Fluid Viscous Dampers Research Articles

Seismic Upgrade of Existing Buildings with Fluid Viscous Dampers: Design Methodologies and Case Study

AbstractExisting structures may be in need of seismic upgrading owing to structural deterioration, change in function or use, increased performance requirements, or modified seismic codes. In recent years, fluid viscous (FV) dampers have received increasing attention because of their notable seismic-reduction capacity and easy installation. This paper outlines the design procedure of seismic upgrading of existing buildings using FV dampers. Discussions are made on some key issues for seismic upgrading using FV dampers, including the analytical damper-brace model under large earthquakes and strategies for damper layout. A case study is made, in which a 21-story hotel built in 1991 was seismic upgraded. One special feature of this project is that only the first six stories can be structurally modified, resulting in limitations on the damper layout. According to the proposed design procedure, 56 FV dampers are suggested for this project, which provide a supplemental damping ratio of 5.3%. As a result, the se...

Hybrid Recentering Energy Dissipative Device for Seismic Protection

A hybrid recentering energy dissipative device that has both recentering and energy dissipation capabilities is proposed and studied in this paper. The proposed hybrid device, referred to as the hybrid shape memory alloy (SMA) recentering viscous fluid (RCVF) energy dissipation device, connects the apex of a chevron brace to an adjoining beam using two sets of SMA wires arranged in series on either side of the brace and a viscous fluid damper arranged in parallel with the SMA wires. The viscous damper is used because being a velocity-dependent device it does not exert any force that counteracts the recentering force from the SMA wires after the vibration of the frame ceases. In the numerical study, the Wilde’s SMA constitutive model is used to model the SMA wires, and the Maxwell model is used to simulate the viscous fluid damper. To demonstrate the viability and effectiveness of the proposed hybrid device, comparative studies are performed on several single-story shear frames and a series of four-story steel frames. The results show that the frames equipped with the hybrid device have noticeably smaller peak top story displacements and residual story drifts when subjected to ground motions at three different intensity levels.

Semi-active magnetorheological dampers for reducing response of high-speed railway bridges

To reduce the resonant response of high-speed railway bridges, semi-active magnetorheological dampers are proposed in this study. The elements are connected to the structure in a double beam configuration. An H∞ control algorithm to drive magnetorheological damping forces of MR dampers is derived. Feasible solutions for an uncertain time-delay model are obtained by using standard linear matrix inequality techniques. Weight functions as a loop shaping procedure are also introduced in the feedback controllers to improve the tracking ability of magnetorheological damping forces. To this end, the effectiveness of magnetorheological dampers controlled by the proposed scheme, along with the effects of the uncertain and the time-delay parameters on the models, are evaluated and compared with the performance of fluid viscous dampers in similar applications reported in previous research through numerical simulations.

Intensity-Reduced Design for Structure with Fluid Viscous Dampers

The intensity-reduced method based on fluid viscous dampers is proposed in this study. The analysis model of fluid viscous dampers is firstly introduced. The intensity-reduced design procedure is thoroughly discussed. Taking an 11-story reinforced concrete frame shear-wall structure as example, the intensity-reduced method is implemented in this study. The dynamic responses of the structure with and without fluid viscous dampers, including the maximum inter-story drift angle, base shear force, are discussed. The results show that the proposed intensity-reduced method for structure with fluid viscous dampers is feasible, and the responses of structure satisfy the code for seismic design of buildings. The earthquake input energy is mainly dissipated by fluid viscous dampers, which guarantees the safety of the main structure.

Performance assessment and optimization of fluid viscous dampers through life-cycle cost criteria and comparison to alternative design approaches

The performance assessment and optimal design of fluid viscous dampers through life-cycle cost criteria is discussed in this paper. A probabilistic, simulation-based framework is described for estimating the life-cycle cost and a stochastic search approach is developed to support an efficient optimization under different design scenarios (corresponding to different seismicity characteristics). Earthquake losses are estimated using an assembly-based vulnerability approach utilizing the nonlinear dynamic response of the structure whereas a point source stochastic ground motion model, extended here to address near-fault pulse effects, is adopted to describe the seismic hazard. Stochastic simulation is utilized for estimation of all the necessary probabilistic quantities, and for reducing the computational burden a surrogate modeling methodology is integrated within the framework. Two simplified design approaches are also examined, the first considering the optimization of the stationary response, utilizing statistical linearization to address nonlinear damper characteristics, and the second adopting an equivalent lateral force procedure that defines a targeted damping ratio for the structure. These designs are compared against the optimal life-cycle cost one, whereas a compatible comparison is facilitated by establishing an appropriate connection between the seismic input required for the simplified designs and the probabilistic earthquake hazard model. As an illustrative example, the retrofitting of a three-story reinforced concrete office building with nonlinear dampers is considered.

Minimum failure cost-based energy dissipation system designs for buildings in three seismic regions – Part II: Application to viscous dampers

A methodology for calculating the life-cycle cost of building structures under seismic loading was presented in the companion appear Shin and Singh, 2014. In this paper, this methodology is applied to obtain the minimum failure cost-based optimal designs of fluid viscous dampers for model structures in three different seismic regions in the USA. Genetic algorithm is utilized to obtain the optimal number and location of dampers to be installed on the buildings. The failure costs are optimally reduced at all seismic intensities that are expected to occur on the site to achieve the minimum life-cycle and object costs. The numerical results show the impact of optimal designs on structural performance in terms of reduced fragilities covering different performance objectives over the spectrum of expected seismic intensities. The results also demonstrate that although the structural system may go in inelastic range at the higher intensities of motion, the response spectrum method can still be effectively used for the failure cost-based optimal design of linear damper.

Seismic performance and probabilistic collapse resistance assessment of steel moment resisting frames with fluid viscous dampers

SUMMARYThis paper evaluates the seismic resistance of steel moment resisting frames (MRFs) with supplemental fluid viscous dampers against collapse. A simplified design procedure is used to design four different steel MRFs with fluid viscous dampers where the strength of the steel MRF and supplemental damping are varied. The combined systems are designed to achieve performance that is similar to or higher than that of conventional steel MRFs designed according to current seismic design codes. Based on the results of nonlinear time history analyses and incremental dynamic analyses, statistics of structural and non‐structural response as well as probabilities of collapse of the steel MRFs with dampers are determined and compared with those of conventional steel MRFs. The analytical frame models used in this study are reliably capable to simulate global frame collapse by considering full geometric nonlinearities as well as the cyclic strength and stiffness deterioration in the plastic hinge regions of structural steel members. The results show that, with the aid of supplemental damping, the performance of a steel MRF with reduced design base shear can be improved and become similar to that of a conventional steel MRF with full design base shear. Incremental dynamic analyses show that supplemental damping reduces the probability of collapse of a steel MRF with a given strength. However, the paper highlights that a design base shear equal to 75% of the minimum design base shear along with supplemental damping to control story drift at 2% (i.e., design drift of a conventional steel MRF) would not guarantee a higher collapse resistance than that of a conventional MRF. At 75% design base shear, a tighter design drift (e.g., 1.5% as shown in this study) is needed to guarantee a higher collapse resistance than that of a conventional MRF. Copyright © 2014 John Wiley & Sons, Ltd.

Passive control system for seismic protection of a multi-tower cable-stayed bridge

The performance of passive control system for the seismic protection of a multi-tower cable-stayed bridge with the application of partially longitudinal constraint system is investigated. The seismic responses of the Jiashao Bridge, a six-tower cable-stayed bridge using the partially longitudinal constraint system are studied under real earthquake ground motions. The effects of the passive control devices including the viscous fluid dampers and elastic cables on the seismic responses of the bridge are examined by taking different values of parameters of the devices. Further, the optimization design principle of passive control system using viscous fluid dampers is presented to determine the optimized parameters of the viscous fluid dampers. The results of the investigations show that the control objective of the multi-tower cable-stayed bridge with the partially longitudinal constraint system is to reduce the base shears and moments of bridge towers longitudinally restricted with the bridge deck. The viscous fluid dampers are found to be more effective than elastic cables in controlling the seismic responses. The optimized parameters for the viscous fluid dampers are determined following the principle that the peak displacement at the end of bridge deck reaches to the maximum value, which can yield maximum reductions in the base shears and moments of bridge towers longitudinally restricted with the bridge deck, with slight increases in the base shears and moments of bridge towers longitudinally unrestricted with the bridge deck.

The dynamic performance of a shear thickening fluid viscous damper

This paper presents a study of the rheological properties of shear thickening fluids (STF) and the performance of a viscous damper filled with an STF by performing a cyclic loading test. In the rheological test, the STF samples were prepared by blending nanoscale fumed silica powder with polypropylene glycol fluid in different weight fractions. Using a strain-controlled rheometer with a cone and plate tool, both steady and oscillatory state experiments were performed and the rheological properties of the STF were observed. Experimental results showed an abrupt increase in complex viscosity beyond a critical dynamic shear strain rate . In this study, a hydraulic steel tube was filled with an STF to develop an innovative passive damper device. The STF-filled damper performance test showed that the area and shape of hysteresis loops can vary with different loading conditions. The analytical models studied and a numerical approach showed that STF-filled dampers are potentially useful in practical engineering applications.

A comparative study on parameter identification of fluid viscous dampers with different models

Fluid viscous dampers are extensively adopted as efficient and cheap energy dissipation devices in structural seismic protection. If we consider the usefulness of these passive control devices, the exact recognition of their mechanical behavior is of outstanding importance to provide a reliable support to design a very efficient protection strategy. In scientific and technical applications, many different constitutive models have been proposed and adopted till now to represent fluid viscous dampers, with different levels of complexity and accuracy. This paper focuses on parameter identification of fluid viscous dampers, comparing different existing literature models, with the aim to recognize the ability of these models to match experimental loops under different test specimens. The identification scheme is developed evaluating the experimental and the analytical values of the forces experienced by the device under investigation. The experimental force is recorded during the dynamic test, while the analytical one is obtained by applying a displacement time history to the candidate mechanical law. The identification procedure furnishes the device mechanical parameters by minimizing a suitable objective function, which represents a measure of the difference between the analytical and experimental forces. To solve the optimization problem, the particle swarm optimization is adopted, and the results obtained under various test conditions are shown. Some considerations about the agreement of different models with experimental data are furnished, and the sensitivity of identified parameters of analyzed models against the frequency excitation is evaluated and discussed.

Supporting brace sizing in structures with added linear viscous fluid dampers: A filter design solution

SUMMARYViscous fluid dampers have proved to be effective in suppressing unwanted vibrations in a range of engineering structures. When dampers are fitted in a structure, a brace is typically used to attach them to the main structure. The stiffness of this brace can significantly alter the effectiveness of the damper, and in structures with multiple dampers, this can be a complex scenario to model. In this paper, we demonstrate that the effects of the brace compliance on the damper performance can be modelled by way of a first‐order filter. We use this result to formulate a procedure that calculates the stiffness required by the supporting brace to provide a specified effectiveness of the damping action. The proposed procedure assumes that viscous dampers have been sized in a previous design step based on any optimal methodology in which, as is usually the case, the presence of supporting braces and their dynamic effects were neglected. Firstly considering a one degree‐of‐freedom system, we show that the proposed method ensures a desired level of damper efficiency for all frequencies within a selected bandwidth. Then the analysis is extended to the case of multi‐degree‐of‐freedom systems to show that the design criteria can be applied in a straightforward and successful manner to more complex structures. © 2014 The Authors. Earthquake Engineering & Structural Dynamics published by John Wiley & Sons Ltd.

Experimental evaluation of dynamic characteristics of seesaw energy dissipation system for vibration control of structures

SUMMARYSeesaw energy dissipation system (SEDS), a vibration control system used to provide enhanced seismic protection, has been proposed and investigated numerically. Because of its complicated arrangement, verification experiments are necessary to demonstrate the SEDS damping capacity. This paper presents the results of experimental investigation of the SEDS using fluid viscous dampers. Free vibration tests are conducted to demonstrate the SEDS damping capacity. Results of the free vibration test show that the SEDS has sufficient damping capacity for reduction of the seismic response of the frames. Parametric experimental investigations of the SEDS were conducted, the results of which demonstrate the effects of the system parameter on the damping capacity. Copyright © 2014 John Wiley & Sons, Ltd.

A two‐step direct method for estimating the seismic response of nonlinear structures equipped with nonlinear viscous dampers

SUMMARYThe insertion of fluid viscous dampers in building structures is an innovative technology that can improve significantly the seismic response. These devices could be very useful also in the retrofit of existing buildings. The effect of this typology of damping system is usually identified with an equivalent supplemental damping ratio, which depends on the maximum displacement of the structure, so that iterative procedures are required. In this paper, a simplified direct assessment method for nonlinear structures equipped with nonlinear fluid viscous dampers is proposed. The method proposed in this study is composed by two steps. The first one yields the direct estimate of the supplemental damping ratio provided by nonlinear viscous dampers in presence of a linear elastic structural response. The second step extends the procedure to structures with nonlinear behavior. Both graphical and analytical approaches have been developed. The proposed method has then been verified through several applications and comparisons with nonlinear dynamic analyses. Moreover, an investigation has been performed with regard to the influence of the relations that define the damping reduction factor and the hysteretic damping. Copyright © 2014 John Wiley & Sons, Ltd.

Passive Hybrid System for Seismic Failure Mode Improvement of a Long-Span Cable-Stayed Bridges in the Transverse Direction

This paper presents a numerical study on the seismic damages and failure modes of a trial designed cable-stayed bridge (CSB) with a central span of 1,400 m under earthquake excitations. A passive hybrid control system is proposed to mitigate the seismic damage and improve the failure mode of the CSB; this is composed of a passive control system and several supplemental nonstructural links used as sacrificial energy dissipation devices. The passive control system, including conventional viscous fluid dampers (VFDs), is presented for comparison with the hybrid system. The results show that the top and bottom regions of the tower are simultaneously subjected to severe damage under extreme ground motion, indicating that the tower experiences an unexpected failure mode with double plastic hinges, whereas the piers experience a typical flexural failure mode, with only one plastic hinge concentrated at the bottom region of the pier in the transverse direction. The effects of the proposed passive hybrid control system on seismic damage control are superior to those of the passive control system with VFDs. As a result, the passive hybrid control strategy can successfully control seismic damage and effectively improve the failure mode of the CSB so that its seismic performance meets damage control targets based on seismic damage criteria.

Seismic performance evaluation and retrofitting with viscous fluid dampers of an existing bridge in Istanbul

In this paper, seismic performance of Kozyatagi Bridge is evaluated by employing nonlinear elasto-plastic dynamic analysis and the deformation-based performance. The time-history records of the 1999 Izmit, 1971 San Fernando and 1989 Loma Prieta earthquakes are modified by adopting a probability of exceedance of 2% in 50 years corresponding to the return period of 2475 years. The analysis is carried out for three different bearing cases which are movable bearings, restrained bearings, and movable bearings with viscous fluid dampers in the radial direction. The analysis results show that the bridge can be retrofitted with viscous fluid dampers. In this case the reinforced concrete piers need not be strengthened by any jacketing techniques in order to preserve the original architectural appearance of the bridge. The retrofitting design of the bridge with viscous fluid dampers is also presented in detail.

H∞ optimization of fluid viscous dampers for reducing vibrations of high-speed railway bridges

This work deals with the optimization of fluid viscous damper systems (FVDs) to reduce the resonant dynamic structural response of high-speed railway bridges by algebraic and numerical approaches. The presented method chooses the objective function based on the H ∞ norm over the frequency band of interest. This function allows taking into account structural damping properties and minimizing simultaneously the structural response associated with multiple modes. Especially, the proposed objective function may also be extended to nonlinear problems to determine optimal parameters of nonlinear fluid viscous dampers which may be an interesting solution in applications where high force levels are expected in the dampers. Finally, the proposed method is validated through numerical simulations. The simulation results show that the optimal FVD coefficients obtained by using the presented method are more exact than those by the previous method. Besides, the effectiveness of the method for solving the problems with the contribution of high modes and the consideration of nonlinear FVDs is also proved.

Harvesting energy via electromagnetic damper: Application to bridge stay cables

Energy harvesting from ambient vibration is an emerging and promising solution to the power supply problem associated with autonomous sensors. This article proposes a novel strategy of harvesting damping energy from vibration control devices. A novel system, termed electromagnetic damper cum energy harvester, is employed to fulfill both vibration damping and energy harvesting functions. Electromagnetic damper cum energy harvester is essentially an electromagnetic device connected to a specially designed energy harvesting circuit, which is a buck–boost converter operating in a discontinuous conduction mode. The energy harvesting circuit can achieve satisfactory efficiency without any feedback loop. The effectiveness of the dual-function electromagnetic damper cum energy harvester is demonstrated through a numerical case study of bridge stay cables under wind excitations, in which the major parameters of electromagnetic damper cum energy harvester are determined through a simple design approach. Simulation results project average output power ranging from 82.5 to 2396.8 mW at a wind speed of 9–15 m/s, corresponding to an overall efficiency of 42.3%. The dual-function electromagnetic damper cum energy harvester also exhibits vibration control performance comparable to an optimally designed viscous fluid damper.

Fluid viscous damper in mitigation of structural vibration effect due to underground blast

Blast induced ground vibration, caused by underground explosions, can result in substantial damage to nearby structures. In the present study, an investigation is made on the possible reduction of structural vibration effect due to underground blast by using the fluid viscous damper (FVD). The blast load is modelled by an exponentially decaying function representative of a typical rock blast. The cylindrical pot FVD is considered for which the fractional-derivative Maxwell model is adopted. The dynamic response analysis of the structure-FVD system is performed in the time domain by an equivalent single degree of freedom (SDOF) viscous oscillator approach which is also compared with the response obtained by the discrete Fourier transform (DFT) approach. It is generally observed that the peak structural displacement due to underground blast can be effectively reduced by the FVD while a limited amount of reduction in the peak absolute acceleration of the structure is obtained.

Dynamic performance of existing high-speed railway bridges under resonant conditions following a retrofit with fluid viscous dampers supported on clamped auxiliary beams

This contribution investigates the application of Passive Control techniques to reduce the severe transverse vibrations that railway bridges of moderate lengths may experience under resonant conditions. The proposed solution consists in connecting the slab to a series of auxiliary beams clamped between the bridge abutments through a set of fluid viscous dampers. A particular configuration minimising the space occupied by the devices and the auxiliary beams under the bridge deck is proposed for two typical typologies in the aforementioned lengths: slabs and girder bridges. First, the dynamic response of a double-beam analytical model is obtained in closed-form under harmonic excitation in order to detect the main governing parameters, capturing the essence of the response at resonance of the main beam fundamental mode. Then conditions are obtained for the optimal damper constants that minimise the main beam amplification. Finally the effectiveness of the solution and the adequacy of the expressions derived from the harmonic case are proven under railway traffic excitation taking into account the three-dimensional deformation of the deck. Throughout the study special attention is given to the beneficial effect arising from clamping the auxiliary beam supports when compared to the simply-supported case, analysed by the authors in previous works. Partial rotational restrictions are admitted to take into consideration the expectable deviation from ideally clamped conditions. Two case studies are presented showing that the auxiliary beams size, if partially clamped, could be significantly reduced for the same main beam vibration mitigation level. If the beams are to be installed under a railway bridge deck in a practical application, this is a crucial issue in order to minimise the free space occupied with the retrofit.

Limits of linearity in squeeze film behavior of a single degree of freedom microsystem

This paper presents a theoretical investigation of squeeze film flow in systems employing microplates parallel to a substrate and undergoing large amplitude normal vibration. Most previous models of squeeze film damping assume small oscillation amplitude with linear system behavior, but it is often unclear how small the vibrations must be to actually elicit this response. In addition, fluid inertia effects are usually overlooked. This study provides a compact nonlinear solution for the incompressible hydrodynamic forces with specific terms describing fluid inertia and viscous damping. Numerical analysis (the explicit Runge-Kutta method) is applied to solve the nonlinear governing equation. The effects of frequency, oscillation amplitude, aspect ratio (of gap to length), and Reynolds number on the dynamic response of the system are investigated. The overall system response depends strongly on the actuation frequency and system properties. It is found that a simple criterion of validity for the linear system assumption is not possible. Near resonance, the vibration input amplitude (relative to the initial gap) must be very small indeed for linearity (∼0.001), while in other cases the relative amplitude can be greater than one.