are parametrically investigated.

Key Words
liquid sloshing; annular cylindrical tank; natural frequency; three flow regions; linearized velocity potential; analytical derivation; experimental verification

Address
H.W. Lee, S.H. Jeon, M.W. Seo1 and W.B. Jeong: School of Mechanical Engineering, Pusan National University, Busan 609-735, Korea
J.R. Cho: Department of Naval Architecture and Ocean Engineering, Hongik University, Sejong 339-701, Korea

Abstract
The objective is to determine the mechanical properties of the composites formed in two types, theoretically. The first composite includes micro-particles in a matrix while the second involves long, thin fibers. A fictitious, homogeneous, linear-elastic and isotropic single material named as effective material is considered during calculation which is based on the equality of the strain energies of the composite and effective material under the same loading conditions. The procedure is carried out with volume integrals considering a unique strain energy in a body. Particularly, the effective elastic shear modulus has been calculated exactly for small-particle composites by the same procedure in order to determine of bulk modulus thereof. Additionally, the transverse shear modulus of fiber reinforced composites has been obtained through a simple approach leading to the practical equation. The results have been compared not only with the outcomes in the literature obtained by different method but also with those of finite element analysis performed in this study.

Key Words
analytical method; composites; fiber reinforced; finite element method (FEM); static analysis

Address
Osman Bulut, Necla Kadioglu and Senol Ataoglu: Civil Engineering Department, Faculty of Civil Engineering, Istanbul Technical University, Maslak 34469 Istanbul, Turkey

Abstract
In this study, a model order reduction technique is applied to solve the transient responses of submerged floating tunnel (SFT) from Mokpo to Jeju under seismic excitations. Because the SFT is a very long structure as well as a transient response analysis requires large amount of computational resources, the model order reduction is mandatory in the design stage of the SFT. Thus, we apply a model order reduction based on Krylov subspace to the simplified finite element model of the SFT. The responses of the reduced order model are compared with those of the full order model and also are verified by referring a previous work. In conclusion, the computational resources are dramatically reduced with an acceptable accuracy by using the model order reduction, which eventually is useful for designing the full-scale model of SFTs.

Key Words
computational mechanics; dynamic analysis; earthquake/seismic ananysis; finite element method (FEM); numerical methods; offshore/coastal structures; simulation; structural design

Address
Boreum Won, Woo-Sun Park and Jin Hwan Ko: 1Coastal Engineering Research Division, Korea Institute of Ocean Science and Technology, Korea
Jeong Sam Han: 2Department of Mechanical Design Engineering, Andong National University, Korea

Abstract
Fiber reinforced polymer (FRP) applications in the structural engineering field include concrete- FRP composite systems, where FRP components are either attached to or embedded into concrete structures to improve their structural performance. This paper presents the results of an analytical study conducted using finite element model (FEM) to simulate the behavior of three-points load beam reinforced with GFRP and/or steel bars. To calibrate the FEM, a small-scale experimental program was carried out using six reinforced concrete beams with 200x200 mm cross section and 1000 mm length cast and tested under three point bending load. The six beams were divided into three groups, each group contained two beams. The first group was a reference beams which was cast without any reinforcement, the second group concrete beams was reinforced using GFRP, and the third group concrete beams was reinforced with steel bars. Nonlinear finite element simulations were executed using ANSYS software package. The difference between the theoretical and experimental results of beams vertical deflection and beams crack shapes were within acceptable degree of accuracy. Parametric study using the calibrated model was carried out to evaluate two parameters (1) effect of number and position of longitudinal main bars on beam behavior; (2) performance of concrete beam with composite longitudinal reinforcement steel and GFRP bars.

Key Words
GFRP bars; concrete beams; finite element model; composite reinforcement

Address
Ahmed S. Elamary: Faculty of Engineering, Department of Civil Engineer, Al-Azhar University, Qena, Egypt
Rafik K. Abd-ELwahab: Faculty of Engineering, Department of Civil Engineer, Al-Azhar University, Qena, Egypt

Abstract
Long-span cross-strait bridges extending into deep-sea waters are exposed to complex marine environments. During the construction stage, the flexible freestanding bridge towers are more vulnerable to environmental loads imposed by wind and wave loads. This paper presents an experimental investigation on the dynamic responses of a 389-m-high freestanding bridge tower model in a test facility with a wind tunnel and a wave flume. An elastic bridge model with a geometric scale of 1:150 was designed based on Froude similarity and was tested under wind-only, wave-only and wind-wave combined conditions. The dynamic responses obtained from the tests indicate that large deformation under resonant sea states could be a structural challenge. The dominant role of the wind loads and the wave loads change according to the sea states. The joint wind and wave loads have complex effects on the dynamic responses of the structure, depending on the approaching direction angle and the fluid-induced vibration mechanisms of the waves and wind.

Key Words
freestanding bridge tower; experimental investigation; wind and wave; offshore/coastal structures

Address
Xiaodong Bai, Anxin Guo, Hao Liu and Hui Li: Ministry-of-Education Key Laboratory of Structural Dynamic Behavior and Control, School of Civil Engineering, Harbin Institute of Technology, Harbin, China
Tianchen Liu and Shangyou Chen: Bridge Technology Research Center, CCCC Highway Consultants Co., Ltd., Beijing, China



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