Sharif Digital Repository

Cable stayed bridge are characterized by a long fundamental period, large flexibility, lightweight and low structural damping, which is vulnerable to large amplitude oscillations when excited by earthquake. So, it is important to study the seismic behavior of cable-stayed bridges. Spatial variation of seismic ground motions denotes the differences in amplitude and phase of seismic motions recorded over extended areas. The result of past analyzes indicate that the effect of the spatial variation on the response of bridges can be detrimental. On the other hand, tuned mass dampers (TMDs) or vibration absorbers are small mass-spring-dashpot units calibrated to be in resonance with a particular... 

The detuning of the structures equipped with Tuned Mass Dampers (TMDs) caused by their nonlinear behavior under strong ground motions is a real concern in their practical application. This thesis presents a feasibility study on the effectiveness of TMDs in reducing the seismic response and the resulting structural damage of reinforced concrete structures under intense ground motion. A number of 2-D concrete moment resisting frames with different numbers of stories are considered. TMDs are used as a mean to protect these structural models against ground excitation. The mass of TMDs are varied from 1% to 5% of the first effective modal mass of the structural models. IDARC 2-D program is used... 

Tuned Mass Dampers(TMD) are among the most studied passive or active control devices that have been used around the world to control the lateral vibration of different building structures. On the other hand, since 2-D structural models are not appropriate for estimating the true response of the eccentric structures, application of 3-D models have been considered for determining their seismic-induced coupled lateral-torsional behavior. In this research, the performance of the Active Tuned Mass Dampers (ATMD) in controlling the seismic response of 3-D structural models was investigated. Three structural models with 4, 8 and 15 number of stories and 3 different eccentricities (0, 10% and 15%)... 

Up to now, many seismic design methods and construction technologies have been investigated to reduce the seismic responses of bridges, buildings and potentially vulnerable structures. [1] Introducing a new effective systems aim to control of vibration caused by earthquake on the structures will be useful. This system is based on repelling of imposed force to the structures with tuned mass dampers (TMDs), to gain minimum damage. The detuning of the structures by equipped with TMDs resulted from nonlinear behavior due to dynamic loads such as strong ground motions are real concern in the practical applications. The application of TMDs, as expected, can reduce the deformation of the... 

The main purpose of this research is to evaluate the probabilistic benefit of the implementation of second isolation layer in isolated structures to both the structure and the constructor. The innovation of this research is in the utilization of a seemingly useless part of the structure, which is the ridge, for mitigating the structure’s displacement. For this purpose, a five-story residential structure and its ridge have been isolated and modeled as an MDOF system with two degree of freedom in MATLAB software and the benefits due to the reduction in displacement and acceleration has been calculated. The results indicate 40 percent reduction in the main structure’s displacement and a benefit... 

One of existing passive control procedures for reducing the seismic response of structures is using tuned mass dampers. This damper consists of three main elements, including mass, damping and stiffness. A conventional tuned mass damper consists of a relatively small auxiliary mass attached to a main structure to be protected. The principle of operation consists in inducing a vibration energy transfer from the main structure to the auxiliary mass, which dissipates the input energy while vibrating out of phase with the structural motion. In this study, the usage of non-conventional tuned mass dampers (TMD) with large mass ratios, in reducing the seismic response of structures and the way to... 

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. The Usage of Endurance Time method (ET) and thus reducing the size of analysis can be a useful tool for excuting Performance Based Design of structures. Endurance Time analysis is based on time history analysis, but in this method structure subjected to an intensifying acceleration function and different damage indices of the structure are evaluated through analysis time. The... 

Offshore platforms are of the economic life lines of oil rich countries. These infrastructures are located at severe environmental conditions, their construction and installation involves expense and these justify utilization of these structures with novel auxiliary vibration control device. Two passive vibration control systems have been evaluated in this study aiming to fatigue damage mitigation in offshore steel jacket platforms. Performances of tuned mass damper and friction damper to suppression of wave induced vibrations in fixed offshore platforms have been investigated in this study. Due to the random nature of ocean waves, a fully stochastic analysis method has been used to evaluate... 

TLP is membership of compliant structures. In these platforms buoyancy is more than the weight and pretension compensates extra buoyancy. TLP is consisting of pontoons, columns and a deck. TLP is vertically moored with tendons and tendons extend from under the columns to sea bed. Marine structures vibrate due to applying environmental loads such as wind, waves, currents, earthquakes. Therefore vibration control of TLP is very important problem not only from motion aspect but also from design and fatigue point of view. In this thesis, passive vibration control of TLP with different TMDs are investigated. In first part, introduction of tension leg platforms, types of control mechanisms and... 

Use of high-rise structures has become very common in recent decades for different purposes. Since, these structures are vulnerable to the wind and earthquake loads, many ways have been proposed to reduce or dissipate the input wind or seismic energy to the building structures. In this study, the effect of the tuned mass damper (TMD) with high mass ratio for high-rise structures is investigated. The proper functioning of the TMD to limit the vibrations of a structure is depended on the appropriate adjustment of its mass, stiffness and damping characteristics according to the load and structural specifications. The vibrational characteristics of the structures could change during sever... 

Existing structural irregularities (in plan and elevation) has always been among the important causes of structural failures under strong earthquakes. The torsional related damages have especially been very important in multi-story buildings as the torsional behavior of structures changes their uniform translational vibration and causes concentration of demands in the elements at the perimeter of the buildings. On the other hand, the Tuned Mass Dampers (TMD) have in general been accepted as an effective passive structural control device to suppress the structural vibration. In this study, Three 3-D, irregular (in plan) steel structural models with 4, 8 and 15 number of floors are considered... 

The aim of this study is to evaluate the seismic performance of structures using a semi-active tuned mass damper minimizing the amount of structural damage caused by earthquakes. One of semi-active control mechanisms, which has been studied in recent years, is the damper with fluid controlled by a magnetic field (Magnetorehological Damper, MR). These type of dampers react to the magnetic fields that cause significant changes in the behavior of fluid flow. These dampers are acknowledged because of their simplicity, broad operating range as well as not requiring high-power energy sources. In this thesis, a MR damper is used instead of the existing viscous element of tuned mass damper. To...