Sharif Digital Repository

Researches carried out on the damages imparted to the building structures under severe earthquakes have shown the importance of asymmetry effects of the buildings on the level of these damages. In these cases, the structures enter into the nonlinear state of their behavior and the structural elements, as well as nonstructural ones undergo large deformations. Additional damping systems have been proposed in many studies to avoid enforcing such large forces on the structures. One example of these systems is viscous fluid damper. The effectiveness of this type of dampers in reduction of the forces has been shown in many previous works. In this research we look for a damping eccentricity which... 

By comparing the control systems, researcherstypically believe that the active systems of control have better performance than passive ones. However, the high costs and the required technology for their erection and maintenance have limited the use of active control systems. In order to improve the control system performance at lower costs, semi-active control systems were also considered. Their performance is based on creating the desired control force by changing the instrument characteristics.Moreover, recent researches have shown that the improved performance of these instruments in structures compared to passive control systems, are typically due to reducing the flexibility of the... 

In this paper, a methodology has been proposed for design of passive energy dissipation systems through active control theory. The passive control system is designed to achieve a structural response as close to that of active control system. It may be needed to reduce the stiffness of the original structure at some locations to reduce the acceleration response. Then, to compensate for the resulting increased interstory drifts, viscous fluid dampers are added to the structure at their optimum locations. The optimal distribution of dampers and the locations with reduced stiffness are obtained using the LQR active control algorithm. It is shown that the response of a properly-designed... 

In the recent decades, outrigger systems have come into widespread use in tall buildings. This structural form has good capability to reduce the response of the high-rise structures subjected to lateral loads. Despite extensive recent use, outrigger is not listed as seismic load resistance system in current building codes and specific design guidelines is not available. In the other hands, inherent damping of structure influence on the analysis and design of the tall buildings. Measurements in actual buildings indicate that the damping in tall buildings is lower than damping in low to mid-rise buildings. Recently, a novel structural system, which is defined as damped outrigger, has been... 

Torsional vibrations of internal combustion engines and reciprocating compressors, is one of the challenges in the design process. It can reduce power of productivity, equipment operating lifetime and increase noise of the system. Torsional viscous damper is a method to reduce torsional vibrations in rotating equipment. In this study, three-dimensional simulations of torsional viscous damper is performed as a matter of FSI, with consider harmonic excitation on the external walls and calculation of damping response inertia ring in CFX software. The viscoelastic non-Newtonian model properties of damping fluid is calculated in MATLAB software with respect to viscoelastic parameters. For... 

In this study, an effective method is developed for design of passive control systems using viscous fluid dampers, considering the flexibility of braces used for installation of dampers. Using control design spectra, this approach provides a way to easily determine the optimum properties of the control system without complicated calculations or iterations.In the fist part of this study, it is attempted to find the optimum damping ratio of system by using the input energy spectra of ground motions. First, the relations among the dissipated energy in viscous dampers the strucutre and control system properties and structural response is evaluated.A theorically exact relation is established... 

Marine structures are always exposed to environmental loadings such as wind, wave, earthquake and sea currents. The wave-induced force could cause the critical stress in elements and due to fatigue failure, because of being random and periodical. In generally, it can be shown that fatigue is an extremely important phenomenon and one of the main problems in the long time destruction of the structure, because of severe corrosion and random loading in the marine environment.In order to reduce the effect of environmental loads, using control mechanisms is a new method to control vibrations of structures. These systems cause the reduction of structure responding such as acceleration, velocity and... 

This study is an investigation of the effects of structural nonlinearities on the performance of different structural vibration control systems, including active control using LQR algorithm and passive control using viscous fluid dampers and hysteretic dampers. By designing the control systems for linear structurs and comparing their performances in nonlinear response range, the abilities of these control systems to handle structural nonlinearities are compared. In other words, the dependency of these control systems on the properties of the structure (which may be altered by nonlinearities or uncertainties in estimations) is assessed. It is demonstrated that as a general trend, the ability... 

In recent decades, most of the codes have placed a high value on Performance Based Design of structures; however, these methods are computationally complex and time-consuming, and caused researchers to seek new and efficient methods to investigate performance of structures under different intensities of seismic loading. This issue is much more obvious when optimum design of structures, which requires repetitive analysis, is investigated. In the present research, using Endurance Time analysis, we are trying to provide better insights into the dynamic behavior of structures in continuous performance levels. Then, as a first step, we will use the verified method to find the optimum outline of... 

In this study, an active control strategy is used for design of passive energy dissipation systems using viscous fluid dampers and structural stiffness modification. The combination of supplemental damping and modification (usually reduction) of stiffness is used to minimize the two main structural response parameters, namely the maximum inter-story drifts and maximum absolute accelerations. In this manner, both structural and nonstructural damages can be controlled.
While active control systems are expected to improve the structural esponse beyond what can be achieved in passive control, the practical implementation of control systems are mostly of passive type.... 

In the last few decades, due to population growth and lack of habitable space, the need for construction of taller buildings with more stories has become an important topic. Design of these high-rise structures include different complex tasks in which the finance of the project is the most important parameter. In order to find an efficient and financially feasible design, engineers have always been looking for new approaches and materials. One of the structural systems to be used for tall buildings is the outrigger system. In this system, the surrounding columns are connected to the central core by deep beams or walls to reduce the core forces. In other words, in this method, a new load... 

The objective of this research is to introduce a new comparative performance measure based on seismic fragility curve of structures. This measure is used here to investigate the efficiency of viscous dampers on the behavior of a weak mid-rise steel structure. Viscous dampers are commonly utilized to reach purposes such as decreasing the risk of the structure failure and restoration costs, weight reduction, and seismic rehabilitation of existing structures. These systems cannot be satisfactorily investigated using static loading concepts, and in order to achieve optimum design, conducting a nonlinear dynamic analysis is usually the most reliable procedure. Therefore, 5-span 12,15 and 18 story... 

Performance-based seismic design method, with a new look and a totally different philosophy, as an alternative design method instead of strength-based design method has been suggested in the new generation of seismic codes. Massive problems such as the need for complex dynamic analysis and consequently, spending high cost and time in researches forced researchers to seek more effective methods to evaluate seismic performance of structures. This idea in the optimal design of structures that require repeated analysis seems to be more effective. In the Endurance Time (ET) method, structures are subjected to specially designed intensifying acceleration functions and their response at various... 

Innovations in laser, microwaves, and similar technologies have significantly advanced thermal treatments for diseases or even injuries concerning skin tissue. For a thorough understanding in the underlying mechanisms of bioheat transfer behavior of skin,a1D unsteady non-dimensional hyperbolic model of heat transfer through this tissue with metabolic heat generation which is subject to specific boundary conditions, is solved numerically using the finite difference method. A thermal shock is generated at the base of the tissue, which moves forward with a finite speed. A Numerical solution for a simple one-layer skin tissue is obtained. Then, the effects of various parameters, time step,... 

The preliminary design of building structures is normally based on the equivalent lateral forces provided in seismic design guidelines. The height-wise distribution of these loads is predominantly based on elastic vibration modes. However, as structures exceed their elastic limits in severe earthquakes, these design load patterns may not necessarily lead to efficient distribution of strength within the structures. To address this issue, several alternative load patterns have been proposed for the seismic design of non-linear structures. However, due to the simplifications involved in the development of these design load patterns, their adequacy needs to be assessed for different structural... 

Recent studies show that the code-compliant structures have faced a lot of damages in earthquakes, and their performance could improve. The structure should have the least initial cost in this approach, which observes all of the code's limits regardless of the structure's life cycle cost. In recent years, value-based design has been considered as an alternative for code-based design procedures. In this method, some other parameters are considered as well as the initial cost of the structure, including risk, resiliency, reliability, and sustainability. In this paper, the structures' total cost is studied by Fema P-58, while it is equipped with viscous dampers. The structures are 4, 8, and 12...