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CONTENTS
Volume 50, Number 1, April10 2014
 

Abstract
In this paper, overstrength, ductility and response modification factors are calculated for frames braced with a different type of buckling restrained braces, called reduced yielding segment BRB (Buckling Restrained Brace) in which the length of its yielding part is reduced and placed in one end of the brace element in comparison with conventional BRBs. Forthermore,these factors are calculated for ordinary BRBF and the results are compared. In this regard incremental dynamic analysis (IDA) method is used for studying 17 records of the most known earthquakes happened in the world. To do that, the considered buildings have different stories and two bracing configurations: diagonal and inverted V chevron, the most ordinary configurations of BRBFs. Static pushover analysis, nonlinear incremental dynamic analysis and linear dynamic analysis have been performed using OpenSees software. Considering the results, it can be seen that, overstrength, ductility and response modification factors of this type of BRBF(Buckling Restrained Braced Frame) is greater than those of conventional types and it shows better seismic performance and also eliminates some of conventional BRBF

Key Words
response modification factor; ductility factor; overstrength factor; reduced length BRB; IDA

Address
Nader Fanaie and Ebrahim Afsar Dizaj : Department of Civil Engineering, K.N.Toosi University of Technology, Tehran, Iran

Abstract
This paper focuses on a model order reduction (MOR) for large-scale rotordynamic systems by using finite element discretization. Typical rotor-bearing systems consist of a rotor, built-on parts, and a support system. These systems require careful consideration in their dynamic analysis modeling because they include unsymmetrical stiffness, localized nonproportional damping, and frequency-dependent gyroscopic effects. Because of this complex geometry, the finite element model under consideration may have a very large number of degrees of freedom. Thus, the repeated dynamic analyses used to investigate the critical speeds, stability, and unbalanced response are computationally very expensive to complete within a practical design cycle. In this study, we demonstrate that a Krylov subspace-based MOR via moment matching significantly speeds up the rotordynamic analyses needed to check the whirling frequencies and critical speeds of large rotor systems. This approach is very efficient, because it is possible to repeat the dynamic simulation with the help of a reduced system by changing the operating rotational speed, which can be preserved as a parameter in the process of model reduction. Two examples of rotordynamic systems show that the suggested MOR provides a significant reduction in computational cost for a Campbell diagram analysis, while maintaining accuracy comparable to that of the original systems.

Key Words
model order reduction; Krylov subspace; rotordynamics; Campbell diagram; damped eigenvalue analysis; whirling frequency; critical speed

Address
Jeong Sam Han : Department of Mechanical Design Engineering, Andong National University, Andong 760-749, Korea

Abstract
The accurate determination of cable tension is important to the monitoring of the condition of a cable-stayed bridge. When applying a vibration-based formula to identify the tension of a real cable under sag, stiffness and boundary conditions, the resulting error must not be overlooked. In this work, by resolving the implicit frequency function of a real cable under the above conditions numerically, indirect methods of determining the cable force and a method to calculate the corresponding cable mode frequency are investigated. The error in the tension is studied by numerical simulation, and an empirical error correction formula is presented by fitting the relationship between the cable force error and cable parameters

Key Words
cable; cable force; implicit frequency function; numerical solution

Address
Danhui Dan, Yanyang Chen : Department of Bridge engineering, Tongji University, Shanghai, PRC, 200092, China
Xingfei Yan : Shanghai Urban Construction Design and Research Institute, Shanghai, PRC, 200125, China

Abstract
A semi-analytical method is developed to consider free vibrations of a functionally graded elastic plate resting on Winkler elastic foundation and in contact with a quiescent fluid. Material properties are assumed to be graded distribution along the thickness direction according to a power-law in terms of the volume fractions of the constituents. The fluid is considered to be incompressible and inviscid. In the analysis, the effect of an in-plane force in the plate due to the weight of the fluid is taken into account. By satisfying the compatibility conditions along the interface of fluid and plate, the fluid-structure interaction is taken into account and natural frequencies and mode shapes of the coupled system are acquired by employing energy methods. The results obtained from the present approach are verified by those from a finite element analysis. Besides, the effects of volume fractions of functionally graded materials, Winkler foundation stiffness and in-plane forces on the dynamic of plate are elucidated.

Key Words
dynamic behavior; fluid-structure interaction; functionally graded material; Winkler elastic foundation; in-plane forces

Address
Ali A. Shafiee, Mojtaba Mahzoon : Faculty of Mechanical Engineering, Shiraz University, Shiraz 71348-51154, Iran
Farhang Daneshmand : Department of Mechanical Engineering, McGill University, 817 Sherbrooke Street W., Montreal, Quebec H3A 2K6, Canada
Ehsan Askari : Australian School of Advanced Medicine, Macquarie University, Sydney, Australia

Abstract
Vibration characteristics of columns are influenced by their axial loads. Numerous methods have been developed to quantify axial load and deformation in individual columns based on their natural frequencies. However, these methods cannot be applied to columns in a structural framing system as the natural frequency is a global parameter of the entire framing system. This paper presents an innovative method to quantify axial deformations of columns in a structural framing system using its vibration characteristics, incorporating the influence of load tributary areas, boundary conditions and load migration among the columns.

Key Words
modal flexibility; axial deformation; load migration; dynamic stiffness matrix; load tributary areas

Address
H.N. Praveen Moragaspitiya, David P. Thambiratnam, Nimal J. Perera and Tommy H.T. Chan : School of Civil Engineering & Built Environment, Queensland University of Technology, Brisbane, Australia

Abstract
According to experimental studies made so far, design formula of shear characteristics suggested by ISO 22762 and JEAG 4614, representative design code for Lead Rubber Bearing(LRB) shows dependence caused by changes in compressive stress. Especially, in the case of atypical special structure, such as a nuclear power structure, placement of seismic isolation bearing is more limited compared to that of existing structures and design compressive stress is various in sizes. As a result, there is a difference between design factor and real behavior with regards to shear characteristics of base isolation device, depending on compressive stress. In this study, a full-scale low hardness device of LRB, representative base isolation device was manufactured, analyzed, and then evaluated through an experiment on shear characteristics related to various compressive stresses. With design compressive stress of the full-scale LRB (13MPa) being a basis, changes in shear characteristics were analyzed for compressive stress of 5 MPa, 10 MPa, 13 MPa, 15 MPa, and 20 MPa based on characteristics test specified by ISO 22762:2010 and based on the test result, a regression analysis was made to offer an empirical formula. With application of proposed design formula which reflected the existing design formula and empirical formula, trend of horizontal characteristics was analyzed.

Key Words
lead rubber bearing; compressive stress dependency; low hardness rubber; shear stiffness; equivalent damping ratio; nuclear power plants

Address
Hong-Pyo Lee, Myung-Sug Cho, Sunyong Kim : Plant Const. & Eng. Lab., KHNP Central Research Institute, Yuseong, Daejeon 305-343, Korea
Jin-Young Park and Kwang-Seok Jang : R&D Center, UNISON eTech Co. Ltd., Cheoan, Soosin 330-882, Korea

Abstract
This study presents a steel container crane movement analysis and assessment based on structural health monitoring (SHM). The accelerometers are used to monitor the dynamic crane behavior and a 3-D finite element model (FEM) was designed to express the static displacement of the crane under the different load cases. The multi-input single-output nonlinear autoregressive neural network with external input (NNARX) model is used to identify the crane dynamic displacements. The FEM analysis and the identification model are used to investigate the safety and the vibration state of the crane in both time and frequency domains. Moreover, the SHM system is used based on the FEM analysis to assess the crane behavior. The analysis results indicate that: (1) the mean relative dynamic displacement can reveal the relative static movement of structures under environmental load; (2) the environmental load conditions clearly affect the crane deformations in different load cases; (3) the crane deformations are shown within the safe limits under different loads.

Key Words
structural health monitoring; finite element model; neural network; container crane

Address
Mosbeh R. Kaloop, Mohamed A. Sayed, Dookie Kim : Department of Civil and Environmental Engineering, Kunsan National University, Kunsan, South Korea
Mosbeh R. Kaloop : Department of Public Works and Civil Engineering, Mansoura University, Mansoura, Egypt
Eunsung Kim : Korea Maintenance Company, Seoul, South Korea

Abstract
Stone masonry structures are widely used around the world, but they deteriorate easily, due to low shear strength capacity. Many techniques have been developed to increase the shear strength of stone masonry constructions. The aim of this experimental study was to investigate the performance of stone masonry walls strengthened by metal connectors as an alternative shear reinforcement technique. For this purpose, three new metal connector (clamp) types were developed. The shear strength of the walls was improved by applying these clamps to stone masonry walls. Ten stone masonry walls were structurally tested in diagonal compression. Various parameters regarding the in-plane behavior of strengthening stone masonry walls, including shear strength, failure modes, maximum drift, ductility, and shear modulus, were investigated. Experimentally obtained shear strengths were confirmed by empirical equations. The results of the study suggest that the new clamps developed for the study effectively increased the levels of shear strength and ductility of masonry constructions.

Key Words
stone masonry wall; clamp; diagonal testing; strengthening; shear strength; failure

Address
Turan Karabork : Division of Structures, Department of Civil Engineering, Aksaray University, 68100, Aksaray, Turkey
Yilmaz Kocak : Inspection and Control Expert, Ministry of Defense, 06000, Ankara, Turkey


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