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۱SEISMIC PERFORMANCE EVALUATION OF STEEL BUILDING RETROFITTED BY NEW HIGH PERFORMANCE SEMI–ACTIVE CONTROL BRACING SYSTEM
نویسنده(ها): ، ،
اطلاعات انتشار: پنجمین کنفرانس بین المللی زلزله شناسی و مهندسی زلزله، سال
تعداد صفحات: ۱۱
Innovative devices to control of structures under seismic excitation are becoming an interesting problem in earthquake engineering. In this paper a new ribbed bracing system (RBS) is proposed capable of performing as a variable stiffness system that can be used for controlling structural deformations and frequency shifting to compensate seismic energy. RBS has two important advantages. Because of ribbed system, the compressive member is rigidly moved like a piston and cylinder and therefore it is a buckling prevented system. Also RBS can act as a semi–active device and decrease the response of structure in two different manners; at first type RBS is closed in all stories during earthquake that called completely closed RBS (CCRBS). In second type of RBS by using of storey drift as a control criterion, RBS become on or off in stories
during seismic excitation that called semi–active RBS (SA–RBS). RBS is semi–active control system because it has no need to any actuator and large power supply, but just a battery–size power supply to switch the ribbed mechanism to be on or off. Nonlinear dynamic analysis of system has been carried out and performances of above RBS systems and conventional bracing system (CBS) have been investigated. Numerical results show the efficiency of CC–RBS in reducing structural damage and improving seismic energy. Also base shear is reduced when SA–RBS is used and structural damage is more uniform in this case.<\div>

۲Applications of wavelet transform in detecting damages in multispan beams and plane frames
نویسنده(ها): ، ،
اطلاعات انتشار: پنجمین کنفرانس بین المللی زلزله شناسی و مهندسی زلزله، سال
تعداد صفحات: ۹
In this paper applications of the wavelet transform for detecting cracks and damages due to earthquake hazards in multi–span beams and plane frames were presented. A brief review of the wavelet transform theory is given, and the ability of wavelets to detect damage in structures after earthquake is demonstrated by means of numerical examples which are analyzed by ANSYS. The proposed method only requires the knowledge of the response of the damaged structure and no information about the original undamaged structure is required which is very handy in most practical cases. It is shown that the procedure can detect the localization of the damage by using a response signal from static or dynamic loads. Moreover, the response needs to be obtained only at the suspicious regions where it is suspected that the damage may be present. Also the effect of the supports on detecting damages where investigated. Results of the analysis show that if a suitable wavelet is selected, the method is quite capable to detect and localize the damage from the response signal in a simple way which can be very useful for retrofit of structures and bridges after earthquakes.<\div>

۳Passive Control of Wave Induced Vibrations in Steel Jacket Platforms
نویسنده(ها): ،
اطلاعات انتشار: دومین همایش صنایع فراساحل و حضور در بازارهای جهانی، سال
تعداد صفحات: ۱۳
Considering the stress cycles in the joints and members due to the wave induced forces in offshore platform, fatigue analysis is therefore on of the most important analysis in the offshore platforms design. Although most of the steel jacket type platforms located in areas with relatively high ratios of operational seastates to maximum design environmental events, fall in acceptable safety margin in inplace and seismic analysis; but in the fatigue analysis will face with critical condition. Therefore it seems that utilizing control mechanisms with the aim of increasing fatigue life in such platforms will be more preferable to merely deck displacement control.
Investigation of tuned mass damper parameters optimality for vibration control of wave excited single degree of freedom systems implies that optimum tuning and damping ratios are strongly dependent to seastate condition to system parameters. Also the efficiency optimally designed friction for fatigue damage mitigation in realistic steel jacket platforms has been evaluated in this study.
Full stochastic spectral analysis methods has been employed to estimate the maximum fatigue damage as objection to be minimized also a stochastic linearization technique has been to take the nonlinear of the hysteretic dampers into account.
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۴A COMPREHENSIVE STUDY OF DYNAMIC RESPONSES OF TLP UNDER REGULAR WAVE LOADS
نویسنده(ها): ، ،
اطلاعات انتشار: سیزدهمین کنفرانس سالانه مهندسی مکانیک، سال
تعداد صفحات: ۸
Tension leg platform (TLP) is a complicated compliant offshore structure used for oil exploitation in deep water. Because of the complexity of the system and excitation force, it is important to comprehensive study of the dynamic responses and engineering interpretation of the results. In this paper the nonlinear dynamic analysis of TLP is carried out in time domain. The time history of regular wave is generated based on wave
data. The hydrodynamic forces are calculated using the modified Morison equation according to Airy’s linear wave theory. The coupling of various degrees of freedom is considered. Differential equation of motion is solved using Modified Euler Method (MEM). The power spectral densities (PSDs) of displacements, velocities and accelerations are calculated from nonlinear responses. The focus of the paper is on the powerful and simple method to solve the equation numerically and also comprehensive interpretation of the responses of the structure related to excitation wave and structural characteristics. As an example a case study is investigated and numerical results are discussed.<\div>
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