Placement Of Dampers Research Articles

Fluid viscous dampers in tackle-damper configuration: An experimental study

This study presents dynamic test results on a recently developed damper placement known as the tackle-damper configuration. This innovative setup integrates a viscous damper alongside two inclined tackles, each comprising multiple turns of wire ropes threaded between upper and lower sheaves. This configuration has the ability to amplify damper deformations and forces based on the mechanical advantage of the tackle. Four specimens of tackle-damper configurations are tested under different dynamic harmonic and seismic loadings. Obtained results indicated that tackle-damper configuration changes pure viscous behaviour of the fluid viscous damper to an amplified viscoelastic behaviour. It is verified that energy dissipation in the tackle-damper configuration arises from two sources, i.e. fluid viscous damper and capstan friction between the wire ropes and the sheaves. Ideally, deformation and force amplification factors in the tackle-damper configuration should depend solely on the number of wire ropes and the inclination angle of the tackle. However, it has been found that true force amplification factor is much larger than the ideal value due to the capstan friction. Moreover, true deformation amplification factor can also be much smaller than the ideal value. This is attributed to the elastic stretching of individual wire ropes within the tackles. Therefore, both friction and wire rope elongation substantially affect the true amplification capabilities of the tackle-damper configuration.

Optimizing Viscous Damper Placement for Stochastic Performance of Buildings with Plan Asymmetry

Optimized viscous dampers mitigate the dynamic response of building with plan asymmetry. Previous research efforts limit the optimization method to time domain requiring time history analyses to optimize damper placement for plan eccentricity-induced torsional response combined with translational response. This can consume high computational effort and lead to the variability in the ground motion selection. To expedite the optimization process while taking ground motion variability into account, this study will offer a novel criterion based on stochastic performance. This technique will skip the traditional approach of employing time history analyses and will take frequency domain variability into account. Through given distance between the center of mass (CM) and the target frame, the study establishes the stochastic criterion for the response at the perimeter of the building where the maximum torsional-translational response occurs. This allows the optimization methods to generate high quality solution with less computational efforts compared to traditional approach (i.e. time domain-based optimization). It is noteworthy that the proposed criterion is applicable to extensive kinds of responses (e.g. peak floor acceleration, story shear and etc.) once the geometric relationship is given. The proposed criterion as the objective function is compared against their counterpart in time domain through a case study. The case study is based on a reinforced concrete (RC) moment-resisting-frame (MRF) building with two-way asymmetric plan and adopts Element Exchange Method (EEM) to optimize the damper placement. The effectiveness of optimized design based in frequency domain and time domain is evaluated for their total running time and maximum peak interstory drift against a suite of ground motions. The result showed that the proposed criterion can offer the improvement against the traditional approach in terms of solution quality (i.e. performance in time domain and frequency domain) and computational efforts (i.e. total running time for optimization).

Study on the Damping Efficiency of a Structure with Additional Viscous Dampers Based on the Shaking Table Test

This study specifically focuses on the damping efficiency of a damped structure with additional viscous dampers. A two-layer steel frame structure with eight sets of viscous dampers is used to conduct a series of seismic simulation shaking table tests, including a non-damped structure without dampers and two damped structures with dampers placed at 1/2 and 1/6 of the beam span, respectively. By conducting these tests, the energy dissipation, force, and displacement of the damper, as well as the parameters of the structure such as floor displacement and acceleration, are obtained. The main damping efficiency indicators of the damped structure are calculated, including the additional damping ratio, inter-story displacement utilization rate, as well as the reduction rate of the vertex displacement and the base shear relative to the non-damped structure. The study shows that the viscous dampers exhibit full hysteresis loops and a strong energy dissipation capacity in the structure. The seismic response of the vertex displacement and base shear in the damped structure is significantly smaller than that in the non-damped structure. Under different seismic levels, including frequent earthquakes, occasional earthquakes, and rare earthquakes, the damping effect of the dampers placed at 1/2 of the beam span is significantly better than that placed at 1/6 of the beam span. For example, the additional damping ratio for the X-direction artificial wave REN is 19% and 11%, 20% and 13%, and 13% and 11%, respectively. The patterns for inter-story displacement utilization ratio, reduction rate of the vertex displacement, and reduction rate of the base shear are similar. The research findings strongly indicate that the damped structure with additional viscous dampers exhibits excellent damping efficiency. In future damping design, designers need to fully consider the placement of viscous dampers within the beam span.

Damping effects of a stay cable attached with a viscous damper and a high damping rubber damper considering cable bending stiffness and damper support flexibility

To mitigate cable oscillations in cable-stayed bridges, a common approach involves using a strategically positioned viscous damper near the cable’s anchorage and bridge deck. However, for longer cables, this method may be insufficient due to installation constraints. In such cases, supplementing the damping system with a high-damping rubber (HDR) damper near the cable’s anchorage point on the bridge tower becomes imperative to enhance the cable’s damping ratio. Conventional designs often overlook crucial factors like viscous damper support stiffness and stay cable bending stiffness when integrating dampers into cable-stayed structures. This study presents findings on achieving an effective damping ratio in stay cables by using both a viscous damper and an HDR damper, considering the influence of viscous damper support stiffness and stay cable bending stiffness. The results indicate that the combined deployment of these dampers achieves a damping efficiency approximately equivalent to the sum of their individual effects. Importantly, decreased viscous damper support stiffness significantly affects the damping effectiveness, leading to a rapid decline in the stay cable’s damping ratio. While stay cable bending stiffness also influences the damping ratio, its impact is relatively less pronounced than that of viscous damper support stiffness. The study outcomes enable a more accurate prediction of the achievable damping ratio for a stay cable with additional components, considering both damper support stiffness and stay cable bending stiffness. Furthermore, the study explores parameters of both the viscous damper and HDR damper, such as the viscous coefficient, loss coefficient, HDR damper stiffness, and damper placement, evaluating their influence on the first damping ratio of the stay cable. The survey results provide valuable insights for determining optimal parameters for both dampers, maximizing the damping efficiency of cable-stayed bridges.

Robust optimal damper placement based on robustness index simultaneously considering variation of elastoplastic design criteria and input level

Dampers should be installed at appropriate quantities and locations to control building vibrations against excitations such as earthquakes and wind loads. One of the objectives of the structural optimization problem for damper placement is to minimize the initial cost of damper installation to satisfy various structural constraints under a set of input levels and target performance values. However, it is arbitrary what input levels should be used in the design, and it is also necessary to account for various uncertainties in the inputs and structural properties. This study presents a new method for assessing the robustness of building structures with design variables while simultaneously considering various phases of structural performance criteria and input amplitudes. The proposed robustness index is a multidimensional function that can take into account the influence of different input levels on the structural performance. In this paper, the proposed new robustness index is applied to the robust optimal design of the damper placement, where the damping coefficient of the linear oil damper added to the building is uncertain. The worst resonant seismic motion for the building is investigated based on the critical double impulse method and its equivalent one-cycle sine wave, which is used as the input seismic motion. By applying the equivalent one-cycle sine wave to the structural response analysis with variations in the input velocity amplitude, the proposed robustness index is effective in comprehensively assessing the relationships between the input velocity amplitude of the seismic motion and the upper response limit of the structure under the variation of the damping coefficient of the oil damper. The comprehensive and efficient evaluation of these relationships enables a more detailed assessment of the influence of uncertainties in design variables on structural performance. In the numerical examples, the optimal damper placement for a 12-story building model is discussed based on the robustness and structural performance of both acceleration and story ductility distribution.

Optimal positioning and distribution of magnetorheological damper

During seismic events, devices are used to disperse energy in buildings, reducing structural damage and preventing collapse. One such device is the magnetically polarizable particle damper, consisting of a hydraulic cylinder filled with magnetically responsive particles in fluid. Recent research optimized damper placement and distribution using detailed mathematical modeling and mode shapes covering over 95% of the building's mass. Researchers identified critical damper positions by correlating these models with maximum force functions in the equations of motion. The study proposed a positioning strategy to reduce costs associated with damper installation in typical building practices. The number of dampers required varied with applied loads: 20kN, 30kN, 90kN, and up to 200kN. For instance, under 20kN and 30kN loads, optimal distribution included assigning 8 dampers to the ground, first, second floors, decreasing to 4 on floors three and four, and 2 on the fifth floor, totaling 14 and 20 dampers, respectively. Optimization values for these loads were calculated at 17.71. Dealing with a 90kN load required 44 dampers, distributed as 8 on lower levels, 4 on the third floor, and 8 each on floors four and five. Remarkably, while 20kN and 30kN damper counts reduced, 24 were added for 90kN, yielding an optimization score of 45.84. For a 200kN load, 17 dampers were strategically allocated, with specific placements adjusted per floor, achieving an efficiency score of 49.616. This underscores the effectiveness of the chosen damper arrangement in bolstering structural resilience against seismic forces.

Performance enhancement of damaged RC structures with viscoelastic dampers: Damage assessment and optimal placement

Evaluating the performance degradation of the earthquake-damaged structure and optimizing the placement of dampers is important for retrofitting post-earthquake structures. In this study, a damage evolution model is developed to evaluate the degradation of strength, stiffness, and energy dissipation capacity for earthquake-damaged structures. The proposed damage model is validated using previous experimental results based on the nonlinear finite element analysis. Then, research on the optimal design of damper parameters and quantity is carried out. Considering the optimization range of earthquake-damaged structures, a genetic algorithm with multi-objective functions is developed to determine the optimal placement of viscoelastic dampers in damaged structures. The results demonstrate that the proposed damage model can effectively describe the performance degradation of damaged structures. The control effects of the acceleration response increase exhibited a maximum enhancement of 3.38 times after accounting for the optimization range of earthquake-damaged structures. The optimization results of the multi-objective function with the optimization range are better aligned with the objectives of designers.

Modelling efficiency of fluid viscous dampers positioning for increasing tall buildings' Resilience to earthquakes induced structural vibrations

Due to limited space, it is now necessary to create higher structures in metropolitan areas. However, as a building's height increases, its natural frequency decreases, which in turn causes it to respond more quickly to dynamic loads like Earthquakes. The building's and its residents' safety are gravely jeopardised by this. Installing fluid viscous dampers in the structure is a popular solution to this issue since they are efficient at controlling vibration and stabilizing the structure under dynamic loads. The purpose of this research is to assess the efficiency of fluid viscous dampers at different placements in reducing earthquake-induced structural vibrations. The findings are compared for three distinct damper placement scenarios: alternately on all stories, on all stories, and on three levels (top, bottom, and center) for a G+20 story framed building. The best model has been compared by two conventional damper placements: first ten stories continuous and first ten stories alternate. The performance of the structure has been assessed in terms of displacement, drift, and shear values during the study. The findings prove that the displacement, drift, and shear values of the structure under Earthquake loads are decreased by the employment of fluid viscous dampers. The most efficient way to lessen the building's seismic reaction is to install dampers on every story. The results of this research may be used to improve the seismic performance of structures and provide useful insights into tall building design and construction in Earthquake-prone locations.

Performance and protection of pre-engineered buildings subjected to blast and earthquake excitations

A pre-engineered building (PEB) refers to a building which is pre-designed at a factory using some simulation and modelling software as per the specifications, codes and the loads that act on the structure before the production of the building components and then finally assembled at site thereby reducing the completion time. In the current study, a case study of an existing PEB structure subjected to wind analysis has been investigated. The main objective of the present study is to evaluate the retrofitting ability of passive control dampers installed in the pre-engineered industrial building subjected to earthquake and blast phenomenon. The study investigates the effectiveness of vibration control techniques in the form of passive dampers in improving the performance of PEB structure subjected to blast and earthquake using fluid viscous dampers. The study also discusses the impact of different damper placement techniques on the structural performance of PEB structure subjected to blast and earthquake loading. Primarily three damper placement techniques are incorporated in the present study, namely single diagonal, V-shaped damper, and inverted V-shaped damper. The study also evaluates the optimum fluid damper properties, namely damping coefficient and damping exponent, in mitigating the blast and earthquake responses of the selected industrial building. The structural performance of PEB structure has been studied using finite element tool considering the nonlinear analysis and comparing the structural responses for with and without damper conditions. The V-shaped and inverted V-shaped damper placement techniques are the most effective approach in resisting the damaging effects against blasts and earthquakes for the selected PEB structure in comparison with the conventional diagonal braced dampers. The study reports reductions in structural displacements and brace forces in the range of 54–68% and 70–90%, respectively, when installed with V-shaped fluid viscous damper.

On the Influence of Unexpected Earthquake Severity and Dampers Placement on Isolated Structures Subjected to Pounding Using the Modified Endurance Time Method

The aim of this study is to investigate the performance of isolated structures by considering the possibility of impact under severe earthquakes. In the design of isolated structures, the required displacement capacity is determined based on the considered earthquake hazard level. However, there is a possibility of an impact caused by moat walls or adjacent structures under severe earthquakes. Dampers are used in this study to improve the performance of structural and nonstructural components. In this regard, three isolated structures (6, 9, and 12 stories) equipped with Triple Friction Pendulum Isolator (TFPI) are designed under earthquake hazard levels of BSE-1 with return periods of 475 years. Based on the different positions of these three structures relative to each other, four scenarios are defined to investigate the effect of impact. Modified endurance time (MET) method, as a cost-efficient nonlinear time history analysis method, is employed for structural evaluation under variable earthquake hazard levels. The placement of dampers is also taken into account in evaluating the effect of dampers. Therefore, the structures have been retrofitted once by adding damping and stiffness devices (ADAS) on the stories and once by adding fluid viscous dampers (FVD) at the isolated level. Results indicate that structures might collapse under earthquake hazard levels of BSE-2 with return periods of 2475 years. This matter is influenced by the adjacency of two isolated structures next to each other, and the severity of this fact depends on the height of the structures and the displacement capacity of the isolators so that the tall, isolated structures have decreased the performance of the adjacent shorter isolated structure. Moreover, the placement of dampers has a significant influence on the performance of structural and nonstructural components, depending on the reason for the impact.

Parametric study on response of multi-storied building equipped with viscous and visco-elastic dampers subjected to ground motions.

Viscous and viscoelastic dampers are passive energy dissipation devices that are used in multi storied buildings to reduce the effect of lateral vibrations arising from earthquakes and wind. Passive devices are those that require no energy to function. The performance of such devices can be affected by many factors like seismic zone, building height, soil type and placement of dampers. In this paper, the effect of using viscous and visco-elastic dampers on response of multi-story building was investigated. For this purpose, multi-story building was modelled in Finite element software. Various parameters like height of building, seismic zone, soil type and placement of dampers were varied in the FEM model. To investigate the seismic response, non-linear time history analysis was performed by subjecting the building to ground motion (Imperial Valley 1940). Seismic responses of the models were studied and compared in terms of results like top floor (roof) displacement, storey drift and ground floor level (base) shear. It was found that viscous dampers are more effective in dissipating energy. Optimum position of dampers was also found out. All the parametric results were obtained and plotted in graphs.

ROBUST OPTIMAL DESIGN BASED ON STORY DUCTILITY RATIO OF ELASTIC-PLASTIC BUILDING STRUCTURES WITH UNCERTAIN OIL DAMPERS SUBJECTED TO CRITICAL DOUBLE IMPULSE

A new robustness evaluation method based on the specified story ductility ratio is proposed for a building model with uncertain oil dampers. Since the influence of input motion uncertainty on the response variation can be simply taken into account, the critical double impulse input is used instead of input ground motions. In the proposed method, the robustness function is derived as a function of the input velocity amplitude for a specified ductility ratio. This procedure is suitable for the performance-based design. A robust optimal design method on damper placement is also presented based on the proposed new robustness function. Numerical examples of robust optimal design of dampers are presented for a 12-story elasto-plastic building model with linear oil dampers.

Optimising Viscous Damper Placement in Frame Buildings with Element Exchange Method for Multiple Seismic Hazard Levels

ABSTRACT Viscous dampers enhance the seismic performance of buildings by increasing the capacity for energy dissipation, or damping. Many placement optimisation algorithms currently exist, though they often do not align with code-based verification procedures nor consider optimising performance at multiple seismic hazard levels, at serviceability and ultimate limits. This paper proposes new damper placement algorithms and compares them against eight existing methods on seismic performance at different hazard levels, design iterations required and total computation effort. The comparison is conducted by means of numerical case studies. All methods are applied to a ten-storey reinforced concrete (RC) moment resisting frame (MRF) building, initially meeting the design requirements of typical buildings in a moderate seismic zone in New Zealand. The result showed that the proposed methods and two existing methods can generate a solution that dominates solutions of other existing methods in at least one aspect (e.g. the objective at a hazard level or running time).

Optimal retrofit strategy using viscous dampers between adjacent RC and SMRFs prone to earthquake-induced pounding

Nowadays, retrofitting-damaged buildings is an important challenge for engineers. Finding the optimal placement of Viscous Dampers (VDs) between adjacent structures prone to earthquake-induced pounding can help designers to implement VDs with optimizing the cost of construction and achieving higher performance levels for both structures. In this research, the optimal placement of linear and nonlinear VDs between the 3-story, 5-story, and 9-story Steel and RC Moment-Resisting Frames (SMRFs and RC MRFs) is investigated. It is shown that the pounding phenomenon can significantly affect the seismic performance capacities of buildings during earthquakes, and using VDs can improve the seismic limit-state capacities of buildings for retrofitting purposes. For this goal, the seismic limit-state capacities of both colliding structures were assessed using Incremental Dynamic Analysis (IDA) assuming Near-fault Pulse-Like, Near-fault No-Pulse, and Far-Fault seismic records suggested by FEMA-P695. To perform IDAs, structures were modeled according to the seismic codes using a developed algorithm in Matlab and OpenSees software with the ability to remove a collapsed structure during the analysis. The results present an optimal placement for using VDs between structures and also compare the possible conditions to implement VDs. Using these results, engineers can approximately predict the seismic performance levels of both structures prone to earthquake-induced pounding and their final performance after retrofitting. Finally, retrofitting modification factors were proposed to help designers to predict the limit-state performance levels of retrofitted colliding structures without involving complicated and time-consuming analyses.

A new reduced model of damped moment frame for rapid optimization of viscous damper placement

AbstractA new model reduction method is presented for moment‐resisting frames with viscous dampers. The proposed method considers (1) the interactive effect of added damping between the horizontal‐vertical directions and (2) the direct effect with regard to the vertical direction different from the conventional static condensation method. When brace‐type dampers are treated, these effects cannot be neglected originally. The proposed method gives a better correspondence of the fundamental eigenmode with that of the non‐reduced moment frame than the static condensation method. In addition, the proposed reduced model can accurately evaluate the maximum interstory drifts of the non‐reduced moment frame. The proposed model reduction method is formulated in the frequency domain. The frequency dependency of the stiffness matrix and the damping matrix of the reduced model is investigated. The influences of the added damping matrix by viscous dampers on the natural circular frequencies, the damping ratios and the participation vectors are also investigated. Finally, it is demonstrated through a numerical example that the displacement‐based optimization of the damper allocation can be accurately and rapidly conducted by using the reduced models throughout the optimization process.

Multi-Objective Optimization of Viscous Damper Placement for Building Structures Subjected to Ground Motion

Viscous dampers mitigate the interstory drift ratios (IDRs) and peak floor accelerations (PFAs) of buildings subjected to earthquakes. This leads to a multi-objective optimization problem (MOOP) for a viscous damper placement along the building height to minimize IDRs and PFAs simultaneously. This paper proposes innovative methods to address the MOOP and compares those proposed methods to non-dominated sorting algorithm II (NSGA-II) through case studies. Subsequently, the meaning of solutions on the Pareto optimal front in future earthquake events is investigated. The case studies apply each method to a two-dimensional ten-story shear building and adopt four measures to evaluate the performance of searched solutions in multiple aspects. The results show that the proposed methods, by executing fewer number of time history analyses and with convergence comparable to that of NSGA-II, successfully offer improvement against NSGA-II in the aspect of productivity and diversity. As for understanding solutions on the Pareto front in future earthquake events, the knee point solution’s design, which proposed methods can arrive at or approach, successfully reduces both peaks IDR and PFA under 20 ground motions.

Investigations on the Dynamic Response of Adjacent Buildings Connected by Viscous Dampers

This paper investigates the seismic performance of two adjacent buildings connected by viscous dampers. Three types of damper placement are discussed, including installing dampers within a single building, connecting two buildings at the same floor level, and connecting two buildings at the inter-story level. Analytical models are established to consider various dynamic properties of the adjacent buildings, and the theoretical solutions are obtained, including the transmissibility curves, additional modal damping, and input energy under the seismic design spectrum. Time history analyses of an engineering project are performed with different damper placements. Different numerical models are compared for frequently and rarely occurred earthquakes. The seismic mitigation effect is discussed with regard to the story drift reduction rate and dynamic energy. Theoretical and numerical results demonstrate that the connecting dampers provide added modal damping while causing the coupled response. As a result, it is less efficient than traditional ways of placement within a building. Furthermore, the connecting dampers significantly increase the reaction of the floors without installed dampers. When designing dampers to connect the adjacent buildings, careful engineering calculations should be made.

Modeling of resilience based on categorized recovery scenario and improving resilience with viscous damper

AbstractIn this study, a model for the evaluation of a building's resilience and recovery time is proposed, and a new method is developed for the optimal viscous damper placement for a targeted resilience. The features of this model are as follows: 1) building components are categorized into systems in view of their functionality, 2) recovery time is regarded as a function of the damage to building components and human resources for repairing the components, 3) the model is applicable to structural design. This design method uses a type of real‐coded genetic algorithm (GA). The effective use of a constraint on the sum of the added damper damping coefficients enables an efficient search for the solution.

Optimizing Viscous Damper Placement with Element Exchange Method and Energy-Based Distribution Methods for Building Structures

Viscous dampers enhance the seismic performance of buildings by increasing the capacity for damping. It remains a challenge to decide on the optimum placement for the added dampers and it has been a continuing subject of research. In this paper, Element Exchange Method and energy-based distribution methods are proposed. The proposed methods are compared against currently available methods through case studies. The case studies are based on a two-dimensional ten-story shear building adopting different nonlinearity of viscous dampers and a three-dimensional steel moment-resisting-frame (MRF) building with varying plan asymmetry. The methods then automatically develop damper placement schemes, and subsequently, the buildings are evaluated for their maximum peak inter-story drift against a suite of ground motions. The result shows that Element Exchange methods and energy-based distribution methods can successfully reduce maximum peak inter-story drift over all case studies.

Fragility-based framework for optimal damper placement in low-rise moment-frame buildings using machine learning and genetic algorithm

Commonly, seismic fragility is used as an assessment tool rather than a design constraint for existing building structures. In addition, the degree of seismic fragility safety margin after retrofitting existing structures is usually unknown during the early retrofit design stage. The current study proposes a framework that allows the designer to assign the preferred seismic fragility margin as a design variable before retrofit of a structure using soft computing techniques. In addition, it provides the design damping ratio to achieve the optimal damper capacity distribution required for retrofit. To this end, a machine learning model (MLM) is used to construct safety margin curve (SMC) graphs for the structural system considering different limit states to obtain the design damping ratio. This MLM is trained with a wide range of structural systems subjected to various levels of ground motion intensities for predicting seismic responses of the system. The main role of the MLM and SMC is to provide a reasonable approximate range for damper capacity in each story to reduce the computational time required for the optimization process. After that, a genetic algorithm (GA) optimization process is implemented to obtain the optimum capacities of the energy dissipation devices (EDDs) required for retrofitting the structure using the design damping ratio obtained from the SMC. Displacement-dependent EDDs are used in the current study because of their effectiveness in dissipating seismic energy. The EDDs are arranged such that the seismic demands are controlled to achieve the required basic seismic safety objective maintaining the optimal EDD capacity for each story. The reliability and robustness of the framework are investigated using various case-study examples and validated by comparing the results with those obtained from nonlinear time history (NLTH) and nonlinear static methods. The proposed framework is validated for low-rise moment-resisting frame buildings that can be represented using a single degree of freedom (SDOF) system. The framework is expected to enable researchers and engineers to effectively implement the required level of seismic safety in retrofitted structures with less computational cost and allows the designer to select the most suitable retrofit scheme considering multiple limit state criteria checks.