Fluid Viscous Dampers Research Articles

Seismic Control of Cable-stayed Bridge Using Negative Stiffness Device and Fluid Viscous Damper under Near-field Ground Motions

ABSTRACT Under near-field ground motions, fluid viscous dampers (FVDs) are effective in controlling deck longitudinal displacement but lead to the increase of bending moment and shear force at tower base. Negative stiffness (NS) devices are introduced in combination of FVDs for the bridge. The NS devices lengthen the fundamental vibration period of the bridge to reduce the spectrum acceleration whereas FVDs introduce extra damping to the bridge system to reduce the deck displacement. After implementing NS devices, designers have more options of designing FVDs for seismic control of the cable-stayed bridges while maintaining the design requirements under near-field seismic excitations.

Seismic Demand on Acceleration-Sensitive Nonstructural Components in Viscously Damped Braced Frames

AbstractThis paper investigates the seismic demand on acceleration-sensitive nonstructural components in buildings equipped with fluid viscous dampers. Nonlinear dynamic response analyses were cond...

Stochastic sensitivity analysis of energy-dissipating structures with nonlinear viscous dampers by efficient equivalent linearization technique based on explicit time-domain method

Nonlinear fluid viscous dampers have been widely used in energy-dissipating structures due to their stable and high dissipation capacity and low maintenance cost. However, the literature on stochastic optimization of nonlinear viscous dampers under nonstationary excitations is limited. This paper is devoted to the stochastic response and sensitivity analysis of large-scale energy-dissipating structures equipped with nonlinear viscous dampers subjected to nonstationary seismic excitations. The analysis procedure is developed in the frame of the equivalent linearization method (ELM) in conjunction with the explicit time-domain method (ETDM). The equivalent linear system and the corresponding statistical moments of responses at a specific time instant are first obtained through a series of stochastic response analyses of the linearized systems. Then the sensitivities of the statistical moments of responses are determined via a series of stochastic sensitivity analyses of the equivalent linear system at the corresponding time instant. The above two iterative procedures are facilitated at high efficiency using ETDM with explicit formulations of the statistical moments of responses and the sensitivities of the statistical moments. This process is repeated for different time instants, and the time histories of the statistical moments and their sensitivities can be obtained. The stochastic response and sensitivity results are further utilized to conduct the stochastic optimal parametric design of the nonlinear viscous dampers. A one-storey building model equipped with a nonlinear viscous damper is analyzed to demonstrate the accuracy of the proposed method, and a suspension bridge with a main span of 1200 m equipped with 4 nonlinear viscous dampers is further investigated to illustrate the feasibility of the proposed method for stochastic optimal design of large-scale structures.

Design and optimization of the micro-vibration isolation system for large space telescope

With increasing demands for better image quality, the aperture and size of a space telescope are becoming larger, and stability requirements are becoming more stringent. To reduce the influence of micro-vibrations on image quality from telescope platform, isolating vibrations of the whole telescope optical payload must be taken into account. To this end, a method to design and optimize a vibration isolation system (VIS) was developed. A dynamic model coupling the telescope optical payload and the platform in orbit was established to assist in the design and optimization of a configuration for the VIS, the objective being to minimize the frequency bandwidth of the integral modes of the telescope optical payload. Isolators with multidirectional elasticity were designed, and the frequency bandwidth of the integral modes was further narrowed by optimizing the structural parameters of the isolators. A viscous fluid damper was designed to suppress the VIS's resonance modes and its damping coefficients tested. Moreover, a micro-vibration integrated optomechanical analysis model was established. The influence of micro-vibration on line-of-sight of a space telescope with VIS was analyzed. The simulation results in the time and frequency domain show that the designed VIS can effectively attenuate the micro-vibrations transmitted to the telescope optical payload.

ANALYSIS OF TALL BUILDING WITH DIFFERENT LATERAL FORCE RESISTING SYSTEM

In the current circumstance, the populace is expanding rapidly, thus, the urban areas are becoming wide by devouring farming and green space and the land esteem is expanding. Another point is the tall vertical structure speaks to the country. As it builds the notoriety of the nation. To keep away from this the structures began developing vertical and thin as it arrives at a specific height the wind force governs the building as the main load more than gravity load, as the building grows higher the stability reduces. Due to a lack of design to face wind loads, as the cross-section decreases the stability reduces. And these structures are more prone to earthquakes and wind. Therefore, much research is proceeding to balance out the structure from an increasingly affordable perspective. To know the best performance and economical for the lateral force-resisting system of different types of 30 story buildings are model-led in ETABS, assuming the site location as BHUJ Gujarat, India. For the different structural systems that are compared for minimum story displacement and minimum story drift, these are the qualities that characterize the human comforts for the structure. the structural system used is conventional, shear wall, truss belt, outrigger, diagrid, and fluid viscous damper are used to compare the best performance of the structure. Above all diagrid and viscous damper shows the less displacement and drift values when compared to others but from the economic point of view viscous damper gives the best result from all the above.

Selection of Suitable placement of Fluid Viscous Damping System for G+10 Multi-Storied Buildings

Selection of Suitable placement of Fluid Viscous Damping System for G+10 Multi-Storied Buildings

Design and dynamic characterization of a large-scale eddy current damper with enhanced performance for vibration control

Eddy current dampers (ECD) are promising devices for vibration control of dynamic systems, but their application in civil structures is very limited due to a low damping density. This study describes the development and dynamic characterization of a large-scale rotary ECD with enhanced performance for structural applications. The rotary ECD consists of a conductive rotor, a stator with permanent magnets, and a set of ball screw which converts the linear motions across the damper into rotations of rotor. The torque at different rotating speeds is evaluated by using a 2-D analytical method considering the reaction magnetic field caused by eddy currents. Laboratory experiments are conducted to validate the numerical results obtained for a simple eddy current torque generator and a large-scale ECD. It is shown that the analytical model agrees with nonlinear finite-element simulations, but is higher than the test results. The large-scale rotary ECD achieves a high damping density up to 24.9 MN·s/m4 at a low speed. Moreover, the damping force of rotary ECD is highly nonlinear and self-limiting as a function of rotating speeds; it first increases with speeds and after reaching a maximum at a critical speed it decreases for higher speeds. Numerical simulation on seismic control of a SDOF system and a 5-DOF system showed that the rotary ECD performs as well as the fluid viscous dampers having the same secant damping coefficients. Finally, effects of changing design parameters on force-speed curve are studied in details.

An Efficient Stochastic Linearisation Procedure for the Seismic Optimal Design of Passive Control Devices

The seismic response of structures is often enhanced by introducing passive control devices that can operate through the dissipation of the input energy or by modifying the dynamic characteristics of the main structure. The inherent non-linearities in the constitutive laws of some of them lead to computation difficulties and have limited the large-scale use and design of these devices. In this study, a procedure for the optimal design of multi passive control devices is proposed. The general case of linear Multi-Degree-Of-Freedom (MDOF) not-classically-damped structural systems controlled by Fluid Viscous Dampers (FVD) are investigated in a stochastic framework. The procedure consists of evaluation of the device optimal pattern by minimizing an objective function related to the dampers cost and subjected to a constraint on the structural behaviour. For each configuration, the complete probabilistic characterization of the response is achieved by employing random vibration theory, Stochastic Linearisation (SL) techniques and a novel analytic model which provides closed-form PSD functions of earthquakes accelerations coherent to response spectra suggested by seismic codes. Exploiting this model, a procedure to speed up the Stochastic Linearisation technique by avoiding any numerical integration is proposed. Applications on MDOF building structures have been carried out to validate the proposed approach in terms of accuracy and reduction of the computational effort and to obtain optimal pattern of the passive control device coherently with the provisions of seismic building codes.

A Design Method for Viscous Dampers Connecting Adjacent Structures

This paper investigates the seismic design of fluid viscous dampers connecting adjacent structural systems. A simplified dampers design strategy is proposed, which relies on a linearized reduced order model of the coupled system. A stochastic linearization technique is adopted with the aim of extending the design method to nonlinear viscous dampers. The effectiveness of the design method and of the coupling strategy are assessed via numerical analysis of two adjacent buildings with shear-type behaviour connected by linear or nonlinear viscous dampers and subjected to Gaussian stochastic base acceleration. Different dampers locations are analysed. The accuracy of the reduced order model is assessed, by comparing the relevant response statistics to those provided by a refined multi degree of freedoms model. Finally, a parametric study is performed to assess the effectiveness of dissipative connection for different values of seismic intensity and dampers parameters (i.e., viscous coefficients and velocity exponents).

Seismic evaluation of cable-stayed bridges considering bearing uplift

Past earthquakes revealed that bearing uplift has possibly occurred at several cable-stayed bridges and is regarded as a critical cause for significant structural damage. To investigate the influence of bearing uplift, a sophisticated bridge model is constructed on an existing cable-stayed bridge and the seismic response of the bridge is evaluated. Nonlinear time-history analysis results show that bearing uplift of the bridge could occur several times under a design earthquake, resulting in an extensive pounding force at bearings and a large uplift displacement at deck end. The pounding force of bearing uplift would damage the bearings, cause shear cracks and even failure of the pier crossbeams. Viscous fluid dampers (VFDs), often used for controlling deck horizontal displacement, are investigated on its potentiality to restrict bearing uplift. It is revealed VFDs are able to slightly reduce the pounding force and effectively control the uplift displacement of deck end, but cannot avoid bearing uplift. To prevent seismic damage from bearing uplift, tension bearings is recommended for the bridge. The effect of VFDs to control the bearing vertical response is utilized in designing the tension force of the bearings. After implementing VFDs, the design tension force of the bearings is reduced by 25% comparing to that of the bridge without VFDs.

Seismic and Time History Performance of RCC Framed Buildings with and without Passive Energy Dissipators

Base isolation is an effective way to protect large structures from earthquake damage. It is a costly approach, as the entire structure must be supported on elastomeric or sliding bearings. Viscous dampers distributed throughout an otherwise conventional structure can achieve the same result at a significantly lower cost. Dampers are used to resist lateral forces coming on the structure. Dampers are the energy dissipating devices which also resist displacement of Reinforced Concrete (RC) buildings during an earthquake. These dampers help the structure to reduce buckling of columns thereby increasing the stiffness of the structure. During earthquakes, multi-storeyed buildings get damaged and as a result, large deformation occurs. Dampers reduce vibration and deformation of structural elements during an earthquake. Retrofitting buildings with fluid viscous dampers (FVDs) can improve Interstorey drifts and floor accelerations. In the present study, an RC framed building is modelled and analysed under Southern Sumatra and Chile earthquakes to evaluate the performance of the structure and its elements with and without energy dissipators. For the study, a model (G+19) with and without energy dissipators is modelled in ETABS. The seismic force is applied based on the time history data of the models pertaining to Southern Sumatra and Chile Earthquake. Response Spectrum analysis has been carried out to find the lateral displacements, storey shear and Base shear for the model with and without dampers. The lateral displacement, storey drift, storey shear and Base shear are found to less for the model with Linear FVDs when compared to the model with Non-Linear FVDs and without FVDs.

Experimental study on seismic control of towers in cable-supported bridges by incorporating fluid viscous dampers between sub-towers

In this article, the seismic control of towers incorporated with fluid viscous dampers between sub-towers is investigated experimentally. To replace one entire tower, an alternative scheme consisting of four separate sub-towers is first proposed. Fluid viscous dampers are utilized as energy dissipation devices to be installed between sub-towers. Experimental tests are conducted to study the damping force characteristics. Three control strategies with various distributions of these dampers between sub-towers are developed. Then, a series of shaking table tests are carried out to evaluate the control performance of the proposed control strategies. Different earthquake records are adopted as seismic loadings. Experimental results clearly show a remarkable reduction in the towers seismic responses, including the accelerations, relative displacements, and strains. Rather than attaching dampers in concentrated ways, the strategy of distributing dampers uniformly behaves better.

An integrated damping system for tall buildings

SummaryThis paper proposes an integrated damping system that aims at providing relatively high damping levels through the mobilization of a proportion of the structure's own mass. This offers significantly higher mass levels and, consequently, considerably more damping compared to conventional tuned mass dampers. Fluid viscous dampers are used to control accelerations in parallel with springs to resist the static loads applied to the moving mass. The advantages of employing relatively large mass levels in achieving considerable damping and reducing sensitivity to tuning are first analyzed using an idealized two degree of freedom structural representation. This is then followed by a description of the proposed “integrated damping system,” which is illustrated through a case study of a 250‐m tall building. The benefits of the proposed damping system are demonstrated through several numerical parametric assessments, as well as a selected suite of earthquake records. For the adopted case study, it is shown that, besides reducing the level of perceivable accelerations, the use of the suggested arrangement can offer an equivalent damping exceeding 50% of the critical damping, resulting in more than 40% reduction in the wind loads as well as over 60% reduction in displacement and acceleration response under seismic excitations.

Multi-objective optimal design of semi-active fluid viscous dampers for nonlinear structures using NSGA-II

This paper presents an effective method to design semi-active fluid viscous damper (SAFVD) system for mitigating the seismic responses of the nonlinear frames considering multiple safety and convenience criteria. This method is based on defining a multi-objective optimization problem with discrete objective functions of minimization of inter-story drift as safety criterion as well as absolute acceleration as convenience criterion where an improved version of the non-dominated sorting genetic algorithm (NSGA-II) has been used to solve it and find out the Pareto-optimal solutions. For this purpose, the maximum damping coefficient of the semi-active damper and parameters of the control algorithm have been selected as design variables. The effect of the uncertainty of the input seismic excitation has been considered using the mean responses under multiple real earthquakes recommended for the site that the structure is located in. To assess the effectiveness of the proposed methodology, a numerical example has been conducted on an eight-story nonlinear shear building frame with hysteretic bilinear elasto-plastic behavior. The results show that the designed optimal SAFVD system has the capability of a significant reduction in seismic responses and improving both the safety and convenience of the entire building. Also comparing the seismic performance of SAFVD system with that of active control system shows that SAFVD could perform as effective as active control system in structural response mitigation.

Retrofit of Reinforced Concrete Moment Frames in NZ Using Dual Supplemental Damping

The repair and seismic strengthening of a mid-1990s building structure in Christchurch, New Zealand, using fluid viscous dampers and buckling-restrained braces provides a case-study for mixed-system retrofit to improve the seismic performance of ductile reinforced concrete moment frames. The building was designed and detailed to essentially current standards but was very flexible and utilised a precast hollow-core floor system with thin topping slab which is vulnerable to deformations associated with moment frames, as demonstrated in recent New Zealand earthquakes. This paper highlights a simple displacement-based approach to setting retrofit design targets and performance verification. The retrofit using viscous dampers provided an efficient means to reduce ground motion-induced deformations and accelerations. The structural benefits to the rest of the project included no need for foundation strengthening and floor diaphragm strengthening being limited to only the perimeter hollow-core units. Development of the final design and viscous damper specification involved close coordination with the manufacturer to optimise the damper design, fabrication tolerances and site installation methods.

A continuous-discrete approach for pre-design of flexible-base tall buildings with fluid viscous dampers

An equivalent coupled-two-beam (CTB) discrete model is presented to compute the dynamic response in time domain of flexible-base buildings with linear fluid viscous dampers (FVDs). The equivalent model consists of a flexural cantilever beam and a shear cantilever beam connected in parallel by a finite number of axially rigid members that allows the consideration of intermediate modes of lateral deformation. The effects of different lateral deformations on the pre-design stage of two high-rise buildings are showed considering four soil types (hard rock, dense soil, stiff soil and soft soil) and three different distribution methods for linear FVDs: uniform-distribution (UD), story-shear-proportional-distribution (SSPD) and story-shear-strain-energy-distribution (SSSED). For UD method, the damping coefficients of FVDs increase as the flexural rigidity of the building decreases; whereas for SSPD and SSSED methods, the damping coefficients of FVDs vary along the height depending on the type of lateral deformation. For the three distribution methods and the same lateral deformation, the damping coefficients of FVDs decrease as the soil flexibility increases, which leads to a significant decrease in controlling earthquake-induced vibrations and wind-induced vibrations in the two high-rise buildings on a soft soil.

Study on the damping efficiency of continuous beam bridge with constant cross-section applied by lead rubber bearings and fluid viscous dampers

Bridges are the lifelines of disasters in earthquake areas. Therefore, it is very necessary to ensure the safety and traffic function after earthquake. Seismic isolation refers to install external energy dissipation devices or external energy input devices in specific parts of engineering structures. There are certain differences in longitudinal and transverse seismic responses of multi-span continuous beam bridges by changing the seismic dynamic characteristics or dynamic effects of structures. It is difficult to achieve the purpose of seismic isolation in both horizontal directions using isolation devices alone. The rubber deformation ability of lead rubber bearings can effectively insulate, and the yield energy consumption ability of its lead core can effectively consume the seismic energy for damping. The horizontal resistance is very small under the creep load, and the stiffness decreases rapidly after yielding under the strong dynamic earthquake load; meanwhile, the seismic energy is dissipated by the hysteresis of bearing. Fluid viscous damper is a velocity-dependent energy dissipation device, which produces viscous damping force, provides strong restoring force for components, and has a good limit function. This process will also dissipate the seismic energy, so as to reduce the structural earthquake response. Using these two methods together, the horizontal seismic responses of multi-span continuous beam bridges can be effectively controlled at the same time. Based on this idea, this article takes a high-speed multi-span continuous beam bridge with equal section as the engineering background, and uses dynamic time history analysis method to discuss the seismic isolation effect of lead rubber bearings and fluid viscous dampers.

Influence of Fluid Viscous Damper on the Dynamic Response of Suspension Bridge under Random Traffic Load

Fluid viscous dampers (FVDs) are widely used in long‐span suspension bridges for earthquake resistance. To analyze efficiently the influences of FVDs on the dynamic response of a suspension bridge under high‐intensity traffic flow, a bridge‐vehicle coupling method optimized by isoparametric mapping and improved binary search in this work was first developed and validated. Afterwards, the traffic flow was simulated on the basis of monitored weigh‐in‐motion data. The dynamic responses of bridge were analyzed by the proposed method under different FVD parameters. Results showed that FVDs could positively affect bridge dynamic response under traffic flow. The maximum accumulative longitudinal girder displacement, longitudinal girder displacement, and longitudinal pylon acceleration decreased substantially, whereas the midspan girder bending moment, pylon bending moment, longitudinal pylon displacement, and suspender force were less affected. The control efficiency of maximum longitudinal girder displacement and accumulative girder displacement reached 33.67% and 57.71%, longitudinal pylon acceleration and girder bending moment reached 31.51% and 7.14%, and the pylon longitudinal displacement, pylon bending moment, and suspender force were less than 3%. The increased damping coefficient and decreased velocity exponent can reduce the bridge dynamic response. However, when the velocity exponent was 0.1, an excessive damping coefficient brought little improvement and may lead to high‐intensity work under traffic flow, which will adversely affect component durability. The benefits of low velocity exponent also reduced when the damping coefficient was high enough, so if the velocity exponent has to be increased, the damping coefficient can be enlarged to fit with the velocity exponent. The installation of FVDs influences dynamic responses of bridge structures in daily operations and this issue warrants investigation. Thus, traffic load should be considered in FVD design because structural responses are perceptibly influenced by FVD parameters.

Vibration response of railway cable-stayed bridges under high-speed train braking loads

With the increase of the running speed of high-speed trains, the longitudinal vibration of the long span railway cable-stayed bridge under train loads has increased significantly. And the probability of high-speed train braking is greater than earthquake. The excessive vibration response will affect the serviceable of the cable-stayed bridge. Fluid viscous dampers (FVDs) and elastic cables (ECs) which are widely used in seismic design of the bridge are adopted to control the longitudinal vibration response of the cable-stayed bridge induced by train braking loads. The influence of the design parameters of FVDs and ECs on the response of the bridge is studied. And the effectiveness of FVDs and ECs on mitigating the longitudinal response of the bridge is also discussed. It is found that installing FVDs and ECs between the deck and the tower is very efficient in reducing the longitudinal vibration of the railway cable-stayed bridge subjected to train braking loads, especially the longitudinal displacement of the deck and the bending moment of the tower.

Seismic behavior of structural and non-structural elements in RC building with bypass viscous dampers

During the last few decades, fluid viscous dampers have been significantly improved in terms of performance and reliability. Viscous dampers dissipate the input energy into heat and the increased temperature may damage internal seals of the damper. As a result, thermal compensation is crucial for almost all fluid viscous dampers. In this study, while referring to the main working principles of the recently developed bypass viscous damper in Iran, a comprehensive case study is conducted on a RC building having diagonal braces equipped with such viscous dampers. Experimental results of a small-scale bypass viscous damper is presented and it is shown that the currently available simplified Maxwell models can simulate behavior of the bypass viscous damper with good accuracy. Using a case study, contribution of bypass viscous dampers to seismic behavior of structural and non-structural elements are investigated. A designed procedure is adopted to increase damping ratio of the building from 3% to 15%. In this way, reductions of 25% and 13% in the required concrete and steel rebar materials have been achieved. From nonlinear time history analyses, it is observed that bypass viscous dampers can greatly improve seismic behavior of structural elements and non-structural elements.