Variable Friction Damper Research Articles

Design, Manufacturing, and Testing of a Non‐Preload Variable Friction Damper for Seismic Application of Buildings

Friction dampers are widely used due to their simple structure, remarkable energy dissipation capacity, and frequency independence. However, existing friction dampers are prone to relaxing the preload force during long‐term service, which can lead to cold bonding or cold solidification. To overcome this critical shortcoming, a novel non‐preload variable friction damper (NVFD) was firstly proposed. The construction of the proposed NVFD is provided in detail. Furthermore, restoring the force model through the amplification factors of friction force and inertial mass was derived based on the principle of the proposed NVFD. Then, pseudo‐static tests with various parameters were conducted. Finally, a single‐degree‐of‐freedom (SDOF) structure was employed to compare the effectiveness of this paper’s new NVFD with a conventional friction damper (FD) under various earthquake levels. The results show that non‐preload characteristics avoided the problems of large preloads by traditional friction dampers; thus, the NVFD had stable and reliable variable friction performance, which can effectively adapt to different hazard levels.

Parametric Investigation of Self-Centering Prestressed Concrete Frame Structures with Variable Friction Dampers

To enhance the structural stiffness and energy-dissipating capacity after the decompression of beam-to-column connections for self-centering prestressed concrete (SCPC) frames, this study presents the seismic performance of a new type of SCPC frame with variable friction dampers (VFDs). The structure is characterized by a third stiffness and a variable energy-dissipating capacity. A 5-story and an 8-story VFD-SCPC frame were selected as the analytical cases, and their numerical models were built based on OpenSees 3.3.0 finite-element software. Sixteen ground-motion records were selected as excitations for the analyses, and the influence of the second stiffness and the third stiffness for the VFD-SCPC connections, as well as the second activation for VFD, on the seismic performance of the structures, was studied. The results showed that increasing the stiffness (number) of prestressed strands and their distance to the center of the beam section can obviously increase the second stiffness of the structures, thus decreasing their displacement, while the distribution mode of inter-story drift along the building’s height cannot be changed. Increasing the third stiffness of the connections (the angle of slope sliding parts and the stiffness for the combination of disc springs) can effectively reduce the deformation of the structures under MCE (maximum-considered earthquakes) seismic levels and improve the energy-dissipation capacity of structures significantly. The premature secondary activation of VFD can enhance the loading capacity and energy-dissipation capacity of structures under both DBE (design-basis earthquakes) and MCE seismic levels, and reduce the inter-story drift of structures effectively.

A self-centering hybrid braced precast wall with replaceable U-shaped flexural plates: Experimental and theoretical analysis

A self-centering hybrid-braced precast wall with replaceable U-shaped flexural plates (UFPs), which is composed of a hybrid braced wall, post-tensioned (PT) strands, and steel wall toes, is proposed. The UFPs bolted inside the steel wall toes, which yield at the same thickness outside the plane of the steel plate when wall rocking, providing plastic bending energy dissipation. The steel wall toe made of H-shaped steel provided increased compressive strength and space for the installation of the UFPs. Four wall specimens with varying initial PT forces, UFPs of different thicknesses, and different dampers were investigated using low-cyclic loading tests. After replacing the UFPs, one wall was retested to assess its performance. The precast walls sustained significantly low damage and showed large self-centering capabilities. The maximum drift was up to 4.5%, which far exceeded the specified requirements, and the lateral load still maintained an increasing trend. When the initial PT force was increased, the bearing capacity, initial stiffness, and self-centering capacity of the precast wall increased. When the thicknesses of the UFPs were increased, the energy-dissipation capacity and self-centering capacity of the wall increased and decreased, respectively. The self-centering and bearing capacities of the repaired wall met the seismic requirements but were slightly lower than those of the original wall. The wall with UFPs performed better bearing capacity and stiffness than the wall with variable friction dampers (VFDs) before 1.5% drift. Additionally, the opening load of the wall, the load at the yield of UFPs, and the load at different compression sections were calculated and compared against the test results. The analysis method was able to predict the behavior of the walls reasonably well.

Seismic response control effects for reinforced-concrete buildings incorporating a passive variable friction device

The seismic response behavior and control effects of reinforced concrete (RC) structures incorporating a variable friction damper were numerically investigated in this study. The damper considered was a passive displacement-dependent variable friction device (VFD), whose sliding force decreases as the device displacement increases. A nonlinear response simulation was carried out using a single-degree-of-freedom system model under various input motions. The results showed that the VFD was effective for controlling the response of the RC structure, not only for reducing the displacement but also for mitigating the increase in the story shear force and acceleration. Also, the nonlinear earthquake response of a three-dimensional frame model representing a historic RC temple building retrofitted with VFDs was assessed. The results showed that the VFDs clearly mitigated the peak story shear of the device-installed story, compared with a passive conventional friction device (CFD). The VFD significantly reduced the peak story drift of the device-installed story compared with the uncontrolled case. Moreover, the peak story drift at the base story for the VFD was decreased compared to the CFD. The VFD contributes to enhancing the aseismic performance of RC superstructures while suppressing the stress increase in the foundation. • Assessment of the response control effects of RC structures with a variable friction device (VFD). • Sliding force of the VFD decreases as the device displacement increases. • Numerical nonlinear responses of SDOF and 3D frame models representing RC structures. • The VFD can mitigate the peak story shear force compared to a conventional friction device. • The VFD can reduce the peak story drift compared with the uncontrolled case.

Seismic behavior and reliability of variable friction damped self-centering prestressed concrete frames considering bolt bearing

This study comprehensively studied the bolt bearing behavior on the influence of friction based self-centering prestressed concrete (SCPC) frames. Based on the mechanism and test results of a SCPC connection with variable friction dampers (VFD), the theoretical analyses for the VFD-SCPC connection considering the whole procedure of friction bolts ranging from bearing to failure were carried out. The numerical model of the VFD-SCPC connection considering the bolt bearing behavior was proposed and the incremental dynamic analyses were carried out to obtain the seismic behavior of the VFD-SCPC frames when the friction bolts in the VFD ranged from bearing to failure. Taking the inter-story drift corresponding to the initiation of friction bolt bearing as variation, the fragility analyses for the SCPC frames with VFD and common constant friction dampers (CFD) were conducted to acquire the reliable design for the allowed bearing of friction bolts. The analyses results shown that to obtain the balance between the acceptable damage and expected reliability, the inter-story drift corresponding to the initiation of friction bolt bearing should be ranged from 2.0% to 2.5% for the VFD-SCPC frames and less than 2.0% for CFD-SCPC frames.

Energy response of a passive variable friction damper and numerical simulation on the control effects for high‐rise buildings

In this study, the behavior of a passive displacement-dependent variable friction damper (VFD) was evaluated. The energy response behavior of a VFD specimen was investigated by conducting full-scale dynamic loading tests. Full-scale tests demonstrated that the VFD specimen produced a lower sliding force when the device response exceeded a predetermined displacement, resulting in a decreased dissipated energy ratio as the displacement increased. The VFD specimen exhibited stable energy response behavior as well as a stable friction sliding force and friction coefficient under sinusoidal, seismic response, and 100-cycle loadings. The energy response of the VFD specimen was almost independent of the loading frequency. Moreover, a response simulation was conducted using a two-dimensional 30-story nonlinear mainframe model with brace-type VFDs under various input motions, including observation records and long-period, long-duration waves. From the numerical simulations, the peak story drift in the case with brace-type VFDs was not significantly greater than in the case with conventional friction dampers (FDs). The dissipated energy ratios of the mainframe and dampers in the case with the VFDs were approximately identical to those in the case with the FDs. In comparison with conventional FDs, VFDs can produce a lower peak story shear force and axial compressive force in the lowest-story columns at the device installation span.

Variable Friction Dampers (VFD) for a modulated mitigation of the seismic response of framed structures: Characteristics and design criteria

In this paper a new approach for the energy dissipation is discussed based on the use of Variable Friction Dampers (VFDs). The VFD device is borrowed from braking systems mechanical engineering, able to modulate its capability of dissipation, providing a constant pure friction force coupled with an additional (variable) damping force with the increasing of the displacement.Resorting to a previous study, the characteristics and the efficiency of the “braking” system in terms of reduction of the displacements and the restoring forces is described for SDOF systems under seismic excitations and compared with the performances achievable by classic constant friction dampers (CFDs). Then, a design criterium based on structure stiffness, viscous damping and seismic demand is proposed evaluating its effectiveness through a statistical assessment of the dynamic response of SDOF models subjected to natural accelerograms.The results obtained by the proposed design approach have proven that is a robust approach and indicate that the device can be really considered suitable for the improvement of the energy dissipation and the reduction of the drift in framed structures in an extended range of the seismic demands (from low to high) differently from the classic friction devices whose characteristics make them effective in a smaller range of the seismic intensities.

Theoretical and experimental study on a dual-stage variable stiffness friction damper for satellite flywheel

Micro-vibration reduction devices are widely utilized to mitigate disturbances from on-board flywheel in order to enhance the performance for high precision payloads in satellite. However, the conventional micro-vibration suppression devices cannot endure the high-level loadings and effectively control the dynamic responses of the flywheel in launching stage. In this paper, firstly, a new type of dual-stage variable stiffness friction damper (DS-VSFD) is proposed and investigated under the on-orbit and launch loads. In order to demonstrate the effectiveness of the developed damper, the mechanism and hysteresis characteristics of the device are introduced in detail and the variable sliding force and displacement of the DS-VSFD are theoretically analyzed. Based on the relationship between output force and displacement of the device, a double-tail-shaped hysteresis curve is illustrated and corresponding stiffness and energy dissipation capacity at different stages are provided. Secondly, a single-degree-of-freedom dynamic model of the flywheel system with the DS-VSFD is constructed. The Harmonic Balance Method (HBM) is adopted to derive the force and displacement transmissibility curves in the frequency domain based on the dynamic model under different excitation conditions. In on-orbit stage, it can be observed that the resonance frequency is shifted to higher frequency and the amplitude is lower than that of the linear case in higher frequencies. In launching stage, the peak of displacement transmissibility of the flywheel system has been decreased in the resonance region comparing with the conventional linear isolator. Besides, the resonant frequency of the system has shifted to higher frequency region. Effects of the external excitation amplitude on the force transmissibility are also examined. Finally, comparison between the theoretical and experimental results has been carried out through static and dynamic tests. According to the static mechanical experimental results, it can be demonstrated that the DS-VSFD with wedge-block configuration exhibits stable and reliable hysteresis characteristics. The actual experimental results agree with the calculation results of the system dynamics model with the DS-VSFD in terms of force and displacement transmissibility. The results discussed in this research indicate that the DS-VSFD guarantees both the structural safety of the flywheel system under the launch loads and the micro-vibration reduction of the flywheel under the on-orbit condition.

An equivalent approach for modelling butterfly-hysteresis passive variable friction damper

This research work proposes an equivalent approach modelling the peculiar hysteretic behavior of passive variable friction damper, for engineers who call for a simplified way to simulate such damper in anti-earthquake engineering practice with acceptable accuracy. This approach models the special nonlinear behavior of the damper via paralleling 3 basic link elements that commonly built-in commercially available structural analysis software, instead of developing direct hysteretic model that demands for both post development functionality on software side and programming skill on engineer side. The mathematical derivation and analytical geometric equating work are comprehensively conducted. The numerical accuracy of analysis output yielded using equivalent model is digitally verified against the one yielded using generic FEM simulation of the same damper subject to several loading cases. Code-automated optimization workflow for yielding product-wise modelling parameters is developed that is convenient and straightforward for application by engineers without requirement of high expertise, which is demonstrated by generating optimized parameters to equivalently model tested specimen.Article highlightsPassive variable friction damper can be modelled by assembling friction spring, elastic spring and wen model into parallel.Code-automated optimization process can locate the most ideal modelling parameters combination in predefined numeral fields.Hysteretic behaviors yielded from equivalent modelling approach match well corresponding ones from generic FEA simulation.

Hysteretic Behavior of Dual-Self-Centering Variable Friction Damper Braces with Low Pretensioned Force

ABSTRACT To satisfy the resilient requirements, a novel dual-self-centering variable friction damper (DSC-VFD) brace with self-centering variable friction damper systems and basalt fiber-reinforced polymer tendons, is proposed. The working mechanism of the DSC-VFD brace was first investigated. Then, four DSC-VFD and SC-VFD braces with different groove angles were designed, and quasi-static experiments were conducted. Finally, finite element models of the DSC-VFD braced frame were created and the seismic responses of the frames were analyzed. The results show that the DSC-VFD brace presents a novel flag shape with large post-yield stiffness and enhanced energy dissipation which can effectively control the structural responses.

Manufacturing, testing and simulation of novel SMA-based variable friction dampers with enhanced deformability

This study presents a novel type of self-centering damper employing NiTi Shape Memory Alloy (SMA) bars combined with variable friction mechanism for tunable hysteretic behavior and enhanced deformability. The new damper, which is called SMA-based variable friction damper (SMA-VFD), aims to significantly amplify the maximum deformability and energy-dissipation capability compared with the existing self-centering devices with tensioning SMA members. The cyclic response, phase transformation behavior, and in-situ observation of the microstructure of individual SMA bars receiving different heat treatments were first investigated to promote an adequate understanding of the link between the microscopic structure and the macroscopic property of the large size SMA bars. This is followed by a detailed discussion of the SMA-VFD, where theoretical equations as well as three performance parameters, i.e., self-centering factor γ, displacement amplification factor ω, and energy-dissipation factor λ, were derived to predict the mechanical behavior of the damper. Proof-of-concept SMA-VFD specimens were manufactured, where different preloads and friction coefficients were considered which could affect the cyclic performance. A three-dimensional finite-element model was then developed to simulate the nonlinear responses of the test specimens. Both the analytical prediction and numerical simulation exhibited good agreements with the experimental results. Utilizing the validated numerical model, the influence of manufacturing tolerance on the initial stiffness of the proposed damper was particularly investigated to help explain some important findings from the present experimental study.

Seismic design and performance of self-centering precast concrete frames with variable friction dampers

This paper presents the numerical investigation of the seismic performance of post-tensioned self-centering precast concrete (SCPC) frames with variable friction dampers (VFDs) and hidden corbels (HCs). The VFDs are characterized by the combination of flat and grooved plates, where the friction forces change as the connection deformation increases, which enables designs to meet target seismic performance objectives at different seismic hazard levels. Theoretical and numerical models for the connection are proposed based on connection geometry, and a performance-based seismic design approach for the SCPC frames is outlined to meet target performance objectives at two common seismic hazard levels, the design basis earthquake (DBE) and the maximum considered earthquake (MCE). SCPC frames for a six-story prototype building located in a high seismic zone in California were designed using this procedure. Three frames with HC-VFD-SPSC connections were designed using various methods to mitigate concentration of drifts in the first story, and one frame was designed with conventional constant friction devices (CFDs) for comparison. Nonlinear time-history analyses were performed for these different designs using two sets of ground motions representing the DBE and MCE seismic hazard levels. The analysis results indicate that the frames with the HC-VFD-SCPC connections achieved the target performance objectives. The proposed approaches of modifying post-tensioning and VFD design parameters or column stiffness in the first story were effective in mitigating the concentration of drifts. Additionally, through comparison with the results of the frame with CFDs, it was found that the VFDs are effective in decreasing overall drift demands at the MCE level, as well as mitigating detrimental higher mode effects observed in SCPC frames with CFDs.

Effects of Loading Rates on the Hysteretic Response of Resilient Variable Friction Dampers

Effects of Loading Rates on the Hysteretic Response of Resilient Variable Friction Dampers

Hysteretic and seismic performance of dual self-centering variable friction damper braces

A novel dual self-centering variable friction damper (DSC-VFD) brace was introduced to achieve greater post-yield stiffness and a better energy dissipation capability. To evaluate its hysteretic response with a novel flag shape, a new uniaxial material with different loading and unloading stiffnesses was developed based on the OpenSees platform in this study. The actual initial stiffness of the DSC-VFD brace was significantly lower than the theoretical value because of the tube length and pin diameter tolerances. The initial stiffness modification coefficients of the DSC-VFD brace were defined, and their calculation equations were established. Because of the uneven gap openings along the friction plates, the matrix displacement method was applied to determine the different gap openings under the tension and compression stages. Then, the hysteretic response of the DSC-VFD brace was calculated with the user-defined model; the model results were in good agreement with the experimental result, verifying the reliability of the proposed model. Simulation models were used to study the crucial parameters for the hysteretic response of the DSC-VFD brace. Finally, nonlinear dynamic analyses of a four-story braced frame were conducted to study the seismic performance of the DSC-VFD brace with a novel flag shape. The results showed that the DSC-VFD brace with a larger post-yield stiffness provided stable self-centering behavior and an effective energy dissipation capability. The high loading stiffness and energy dissipation ability effectively decreased the deformations of the braced structures and improved their seismic responses.

Quantification of higher mode effects of steel frame and control method using dual self-centering variable friction damper brace

Self-centering energy dissipation braced frames (SCEDFs) have been developed to satisfy the requirements of resilience. However, low post-yield stiffness in such systems often leads to a higher mode effect, resulting in a significant deformation concentration that may exceed the design objectives. A novel dual self-centering variable friction damper (DSC-VFD) brace with high post-yield stiffness and enhanced energy dissipation capability was proposed. Its hysteretic behavior, characterized by a loading stiffness that is larger than the unloading stiffness, was developed by incorporating the C++ language into the OpenSees platform. To evaluate the higher mode effect in different types of frames, a quantification measure based on the higher mode results of the steel frames, considering the seismic responses around the peak value, was therefore established. Then, the seismic responses of the DSC-VFD frames (DSC-VFDFs) using the proposed uniaxial material were calculated and compared with those of the traditional moment resisting frame (MRF) and SCEDF with the same design process. Finally, the four parameters, including the first stiffness modification coefficient α1, second stiffness ratio α2, strength ratio β, and fourth stiffness ratio α4, were considered to evaluate their influences on nonlinear seismic responses and the higher mode effect of the DSC-VFDF by the above-mentioned quantification measures. The results indicate that the influence of higher modes should not be ignored in the design of self-centering braced frames, and the higher mode quantification results of base shear are more sensitive than those of effective displacement. The DSC-VFD brace can more effectively improve the seismic responses and control the higher mode effect than the traditional SCEDF.

Dynamic response control of engineering structure equipped with smart compound damper

To better control engineering structures subjected to external disturbances, such as earthquakes of varying magnitudes, a smart compound damper is developed and its performance is investigated in this paper. Unlike devices for passive control systems without adjustable control force, the dynamic responses of the engineering structure can be more effectively suppressed under seismic excitation by using devices for active control systems that feature active input to the actuators. A compound damper designed in this vein consists of shape memory alloy (SMA) wires and a variable-friction damper that can provide an adjustable control force according to the level of ground motion by changing the voltage of piezoelectric ceramic (PZC) actuators. Numerical simulations of a seismically excited two-storey steel frame structure were implemented to evaluate the performance of the proposed SMA/PZC compound damper. A back-propagation neural network model was developed using experimentally obtained data to describe the hysteretic behaviour of the SMA wires. A Takagi–Sugeno (T-S) fuzzy controller was used to determine the command voltage of the PZC actuators, such that the compound damper could perform well when applied to structural control. The resulting solution, hybrid control modulated with a T-S fuzzy control strategy, was found to be more effective than passive control.

Dynamic mechanical properties of variable friction damper based on new piezoelectric ceramic tubular actuator

Based on ANSYS finite element software and combined with the physical properties of piezoelectric materials, the actuating properties of the new piezoelectric ceramic tubular actuator was simulated. In addition, the maximum displacement, output and response frequency characteristics of the actuator were obtained. The results shown that the actuator was suitable for the development of structural vibration control device. The intelligent damper for adjusting friction in real-time was proposed by using the above-mentioned new actuator. In addition, the dynamic mechanical properties of the intelligent damper were analyzed, the constitutive relationship under the sinusoidal simple harmonic action and the calculation formula of the energy consumed in one cycle were obtained.

Numerical evaluation of a novel passive variable friction damper for vibration mitigation

This study assesses the performance of a novel passive variable friction damper (PVFD) at mitigating wind- and seismic-induced vibrations. The PVFD consists of two friction plates upon which a cam profile modulates the normal force as a function of its rotation. A unique feature of the PVFD is its customizable shape, yielding a customizable friction hysteresis. The objective of the study is to assess the benefits of crafting the friction behavior to satisfy motion criteria. This is done numerically on two example buildings: a 5-story structure subjected to seismic loads, and a 20-story structure subjected to non-simultaneous seismic and wind loads. A probabilistic performance-based design procedure is introduced to select the optimum cam configurations throughout each building under the design loads. After that, numerical simulations are conducted to compare their performance against that of two equivalent damping schemes: viscous dampers and passive friction dampers. Results show that customization of the hysteresis behaviors throughout a structure is necessary to yield optimal performance. Also, the PVFD outperforms the other damping schemes for wind mitigation by yielding a more stable response in terms of lower accelerations over the entire wind event. Under seismic loads, all three damping schemes exhibited comparable performance, but the PVFD yielded a significantly more uniform drift for the 20-story building.

Theoretical analysis and experimental investigation of hysteretic performance of self-centering variable friction damper braces

Traditional buildings, even with normal self-centering energy dissipation (SCED) braces, might suffer from large deformations and high mode effects under an extremely strong earthquake, leading to a concentration of inter-story drift in upper floors. To satisfy the requirements of resilience, larger post-yield stiffness and higher energy dissipation, a novel brace with pretensioned basalt fiber-reinforced polymer (BFRP) tendons and variable friction dampers (VFDs) was developed, and this brace was termed the self-centering variable friction damper (SC-VFD) brace. The variable stiffness and sliding force of the VFD system were theoretically analyzed. This was followed by quasi-static experiments on two VFD and two SC-VFD braces with different parameters. The theoretical analysis and experimental results revealed the same tendencies, demonstrating the reliability and feasibility of SC-VFD braces. The hysteretic curve of the SC-VFD braces exhibited stable and normal flag-shape behavior before the second activation, while the hysteresis curve indicated a variable flag-shape behavior with second activation, variable friction force, and larger post-yield stiffness when the brace slid at slope section. Compared with the VFD brace, the SC-VFD brace had the same energy dissipation ability but less residual displacement and lower equivalent viscous damping ratio. More combinations of disc springs in series resulted in smaller axial forces and lowers post-yielding stiffness, thereby decreasing the energy dissipation capability.

Variable friction damped self-centering precast concrete beam–column connections with hidden corbels: Experimental investigation and theoretical analysis

A new self-centering precast concrete (SCPC) beam–column connection with variable friction dampers (VFDs) is proposed to enhance the stiffness and energy dissipation after gap opening occurs at the beam–column interface, where a hidden corbel (HC) is placed to increase the vertical shear capacity and construction efficiency. Especially, the VFDs are composed of grooved steel plates instead of the flat steel plates used in most common friction dampers, which enhances the flexibility of seismic design. Applying grooved steel plates with different geometric characteristics and adjusting the key design parameters including the initial post-tensioned (PT) forces, pre-stressing clamping forces applied to friction bolts, and number of PT tendons, a series of tests was conducted on a full-scale beam–column specimen to investigate the hysteretic behavior of such HC–VFD–SCPC beam–column connections. Incorporating the characteristics of twice activation for VFDs with the different seismic requirements for various seismic levels, the theoretical basis was proposed and some recommendations were obtained for the seismic design of structures containing such beam–column connections. The experimental and theoretical results show that the arrangement of these VFDs in the beam–column connection achieved the expected self-centering capacity and hysteretic behavior of variable stiffness and energy dissipation after gap opening occurred at the beam–column connection. The hysteretic behavior of variable stiffness and energy dissipation is observed to be sensitive to the details of the VFDs, initial force, number of PT tendons, and pre-stressing clamping forces applied to friction forces.