Friction Devices Research Articles

A novel kind of electrohydraulic loading system based on friction for actuator test

Conventional electric or electrohydraulic load simulator is disturbed by the motion of the tested system. To eliminate the strong motion disturbance and improve loading performance, a novel kind of friction electrohydraulic loading system is proposed. The mechanism of friction electrohydraulic loading system is described in detail. The math model for the loading torque and the input signal has been deduced, which indicates that this proposed friction electrohydraulic loading system has no disturbances resulting from tested actuators under ideal conditions. However, friction coefficient is time-varying and uncertain. The friction device increases the load inertia of the actuator. The additional inertia may affect the loading performance. The structure mechanism has been optimised to reduce the rotary inertia. To verify the loading performance of friction electrohydraulic loading system, simulations and experiments are carried out. Compared with conventional electrohydraulic load simulator, the theoretical analysis and experimental results validate the feasibility of the friction electrohydraulic loading method. The novel friction electrohydraulic load simulator, with a simple control principle and easy engineering constructability, can provide accurate torque simulation for actuator test.

A novel kind of electrohydraulic loading system based on friction for actuator test

Conventional electric or electrohydraulic load simulator is disturbed by the motion of the tested system. To eliminate the strong motion disturbance and improve loading performance, a novel kind of friction electrohydraulic loading system is proposed. The mechanism of friction electrohydraulic loading system is described in detail. The math model for the loading torque and the input signal has been deduced, which indicates that this proposed friction electrohydraulic loading system has no disturbances resulting from tested actuators under ideal conditions. However, friction coefficient is time-varying and uncertain. The friction device increases the load inertia of the actuator. The additional inertia may affect the loading performance. The structure mechanism has been optimised to reduce the rotary inertia. To verify the loading performance of friction electrohydraulic loading system, simulations and experiments are carried out. Compared with conventional electrohydraulic load simulator, the theoretical analysis and experimental results validate the feasibility of the friction electrohydraulic loading method. The novel friction electrohydraulic load simulator, with a simple control principle and easy engineering constructability, can provide accurate torque simulation for actuator test.

Seismic response of MRF-CBF dual systems equipped with low damage friction connections

The work herein presented proposes an innovative approach to the use of friction dampers in seismic resistant steel structures. In fact, reference is made to dual systems where dissipative devices are located at beam ends, column bases and intersections of chevron braces. Friction devices are those investigated in the framework of the European Research Project “FREEDAM” (FREE from DAMage steel connections), supported by Research Found for Coal and Steel (RFCS). The aim of this project is the development of beam-to-column connections equipped with friction dampers showing low damage. Investigations concerning the prototype structure herein presented have been carried out to gain relevant information in the framework of the research project. Incremental Dynamic Analyses (IDA) are developed with reference to the maximum interstorey drift ratio, the maximum slippage velocity and the cumulative displacement, i.e. the travelled distance of the friction dampers. Moreover, the influence of the seismic intensity measure on the required friction damper stroke is investigated.

Seismic Analysis of Friction-Damped Self-Centering Coupled-Beams for Moment-Resisting-Frames without Floor Elongation

The common characteristic of self-centering (SC) post-tensioned (PT) connections is the gap opening and closing at the beam-column interface, which often face the problem of deformation incompatibility with floor system and cause severe damage of floor slab. To address this drawback of PT frame expansion, an innovative friction-damped SC coupled-beams (CBs) that incorporate PT strands to provide a SC capacity along with friction devices (FDs) to dissipate energy is presented. The global mechanics of this system are briefly explained. An individual FD is tested to investigate the wear resistant properties and friction coefficients of friction materials for the energy dissipation system of SC-CBs. Detailed three-dimensional finite element models (FEMs) of a single-story single-bay frame using SC-CBs are developed with consideration of different FDs installation positions. Analytical results indicate that SC-CBs can sustain large lateral deformations without structural damage under cyclic loading. Then, simplified computational models are validated based on the solid models and applied in nonlinear dynamic analysis of a five-story MRFs using SC-CBs. The frame using SC-CBs minimizes the residual drift and displays good energy dissipation capacity under both the design basis and maximum considerable levels of seismic loading.

Experimental response of a low-yielding, self-centering, rocking column base joint with friction dampers

The sliding hinge joint (SHJ) is a supplemental energy dissipation system for column bases or beam-to-column connections of steel Moment Resisting Frames (MRFs). It is based on the application of symmetric/asymmetric friction dampers to develop a dissipative mechanism alternative to the column/beam yielding. This typology was initially proposed in New Zealand and, more recently, is starting to be tested and applied also in Europe. While on the one hand this technology provides great benefits such as the damage avoidance, on the other hand, due to the high unloading stiffness of the dampers in tension or compression, its cyclic response is typically characterized by a limited self-centering capacity.To address this shortcoming, the objective of the work herein presented is to examine the possibility to add to these connections also a self-centering capacity proposing new layouts based on a combination of friction devices (providing energy dissipation capacity), pre-loaded threaded bars and disk springs (introducing in the joint restoring forces).In this paper, as a part of an ongoing wider experimental activity regarding the behavior of self-centering connections, the attention is focused on the problem of achieving the self-centering of the column bases of MRFs by studying a detail consisting in a column-splice equipped with friction dampers and threaded bars with Belleville disk springs, located above a traditional full-strength column base joint. The main benefits obtained with the proposed layout are that: (i) the self-centering capability is obtained with elements (threaded bars and Belleville springs) which have a size comparable to the overall size of the column-splice cover plates; (ii) all the re-centering elements are moved far from the concrete foundation avoiding any interaction with the footing. The work reports the main results of an experimental investigation and the analysis of a MRF equipped with the proposed column base joints.

HYDROGEN POWER PLANTS FOR AIRCRAFT

The paper considers the prospects of using fuel cells as a source of energy for aircraft. For their supply, it is suggested to use hydrogen accumulation systems based on aluminum hydrides which are the most safe and efficient in terms of energy capacity, extraction temperature. The technologies for obtaining materials based on aluminum hydrides can be transferred from previously developed technologies of the production of electrolytic capacitors. The brief comparative analysis of existing fuels and forms of fuel storage is given. The paper substantiates the use of aluminum for the accumulation of hydrogen in the form of metal hydride. The most detailed consideration is given to the anodic treatment of aluminum, because the formation of aluminum hydride needs a foil with a high degree of surface development. A high degree of development of the material surface makes it possible to carry out processes of rapid charging of the material with hydrogen ions in the formation of aluminum hydrides. The presence of pores on the foil surface provides an increase in the degree of adaptation of the functional properties of the drive to the operating modes of the power plant. This property is due to the ability to flexibly control the process of the pore structure formation of a given morphology providing the necessary reduction effect. The paper presents the basic positions determining the peculiarity of the anodic processing of aluminum foil. These positions deal with the physicochemical properties of the pure aluminum and its compounds, oxides and hydrides, and their behavior under the conditions of the electrochemical reactions. Moreover, the paper indicates the possibility of parallel processes on electrodes: the oxidation and reduction of water, which are necessary condition for ensuring the self-consistent processes in the processing of aluminum. The experimental data have been obtained using the internal friction devices. We have shown the prospects of using of the aluminum hydrides in aviation and substantiated the solution to energy problems in aviation on the basis of deepening and expanding the scale of research into hydrogen energy technologi es. The results of the work can be used for the technology of volumetric storage and transport of electric energy.

Seismic Performance and Fragility Analyses of Self-Centering Prestressed Concrete Frames with Infill Walls

ABSTRACT This paper presents a seismic response evaluation of self-centering prestressed concrete frames with infill walls (SCPC-IW frames). Three types of infill walls with different load capacity were selected to be installed in a bare self-centering prestressed concrete frame (SCPC-Bare frame). Beam web friction devices are included in the beam-column connections to provide energy dissipation capacity. Numerical models of the SCPC frame, and the three SCPC-IW frames were established and analyzed in a finite element software, OpenSees. Firstly, the nonlinear static analyses and nonlinear dynamic analyses under 44 ground motions were performed. Secondly, the incremental dynamic analyses (IDAs), seismic fragility analyses, and collapse resistance capacity evaluation were conducted. The results showed that the initial stiffness, energy dissipating capacity of SCPC-IW frames are increased in comparison to SCPC frames. After adding infill walls, the lateral displacement of the SCPC-IW frames decreases. However, the residual deformation and axial compression ratio of the SCPC-IW frame increases. As the infill walls strength increases, the increased amplitude of residual displacement becomes much larger than the decreased amplitude of the drift. It is concluded that when the load capacity of infill walls ranges from 37% to 79% of the web friction force, the SCPC-IW frames can achieve a good balance in terms of stiffness, energy dissipation, and self-centering capability as well as collapse resistance capability.

Performance evaluation of phase‐controlled semiactive resettable TMD (PCRTMD) with the stiffness retuning ability under strong seismic motions

SummaryTuned mass dampers (TMDs), despite being efficient because the structure has not experienced damage and properties degradation, lose efficiency when the mechanical properties of the structure changes and detuning effects occur. Semiactive TMDs have been shown superior to the traditional passive ones and more efficient and reliable than the active counterparts for the detuning problem. This study presents a novel semi active system that is able to respond efficiently and maintain such a performance even in the case of structural damage. This scheme is composed of a variable stiffness component, a resettable element, and a friction brake. The system dissipates energy using the resetting mechanism and is able to change stiffness when the tuned frequency of the structure changes due to structural damage. The friction device is responsible for maintaining the TMD in the optimal phase lag to the structure, that is, −90°, and thus keeping the TMD in the optimal performance. This strategy has been tested on a single‐degree‐of‐freedom frame, to understand the system behavior under harmonic excitation, as well as a 10‐story shear type frame under strong seismic motions. The proposed system has shown to be effective and competent comparing analysis results to active and passive TMDs.

Structural evaluation of steel self-centering moment-resisting frames under far-field and near-field earthquakes

The design formulations, structural performance, and energy-based results of steel buildings of self-centering moment-resisting frames (SC-MRFs) with post-tensioned (PT) connections of three different energy dissipation devices including bolted top and seat angles, beam bottom flange friction devices, and bolted web friction devices are investigated under far-field and near-field earthquakes. The results of nonlinear time-history analysis using DRAIN-2DX program show that the simplified analysis used to estimate the inertial forces distributed through collector beams is not sufficiently precise since it leads to the underestimation of design beam axial forces and connection moments in exterior bays. The overestimation of design displacement demands of SC-MRFs with bottom flange friction devices results in bigger sections of beams and columns than are necessary. In addition, this SC-MRF system is not as effective as other two systems to dissipate the input energy. It is recommended to symmetrically use beam flange friction devices to achieve higher level of energy dissipation and lower fabrication costs. On the other hand, SC-MRFs with web friction devices is identified as the most efficient system to minimize the recoverable energy and SC-MRFs with top and seat angles provides medium level of energy dissipation. Different from far-field earthquakes, the input energies of SC-MRF structures under near-field ground motions are distinguishable by hikes of maximum values at the early stages of earthquakes. Furthermore, absolute energy components are substantially higher than relative energy components under near-field earthquakes. These phenomena should be considered in the formulations of energy factor and energy-based design procedures of SC-MRF systems.

Virtually clipless parenchymal transection for right hepatectomy using a zero forward frictional energy device

Virtually clipless parenchymal transection for right hepatectomy using a zero forward frictional energy device

Nonlinear modal synthesis for analyzing structures with a frictional interface using a generalized Masing model

The objective of this paper is to present a numerical scheme for applying nonlinear modal synthesis to study the dynamic performance of assembled structures with a frictional interface. A generalized Masing model is introduced to describe the frictional mechanism in steady state to enable obtaining the harmonic components of the friction force. By employing the concept of nonlinear modes based on normal form theory, a reduction technique based on branch modes can be applied to obtain a reduced order model. Both complex nonlinear modes and real nonlinear modes depending on the modal amplitude are used in the nonlinear modal synthesis approach, leading to a particular damping term representing energy dissipation due to friction. The implementation of the nonlinear modal synthesis combined with the generalized Masing model provides a simple, fast and efficient numerical method for describing the nonlinear performance of structures with dry friction devices. The proposed approach is applied to three increasingly complex case studies. Numerical simulations are carried out to demonstrate the efficiency and reliability of the method.

Cyclic response of low yielding connections using different friction materials

The experimental activity presented in this work intends to study in detail the cyclic behaviour of a set of three different friction shims preliminary selected in a previous experimental work regarding the behaviour of friction dampers of Sliding Hinge Joints (SHJs). These connections are able to dissipate seismic energy by means of friction through a proper application of capacity design principles. Their bending resistance is proportional to the slip resistance of a friction device which is usually installed at the bottom beam flange and can be governed controlling only two parameters: the friction coefficient and the clamping force of the high strength bolts.The main goal of the experimental campaign presented is to investigate the dependence of the friction coefficient on some of possible significant parameters. In particular, the 51 tests presented are devoted to evaluate the response of the interfaces taking into account the effect of the bolts preloading, the effect of the type of washers and the influence of the random material variability. In detail, the tests have been carried out with four different configurations of washers (with flat washers and disk springs), considering a possible range of values of the clamping forces (between 40% and 100% of the standard proof preload). The results of the experimental activity are reported in the paper proposing a possible definition of the values of the friction coefficients to be used in design and regression analyses of the experimental data of the slip tests to be used in simplified rigid-plastic modelling for seismic analyses.

A lattice‐shaped friction device and its performance in weak‐story prevention

SummaryDisplacement‐dependent dampers with relatively low post‐yielding stiffness exhibits abrupt stiffness loss and can even induce notable damage concentrations under strong vibrations. A lattice‐shaped friction unit (LSFU) composed of steel strips and friction discs is proposed and it can dissipate most input energy through translational friction and rotational friction and provide post‐yielding stiffness through the axial strength of vertical strips. Measurements of the friction coefficient and torque coefficient ratio and quasi‐static analysis of the LSFU are conducted, the results indicate that the ratio rises first and then drops to a constant value. Under cyclic loading, the two friction mechanisms could work together effectively and the contribution of each component contained in the restoring force could be controlled by adjusting design parameters of the LSFU; the assembly accuracy of the components affect the resistance of vertical strips. The experiment results of two specimens are compared with those obtained from the developed formulas and numerical simulations. A design procedure and applicable style are proposed. Nonlinear seismic response analysis results show that these devices can reduce the displacement response effectively under small and moderate earthquakes and can also prevent concentrated damage and weak‐story occurrence in the structure relative to friction‐damped brace frame in strong earthquakes.

Semi-active phase control of tuned mass dampers for translational and torsional vibration mitigation of structures

The present study aims at demonstrating the feasibility of semi-active phase control of tuned mass dampers (TMDs) implemented in structures for simultaneous reduction in translational and torsional vibration. The semi-active phase control, which employs a semi-active friction device, applies the friction force at certain situations to adjust the TMD phase back to the 90° phase lag. Thus, the phase control tuned mass dampers (PC-TMDs) can develop the best power flow to reduce the structural vibration. In this paper, a complete phase control algorithm is proposed by considering a full range of phase differences. The proposed PC-TMDs not only improve the control performance but also prevent the TMD power from flowing back to the main structure. Furthermore, conventional suspension-type TMDs have only one tuning frequency and exhibit a potential off-tuning issue, lacking an ability to simultaneously suppress the structural translational and torsional vibration. The feasibility of application of the PC-TMDs is verified through various numerical simulations, and a practical mechanism for the PC-TMDs is introduced. The simulation results reveal the robustness of the PC-TMDs, particularly when the PC-TMDs are de-tuned to the structure. Therefore, the PC-TMDs outperform the conventional TMDs in terms of suppressing the structural responses in all the translational and torsional directions.

Comparison Between Different Design Strategies For Freedam Frames: Push-Overs and Ida Analyses

Background:Modern seismic code design rules are known to be based on capacity design principles. They try to assure the damage to occur in the ductile parts of the structure, such as beam ends while the other have to remain in elastic range. Therefore, in the aftermath of design earthquakes, plastic deformations at member or connection level will imply high repair costs. In the last decades, innovative structural solutions based on the so-called supplementary energy dissipation strategy allow increasing the dissipative capacity of structures through equipping it with special damping devices. In the case of substitution of dissipative zones with dissipative devices the strategy takes the name of substitutive strategy. This is the case of Moment Resisting Frames investigated in this paper, where traditional dissipa-tive zones, are equipped with innovative low damage frictional devices. However, the current version of codes does not provide any rules to design of MRFs equipped with this type of friction joints.Methods:Therefore, this paper reports two design approaches amply investigated and compared. The first one is based on the application of the Beam-to-Column Hierarchy Criterion (BCHC) while the second one exploits the Theory of Plastic Mechanism Control (TPMC). The comparison between them is herein discussed on the basis of the results of nonlinear static and dynamic analyses.Conclusions:Structures equipped with low damage frictional connections show larger drift demand than conventional Moment Resisting Frames. However, differently from traditional structures, the larger displacement demand of MRFs equipped with friction joints does not corre-spond to structural damage, thus allowing the reparability of the structure.

Friction device converts hair frizz to electricity

The same properties that cause hair to become frizzy and flyaway on dry winter days make the material a low-cost choice for generating power (ACS Sustainable Chem. Eng. 2018, DOI: 10.1021/acssuschemeng.8b00136). So-called triboelectric generators convert friction to electricity by capturing energy released when paired surfaces that attract opposite charges move past one another. Recently, researchers have demonstrated that these renewable-energy devices can be incorporated into clothing, walkways, and other familiar objects and thereby power cell phones and other electronics through vibrations and ordinary human motion. A variety of common synthetic materials often serve as the negative side of these circuits. But few positive materials are known. A team led by Jang-Kun Song of Sungkyunkwan University demonstrated that hair readily fills that need. The researchers treated human hair with alkaline ethanol solution, then applied the resulting paste as a micrometer-thick film to indium tin oxide electrodes using various low-tech deposition methods.

Input space dependent controller for civil structures exposed to multi-hazard excitations

A challenge in the control of civil structures exposed to multiple types of hazards is in the tuning of control parameters to ensure a prescribed level of performance under substantially different excitation dynamics, which could be considered as largely uncertain. A solution is to leverage data driven control algorithms, which, in their adaptive formulation, can self-tune to uncertain environments. The authors have recently proposed a new type of data-driven controller, termed input space dependent controller (ISDC), that has the particularity to adapt its input space in real-time to identify key measurements that represent the essential dynamics of the system. Previous studies have focused on time delay formulations, where the adaptive control rule would use time delayed measurements as inputs. In this configuration, termed variable multi-delay controller (VMDC), the time delay itself was adaptive, which provided the input space dependence capabilities. However, the size, or embedding dimension, of the input space was kept constant. In this paper, the authors formulate and study a strategy to also have the embedding dimension vary, therefore providing full adaptive input space capabilities. This generalization of the ISDC algorithm will allow the controller to adapt to excitations with higher levels of chaos, such as a seismic event. The performance of ISDC under multi-hazard excitations is first investigated on a single-degree-of-freedom system and compared with the previously developed and demonstrated VMDC. Results show that the adaptive embedding dimension provides significantly enhanced mitigation performance. After, the ISDC performance is assessed on two benchmark buildings equipped with a semi-active friction device and subjected to non-simultaneous multi-hazard excitations (wind, blast and earthquake). Results are compared with a sliding mode controller, where the ISDC is shown to provide better mitigation capabilities.

Seismic Design, Analysis and Testing of a Friction Steel Braced Frame System for Multi-Storey Buildings in Vancouver

This article describes the application of the Friction Braced Frames (FBF) system for 4-and 10-storey buildings located in Vancouver, BC, in Canada. The FBF is coupled with a secondary moment resisting frame that provides back-up elastic stiffness and re-centring capacity that contribute to reduce storey drifts and more evenly distribute seismic energy dissipation over the frame height. In this study, the energy dissipation components consist of Pall friction devices and the system was designed using a conventional force-based method. The moment frame was proportioned to remain essentially elastic under the design seismic displacements. The seismic response of the system is examined through nonlinear response history dynamic analysis. An exhaustive test program was developed to verify the capacity of the system to sustain the anticipated seismic demand. Full-scale testing was performed on brace sub-assemblages and individual brace specimens equipped with friction elements. The experimental program included full-scale dynamic testing under real-time seismic displacement histories as obtained from response history analysis. The numerical simulations and test program showed that the dual FBF system represents an effective system for enhanced seismic response of multi-storey building applications in high seismic regions.

Report on the seismic performance of three-dimensional moment-resisting timber frames with frictional damping in beam-to-column connections

The seismic performance of three-dimensional moment-resisting timber frames with frictional damping devices was investigated experimentally. This article describes a novel three-dimensional beam-to-column connection which was designed to behave rigidly up to moderate seismic intensities and to start the frictional dissipating behavior at higher intensities. The three-dimensional beam-to-column connection component was initially tested under cyclic loading, and then the connection was mounted in a three-level prototype frame and tested on a shake table. From the cyclic loading tests, the energy dissipation of the proposed beam-to-column connection was higher than the equivalent rigid connection. The frame demonstrated self-aligning capabilities without permanent drift at seismic intensities up to 1.4 g and maintained strength up to high seismic intensities of 2 g. Because wood frames allow for large elastic deflections and can exhibit excellent self-aligning capabilities ( i.e., connections tolerate large rotations within safe stress levels), the proposed frictional beam-to-column connection is a promising alternative for moment-resisting timber frames that can be used to prevent structural members from reaching critical stresses.

Seismic design and assessment of steel frames with visco-plastic dampers

This paper evaluates the seismic performance of steel frames with visco-plastic dampers. The visco-plastic damper is realised by the in-series combination of a viscoelastic damper and a friction device. Its main goal is the reduction of storey drifts without significantly increasing the base shear force. A prototype steel building is designed as a high ductility steel moment-resisting frame (MRF). The MRF is then equipped with viscoelastic or visco-plastic dampers to achieve high seismic performance. Parametric designs of visco-plastic dampers with different activation forces for their friction devices are carried out. Nonlinear dynamic analyses for a set of 20 earthquake ground motions scaled to the design and maximum considered earthquake (MCE) intensities are carried out in OpenSees. Moreover, incremental dynamic analyses (IDA) up to collapse are conducted. The response results highlight the effectiveness of the visco-plastic damper to control drifts, residual drifts, and the base shear force, while also providing an adequate seismic collapse resistance.