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CONTENTS
Volume 59, Number 6, September25 2016
 

Abstract
The purpose of this study is to illustrate the propagation of the shear waves (SH-waves) in a prestressed hetrogeneous orthotropic media overlying a pre-stressed anisotropic porous half-space with self weight. It is considered that the compressive initial stress, mass density and moduli of rigidity of the upper layer are space dependent. The proposed model is solved to obtain the different dispersion relations for the SH-wave in the elastic-porous medium of different properties. The effects of compressive and tensile stresses along with the heterogeneity, porosity, Biot‟s gravity parameter on the dispersion of SH-wave are shown numerically. The wave analysis further indicates that the technical parameters of upper and lower half-space affect the wave velocity significantly. The results may be useful to understand the nature of seismic wave propagation in geophysical applications and in the field of earthquake and material science engineering.

Key Words
SH-wave; Biot‟s parameter; porous; orthotropic; heterogeneity; initial stress

Address
Rajneesh Kakar : 163, Phase-1, Chotti Baradari Garah Road, Jalandhar, India
Shikha Kakar : Department of Electronics, SBBS University, Padhiana, India

Abstract
A direct and relatively simple method for controlling nodal displacements and/or internal bar forces has been developed for prestressable structural assemblies including complex elements (\"macroelements\", e.g., the pantographic element), involving Matrix Condensation, in which structural matrices being built up from matrices of elementary elements. The method is aimed at static shape control of geometrically sensitive structures. The paper discusses identification of the most effective bars for actuation, without incurring violation in bar forces, and also with objective of minimal number of actuators or minimum actuation. The advantages of the method is that the changes for both force and displacement regimes are within a single formulation. The method can also be used for adjustment of bar forces to either reduce instances of high forces or increase low forces (e.g., in a cable nearing slack).

Key Words
force method; matrix condensation; static shape control; displacement control; bar force control; actuator placement; actuation

Address
Najmadeen M. Saeed : Civil Engineering Department, University of Raparin, Rania, Kurdistan Region, Iraq
Alan S.K. Kwan : Cardiff School of Engineering, Cardiff University, Cardiff CF24 3AA, U.K.

Abstract
Helicopters are essential for supporting offshore oil and gas activities around the world. To ensure accessibility for helicopters, helideck structures must satisfy the safety requirements associated with various environmental and accidental loads. Recently, offshore helideck structures have used aluminium because of its light weight, low maintenance requirements, cost effectiveness and easy installation. However, section designs of aluminum pancakes tend to modify and/or change from the steel pancakes. Therefore, it is necessary to optimize section design and evaluate the safety requirements for aluminium helideck. In this study, a design procedure was developed based on section optimization techniques with experimental studies, industrial regulations and nonlinear finite element analyses. To validate and verify the procedure, a new aluminium section was developed and compared strength capacity with the existing helideck section profiles.

Key Words
safety helideck; nonlinear structural response analysis; optimization; aluminium pancake; accidental load

Address
Jung Kwan Seo, Dae Kyeom Park : The Korea Ship and Offshore Research Institute (The Lloyd\'s Register Foundation Research Centre of Excellence), Pusan National University, Busan, Korea
Sung Woo Jo : Department of Naval Architect and Ocean Engineering, Pusan National University, Busan, Korea
Joo Shin Park,Jeong Bon Koo, Yeong Su Ha, Ki Bok Jang : Central Research Institute, Samsung Heavy Industries Co., Ltd., Geoje, Republic of Korea

Abstract
This paper proposes a new foundation model called \"Dynamic foundation model\" for the dynamic analysis of plates on foundation subjected to a moving oscillator. This model includes a linear elastic spring, shear layer, viscous damping and the special effects of mass density parameters of foundation during vibration. By using finite element method and the principle of dynamic balance, the governing equation of motion of the plate travelled by the oscillator is derived and solved by the Newmark\'s time integration procedure. The accuracy of the algorithm is verified by comparing the numerical results with the other numerical results in the literature. Also, the effects of mass and damping ratio of system components, stiffness of suspension system, velocity of moving oscillator, and dynamic foundation parameters on dynamic responses are investigated. A very important role of these factors will be shown in the dynamic behavior of the plate.

Key Words
Winkler foundation; pasternak foundation; dynamic foundation; mass density of foundation; dynamic analysis of plate; moving oscillator; FEM

Address
Phuoc T. Nguyen : Department of Civil Engineering - Architecture, Ho Chi Minh City Open University, 97 Vo Van Tan St., Ho Chi Minh City, Vietnam
Trung D. Pham : Department of Civil Engineering, Quang Trung University, Dao Tan St., Qui Nhon City, Vietnam
Hoa P. Hoang : Department of Construction of Bridge and Road, University of Science and Technology, The University of Danang, 54 Nguyen Luong Bang St., Danang City, Vietnam

Abstract
Structural parameter evaluation and external force estimation are two important parts of structural health monitoring. But the structural parameter identification with limited input information is still a challenging problem. A new simultaneous identification method in time domain is proposed in this study to identify the structural parameters and evaluate the external force. Each sampling point in the time history of external force is taken as the unknowns in force evaluation. To reduce the number of unknowns for force evaluation the time domain measurements are divided into several windows. In each time window the structural excitation is decomposed by orthogonal polynomials. The time-variant excitation can be represented approximately by the linear combination of these orthogonal bases. Structural parameters and the coefficients of decomposition are added to the state variable to be identified. The extended Kalman filter (EKF) is augmented and selected as the mathematical tool for the implementation of state variable evaluation. The proposed method is validated numerically with simulation studies of a time-invariant linear structure, a hysteretic nonlinear structure and a time-variant linear shear frame, respectively. Results from the simulation studies indicate that the proposed method is capable of identifying the dynamic load and structural parameters fairly accurately. This method could also identify the time-variant and nonlinear structural parameter even with contaminated incomplete measurement.

Key Words
simultaneous identification; time-variant structure; nonlinear structure; extended Kalman filter; orthogonal decomposition

Address
Yong Ding : School of Civil Engineering, Harbin Institute of Technology, Harbin, 150090, People\'s Republic of China;
Key Lab of Structures Dynamic Behavior and Control of the Ministry of Education (Harbin Institute of Technology), Harbin, 150090, China
Lina Guo : School of Civil Engineering, Harbin Institute of Technology, Harbin, 150090, People\'s Republic of China;
Key Lab of Structures Dynamic Behavior and Control of the Ministry of Education (Harbin Institute of Technology), Harbin, 150090, China;
Jiangsu Key Laboratory of Engineering Mechanics, Southeast University, 210096, China

Abstract
The aim of this experimental study is to investigate the free vibration and buckling behaviors of hybrid composite beams having different span lengths and orientation angles subjected to different impact energy levels. The impact energies are applied in range from 10 J to 30 J. Free vibration and buckling behaviors of intact and impacted hybrid composite beams are compared with each other for different span lengths, orientation angles and impact levels. In free vibration analysis, the first three modes of hybrid beams are considered and natural frequencies are normalized. It is seen that first and second modes are mostly affected with increasing impact energy level. Also, the fundamental natural frequency is mostly affected with the usage of mold that have 40 mm span length (SP40). Moreover, as the impact energy increases, the normalized critical buckling loads decrease gradually for 0o and 30o oriented hybrid beams but they fluctuate for the other beams.

Key Words
hybrid composites; vibration; buckling; impact behaviour; damage mechanism

Address
Emin Ergun, Yasin Yilmaz : Mechanical Engineering Department, Pamukkale University, Denizli, 20070, Turkey
Hasan Çallioğlu : Automotive Engineering Department, Pamukkale University, Denizli, 20070, Turkey

Abstract
We employ the so-called problem-dependent linked interpolation concept to develop two cubic 4-node quadrilateral plate finite elements with 12 external degrees of freedom that pass the constant bending patch test for arbitrary node positions of which the second element has five additional internal degrees of freedom to get polynomial completeness of the cubic form. The new elements are compared to the existing linked-interpolation quadratic and nine-node cubic elements presented by the author earlier and to the other elements from literature that use the cubic linked interpolation by testing them on several benchmark examples.

Key Words
Mindlin plate theory; quadrilateral displacement-based plate finite elements; problemindependent and problem-dependent linked interpolation

Address
Dragan Ribarić : Faculty of Civil Engineering, University of Rijeka, R. Matejčić 3, 51000 Rijeka, Republic of Croatia

Abstract
This paper investigates the change of structural characteristics of steel cable-stayed bridges after cable failure. Cables, considered as the intermediate supports of cable-stayed bridges, can break or fail for several reasons, such as fire, direct vehicle clash accident, extreme weather conditions, and fatigue of cable or anchorage. Also, the replacement of cables can cause temporary disconnection. Because of the structural characteristics with various geometric nonlinearities of cable-stayed bridges, cable failure may cause significant change to the structural state and ultimate behavior. Until now, the characteristics of structural behavior after cable failure have rarely been studied. In this study, rational cable failure analysis is suggested to trace the new equilibrium with structural configuration after the cable failure. Also, the sequence of ultimate analysis for the structure that suffers cable failure is suggested, to study the change of ultimate behavior and load carrying capacity under specific live load conditions. Using these analysis methods, the statical behavior after individual cable failure is studied based on the change of structural configuration, and distribution of internal forces. Also, the change of the ultimate behavior and load carrying capacity under specific live load conditions is investigated, using the proposed analysis method. According to the study, significant change of the statical behavior and ultimate capacity occurs although just one cable fails.

Key Words
cable-stayed bridges; cable failure; cable failure analysis; nonlinear analysis; ultimate analysis

Address
Seungjun Kim : Department of Construction Safety and Disaster Prevention Engineering, Daejeon University, 62 Daehak-ro, Dong-gu, Daejeon 34520, Republic of Korea
Young Jong Kang : School of Architectural, Civil and Environmental Engineering, Korea University, 145 Anam-ro, Seoul 02841, Republic of Korea

Abstract
A large number of structure in the world were build with poor seismic details, with or without any lateral load resisting system like concentrically braced frames and steel plate shear walls. These structures can reveal deteriorating hysteretic behaviors with stiffness and strength degradation. Therefore, seismic retrofitting of such structures for drift control has vital importance. In this study a retrofit methodology has been developed, which involves diagonal bracing of steel frames with different cable arrangements. In the experimental and numerical program 5 different lateral load resisting system were tested and results compared with each other. The results indicated that multi-cable arrangements suggested in this study showed stable ductile behavior without any sudden decrease in strength. Due to the usage of more than one diagonal cable, fracture of any cable did not significantly affect the overall strength and deformation capacity of the system. In cable braced systems damages concentrated in the boundary zones of the cables and beams. That is why boundary zone must have enough stiffness and strength to resist tension field action of cables.

Key Words
cable; steel wire rope; concentrically braced frame; steel plate shear wall; FEA

Address
Metin Husem, Serhat Demir, Suleyman I. Cosgun : Department of Civil Engineering, Karadeniz Technical University, 61080, Trabzon, Turkey
Hong G. Park : Department of Architecture,Seoul National University, Seoul 151-742, South Korea

Abstract
Elastic constraints are usually simplified as \"spring forces\" exerted on beam ends without considering the \"spring deformation\". The partial differential equation governing the free vibrations of a cantilever Bernoulli-Euler beam considering the deformation of elastic constraints is firstly established, and is nondimensionalized to obtain two dimensionless factors, kv and kr, describing the effects of elastically vertical and rotational end constraints, respectively. Then the frequency equation for the above Bernoulli-Euler beam model is derived using the method of separation of variables. A numerical analysis method is proposed to solve the transcendental frequency equation for the continuous change of the frequency with kv and kr. Then the mode shape functions are given. Finally, effects of kv and kr on free vibration characteristics of the beam with different slenderness ratios are calculated and analyzed. The results indicate that the effects of kv are larger on higher-order free vibration characteristics than on lower-order ones, and the impact strength decreases with slenderness ratio. Under a relatively larger slenderness ratio, the effects of kv can be neglected for the fundamental frequency characteristics, while cannot for higher-order ones. However, the effects of kr are large on both higher- and lower-order free vibration characteristics, and cannot be neglected no matter the slenderness ratio is large or small.

Key Words
deformation; elastic constraint; free vibration characteristic; cantilever beam; Bernoulli-Euler beam; frequency equation; mode shape function

Address
Tong Wang : College of Civil Engineering, Shanghai Normal University, Shanghai, 201418, China
Tao He : College of Civil Engineering, Shanghai Normal University, Shanghai, 201418, China;
School of Civil Engineering, University of Birmingham, Birmingham, B15 2TT, UK
Hongjing Li : College of Civil Engineering, Nanjing Tech University, Nanjing, 211816, China


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