Pure Friction Research Articles

Planar clamping anchorage for CFRP plate: Experimental research, friction-adhesion synergistic mechanism and theoretical model

Carbon fiber-reinforced polymer (CFRP) is an anisotropic material, which poses great challenge to its anchorage. In this paper, the performance of a planar clamping anchorage (PCA) for single-layer CFRP plate cable was investigated through the static tensile test. Influencing parameters included interface treatment form, clamping stress, and anchor length. Two interfacial treatment forms were considered: pure friction and friction-adhesion action. Furthermore, the bearing capacity calculation method of friction-adhesion coupling anchor was developed based on the analysis of the process of adhesion and friction. The results indicate that friction-adhesion coupling action significantly improved the anchor bearing capacity compared to pure friction, and the rate of increase in ultimate load displayed a decreasing trend as the clamping stress increased. Additionally, the error between the theoretical and experimental values of anchor bearing capacity for specimens with friction-adhesion coupling anchor was generally within approximately ±10 %.

Study on tribocorrosion properties of cold spray additively manufactured 2024 Al alloy

This study was conducted with a high level of thoroughness. X-ray diffraction (XRD), Scanning Electron Microscope (SEM), and Transmission Electron Microscope (TEM) were used to analyze the phase composition and microstructure of the AM-2024Al and the RO-2024Al. The hardness and porosity of the AM-2024Al, as well as the bonding strength between AM-2024Al and RO-2024Al, were also investigated. Furthermore, the corrosion and tribocorrosion properties and failure mechanisms of the AM-2024Al and the RO-2024Al were systematically and thoroughly compared and analyzed. The results of this comprehensive study revealed that the AM-2024Al displayed a similar phase structure and higher hardness in comparison to the RO-2024Al, and the AM-2024Al was compact and tightly bound to the RO-2024Al with a bonding strength of over 55.5 MPa. Furthermore, the AM-2024Al exhibited better corrosion resistance under PDP (potentiodynamic polarization) corrosion and similar wet sliding wear resistance under an approximate pure friction process (OCP corrosion, namely open circuit potential corrosion) and tribocorrosion compared with the RO-2024Al. These findings provide a high level of confidence in the potential of cold spraying additive manufacture 2024Al as a reliable way to repair damaged RO-2024Al.

Three-Stage Analysis Method for Calculating the Settlement of Large-Diameter Extralong Piles

In terms of safety, large-diameter extralong piles require highly accurate settlement prediction because of their high load-bearing capacity. According to the bearing mechanism of the large-diameter extralong pile, in this paper, a novel and scientifically accurate three-stage analysis method is proposed for predicting pile settlement based on Randolph’s study of pile forces in homogeneous soils, in view of the limitation that the accuracy of the conventional settlement calculation method is only applicable to the pile in the end-bearing frictional bearing condition. The three-stage analysis method fully considers the deformation characteristics of the pile in three different bearing states: pure friction bearing stage, end-bearing friction bearing stage, and damage stage. The critical load of TP4-1 in this paper is 9620.89 kN, and the ultimate compressive bearing capacity is 19279.09 kN, as calculated using the three-stage analysis method, and thus the three bearing states are clearly defined. The settlement under all levels of load obtained using this method can be very close to the real-case settlement, and the maximum error of the TP4-1 pile is only 0.52 mm, as observed by numerical simulation, static load test of TP4-1, and experiments on the other three test piles.

3D numerical characterization of a dissipative connection system for retrofit of prefabricated existing RC sheds

Prefabricated industrial sheds featured a high seismic vulnerability during the 2012 Emilia earthquake (Italy). The buildings typically exhibited a rigid collapse mechanism that was a consequence of the loss of support between columns, beams and roof elements.The study presents a numerical characterization of a novel dissipative connection system (DCS) designed to improve the seismic performance of industrial sheds. The device, which is placed on the top of the columns, exploits the movement of a rigid body on a sloped surface to provide horizontal stiffness and control the lateral displacement of the beam.A 3D finite element model of the prototype is formulated in Abaqus and used to switch the backbone curve from the scaled model to the full-scale device. A parametric study is conducted to evaluate the influence of the slope of the contact surface and the coefficient of friction on the output force of the system.In the second part of the study, non-linear dynamic analyses are performed on a finite element model of a portal frame implementing, at beam-column joints, either the DCS or a pure friction connection. The results highlight the effectiveness of the DCS in controlling beam-to-column displacements, reducing shear forces on the top of columns, and limiting residual displacements that can accrue during ground motion sequences.

The relationship between adhesion morphology and cutting force in orthogonal cutting of 6061-T6 aluminum alloy

Due to the sticky and soft characteristics of aluminum alloy, it is easy to form adhesion on the tool rake face during cutting process. In this work, the orthogonal cutting tests for 6061-T6 aluminum were carried out at cutting speeds of 20–300 m/min and feed rates of 0.05–0.3 mm, and the relationship between adhesion and cutting force has been explored. A slip-line model was used to separate the edge force of cutting edge to obtain the pure friction force of tool rake face, thereby obtaining the average friction coefficient. Adhesion morphologies were observed under the scanning electron microscope (SEM) and compared with the average friction coefficients. It was found that different adhesion morphologies correspond to different friction coefficient ranges. Simultaneously, the relationship between the temperature and normal stress on the tool rake face and the adhesion morphology and friction coefficient was investigated. The results showed that the temperature is the major factor of adhesion evolution and friction coefficient change. Combining the tool rake face temperature and the adhesion morphology, it was noted that the reduction of the friction coefficient is not only owing to the self-lubrication caused by thermal softening, but also due to the decrease of the total shear force caused by the incomplete contact. Finally, the relationship between the friction coefficient of tool rake face and the cutting force and specific cutting energy was discussed, with the conclusion that the friction coefficient has an impact on the cutting force and specific cutting energy by changing the shear angle.

Adaptive LuGre Friction Compensation for Servo System Based on Backstepping Control and Feedforward Control

Aims: The study aims to improve the position control accuracy of a class of permanent magnet synchronous motors under friction. Background: Permanent magnet synchronous motor and servo system are important parts of modern industry, in which the friction effect is a typical nonlinear factor. To overcome the nonlinear friction effect, it is necessary to design a compound feedforward algorithm to improve the motion control accuracy. Objective: The objective of the study is to design a compound adaptive friction feedforward controller to overcome the nonlinear friction effect in the servo system while ensuring tracking accuracy. Methods: A compound algorithm combining velocity-acceleration double feedforward and adaptive friction feedforward is proposed to ensure the control accuracy, and then the backstepping control is used to ensure strict convergence. Finally, the friction parameter observer is used to estimate the parameters, and the performance of the control system is simulated in the Simulink module Results: Compared to Pure Friction Feedforward Compensation (PFFC) and Adaptive Friction Compensation (AFC), Adaptive Backstepping Feedforward Friction Compensation (ABFFC) has a faster convergence speed, higher steady-state accuracy, and less friction nonlinear effect Conclusion: The servo system with adaptive backstepping and feedforward friction compensation improves the accuracy and convergence of control performance. Moreover, the adaptive permanent magnet synchronous motor control system can effectively overcome the nonlinear friction effect.

Sliding Isolation Systems: Historical Review, Modeling Techniques, and the Contemporary Trends

Base isolation techniques have emerged as the most effective seismic damage mitigation strategies. Several types of aseismic devices for base isolation have been invented, studied, and used. Out of several isolation systems, sliding isolation systems are popular due to their operational simplicity and ease of manufacturing. This article discusses the historical development of passive sliding isolation systems, such as pure friction systems, friction pendulum systems, and isolators with other sliding surface geometries. Moreover, multiple surface isolation systems and their behavior as well as the effectiveness of using complementary devices with standalone passive isolation devices are examined. Furthermore, the article explored the various modeling techniques adopted for base-isolated single and multi-degree freedom building structures. Special attention has been given to the techniques available for modeling the complex phenomena of sliding and non-sliding phases of sliding bearings. The discussion is further extended to the development in the contemporary areas of seismic isolation, such as active and hybrid isolation systems. Although a significant amount of research is carried out in the area of active and hybrid isolation systems, the passive sliding isolation system still has not lost its appeal due to its ease of adaptability to the structures.

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.

Seismic analysis of liquid storage tank using oblate spheroid base isolation system based on rolling friction

The seismic isolation of ground-supported cylindrical liquid storage tank using the newly developed oblate spheroid base isolation (OSBI) system is investigated. The OSBI is an ellipsoidal-shaped isolator in both of its horizontal axes and dissipates seismic input energy in rolling friction apart from period lengthening achieved through the oblateness. The detailed mathematical formulation and governing dynamical equations of motion for a tank mounted on the non-linear OSBI are derived and analyzed using the numerical integration technique to unravel the underlying mechanics behind its dynamic behavior. An idealized mechanical model of the tank consists of three-lumped masses: convective, impulsive, and rigid. The dynamic responses are investigated for the tank subjected to uni-directional sinusoidal harmonic motion as well as to five time-varying, bi-directional horizontal components of earthquakes. The seismic response of the liquid storage tanks with the OSBI system is compared with that of the same tank either isolated using pure-friction (P-F) system or kept non-isolated. In order to understand the dynamic behavior of the tank mounted on the OSBI system, the influence of different isolator parameters such as eccentricity, coefficient of rolling friction, and aspect ratio of the tank are studied. The energy responses are also evaluated to assess the performance of the OSBI system. From the present study, it is found that the OSBI system is effective in mitigating the seismic response in the liquid storage tanks.

Seismic assessment of existing precast RC industrial buildings in Portugal

Precast reinforced concrete (PRC) buildings are common on European industrial parks. In past earthquakes, namely in Italy and Turkey, this typology of buildings showed a poor performance, namely at structural level. One of the major concerns at structural level regards the connection between the beams and columns. Two types of beam-to-column connections are more common in this type of buildings: the pure friction and a mechanical one including steel dowels. The seismic performance of six existent Portuguese PRC buildings built with these two solutions are analyzed considering nonlinear static and dynamic analyses addressing both global (columns) and local (connections) response parameters. The seismic assessment in view of the regulation for existing buildings (Eurocode 8 –Part 3) showed that, overall, this typology of buildings, present an acceptable structural performance. Nonetheless, unsatisfactory performance was observed at the beam-to-column connection in one of the buildings built without steel dowels. In terms of non-structural performance, namely in terms of the cladding elements, a poor performance is foreseen, for regions of moderate to high seismic action, regardless of the period of construction of the building.

Cyclic behaviour of precast beam‐to‐column connections with low seismic detailing

AbstractBeam‐to‐column connections are a crucial element in industrial precast reinforced concrete (PRC) buildings. They are also the source of several damages reported after recent earthquakes. This typology of buildings is very common both in the Portuguese industrial park and throughout Europe. In order to have a better knowledge of the connection behaviour an extensive experimental work was done and it is here presented to characterize, under cyclic loading, the pure friction behaviour and friction and dowel beam–to–column behaviour. The research was focused on the parameters that might influence the seismic performance of the connections. These are the friction between elements, the absence or presence of dowels and their position on the column's corbel, and finally the different axial load level applied on the connections. The results presented in this study pointed to the importance of using neoprene pad between concrete faces, with the main objective of damage control. The use of mechanical connectors (dowels) was also highlighted as a source of increasing the strength of the beam–to–column connection in values greater than 50%.

Experimental and Numerical Investigation of a Dissipative Connection for the Seismic Retrofit of Precast RC Industrial Sheds

Past earthquakes have highlighted the seismic vulnerability of prefabricated industrial sheds typical of past Italian building practices. Such buildings typically exhibited rigid collapse mechanisms due to the absence of rigid links between columns, beams, and roof elements. This study aims at presenting the experimental and numerical assessment of a novel dissipative connection system (DCS) designed to improve the seismic performance of prefabricated sheds. The device, which is placed on the top of columns, exploits the movement of a rigid slider on a sloped surface to dissipate seismic energy and control the lateral displacement of the beam, and to provide a recentering effect at the end of the earthquake. The backbone curve of the DCS, and the effect of vertical load, sliding velocity, and number of cycles were assessed in experimental tests conducted on a scaled prototype, according to a test protocol designed accounting for similarity requirements. In the second part of the study, non-linear dynamic analyses were performed on a finite element model of a portal frame implementing, at beam-column joints, either the DCS or a pure friction connection. The results highlighted the effectiveness of the DCS in controlling beam-to-column displacements, reducing shear forces on the top of columns, and limiting residual displacements that can accrue during ground motion sequences.

Simulating the model for consolidation of short bored pile in pure friction soil media

Simulating the model for consolidation of short bored pile in pure friction soil media

Simulating the model for consolidation of short bored pile in pure friction soil media

In this paper, the analysis of a numerical study for consolidation analysis of short bored pile subjected to axial loads is presented. An analysis of short-bored pile is performed using finite element analysis software Abaqus CAE with the base of procured experimental data in sand media and a comparative analysis on Ansys FEA. Three models in combination of pile and footing system were developed by the application of incremental axial load for which the displacement upon each load was analyzed taking in consideration the stresses and strains. A parametric study was conducted to study the effect of load on and it’s observed displacement on the pile with or without footing. A close correlation is found between the results obtained by the FE models and the Experimental Model solution. The results indicates that the load bearing capacity of pile–footing system increases drastically when both acts together instead of acting individually.

Errors of structural seismic responses caused by frequency filtering based on seismic wave synthesis

In order to meet the requirements of shake tables, frequency filtration of seismic input is usually performed before tests. Aiming to study the error of seismic analysis caused by filtering, the artificial seismic waves before and after filtering with four different waveforms were synthesized in this paper. Based on a spring-friction isolation system, the effects of filtering on seismic responses with various spring constants, friction coefficients and envelope functions were investigated. The results show that the maximum acceleration of the pure friction system is not affected by filtering while the error of maximum relative displacement caused by filtering can reach 60% and decreases with the increment of the friction coefficient. For the spring-friction system, the friction coefficient corresponding to a smaller structural seismic response is exactly the most unfavorable friction coefficient for filtering error and hence needs more attention during shaking table tests. Filtering errors based on different waveforms have the same tendency despite some slight differences owing to the different responses.

Experimental and numerical investigation of carbon textile/cementitious matrix interfacebehaviourfrom pull-out tests

In the context of the application of textile-reinforced concrete composite (TRC) for strengthening or reinforcing of structural elements, an important factor that significantly influences its mechanical behaviour is the bond strength of the textile/cementitious matrix interface. In order to improve this bond, reinforcement textile is usually treated with different products in the manufacturing procedure. This paper presents the experimental and numerical results concerning the mechanical behaviour of carbon textile/cementitious matrix interface from the pull-out tests. The carbon textile was treated with an amorphous silica product to improve the bond with the cementitious matrix and embedded in the cementitious matrix with different lengths. The experimental results showed that all pull-out tests gave typical “force – slip” curves of interface behaviour as shown in the literature with three phases: perfect bonding phase, debonding phase, and pure friction phase. The effects of carbon textile and embedded length on pull-out behaviour and failure mode of textile/matrix interface specimens could be found and analyzed. Concerning the mesoscale modeling work, the numerical model was developed and validated by using a nonlinear spring model for interface behaviour and taking into account the crack damage of the cementitious matrix in the calculation. The numerical results highlighted that the numerical model could predict the relationship of pull-out force and slip for all cases of the embedded length of carbon textiles within the cementitious matrix. This paper shows that both experimental and numerical results on the carbon textile/cementitious matrix interface has a good agreement in pull-out behaviour and failure mode.

Multihazard Response Control of Base-Isolated Buildings under Bidirectional Dynamic Excitation

The issues of safety and posthazard functionality of structures under multihazard scenarios are some of the significant challenges in the current dynamic and rapidly growing urban environment. In this paper, multistory base-isolated buildings are investigated under the independent multihazard scenario of earthquake and blast-induced ground motion (BIGM). Multistory building models equipped with five different types of isolation systems, namely, the laminated rubber bearing (LRB), lead-rubber bearing (N-Z system), pure friction (PF) system, friction pendulum system (FPS), and resilient-friction base isolator (R-FBI) are assessed under bidirectional multihazard excitations. The suitability of the isolation systems and their key parameters in protecting multistory buildings is evaluated. Furthermore, the influence of the superstructure characteristics, such as the superstructure damping and the number of stories, is also assessed. The effect of bidirectional hazards on fixed-base buildings is also presented for comparison. The key response quantities of base-isolated buildings are presented and compared for different isolation systems. Parametric investigations are also conducted, and the trends of the response quantities are presented to study the influence of important parameters of isolation systems in protecting the buildings under the multihazard scenario of earthquake and BIGM. The results of the investigation show that the behaviors of the buildings equipped with various isolation systems are different for the two hazards. Moreover, the influences of the key parameters of the isolation systems are found to be different for various hazards. Therefore, the selection of design parameters of isolation systems shall be made with due consideration of the influence of multiple hazards. Additionally, the influence of the properties of the superstructure, such as the number of stories and the damping of the superstructure, on the behavior of the base-isolated buildings under the multihazard loading, is presented.

Optimal reliability design of pure friction isolators using asymptotic sampling

Probabilistic methods are widely being used in structural design due to the vital effects on the structural safety prediction. In the present study, reliability-based analysis of a shear frame supported on pure friction base isolators equipped with a restoring device is performed and changing of friction coefficient of the base isolator, the mass of the base raft ratio and the damping ratio of the restoring device are investigated. The earthquake herein is treated as a non-stationary random process. The probability of failure is computed using first-passage probability which is determined utilizing a new sampling technique called asymptotic sampling. This study introduces the safe range for each variable on the design space based on reliability indices. The assessment is done for different circumstances in which there are one determined variable and two uncertain. In each circumstance, a Pareto-type optimization is done in order to achieve the optimum design variables. Finally, a total optimization is done for all three design variables to determine the optimum values. Moreover, the reliability analysis of the isolated frame without a restoring device is conducted to show the substantial impact of adding the restoring device to the isolator by achieving considerably higher safety indices.

A Comparative Study on Effectiveness of Using Horasan Mortar as a Pure Friction Sliding Interface Material

In this study, the possibility to use Horasan mortar as a sliding interface material for pure friction aseismic isolation system is investigated. Both experimental and numerical studies are conducted to examine the effectiveness of using this material in structural isolation systems of buildings with no overturning moment, as it has shown some attractive experiences in time based on the existing related literature. Responses of four storey lightweight building are numerically investigated by finite element modelling in MATLAB; whereas the University Consortium on Instructional Shake Table (UCIST) is used to study the responses of the same building during experimental works. Comparison of both studies is shown to be in a good agreement in terms of resulting structural response accelerations, velocity and displacements. Approximately 28 - 31 % reduction of base floor acceleration is achieved; and the maximum sliding velocity and displacement are found to lie between 0.33-0.45 m/sec and 0.0353-0.0559 m respectively; which fall within the recommended standards’ limits. As a result, these findings demonstrate the effectiveness of using Horasan mortar as friction interface material which has additionally gained experience in more than ten centuries.

A Comparative Study on Effectiveness of Using Horasan Mortar as a Pure Friction Sliding Interface Material

In this study, the possibility to use Horasan mortar as a sliding interface material for pure friction aseismic isolation system is investigated. Both experimental and numerical studies are conducted to examine the effectiveness of using this material in structural isolation systems of buildings with no overturning moment, as it has shown some attractive experiences in time based on the existing related literature. Responses of four storey lightweight building are numerically investigated by finite element modelling in MATLAB; whereas the University Consortium on Instructional Shake Table (UCIST) is used to study the responses of the same building during experimental works. Comparison of both studies is shown to be in a good agreement in terms of resulting structural response accelerations, velocity and displacements. Approximately 28 - 31 % reduction of base floor acceleration is achieved; and the maximum sliding velocity and displacement are found to lie between 0.33-0.45 m/sec and 0.0353-0.0559 m respectively; which fall within the recommended standards’ limits. As a result, these findings demonstrate the effectiveness of using Horasan mortar as friction interface material which has additionally gained experience in more than ten centuries.