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CONTENTS
Volume 8, Number 5, November 2011
 

Abstract
The present paper addresses the nonlinear response of a FG square plate with two smart layers as a sensor and actuator under pressure. Geometric nonlinearity was considered in the strain-displacement relation based on the Von-Karman assumption. All the mechanical and electrical properties except Poisson

Key Words
plate; mechanical properties; electrical properties; nonlinear; functionally graded material; piezoelectric; sensor.

Address
M. Arefi and G.H. Rahimi : Department of Mechanical Engineering, Tarbiat Modares University, Tehran, Iran, 14115-143

Abstract
During the last thirty years many structural control concepts have been proposed for the reduction of the structural response caused by earthquake excitations. Their research and implementation in practice have shown that seismic control of structures has a lot of potential but also many limitations. In this paper the importance of two practical issues, time delay and saturation effect, on the performance of controlled structures, is discussed. Their influence, both separately and in interaction, on the response of structures controlled by a modified pole placement algorithm is investigated. Characteristic buildings controlled by this algorithm and subjected to dynamic loads, such as harmonic signals and actual seismic events, are analyzed for a range of levels of time delay and saturation capacity of the control devices. The response reduction surfaces for the combined influence of time delay and force saturation of the controlled buildings are obtained. Conclusions regarding the choice of the control system and the desired properties of the control devices are drawn.

Key Words
structural control; time delay; saturation control; pole placement; structural dynamics; earthquake engineering.

Address
Nikos G. Pnevmatikos and Charis J. Gantes :
1. Department of Civil Infrastructure Works, Faculty of Technological Application, Technological Educational Institution of Athens, Ag. Spyridonos Str., P.O. 12210 Egaleo-Athens, Greece
2. Metal Structures Laboratory, School of Civil Engineering, National Technical University of Athens,
9 Heroon Polytechneiou, GR-15780 Zografou, Greece

Abstract
Various types of strain sensors have been developed and widely used in the field for monitoring the mechanical deformation of structures. However, conventional strain sensors are not suited for measuring large strains associated with impact damage and local crack propagation. In addition, strain sensors are resistive-type transducers, which mean that the sensors require an external electrical or power source. In this study, a gold nanoparticle (GNP)-based polymer composite is proposed for large strain sensing. Fabrication of the composites relies on a novel and simple in situ GNP reduction technique that is performed directly within the elastomeric poly(dimethyl siloxane) (PDMS) matrix. First, the reducing and stabilizing capacities of PDMS constituents and mixtures are evaluated via visual observation, ultraviolet-visible (UV-Vis) spectroscopy, and transmission electron microscopy. The large strain sensing capacity of the GNP-PDMS thin film is then validated by correlating changes in thin film optical properties (e.g., maximum UV-Vis light absorption) with applied tensile strains. Also, the composite

Key Words
Beer-Lambert law; gold nanoparticles; nanocomposites; PDMS; strain sensing; thin film.

Address
Donghyeon Ryu and Kenneth J. Loh :Department of Civil & Environmental Engineering, University of California, Davis, CA 95616, USA
Robert Ireland, Mohammad Karimzada, Frank Yaghmaie and Andrea M. Gusman: Northern California Nanotechnology Center (NC2), University of California, Davis, CA 95616, USA

Abstract
The parametric resonance problems of axisymmetric sandwich annular plate with an electrorheological (ER) fluid core and constraining layer are investigated. The annular plate is covered an electrorheological fluid core layer and a constraining layer to improve the stability of the system. The discrete layer annular finite element and the harmonic balance method are adopted to calculate the boundary of instability regions for the sandwich annular plate system. Besides, the rheological property of an electrorheological material, such as viscosity, plasticity, and elasticity can be changed when applying an electric field. When the electric field is applied on the sandwich structure, the damping of the sandwich system is more effective. Thus, variations of the instability regions for the sandwich annular plate with different applying electric fields, thickness of ER layer, and some designed parameters are presented and discussed in this study. The ER fluid core is found to have a significant effect on the location of the boundaries of the instability regions.

Key Words
parametric resonance; dynamic instability; electrorheological; annular plate; discrete layer annular finite element.

Address
Jia-Yi Yeh : Department of Information Management, Chung Hwa University of Medical Technology,89, Wen-Hwa 1st ST. Jen-Te Hsiang, Tainan Hsien 717, Taiwan, R.O.C.

Abstract
Recent studies have discovered that a conventional passive isolation system may suffer from an excessive isolator displacement when subjected to a near-fault earthquake that usually has a long-period velocity pulse waveform. Semi-active isolation using variable friction dampers (VFD), which requires a suitable control law, may provide a solution to this problem. To control the VFD in a semi-active isolation system more efficiently, this paper investigates experimentally the possible use of a control law whose control logic is similar to that of the anti-lock braking systems (ABS) widely used in the automobile industry. This ABS-type controller has the advantages of being simple and easily implemented, because it only requires the measurement of the isolation-layer velocity and does not require system modeling for gain design. Most importantly, it does not interfere with the isolation period, which usually decides the isolation efficiency. In order to verify its feasibility and effectiveness, the ABS-type controller was implemented on a variable-friction isolation system whose slip force is regulated by an embedded piezoelectric actuator, and a seismic simulation test was conducted for this isolation system. The experimental results demonstrate that, as compared to a passive isolation system with various levels of added damping, the semi-active isolation system using the ABS-type controller has the better overall performance when both the far-field and the near-fault earthquakes with different PGA levels are considered.

Key Words
anti-lock braking system; ABS system; shaking table test; seismic isolation; semi-active control; variable friction damper; piezoelectric actuator; near-fault earthquake.

Address
Lyan-Ywan Lu : Department of Construction Engineering, National Kaohsiung First University of Science and Technology, Kaohsiung, Taiwan
Ging-Long Lin : Department of Civil Engineering, National Chung Hsing University, Taichung, Taiwan
Chen-Yu Lin: National Center for Research on Earthquake Engineering, Taipei, Taiwan


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