• Tribology and Lubricants
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• 제24권6호
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• pp.378-385
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• 2008

In foil bearings, the friction between bumps and their mating surfaces is the major factor which exerts great influence on the bearing performance. From this point of view, many efforts have been made to improve the understanding of the influence of the friction on the foil bearing performance by developing a number of analytical models. However, most of them did not consider the hysteretic behavior of the foil structure resulting from the friction. The present work developed the static structural model in which hysteretic behavior of the friction was considered. The foil structure was modeled using finite element method and the algorithm which determines the conditions of the contact nodes and the directions of the friction forces was used to take into account the friction. The developed model was integrated into the foil bearing prediction code to investigate the effects of the friction on the static performance of the bearing. The results of analysis show that multiple static equilibrium positions are presented for the one static load under the influence of the friction, inferring its great effects on the dynamic performance. However, the effect of friction on the minimum film thickness which determines load capacity of the bearing is negligible.

• Earthquakes and Structures
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• 제7권4호
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• pp.511-525
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• 2014

The main object of this study is to determine and compare the structural behavior of base isolated long span highway bridge, $G\ddot{u}lburnu$ Highway Bridge, using single concave friction pendulum (SCFP) and triple concave friction pendulum (TCFP). The bridge is seismically isolated in the design phase to increase the main period and reduce the horizontal forces with moments using SCFP bearings. In the content of the paper, firstly three dimensional finite element model (FEM) of the bridge is constituted using project drawings by SAP2000 software. The dynamic characteristics such as natural frequencies and periods, and the structural response such as displacements, axial forces, shear forces and torsional moments are attained from the modal and dynamic analyses. After, FEM of the bridge is updated using TCFP and the analyses are performed. At the end of the study, the dynamic characteristics and internal forces are compared with each other to extract the TCFP effect. To emphasize the base isolation effect, the non-isolated structural analysis results are added to graphics. The predominant frequencies of bridge non-isolated, isolated with SCFP and isolated with TCFP conditions decreased from 0.849Hz to 0.497Hz and 0.338Hz, respectively. The maximum vertical displacements are obtained as 57cm, 54cm and 44cm for non-isolated, isolated with SCFP and isolated with TCFP conditions, respectively. The maximum vertical displacement reduction between isolated with TCFP bearing and isolated with SCFP bearing bridge is %23. Maximum axial forces are obtained as 60619kN, 18728kN and 7382kN, maximum shear forces are obtained as 23408kN, 17913kN and 16249kN and maximum torsional moments are obtained as 24020kNm, 7619kNm and 3840kNm for non-isolated, isolated with SCFP and isolated with TCFP conditions, respectively.

• 한국소음진동공학회논문집
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• 제17권9호
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• pp.862-873
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• 2007

Energy dissipation devices can be considered as an alternative for the seismic performance enhancement of existing structures based on the strengthened seismic design code. In this study, seismic response mitigation effects of friction dampers are investigated through the shaking table test of a full scale 3 story building structure. Frist, the bilinear force-displacement relationship of a structure-brace-friction damper system and the effect of brace-friction damper on the increase of frequency and damping ratio are identified. Second, frequency, displacement, and torque dependent characteristics of the friction damper are investigated by using harmonic load excitation tests. Finally, the shaking table tests are performed for a full scale 3 story steel frame. System identification results using random signal excitation indicated that brace-friction damper increased structural damping ratio and frequency, and El Centro earthquake test showed that brace-friction damper reduced the peak displacement and acceleration significantly. In particular, it was observed that the damping effect due to friction damper becomed obvious when the structure was excited by more intensive load causing frequent slippage of the friction dampers.

• Steel and Composite Structures
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• 제44권4호
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• pp.569-586
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• 2022

This study introduces a novel friction damper as a component of a recentering frame connection, to solve the problem of structural repair costs, caused by stiffness deterioration and brittle fracture of the central brace frame (CBF). The proposed damper consists of shape memory alloy (SMA) bars with pretension applied to them to improve the stability. SMAs reduce the residual displacement by virtue of the properties of the materials themselves; in addition, a pretension can be applied to partially improve their energy dissipation capacity. The damper also consists of a friction device equipped with friction bolts for increased energy dissipation. Therefore, a study was conducted on the effects of the friction device as well as the pretension forces on the friction damper. For performance verification, 12 cases were studied and analyzed using ABAQUS program. In addition, the friction and pretension forces were used as variables in each case, and the results were compared. As a result, when the pretension and friction force are increased, the energy dissipation capacity gradually increases by up to about 94% and the recentering capacity decreases by up to about 55%. Therefore, it has been shown that SMA bars with adequate pretension in combination with bolts with adequate frictional force effectively reduce residual deformation and increase damper capacity. Thus, this study has successfully proposed a novel friction damper with excellent performance in terms of recentering and energy dissipation capacity.

• 대한기계학회논문집
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• 제7권1호
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• pp.52-63
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• 1983

The purpose of the study is to find development of contact area, contact pressure and friction forces occurring at joints or connection areas inbetween structural members or mechanical parts. The problem has a pair of difficulties intrinsically; a constraint of displacement due to contact, and presence of work term by nonconservative friction force in the variational principle of the problem. Because of these difficulties, the variational principle remains in the form of inequality. It is resolved by penalty method and perturbation method making the inequality to an equality which is proper for computational purposes. A contact problem without friction is solved to find contact area and contact pressure, which are to be used as data for the analysis of the friction problem using perturbed variational principle. For numerical experiments, a Hertz problem, a rigid punch problem, and the latter one with friction effects are solved using $Q_2$-finite elements.

• Structural Engineering and Mechanics
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• 제4권3호
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• pp.313-329
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• 1996

A mathematical model of a cable as a system of interacting wires with interwire friction taken into account is presented in this paper. The effect of friction forces and the interwire slip on the mechanical properties of tension cables is investigated. It is shown that the slip occurs due to the twisting and bending deformations of wires, and it occurs in the form of micro-slips at the contact patches and macro-slips along the cable. The latter slipping starts near the terminals and propagates towards the middle of the cable with the increase of tension, and its propagation is proportional to the load. As the result of dry friction, the load-elongation characteristics of the cable become quadratic. The energy losses during the extension are shown to be proportional to the cube of the load and in inverse proportion to the friction force, a result qualitatively similar to that for lap joints. Presented examples show that the model is in qualitative agreement with the known experimental data.

• Journal of Welding and Joining
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• 제16권2호
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• pp.57-63
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• 1998

This study deals with the friction weldability of machine structural carbon steel (SM45C) to Al-Mg-Si aluminium alloy (A6063). The bonding strength of friction welded joints, from all mechanical test, exceeded that of A6063 base metal, under the condition of friction time 1.5 sec, upset pressure 80MPa. The friction welded joints under these conditions exhibited tensile strength of 262MPa, bending angle of 90$^{\circ}$ without crack at weld interface and shear strength of 113MPa. Consequently, the friction weldability of SM4C to A6063 was very excellent, and that was possible without special preparation of weld surfaces.

• Computers and Concrete
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• 제24권1호
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• pp.51-61
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• 2019

Compressive ability is one of the most important mechanical properties of concrete material. The compressive failure process of concrete is pretty complex with internal tension, shear damage and friction between cracks. To simulate the complex fracture process of concrete at meso level, methodology for meso-structural analysis of concrete specimens is developed; the zero thickness cohesive elements are pre-inserted to simulate the crack initiation and propagation; the constitutive applied in cohesive element is established to describe the mechanism of crack separation, closure and friction behavior between the fracture surfaces. A series of simulations were carried out based on the model proposed in this paper. The results reproduced the main fracture and mechanical feature of concrete under compression condition. The effect of key material parameters, structure size, and aggregate content on the concrete fracture pattern and loading carrying capacities was investigated. It is found that the inner friction coefficient has a significant influence on the compression character of concrete, the compression strength raises linearly with the increase of the inner friction coefficient, and the fracture pattern is sensitive to the mesostructure of concrete.

• Structural Engineering and Mechanics
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• 제77권3호
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• pp.407-416
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• 2021

Seismic isolation is one of the best-advanced methods for controlling seismic vibrations in buildings, bridges and nuclear facilities. A new Friction Multi-Layer Elastomeric Seismic Isolator (FMESI) has been modeled, analyzed and investigated by ABAQUS finite element analysis software and then, compared to real models. A number of friction cores have been used instead of the lead core therefore, some of the previous isolator problems have been almost resolved. Moreover, Studies show that the proposed isolator provides suitable initial stiffness and acceptable hysteresis behavior under different vertical and horizontal loading conditions and also internal stresses in different layers are acceptable. Also, as a result, the initial stiffness and overall area of the curves increase, as friction coefficients of the cores increase, although the frictional coefficients must be within a certain range.

• Structural Engineering and Mechanics
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• 제82권2호
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• pp.205-224
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• 2022

This paper presents a refined finite element formulation for nonlinear static and dynamic analysis of sliding cable structures, overcoming the limitation of the existing approaches that neglect or approximate the friction, pulley dimension, temperature and geometric nonlinearity. A new family of elements with the same framework is proposed, consisting of the cable-pulley (CP) elements considering sliding friction, and the non-sliding cable-pulley (NSCP) elements considering static friction. Thereafter, the complete procedure of static and dynamic analysis using the proposed elements is developed, with the capability of accurately dealing with the friction at each pulley. Several examples are utilized to verify the validity and accuracy of the proposed elements and analysis strategy, and investigate the frictional, thermal and pulley-dimension effects as well. The numerical examples show that the results obtained in this work are in good accordance with the existing works when using the same approximations of friction, pulley dimension and temperature. By avoiding the approximations, the proposed formulation can be effectively adopted in predicting the more precise nonlinear responses of sliding cable structures.