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Nicolae Lobontiu - One of the best experts on this subject based on the ideXlab platform.
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compliance based matrix method for modeling the quasi static response of planar serial flexure hinge mechanisms
Precision Engineering-journal of The International Societies for Precision Engineering and Nanotechnology, 2014Co-Authors: Nicolae LobontiuAbstract:Abstract A matrix method is proposed to model the direct and inverse quasi-static response of constrained/over-constrained planar serial mechanisms with flexure Hinges under bending, axial, and shear planar (three-dimensional) loading and small-deformations. The method uses a basic three-point compliance matrix corresponding to one rigid link and one adjacent flexure hinge that are subjected to one point load. This matrix connects the displacements at a point on the rigid link with the load that is applied at another point on it, and the deformations of the flexure hinge at its distal point. The quasi-static model of planar serial flexure-based mechanisms with multiple links under single/multiple point loading results from linearly superimposing all relevant hinge-link-load triads defined by their three-point matrices. A displacement-amplification planar device with right circularly corner-fileted flexure Hinges is studied using several refinement stages of the matrix method to generate a model whose predictions are confirmed by finite element simulation.
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Out-of-Plane (Diaphragm) Compliances of Circular-Axis Notch Flexible Hinges with Midpoint Radial Symmetry
Mechanics Based Design of Structures and Machines, 2014Co-Authors: Nicolae LobontiuAbstract:A small-displacement analytical model is proposed for the out-of-plane compliances of notch flexure Hinges with circular longitudinal axis and midpoint radial symmetry that function as monolithic joints in flexible mechanisms. The Hinges are constructed from several serially connected segments with small and constant out-of-plane width, variable in-plane thickness, and are subjected to coupled bending and torsion. The six compliances of a symmetric notch hinge are obtained as linear combinations of compliances defining the segments that form one half of the full flexible hinge. The general analytical model is applied to the circular-axis, right circularly corner-filleted hinge design whose compliances are validated by finite element simulation. A comparison is performed between the out-of-plane and the in-plane compliances of this flexure hinge. The right circularly corner-filleted configuration is also compared to the circular-axis, constant-thickness flexure hinge with respect to the out-of-plane static...
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planar compliances of thin circular axis notch flexure Hinges with midpoint radial symmetry
Mechanics Based Design of Structures and Machines, 2013Co-Authors: Nicolae Lobontiu, Matt Cullin, Jeffrey HoffmanAbstract:The new class of flexure Hinges with circular longitudinal axis and midpoint radial symmetry is introduced. Using rotation and mirroring, the symmetric flexure hinge is obtained from one half flexure. The six planar-bending compliances of the full hinge are determined analytically for small deformations by combining only three compliances of the half flexure. To illustrate the general flexure hinge category, the novel circular-axis, right circularly corner-filleted design is introduced. Experimental and finite element results correlate well with the analytical model predictions. The new flexure hinge design is compared to the circular-axis, constant-thickness flexure and the straight-axis, right circularly corner-filleted hinge.
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design of circular cross section corner filleted flexure Hinges for three dimensional compliant mechanisms
Journal of Mechanical Design, 2002Co-Authors: Nicolae Lobontiu, Jeffrey S N PaineAbstract:The paper introduces the circular cross-section corner-filleted flexure Hinges as connectors in three-dimensional compliant mechanism applications. Compliance factors are derived analytically for bending, axial loading and torsion. A circular cross-section corner-filleted flexure hinge belongs to a domain delimited by the cylinder (no fillet) and the right circular cross-section flexure hinge (maximum fillet radius). The analytical model predictions are confirmed by finite element simulation and experimental measurements. The circular cross-section corner-filleted flexure Hinges are characterized in terms of their compliance, precision of rotation and stress levels.
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design of symmetric conic section flexure Hinges based on closed form compliance equations
Mechanism and Machine Theory, 2002Co-Authors: Nicolae Lobontiu, Jeffrey S N Paine, Ephrahim Garcia, Michael GoldfarbAbstract:The paper develops closed-form compliance equations for conic-section (circular, elliptic, parabolic and hyperbolic) flexure Hinges. Finite element simulation results confirm the theoretical formulation data. The main objectives are to predict the deformation/displacement field of a flexure hinge under loading and to assess the precision of rotation for a specific conic flexure hinge. A non-dimensional analysis is carried out to discuss both problems. Conclusions are formulated regarding the performance of circular, elliptic, parabolic, and hyperbolic flexure Hinges.
Saiidi, Mehdi S. - One of the best experts on this subject based on the ideXlab platform.
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Effects of Hinge Restrainers on the Response of the San Gregorio Bridge during the Loma Prieta Earthquake
9999Co-Authors: Maragakis, Emmanuel M., Saiidi, Mehdi S., Feng Shiping, Flournoy LindaAbstract:Report No. CCEER-93-5The primary objective of this study is to study the effects of cable restrainers on the nonlinear seismic response of the San Gregorio Bridge. The computer program NEABS-86 was used in the nonlinear analyses. The earthquake analyses focus on the relative displacements at the Hinges, the restrainer stresses, and the abutment forces in both the longitudinal and the transverse directions of the bridge. The peak ground acceleration of the earthquake input, the seismic retrofit, the restrainer gap, and the hinge gap were varied. It was found that, in general, the cable restrainer system reduces the hinge responses in both the longitudinal and the transverse directions. Also found was that, when a zero restrainer gap is assumed, the hinge responses change significantly. It is recommended that the restrainer design be based on cases with both zero and non-zero restrainer gaps, to encompass all the critical forces, stresses and displacements. Finally, some design methods for the longitudinal restrainer cable at intermediate Hinges of the bridge were evaluated. A modified "Dynamic-Caltrans" design procedure was tested preliminarily, and showed some promising results (Abstract by authors)
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Response of Bridge Hinge Restrainers during Earthquakes -Field Performance, Analysis, and Design
9999Co-Authors: Saiidi, Mehdi S., Maragakis, Emmanuel M., Feng Shiping, Abdel-ghaffar, Saber M., O'connor DanAbstract:Report No. CCEER-93-6This report presents a summary of the important findings of a study aimed at several aspects of the behavior of hinge restrainers used as a seismic retrofit measure. Details of the study are described in five other reports [15 to 19]. The study included field investigations, extensive analytical studies, and an evaluation of the restrainer design method. The objectives of the study were: To review the actual performance of bridge hinge restrainers during the 1989 Loma Prieta earthquake To simulate the earthquake effect on the analytical models of several selected bridges and study their responses To carry out a parametric study of these bridges to determine the effect of stronger earthquakes and the effect of changes in the restrainer gaps To review the restrainer design procedure and recommend any needed refinements A data base of the bridges with hinge restrainers which had been damaged by the 1989 ~Loma Prieta earthquake was formed. Twenty-three bridges were in the data base. The damage reports prepared by Caltrans maintenance Division were reviewed. Three bridges, namely, the Central Viaduct, the Route 580/24/980 Separation, and the Route 92/101 Separation were investigated in the field. Measurements were made of crack widths and patterns, and the condition of the restrainers was examined. An analysis of locally damaged components was subsequently made. The field investigations pointed out the need to consider the performance of the restrainer system and not merely the restrainers. In addition to the restrainers, the system includes (a) the connection between the restrainers and the superstructure including any diaphragms, and (b) the superstructure adjacent to the hinge. The data base of the damaged bridges was also used to select four bridges for detailed nonlinear response history analyses using computer program NEABS-86. The four structures ranged from three to eleven spans. They had different number of Hinges and different substructure characteristics. The earthquake intensity also varied considerably from one bridge to another. Two groups of earthquake analyses were carried out: in one analysis the input acceleration records collected at sites near the bridges were used, and in the other a series of parametric studies with larger peak ground acceleration (PGA) was conducted. The field investigations and the analyses showed that the Loma Prieta earthquake activated the hinge restrainers in the majority of the bridges investigated in this study. Except for a few instances, the restrainers and their supporting systems performed well. It was also noted that bridges with a small ratio of number of Hinges to the number of spans and in which the substructure is relatively stiff, are less likely to be susceptible to support loss. The evaluation of the current Caltrans restrainer design method consisted of two parts: (1) a study of the effect of refinement in the current methods, and (2) a large number of nonlinear analyses of the Caltrans example bridge for different earthquakes, hinge gaps, and the number of restrainers. Based on these studies, a new method for the computation of the relative hinge movement was proposed, and demonstrated for one of the four bridges which had been the subject of detailed nonlinear analyses. It was found that the current Caltrans method for restrainer design leads to a conservative and safe design in terms of the number of restrainers. However, the degree of conservatism for different Hinges is not uniform. It was also determined that a more refined method to compute relative hinge displacements can lead to fewer restrainers even in Hinges with a nominal seat width of 6 in. The refined method would explicitly incorporate the nonlinearity of soil at the footings and abutments, plastic hinging of the columns, and the nonlinearity of the Hinges (Summary by authors)
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Behavior, Design, and Retrofit of Reinforced Concrete One-way Bridge Column Hinges
9999Co-Authors: Jiang Yang, Saiidi, Mehdi S.Abstract:Report No. CCEER-93-1This report describes an experimental and analytical investigation of one-way reinforced concrete Hinges, frequently used at the base of highway bridge columns, when subjected to axial compression, shear, and uniaxial moment transfer in the strong direction. Attempts were made to develop recommendations for more reliable hinged column design, to conduct a preliminary study of the response of hinged columns with inadequate reinforcement development length, and to develop and test a repair method for damaged columns. Many variables, including column aspect ratio, monotonic or cyclic loading, hinge steel arrangement, and hinge thickness relative to hinge width, were examined to study their effects on hinge flexural and shear strength, energy dissipation capacity, shear slip, and hinge throat concrete confinement. A linear finite element analysis was performed to study stress distribution in the hinge throat area. Analytical studies also included inelastic analyses of bridges with hinged columns. Focus was placed on the influence of deck torsional stiffness and abutment spring stiffness on inflection point height. The inflection point represents the point where the lateral load should be applied for the purpose of calculating lateral hinge strength. A new approach was developed for estimating the lateral load strength of hinged columns. This approach can be used for design purpose as well as for calculating the shear capacity for existing hinged pier columns (Abstract by authors)
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Development of a Seismic Design Method for Reinforced Concrete Two-Way Bridge Column Hinges
9999Co-Authors: Cheng Zhiyuan, Saiidi, Mehdi S., Sanders, David H.Abstract:Report No. CCEER-06-01Two-way Hinges are commonly used in bridge columns to reduce column moment transfer to foundation. Currently the shear capacity of two-way Hinges is determined using the shear friction method. When subjected to lateral forces such as earthquake load, Hinges are under a combination of axial load, shear as well as moment. The shear transfer mechanism is different from the assumptions in the standard shear friction theory. However, limited studies are available and no rational code provision for two-way hinge design exists. The main objective of this study was to investigate the performance of two-way Hinges subjected to combine vertical and lateral loads including seismic forces, and to develop a comprehensive and reliable design method for practical application. Five 1/3-scale reinforced concrete bridge column specimens with two-way hinge details were tested under real earthquake motion using shake table. Several major parameters that may affect the hinge and column performance were included in tests, such as the level of axial load, column aspect ratio, column and hinge steel ratio, and the size of Hinges. The test data showed that regardless of the variation of different parameters, the shear capacity of two-way Hinges is much lower than the shear friction theory estimates. A procedure for two-way hinge design including a rational method to determine the shear capacity of the hinge is proposed in this study. The proposed design method produced a close and conservative estimation of the lateral-load strength of two-way Hinges. Additional analytical studies also included push-over analysis, development of a two-way hinge concrete confinement stress-strain relationship, and development of a two-way hinge plastic hinge length model for two-way hinge rotation and gap closure calculation. The proposed hinge shear force-slippage model improved the deflection calculation of the column with two-way hinge detail
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Scale Model Testing of One-Way Reinforced Concrete Pier Hinges Subject to Combined Axial Force, Shear and Flexure
9999Co-Authors: Straw D.l., Saiidi, Mehdi S.Abstract:Report No. CCEER-92-1This report presents the results of the second phase of an ongoing study at the University of Nevada, Reno. This phase involved laboratory and analytical evaluation of one-way reinforced concrete pier Hinges subjected to a combination of uniaxial moment transfer, shear, and axial compression. Four one-sixth scale hinge models were built and tested in the strong direction. There were two primary variables in the testing sequence: shear-span to depth ratio (aspect ratio), and monotonic versus cyclic loading. Analysis of the hinged specimens involved determining flexural and shear strengths, concentrated hinge rotations, and displacement of the column elements. A comparison between the measured and the calculated yield and failure loads is presented for each specimen. Various shear capacity equations and their accuracies are also examined relative to the measured data. Hinge rotation and column deflection consisted of two components: reinforcement bond slippage and plastic deformation. Flexural displacements were determined from the curvature distribution along the column and included elastic deformation of the column and plastic deformation of the hinge. Empirical formulas used to estimate the rotations and displacements are discussed. Results of the testing indicate that cyclic loading reduces the stiffness of the connection substantially and reduces the energy absorbing capabilities of the hinge (Abstract by authors)
Gregory L. Fenves - One of the best experts on this subject based on the ideXlab platform.
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plastic hinge integration methods for force based beam column elements
Journal of Structural Engineering-asce, 2006Co-Authors: Michael H. Scott, Gregory L. FenvesAbstract:A new plastic hinge integration method overcomes the problems with nonobjective response caused by strain-softening behavior in force-based beam-column finite elements. The integration method uses the common concept of a plastic hinge length in a numerically consistent manner. The method, derived from the Gauss-Radau quadrature rule, integrates deformations over specified plastic hinge lengths at the ends of the beam-column element, and it has the desirable property that it reduces to the exact solution for linear problems. Numerical examples show the effect of plastic hinge integration on the response of force-based beam-column elements for both strain-hardening and strain-softening section behavior in the plastic hinge regions. The incorporation of a plastic hinge length in the element integration method ensures objective element and section response, which is important for strain-softening behavior in reinforced concrete structures. Plastic rotations are defined in a consistent manner and clearly related to deformations in the plastic Hinges.
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simplified restrainer design procedure for multiple frame bridges
Earthquake Spectra, 2001Co-Authors: Reginald Desroches, Gregory L. FenvesAbstract:The collapse of existing bridges due to unseating at supports and intermediate (in-span) Hinges with inadequate seat-width can be prevented by the use of restrainers to limit the relative hinge opening. A new simplified procedure for the design of restrainers in bridges accounts for the dynamic characteristics and out-of-phase motion of adjacent frames as well as the inelastic behavior of the bridge. The simplified procedure is developed from an empirical relationship for the restrainer stiffness as a function of the frame stiffnesses, initial hinge displacement, target displacement, and target ductility of the structure. Parameter studies and case studies show that the simplified procedure limits the relative hinge displacement to a designer-specified value.
Omer Soykasap - One of the best experts on this subject based on the ideXlab platform.
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analysis of tape spring Hinges
International Journal of Mechanical Sciences, 2007Co-Authors: Omer SoykasapAbstract:Abstract In this paper, the performance of four different tape spring Hinges are studied. The tape spring Hinges consist of pairs of short-length hardened-steel tape springs side by side but mounted in different ways, and can be used to fold and deploy structural elements on spacecraft. Behaviour of a tape spring subject to two- and three-dimensional folds is investigated by both analytical and non-linear finite element methods. The moment–rotation profiles of the Hinges are obtained experimentally. It is observed that two hinge configurations yield negative moments in their moment–rotation profiles during deployment. The results of finite element analysis are compared with the experimental measurements, and are in good agreement.
Shumin Feng - One of the best experts on this subject based on the ideXlab platform.
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parameters in bridge restrainer design for seismic retrofit
Journal of Structural Engineering-asce, 1996Co-Authors: Mehdi S Saiidi, Emmanuel A Maragakis, Shumin FengAbstract:The primary objective of this study was to determine the effects of changing (1) the cross-sectional area of restrainers; and (2) the restrainer gap on the nonlinear seismic response of a representative bridge with several Hinges. The computer program NEABS-86 was used in the nonlinear analyses. The focus of the study was the relative displacements at the Hinges, restrainer stresses, and abutment forces. The input earthquake, the number of restrainers at each hinge, the restrainer gap, and the hinge gap were varied. It was found that restrainer forces can become critical in cold weather, when the restrainer gap is minimum. It is recommended that the design should be based on cases with and without restrainer gaps to encompass all the critical forces, stresses, and displacements.
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EVALUATION OF THE CURRENT CALTRANS SEISMIC RESTRAINER DESIGN METHOD
1992Co-Authors: Mehdi S Saiidi, Emmanuel A Maragakis, Shumin FengAbstract:The focus of this study was to understand the implications of the current Calif. Department of Transportation (Caltrans) hinge restrainer design procedure. Two aspects were studied. One was the effects of changing the cross sectional area of restrainers and the restrainer gap on the nonlinear response of a bridge with several Hinges. The second was the sensitivity of the number of required restrainers to changes in some of the simplifying assumptions which are made in the current Caltrans restrainer design method. The focus of the nonlinear analyses was the relative displacements at the joints, restrainer forces, and restrainer stresses. The level of ductility demand in the piers was also examined to identify the extent of nonlinearity. Different earthquake records were used for insuring that conclusions reflect the effects of a variety of ground excitations. In addition to the input earthquake, the number of restrainers at each hinge, the restrainer gap, and the hinge gap were also varied. Only longitudinal bridge response was considered to be consistent with the design method. In order to study the effects of design assumptions on the required number of cables, several manual calculations of the design example in the Caltrans restrainer design guidelines were carried out. The deviations from the method included a different treatment of mass and stiffness as different Hinges closed as a result of the earthquakes. Another variable was the simultaneous change in the restrainer and the hinge gaps.
