One of the new challenges in structural engineering is the mitigation of seismic hazards from structures using flexibility and energy dissipation approaches. This is in contrast with the typical seismic design methodologies in which strength and ductility resources of structural members are tapped to tackle earthquake demands. In this approach, adding to the flexibility of the structure should be in accordance with the energy dissipation potential in the system. In this case, earthquake demands for lateral strength in structures reduces, but energy dissipation devices are needed to subside the lateral deformation of such flexible structural systems.To meet the huge demand for energy dissipation potential in these structural systems, large scale damping devices are required. Such equipment, to mention a few, comes in the form of metallic, frictional, viscoelastic, memory shaped alloys and viscous dashpots. Among the others, viscous dashpots are considered the most favorite ones to use in large structural systems due to their sizable capacity and impartiality to ambient vibration and temperature loads. Moreover, since these devices are velocity dependent energy dissipaters, they are capable of reducing both deformation and acceleration responses of the structural systems more effectively.viscous dashpots are typically made from a metallic cylinder, a piston, a shaft, cylinder caps and elastomeric seals (to provide confinement on the liquid inside of the cylinder). The existence of elastomeric seals in configuration assembly of these devices is considered a weak point in mechanical design of such dashpots considering maintenance issues. To address this problem, a contractible viscous dashpot was introduced earlier in which there was no need for elastomeric seals. In this work, a new version of this dashpot with variable damping constant have been tested for determination of its functionality and characteristics.Contractible viscous dashpots are made from two flexible chambers that axially contract or expand to accommodate liquid movement between the two. In this mechanism all parts of the device are made of steel and there is no relative movement between cylinder caps and the main shaft. Therefore, there is no need for elastomeric seals to confine the liquid inside of cylinders at cylinder caps.The Dashpot was designed for load capacity of and the maximum stroke of. In the test procedure, however, due to some limitations in the test setup, the attainable load was around 310 KN. The test results show stable hysteretic loops under sinusoidal excitations with the amplitude of in the frequency range of 0.1-0.25 Hz. The hysteresis loops resemble a viscous device with viscoelastic behavior that can be roughly represented by Kelvin model. As expected, damping constant of the dashpot reduces by an increase in excitation frequency. The capability of change in damping characteristics of the dashpot was embedded in the device. This ability was shown in the experiments where damping constant of the device became almost tripled during the test process by adjusting the embedded mechanism in the device.The contractible dashpot used in this study has shown an initial frictional behavior due to imperfection in its manufacturing process. Increase in the internal liquid pressure in the device expands this frictional behavior to about 10% of total capacity of the dashpot. The initial frictional force in the device can be easily improved to help the functionality of the dashpot.This dashpot has shown acceptable performances in all the experimental investigations carried out in the course of this study. Considering its simplicity and practicality (low maintenance costs), there would be a good chance for such devices to be used in large structures in near future.

viscous dampers are parts of energy dissipation devices which have received considerable attention in modern seismic design approaches. One of the most important challenges of them is fluid seals which needs maintenance. Considering technologies in Iran and idea of removing seals and so the need of maintenance, a dashpot using some parts of expansion joints was designed. The manufactured dashpot is a practical one, which has appropriate stroke, 65 mm, and efficient capacity, 224 kN, and also displays nonlinear damping behavior.Constitutive law characteristics of the dashpot using Kelvin Model is determined, and also Equivalent Linear damping is calculated.

Identification of damping properties for a mixed structure and its interaction with underlying soil is a challenge for structural designers. Current codes and available commercial software packages do not provide analytical solutions for such structural systems. Due to irregular damping ratios, dynamic response of each part of a mixed structure differs significantly. In addition, when the structure is subjected to seismic loads, the soil-structure interaction effects cannot be neglected. To manage these issues, this paper proposes an Equivalent damping ratio for mixed structures by means of a semi-empirical error minimization method which considers soil-structure interaction. The results of numerical simulations indicate that the use of the Equivalent damping ratios makes the results of dynamics analyses closer to the ones obtained by the actual damping ratios. Consequently, proposed method provides a much better approximation than the case in which the conservative overall ratio of 2% or 5% is used.

Energy dissipation systems have been broadly used in structures during the recent decades in order to reduce earthquake and wind forces as well as reduction of structural lateral drifts within the code limits. viscous damper is considered as one of the energy dissipation systems which are classified as velocity-dependent dampers among passive control systems and have been paid attention and their further detailed properties taken into account by many researchers. viscous damper consists of a piston with some orifices inside the cylinder which contains highly viscous fluid. Energy dissipation of this damper is through pushing viscous fluid out of the orifices.These are two types of these dampers: linear and nonlinear from which linear type with velocity power of one is more practical. The structural damping force is usually set according to the procedure described in FEMA273 and are optimized by three controlled modes of displacement, velocity and acceleration.This study examines the effect of adding viscous dampers on seismic behavior of steel moment frames. For this purpose, three steel moment frames of 1, 3 and 6-story all in 3 bays, with viscous dampers having power factor of 1, 0.8 and 0.6 are selected. These sample structures are subjected to the nonlinear time history analysis under the El Centro, Kobe and Northridge earthquakes, and their response including displacement, acceleration and base shear is compared in two cases of with and without viscous dampers.Finally, regarding nonlinear time history analysis results based on the structural behavior in three modes controlled by displacement, velocity and acceleration, proper damping forces are specified as 94.7, 240.1 and 557.1 kN respectively for one, three and six story structures based on maximum acceleration and base share obtained from FEMA273.

The use of dampers for retroftting and reducing seismic induced vibrations of structures is rising. Among all types of dampers, viscous and visco-elastic dampers are extensively used for buildings. Adding dampers increases Equivalent damping ratio of structure which decreases displacement and member stresses. FEMA-356 has proposed an equation for calculating Equivalent damping ratio of shear buildings with added dampers, based on the frst mode of vibration. In the present research, the goal was to study the accuracy of FEMA-356 formula for evaluating Equivalent damping ratio with dampers as compared with the theoretical one. For the latter, the calculation is based on the hysteresis force-displacement response of the dampers. For obtaining hysteresis response, dynamic equation of motion of 2 to 12 stories 2D shear buildings equipped with viscous and visco-elastic dampers subjected to harmonic base excitation were solved. Both regular and mass distributed in height irregular structures with added dampers at all levels were considered. In addition to that, dampers were considered at random stories of the buildings and accuracy of Equivalent damping ratios of FEMA-356 were evaluated. This study has shown that for viscous dampers, error of FEMA-356 formula in comparison with theoretical formula for viscous dampers would be in the range of 1 to 3 percent and for visco-elastic ones in which stiffness ratio of visco-elastic dampers to story shear stiffness is 10 percent, would be in the range of 1 to 17 percent. When the stiffness ratio is decreased to 5 percent, the error would decrease to 2, in the worst case. Also, it has been shown that mass irregularity in the height of the buildings increases the maximum error from 17% to 58% for viscoelastic dampers; no signifcant effect for viscous dampers. Moreover, addition of dampers in random stories of buildings up to six stories would increase error of FEMA-356 formula about 42 and 50 percent, respectively, for viscous and visco-elastic dampers.

Identification of damping parameter is usually more complicated and unreliable comparing to mass or stiffness identification in structural dynamics. There are many factors such as intermolecular friction, Coulomb friction and viscous damping affecting the damping mechanisms in a structure. Therefore it is difficult, and in some cases impossible, to describe the details of damping mechanisms by using mathematical tools. In order to overcome the difficulties arising when using different damping models, the Equivalent viscous damping is used. The coefficient of Equivalent viscous damping can be identified experimentally by measuring the structural response. During the past decades, many methods have been proposed for damping parameter identification employing time domain data (e.g. logarithmic decrement method) or frequency domain data (e.g. using frequency response functions). There are also time-frequency methods such as wavelet transform. This paper deals with identification of modal damping coefficients and natural frequencies of a structure using wavelet transform. The results obtained by using wavelet transform has a good agreement with those resulted from model updating in lower modes.

Researchers have shown that using viscous dampers can have influential role in controlling response of structures against wind, explosion and earthquake. Most of structures, with the help of ductility, resist severe earthquakes which cause damages to nonstructural and structural components. Using viscous dampers can reduce large displacements and accelerations of structures and consequently reduce the ductility demand. This research studies different process of designing, construction and experiments of viscous dampers with the capability of adjusting damping for determine their mechanical characteristics. These experiments have done for the first time in country. The results show an acceptable function of these dampers.

Today, the use of energy-dissipating system such as yielding metal damper in structures can improve the seismic performance of structures. One of the characteristics of metal yielding dampers is the ability to dissipate high energy and increase the ductility of the structural system, which can improve the ductility and energy absorption characteristics of the metal frame equipped with braces and prevent the brace from buckling during an earthquake. The purpose of this research is introduce a new form of yielding dampers called honeycomb yielding damper (HYD) with different dimensions and thickness along with evaluating and comparing the force-displacement diagrams and investigating the seismic parameters of this type of yielding damper. All modeling and validation of numerical samples were done by Ansys software. Non-linear analysis method is used in this research. The hysteresis curves are obtained under in-plane cyclic loads. The mechanical parameters such as ductility ratio, initial hardness, effective hardness and damping coefficient can be determin. The results of this research showed that the effective stiffness increases by increasing the length and thickness of the sample. The ductility ratio decreases by increasing the height of the sample. the effective stiffness decreases by increasing the height of the sample. The ductility ratio increases by increasing the height of the sample. Also, the effective damping coefficient decreases with the increase in the height of the samples, the effective damping coefficient increases with the increase in length and thickness of the samples.