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.

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.

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.

Given the importance of seismic resilience in the design and performance evaluation of structures under earthquakes, implementing strategies to enhance this resilience has become a necessity in structural engineering. Among these strategies, the use of VISCOUS dampers has gained attention as an effective method for controlling structural seismic responses. However, a quantitative investigation into the effect of increased effective DAMPING on the seismic resilience index (particularly in reinforced concrete structures) has not yet been thoroughly conducted. This research investigates the impact of increased effective DAMPING on the seismic resilience of a reinforced concrete moment frame. To achieve this, a four-story, three-bay reinforced concrete moment frame was modeled in the OpenSees software, and VISCOUS dampers with a uniform distribution were installed on all floors. The DAMPING coefficients of the dampers were adjusted in two different scenarios to achieve effective DAMPING ratios of 15% and 35% for the frame, respectively. Nonlinear dynamic analyses were performed on the model, and the seismic resilience index of the frame was calculated for each DAMPING level. The results indicate that the seismic resilience index of the frame increases with increasing effective DAMPING. This suggests that the use of VISCOUS dampers can significantly improve the seismic performance of structures. Increasing DAMPING not only reduces the seismic responses of the structure, including story drifts and floor accelerations, but also helps improve the seismic resilience of the structure against earthquakes. The findings of this research can serve as a scientific basis for the optimal design of VISCOUS damper systems in reinforced concrete structures.

In the Seismic design of Structures, in order to energy DAMPING applied to Structure, when an earthquake occurs, various solutions have been proposed that dampers are also in this category. Due to the relatively simple design and also more economical than other methods of energy dissipations, dampers have been more attention of researchers, In this study, in order to performance improvement of rotational inertia damper, friction and VISCOUS mechanisms added to this type of damper. The experimental sample of rotational friction damper was made in the Urmia university earthquake laboratory and studied in a simple frame. The 8-story structure under Kobe and Tabas will be analyzed to study the effects of made hybrid damper compared with the rotational inertia damper. These intended dampers can be used with different type of braces that embedded in the structure such as Chevron and diameter. At the first in the model studied the 8-story symmetrical structure are modeled in Sap2000. Subsequently the resulting section is modeled in Abaqus2016 to study the effects of different dampers. Experimental laboratory result, is significantly improved Rotational inertia friction damper compared to other friction damper and the loss of their sudden brakes.Also the dynamic responses of structure indicate the reduction of maximum roof displacement and also the base shear of structure. Analytical results indicate that Rotational inertia VISCOUS damper act quickly compared with Rotational inertia friction damper and dissipate the energy applied to structure. But finally Rotational inertia friction damper will behavior better than similar VISCOUS damper.

The first part of this paper discusses the importance of porous materials in passive noise reduction, types of porous materials, various applications of these materials, relevant acoustical and non-acoustical parameters, and different methods to measure them based on international standards were explained. In this part of the paper, definitions and experimental methods used in measuring the acoustic properties of the absorption coefficient and the sound transmission loss based on international standards are presented. Then, while providing a comprehensive discussion of the sound absorption mechanisms in porous materials, the types of sound absorption mechanisms, including VISCOUS, thermal, and structural losses, are described. The effect of different parameters on the variation of sound absorption of porous materials has been presented. Also, various models, including experimental, laboratory, and analytical models used for expressing the acoustical and mechanical properties of porous materials, are discussed. Finally, a brief review is present for recent research areas on porous materials.

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.