• Smart Structures and Systems
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• v.2 no.4
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• pp.305-312
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• 2006

In the case of hospital buildings, where seismic design requirements are very high, existing structuresand especially those attacked by past earthquakes, appear, often, unable to fulfil the necessary safety prerequisites. In this paper, the retrofitting of hospital buildings is investigated, using alternative methods of repair and strengthening. Analysis of an existing hospital building in Patras, Greece, is performed. The load-bearing system is a reinforced concrete system. Two solutions are proposed: strengthening using concrete jackets around column and beam elements and application of viscoelastic dampers for the increase of the stability of the structure. Adequate finite element models are constructed for each case and conclusions are drawn on the efficiency of each rehabilitation method.

• Structural Engineering and Mechanics
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• v.35 no.2
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• pp.205-215
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• 2010

Recently, earthquake proof technology has been widely applied to both new and existing structures and bridges. The analysis of bridge systems equipped with structural control devices, which possess large degrees of freedom and nonlinear characteristics, is a result in time-consuming task. Therefore, a piecewise exact solution is proposed in this study to simplify the seismic mitigation analysis process for bridge systems equipped with sliding-type isolators. In this study, the simplified system having two degrees of freedom, to reasonably represent the large number of degrees of freedom of a bridge, and is modeled to obtain a piecewise exact solution for system responses during earthquakes. Simultaneously, we used the nonlinear finite element computer program to analyze the bridge responses and verify the accuracy of the proposed piecewise exact solution for bridge systems equipped with sliding-type isolators. The conclusions derived by comparing the results obtained from the piecewise exact solution and nonlinear finite element analysis reveal that the proposed solution not only simplifies the calculation process but also provides highly accurate seismic responses of isolated bridges under earthquakes.

• Smart Structures and Systems
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• v.29 no.4
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• pp.577-588
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• 2022

Oil refineries' Fluid Catalytic Cracking Units (FCCU) when in full operation may exhibit strong fluid dynamics caused by turbulent flow in the piping system that may induce vibrations in other mechanical and structural components of the Unity. This paper reports on the experimental-theoretical-computational program performed to get the vibration properties and the dynamic response amplitudes to find out alternative solutions to attenuate the excessive vibrations that were causing fatigue fractures in components of the bottle like reactor-regenerator of an FCC unit in operation in an existing oil refinery in Brazil. Solutions to the vibration problem were sought with the aid of a 3D finite element model calibrated with the results obtained from experimental measurements. A short description of the found solutions is given and their effectiveness are shown by means of numerical results. The solutions were guided by the concepts of structural stiffening and dynamic control performed by a nonlinear pendulum controller whose mechanical design was based on parameters determined by means of a parametric study carried out with 2D and 3D mathematical models of the coupled pendulum-structure system. The effectiveness of the proposed solutions is evaluated in terms of the fatigue life of critical welded connections.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.12
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• pp.1232-1239
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• 2010

A high-resolution electro-optical camera (EOS-C Ver.3.0), the mission payload of an Earth observation satellite, is under development in Satrec Initiative. We designed this system to give improved thermal performance compared with the EOS-C Ver.2.0 which is the main payload of DubaiSat-1 by optimizing the active and passive thermal control design. We developed the Structural-Thermal Model (STM) and verified the design margin by performing the qualification level thermal vacuum test. We also conducted the verification of its Thermal Mathematical Model (TMM) through the thermal balance test. As a result, it was confirmed that TMM faithfully represents the thermal characteristics of the EOS-C Ver.3.0.

• Earthquakes and Structures
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• v.6 no.2
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• pp.127-140
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• 2014

Laminated rubber bearing is very popular base isolation of earthquake engineering pertaining to the passive structural vibration control technologies. Rubber used in fabricating NRB and LRB can be easily attacked by various environmental factors such as oxygen, heat, light, dynamic strain, and organic liquids. Among these factors, this study carried out thermal aging test to investigate the effect of thermal aging on the mechanical properties of laminated rubber bearings in accelerated exposure condition of $70^{\circ}C$ temperature for 168 hours. The compressive-shear test was carried out to identify the variation of compressive and shear properties of the rubber bearings before and after thermal aging. In contrast to tensile strength and elongation tests, the hardness of rubber materials showed the increasing tendency dependent on exposure temperature and period. Based on the test results, the property changes of rubber bearing mainly aged by heat are quantitatively presented.

• Smart Structures and Systems
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• v.13 no.2
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• pp.319-341
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• 2014

A family of smart tuned mass dampers (STMDs) with variable frequency and damping properties is analyzed under harmonic excitations and ground motions. Two types of STMDs are studied: one is realized by a semi-active independently variable stiffness (SAIVS) device and the other is realized by a pendulum with an adjustable length. Based on the feedback signal, the angle of the SAIVS device or the length of the pendulum is adjusted by using a servomotor such that the frequency of the STMD matches the dominant excitation frequency in real-time. Closed-form solutions are derived for the two types of STMDs under harmonic excitations and ground motions. Results indicate that a small damping ratio (zero damping is the best theoretically) and an appropriate mass ratio can produce significant reduction when compared to the case with no tuned mass damper. Experiments are conducted to verify the theoretical result of the smart pendulum TMD (SPTMD). Frequency tuning of the SPTMD is implemented through tracking and analyzing the signal of the excitation using a short time Fourier transformation (STFT) based control algorithm. It is found that the theoretical model can predict the structural responses well. Both the SAIVS STMD and the SPTMD can significantly attenuate the structural responses and outperform the conventional passive TMDs.