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Buckling
Kinds of Buckling Terms modified by Buckling Selected AbstractsSeismic performance evaluation of a 34-story steel building retrofitted with response modification elementsEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 6 2009Yuan-Tao Weng Abstract The original structural design of this case study consisted of five basement floors and a 34-story hotel tower in Kaohsiung, Taiwan. The construction started in 1993, and the erection of the entire steel frame and the pouring of concrete slabs up to the 26th floor were completed before 1996. However, construction of the original hotel was subsequently suspended for 10 years. Recently, this building has been retrofitted for residential purposes. Buckling restrained braces (BRBs) and eccentrically braced frames were incorporated into the seismic design of the new residential tower. This paper presents the seismic resisting structural system, seismic design criteria, full-scale test results of one BRB member and the as-built welded moment connections. Test results confirm that the two side web-plate stiffening details can effectively improve the rotational capacity of welded moment connection. The paper also discusses the analytical models for simulating the experimental responses of the BRB members and the welded moment connections. Nonlinear response history analyses (NLRHA) indicate that the inelastic deformational demands of the original and the redesigned structures induced by the maximum considered earthquakes are less than those found in the seismic building codes or laboratory tests. This paper also proposes a ground motion scaling method considering multi-mode effects for NLRHA of the example building. It is shown that the proposed scaling method worked well in reducing the scatter in estimated peak seismic demands. Copyright © 2008 John Wiley & Sons, Ltd. [source] Mechanical Buckling: Mechanics, Metrology, and Stretchable ElectronicsADVANCED FUNCTIONAL MATERIALS, Issue 10 2009Dahl-Young Khang Abstract Mechanical buckling usually means catastrophic failure in structural mechanics systems. However, controlled buckling of thin films on compliant substrates has been used to advantage in diverse fields such as micro-/nanofabrication, optics, bioengineering, and metrology as well as fundamental mechanics studies. In this Feature Article, a mechanical buckling model is presented, which sprang, in part, from the buckling study of high-quality, single-crystalline nanomaterials. To check the mechanical-buckling phenomenon down to the nano-/molecular scale, well-aligned single-walled carbon nanotube arrays and cross linked carbon-based monolayers are transferred from growth substrate onto elastomeric substrate and then they are buckled into well-defined shapes that are amenable to quantitative analysis. From this nano- or molecular-scale buckling, it is shown that the mechanical moduli of nanoscale materials can easily be determined, even using a model based on continuum mechanics. In addition, buckling phenomena can be utilized for the determination of mechanical moduli of organic functional materials such as poly(3-hexylthiophene) (P3HT) and P3HT/6,6-phenyl-C61 -butyric acid methyl ester (PCBM) composite, which are widely used for organic transistors and organic photovoltaics. The results provide useful information for the realization of flexible and/or stretchable organic electronics. Finally, the fabrication and applications of "wavy, stretchable" single-crystal Si electronics on elastomeric substrates are demonstrated. [source] A complex, young subduction zone imaged by three-dimensional seismic velocity, Fiordland, New ZealandGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2001Donna Eberhart-Phillips Summary The Fiordland subduction zone, where subduction developed in the late Miocene, has been imaged with P and S,P arrival-time data from 311 earthquakes in a simultaneous inversion for hypocentres and 3-D VP and VP/VS models. The three-month microearthquake survey, recorded with 24 portable seismographs, provides excellent coverage, and, since earthquakes to depths of 130 km are included, parts of the model are well-resolved to depths of 100 km. The crustal features are generally consistent with geology. The low velocity in the upper 10 km is associated with the Te Anau and Waiau basins. The Western Fiordland Orthogneiss is associated with a prominent feature from near-surface to over 40 km depth, which includes the residue from the basaltic source rocks. It is defined by high VP (7.4 km s,1 at 15 km depth) and slightly low VP/VS, and has distinct boundaries on its southern and eastern margins. Adjacent to the deepest earthquakes, there is high-velocity Pacific mantle below 80 km depth, inferred to be the mantle expression of ongoing shortening since the early Miocene. As the subducting slab moves down and northeast, it is hindered by the high-velocity body and bends to near-vertical. Bending is accommodated by distributed fracturing evidenced by high VP/VS and persistent deep earthquake activity. Buckling of the subducted plate pushes up the Western Fiordland Orthogneiss. In the transition to the Alpine fault in northern Fiordland, a prominent low-velocity crustal root is consistent with ductile thickening in combination with downwarp of the subducted plate. [source] 1233: How to choose the best surgical procedure?ACTA OPHTHALMOLOGICA, Issue 2010CJ POURNARAS Purpose Dealing to the localization and sealing retinal breaks, the surgical success rate for the cure of rhegmatogenous retinal detachment greatly changed with the introduction of scleral buckling (SB), intraocular gas injection, and pars plana vitrectomy (PPV). Methods In localized cases, pneumatic retinopexy and scleral buckling surgery (SB) remains the most popular surgical methods. Complicated cases with PVR grade B or C, giant tears, or macular holes are most commonly treated with primary pars plana vitrectomy. A large group of rhegmatogenous RDs with medium severity that comprise about 30% of all primary rhegmatogenous RDs in the Scleral Buckling versus Primary Vitrectomy in Rhegmatogenous Retinal Detachment recruitment study, were treated by SB and PPV. Advances in vitrectomy instrumentation and wideangle imaging systems have increased the popularity of PPV. Results The decision by the surgeon to use scleral buckling rather than PPV depends on a number of factors, including the lens status, size and location of breaks, patient compliance, and individual experience. Initial PPV may be successful for phakic patients. However, the SPR study shows a benefit of SB in phakic eyes with respect to BCVA improvement. Although no difference in BCVA was demonstrated in the pseudophakic trial, PPV was recommend for pseudophakic RD based on a better anatomical outcome. Conclusion There was a significant trend towards more frequently employing primary PPV (with or without SB) for the management of primary RRD. A significant improvement in the primary success rates for RD, were shown for all retinal surgical modalities applied for the treatment of rhegmatogenous retinal detachment. [source] A mechanical model for elastomeric seismic isolation bearings including the influence of axial loadEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 2 2009Sachie Yamamoto Abstract For the purpose of predicting the large-displacement response of seismically isolated buildings, an analytical model for elastomeric isolation bearings is proposed. The model comprises shear and axial springs and a series of axial springs at the top and bottom boundaries. The properties of elastomeric bearings vary with the imposed vertical load. At large shear deformations, elastomeric bearings exhibit stiffening behavior under low axial stress and buckling under high axial stress. These properties depend on the interaction between the shear and axial forces. The proposed model includes interaction between shear and axial forces, nonlinear hysteresis, and dependence on axial stress. To confirm the validity of the model, analyses are performed for actual static loading tests of lead,rubber isolation bearings. The results of analyses using the new model show very good agreement with the experimental results. Seismic response analyses with the new model are also conducted to demonstrate the behavior of isolated buildings under severe earthquake excitations. The results obtained from the analyses with the new model differ in some cases from those given by existing models. Copyright © 2008 John Wiley & Sons, Ltd. [source] Seismic performance of a 3D full-scale high-ductile steel,concrete composite moment-resisting frame,Part II: Test results and analytical validationEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 14 2008A. Braconi Abstract This paper presents the results of a multi-level pseudo-dynamic seismic test program that was performed to assess the performance of a full-scale three-bay, two-storey steel,concrete composite moment-resisting frame built with partially encased composite columns and partial-strength beam-to-column joints. The system was designed to develop a ductile response in the joint components of beam-to-column joints including flexural yielding of beam end plates and shear yielding of the column web panel zone. The ground motion producing the damageability limit state interstorey drift caused minor damage while the ultimate limit state ground motion level entailed column web panel yielding, connection yielding and plastic hinging at the column base connections. The earthquake level chosen to approach the collapse limit state induced more damage and was accompanied by further column web panel yielding, connection yielding and inelastic phenomena at column base connections without local buckling. During the final quasi-static cyclic test with stepwise increasing displacement,amplitudes up to an interstorey drift angle of 4.6%, the behaviour was ductile although cracking of beam-to-end-plate welds was observed. Correlations with numerical simulations taking into account the inelastic cyclic response of beam-to-column and column base joints are also presented in the paper together. Inelastic static pushover and time history analysis procedures are used to estimate the structural behaviour and overstrength factors of the structural system under study. Copyright © 2008 John Wiley & Sons, Ltd. [source] Estimation of seismic drift and ductility demands in planar regular X-braced steel framesEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 15 2007Theodore L. Karavasilis Abstract This paper summarizes the results of an extensive study on the inelastic seismic response of X-braced steel buildings. More than 100 regular multi-storey tension-compression X-braced steel frames are subjected to an ensemble of 30 ordinary (i.e. without near fault effects) ground motions. The records are scaled to different intensities in order to drive the structures to different levels of inelastic deformation. The statistical analysis of the created response databank indicates that the number of stories, period of vibration, brace slenderness ratio and column stiffness strongly influence the amplitude and heightwise distribution of inelastic deformation. Nonlinear regression analysis is employed in order to derive simple formulae which reflect the aforementioned influences and offer a direct estimation of drift and ductility demands. The uncertainty of this estimation due to the record-to-record variability is discussed in detail. More specifically, given the strength (or behaviour) reduction factor, the proposed formulae provide reliable estimates of the maximum roof displacement, the maximum interstorey drift ratio and the maximum cyclic ductility of the diagonals along the height of the structure. The strength reduction factor refers to the point of the first buckling of the diagonals in the building and thus, pushover analysis and estimation of the overstrength factor are not required. This design-oriented feature enables both the rapid seismic assessment of existing structures and the direct deformation-controlled seismic design of new ones. A comparison of the proposed method with the procedures adopted in current seismic design codes reveals the accuracy and efficiency of the former. Copyright © 2007 John Wiley & Sons, Ltd. [source] Performance evaluation of steel reduced flange plate moment connectionsEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 14 2007Chung-Che Chou Abstract This study details a new moment connection that overcomes difficulties in achieving field-weld quality and eliminates steel beam buckling encountered in steel moment connections. This study presents cyclic test and finite element analysis results of full-scale subassemblies using steel reduced flange plates (RFPs) to connect steel beam flanges and the column without any other direct connection. Since the RFP connection is designed as strong column-strong beam-weak RFPs, the RFP functions as a structural fuse that eliminates weld fractures and beam buckling. Test and analytical results show that (1) the connections transferred the entire beam flexural strength to the column and reached an interstorey drift of 4% with minor strength degradation, (2) failure of the connections was owing to buckling or fracturing of the RFP and not of the beam, and (3) the RFP connection subassembly, modelled using the nonlinear finite element computer program ABAQUS, exhibited hysteretic behaviour similar to that of the flange plate (FP) moment connection subassembly. The inelastic buckling force of the RFP was also evaluated by nonlinear regression analyses performed on a nonlinear model that relates buckling force to RFP geometries. Copyright © 2007 John Wiley & Sons, Ltd. [source] Test on full-scale three-storey steel moment frame and assessment of ability of numerical simulation to trace cyclic inelastic behaviourEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 1 2006Masayoshi Nakashima Abstract A test on a full-scale model of a three-storey steel moment frame was conducted, with the objectives of acquiring real information about the damage and serious strength deterioration of a steel moment frame under cyclic loading, studying the interaction between the structural frame and non-structural elements, and examining the capacity of numerical analyses commonly used in seismic design to trace the real cyclic behaviour. The outline of the test structure and test program is presented, results on the overall behaviour are given, and correlation between the experimental results and the results of pre-test and post-test numerical analyses is discussed. Pushover analyses conducted prior to the test predicted the elastic stiffness and yield strength very reasonably. With proper adjustment of strain hardening after yielding and composite action, numerical analyses were able to accurately duplicate the cyclic behaviour of the test structure up to a drift angle of 1/25. The analyses could not trace the cyclic behaviour involving larger drifts in which serious strength deterioration occurred due to fracture of beams and anchor bolts and progress of column local buckling. Copyright © 2005 John Wiley & Sons, Ltd. [source] Seismic performance evaluation of steel arch bridges against major earthquakes.EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 14 2004Part 2: simplified verification procedure Abstract The performance-based philosophy has been accepted as a more reasonable design concept for engineering structures. For this purpose, capacity evaluation and demand prediction procedures for civil engineering structures under earthquake excitations are of great significance. This work presents a displacement-based seismic performance verification procedure including capacity and seismic demand predictions for steel arch bridges and investigates its applicability. Pushover analyses is employed as a basis in this method to investigate the structure's behaviors. A failure criterion for steel members accounting for the effect of local buckling is involved and an equivalent single-degree-of-freedom (ESDOF) system with a simplified bilinear hysteretic model formulated using pushover analyses results is introduced to estimate the displacement capacity and maximum demand of steel arch bridges under major earthquakes. To check the accuracy of the proposed method, seismic capacities and demands from multi-degree-of-freedom (MDOF) time-history analyses with Level-II design earthquake record inputs modeling major earthquakes are used as benchmarks for comparison. By a case study, it is clarified that the proposed prediction procedure can give accurate estimations of displacement capacities and demands of the steel arch bridge in the transverse direction, while insufficient for the longitudinal direction, which confirms the conclusion drawn in other structure types about the applicability of pushover analyses. Copyright © 2004 John Wiley & Sons, Ltd. [source] Experimental techniques for fracture instability toughness determination of unidirectional fibre metal laminatesFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 11 2002E. M. CASTRODEZA ABSTRACT The aim of this work is to propose procedures for the measurement of the fracture toughness of fibre metal laminates (FMLs) reinforced with unidirectional fibres of aramid or glass. Experimental techniques for fracture toughness evaluation by using Compact (C(T)) and Single-Edge Bend (SE(B)) specimens obeying ASTM standards are introduced. Procedures from the standard for thick metallic materials were modified in order to overcome problems, which can arise when testing FMLs , that is, specimen buckling, indentations and crack growth in planes other than the plane of the fatigue pre-crack or notch. The methodology proposed was experimentally tested leading to satisfactory results. [source] In situ Mechanical Testing Reveals Periodic Buckle Nucleation and Propagation in Carbon Nanotube BundlesADVANCED FUNCTIONAL MATERIALS, Issue 14 2010Shelby B. Hutchens Abstract Uniaxial compression studies are performed on 50-µm-diameter bundles of nominally vertical, intertwined carbon nanotubes grown via chemical vapor deposition from a photolithographically defined catalyst. The inhomogeneous microstructure is examined, demonstrating density and tube orientation gradients, believed to play a role in the unique periodic buckling deformation mechanism. Through in situ uniaxial compression experiments it is discovered that the characteristic bottom-to-top sequential buckling proceeds by first nucleating on the bundle surface and subsequently propagating laterally through the bundle, gradually collapsing the entire structure. The effects of strain rate are explored, and storage and loss stiffnesses are analyzed in the context of energy dissipation. [source] Bioinspired Material Approaches to SensingADVANCED FUNCTIONAL MATERIALS, Issue 16 2009Michael E. McConney Abstract Bioinspired design is an engineering approach that involves working to understand the design principles and strategies employed by biology in order to benefit the development of engineered systems. From a materials perspective, biology offers an almost limitless source of novel approaches capable of arousing innovation in every aspect of materials, including fabrication, design, and functionality. Here, recent and ongoing work on the study of bioinspired materials for sensing applications is presented. Work presented includes the study of fish flow receptor structures and the subsequent development of similar structures to improve flow sensor performance. The study of spider air-flow receptors and the development of a spider-inspired flexible hair is also discussed. Lastly, the development of flexible membrane based infrared sensors, highly influenced by the fire beetle, is presented, where a pneumatic mechanism and a thermal-expansion stress-mediated buckling-based mechanism are investigated. Other areas that are discussed include novel biological signal filtering mechanisms and reciprocal benefits offered through applying the biology lessons to engineered systems. [source] Repeated Transfer of Colloidal Patterns by Using Reversible Buckling ProcessADVANCED FUNCTIONAL MATERIALS, Issue 13 2009Dong Choon Hyun Abstract The reversible nature of buckling is employed to repeatedly transfer colloids assembled in buckling patterns to flat surfaces. The cycle of colloidal loading,transfer,buckling is repeatedly carried out to fabricate the same colloidal patterns. The key to success is the reduction in the amplitude of the buckling patterns to a few nanometers as well as the recovery of initial buckling patterns after repeated stretching. The reduced buckling amplitude by poststretching or thermal annealing embosses the colloids assembled in the trenches of the buckling patterns, which enables the transfer regardless of the size, species, or layer thickness of the particles. This report demonstrates various transferred patterns composed of colloidal crystals, fluorescence hydrogel colloids, Au nanoparticles, and iron oxide magnetic particles. Since the process does not require surface modification of the colloids, it can be used to fabricate any colloidal patterns. [source] Mechanical Buckling: Mechanics, Metrology, and Stretchable ElectronicsADVANCED FUNCTIONAL MATERIALS, Issue 10 2009Dahl-Young Khang Abstract Mechanical buckling usually means catastrophic failure in structural mechanics systems. However, controlled buckling of thin films on compliant substrates has been used to advantage in diverse fields such as micro-/nanofabrication, optics, bioengineering, and metrology as well as fundamental mechanics studies. In this Feature Article, a mechanical buckling model is presented, which sprang, in part, from the buckling study of high-quality, single-crystalline nanomaterials. To check the mechanical-buckling phenomenon down to the nano-/molecular scale, well-aligned single-walled carbon nanotube arrays and cross linked carbon-based monolayers are transferred from growth substrate onto elastomeric substrate and then they are buckled into well-defined shapes that are amenable to quantitative analysis. From this nano- or molecular-scale buckling, it is shown that the mechanical moduli of nanoscale materials can easily be determined, even using a model based on continuum mechanics. In addition, buckling phenomena can be utilized for the determination of mechanical moduli of organic functional materials such as poly(3-hexylthiophene) (P3HT) and P3HT/6,6-phenyl-C61 -butyric acid methyl ester (PCBM) composite, which are widely used for organic transistors and organic photovoltaics. The results provide useful information for the realization of flexible and/or stretchable organic electronics. Finally, the fabrication and applications of "wavy, stretchable" single-crystal Si electronics on elastomeric substrates are demonstrated. [source] Micromechanical analysis of failure propagation in frictional granular materialsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 15 2009Antoinette Tordesillas Abstract The extent to which the evolution of instabilities and failure across multiple length scales can be reproduced with the aid of a bifurcation analysis is examined. We adopt an elastoplastic micropolar constitutive model, recently developed for dense cohesionless granular materials within the framework of thermomicromechanics. The internal variables and their evolution laws are conceived from a direct consideration of the dissipative mechanism of force chain buckling. The resulting constitutive law is cast entirely in terms of the particle scale properties. It thus presents a unique opportunity to test the potential of micromechanical continuum formulations to reproduce key stages in the deformation history: the development of material instabilities and failure following an initially homogeneous deformation. Progression of failure, initiating from frictional sliding and rolling at contacts, followed by the buckling of force chains, through to macroscopic strain softening and shear banding, is reproduced. Bifurcation point, marking the onset of shear banding, occurred shortly after the peak stress ratio. A wide range of material parameters was examined to show the effect of particle scale properties on the progression of failure. Model predictions on the thickness and angle of inclination of the shear band and the structural evolution inside the band, namely the latitudinal distribution of particle rotations and the angular distributions of contacts and the normal contact forces, are consistent with observations from numerical simulations and experiments. Copyright © 2009 John Wiley & Sons, Ltd. [source] Applying discontinuous deformation analysis to assess the constrained area of the unstable Chiu-fen-erh-shan landslide slopeINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 5 2007Jian-Hong Wu Abstract Chiu-fen-erh-shan landslide is a remarkable slope failure occurred during the Chi-Chi earthquake in 1999. In November of 2002, abnormal geomorphologic features, including buckling and ground subsidence, were observed on the lower slope of the Chiu-fen-erh-shan landslide. This study attempts to assess the constrained area of a future collapsing on the slope using a dynamic discrete numerical analysis method, discontinuous deformation analysis (DDA). The simulation results show that the depression in front of the toe of the slope provides a space for arresting the whole sliding rocks when only the unstable lower slope fails. However, as the whole slope slides, the rock fragments move farther into the memorial park and can impact other facilities resulting in the enlarging of constrained area. The authority should prohibit people from entrancing the constrained area in the rainy season. Copyright © 2006 John Wiley & Sons, Ltd. [source] A numerical study of flexural buckling of foliated rock slopesINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 9 2001D. P. Adhikary Abstract The occurrence of foliated rock masses is common in mining environment. Methods employing continuum approximation in describing the deformation of such rock masses possess a clear advantage over methods where each rock layer and each inter-layer interface (joint) is explicitly modelled. In devising such a continuum model it is imperative that moment (couple) stresses and internal rotations associated with the bending of the rock layers be properly incorporated in the model formulation. Such an approach will lead to a Cosserat-type theory. In the present model, the behaviour of the intact rock layer is assumed to be linearly elastic and the joints are assumed to be elastic,perfectly plastic. Condition of slip at the interfaces are determined by a Mohr,Coulomb criterion with tension cut off at zero normal stress. The theory is valid for large deformations. The model is incorporated into the finite element program AFENA and validated against an analytical solution of elementary buckling problems of a layered medium under gravity loading. A design chart suitable for assessing the stability of slopes in foliated rock masses against flexural buckling failure has been developed. The design chart is easy to use and provides a quick estimate of critical loading factors for slopes in foliated rock masses. It is shown that the model based on Euler's buckling theory as proposed by Cavers (Rock Mechanics and Rock Engineering 1981; 14:87,104) substantially overestimates the critical heights for a vertical slope and underestimates the same for sub-vertical slopes. Copyright © 2001 John Wiley & Sons, Ltd. [source] On the investigation of shell buckling due to random geometrical imperfections implemented using Karhunen,Loève expansionsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 12 2008K. J. Craig Abstract For the accurate prediction of the collapse behaviour of thin cylindrical shells, it is accepted that geometrical and other imperfections in material properties and loading have to be accounted for in the simulation. There are different methods of incorporating imperfections, depending on the availability of accurate imperfection data. The current paper uses a spectral decomposition of geometrical uncertainty (Karhunen,Loève expansions). To specify the covariance of the required random field, two methods are used. First, available experimentally measured imperfection fields are used as input for a principal component analysis based on pattern recognition literature, thereby reducing the cost of the eigenanalysis. Second, the covariance function is specified analytically and the resulting Friedholm integral equation of the second kind is solved using a wavelet-Galerkin approach. Experimentally determined correlation lengths are used as input for the analytical covariance functions. The above procedure enables the generation of imperfection fields for applications where the geometry is slightly modified from the original measured geometry. For example, 100 shells are perturbed with the resulting random fields obtained from both methods, and the results in the form of temporal normal forces during buckling, as simulated using LS-DYNA®, as well as the statistics of a Monte Carlo analysis of the 100 shells in each case are presented. Although numerically determined mean values of the limit load of the current and another numerical study differ from the experimental results due to the omission of imperfections other than geometrical, the coefficients of variation are shown to be in close agreement. Copyright © 2007 John Wiley & Sons, Ltd. [source] A comprehensive catastrophe theory for non-linear buckling of simple systems exhibiting fold and cusp catastrophesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 2 2002X. A. Lignos Abstract Non-linear static buckling of simple systems associated with typical discrete critical points is comprehensively presented using elementary Catastrophe Theory. Attention is focused on the Fold and Cusp Catastrophe, all local properties of which are assessed in detail. Hence, in dealing with stability problems of potential systems there is no need to seek any of these properties since all of these are known a priori. Then, one has only to classify, after reduction, the total potential energy of a system into one of the universal unfoldings of the above types of catastrophe. Two illustrative numerical examples show the methodology of the proposed technique. Copyright © 2002 John Wiley & Sons, Ltd. [source] GENSMAC3D: a numerical method for solving unsteady three-dimensional free surface flowsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 7 2001M.F. Tomé Abstract A numerical method for solving three-dimensional free surface flows is presented. The technique is an extension of the GENSMAC code for calculating free surface flows in two dimensions. As in GENSMAC, the full Navier,Stokes equations are solved by a finite difference method; the fluid surface is represented by a piecewise linear surface composed of quadrilaterals and triangles containing marker particles on their vertices; the stress conditions on the free surface are accurately imposed; the conjugate gradient method is employed for solving the discrete Poisson equation arising from a velocity update; and an automatic time step routine is used for calculating the time step at every cycle. A program implementing these features has been interfaced with a solid modelling routine defining the flow domain. A user-friendly input data file is employed to allow almost any arbitrary three-dimensional shape to be described. The visualization of the results is performed using computer graphic structures such as phong shade, flat and parallel surfaces. Results demonstrating the applicability of this new technique for solving complex free surface flows, such as cavity filling and jet buckling, are presented. Copyright © 2001 John Wiley & Sons, Ltd. [source] S/e-PTFE episcleral buckling implants: An experimental and histopathologic studyJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 6 2002B. Mortemousque Abstract To investigate tissue changes induced by the implantation of a silicone band coated with expanded polytetrafluoroethylene (S/e-PTFE) used as scleral buckling, an experimental and histopathological study was performed in rabbits. The right eyes of eight rabbits were implanted for 28,85 days with S/e-PTFE. No complications were encountered in any of the eyes, so histopathological examinations could be performed. Encapsulations combined with numerous giant cells were found to be surrounding the implants in seven eyes, and deposits from the mineral salts of calcium were found in three eyes, forming granulomas possibly caused by irregularities of the implant surface. The porous structure allowed a peripheral colonization by fibrovascular tissue. Taking into account the histological results, the use of this material does not appear suitable. However, this inflammation was limited and did not merge on surrounding tissues. © 2002 Wiley Periodicals, Inc. J Biomed Mater Res (Appl Biomater) 63: 686,691, 2002 [source] Piezospectroscopic Analysis of Interface Debonding in Thermal Barrier CoatingsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2000Xiao Peng One of the principal modes by which electron-beam-evaporated thermal barrier coatings fail is via the nucleation of local regions of debonding, which grow and link together until reaching a critically sized flaw for spontaneous buckling and spalling. This progressive-failure mode is used as a basis for analyzing the changes that can occur in photostimulated luminescence spectra that have been recorded from the thermally grown oxide. This process also provides a basis for the quantitative determination of the extent of local damage prior to spalling from an analysis of the shape of the luminescence spectra. [source] The Krein,von Neumann extension and its connection to an abstract buckling problemMATHEMATISCHE NACHRICHTEN, Issue 2 2010Mark S. Ashbaugh Abstract We prove the unitary equivalence of the inverse of the Krein,von Neumann extension (on the orthogonal complement of its kernel) of a densely defined, closed, strictly positive operator, S , ,IH for some , > 0 in a Hilbert space H to an abstract buckling problem operator. In the concrete case where in L2(,; dnx) for , , ,n an open, bounded (and sufficiently regular) domain, this recovers, as a particular case of a general result due to G. Grubb, that the eigenvalue problem for the Krein Laplacian SK (i.e., the Krein,von Neumann extension of S), SKv = ,v, , , 0, is in one-to-one correspondence with the problem of the buckling of a clamped plate, (-,)2u = , (-,)u in ,, , , 0, u , H02(,), where u and v are related via the pair of formulas u = SF -1 (-,)v, v = , -1(-,)u, with SF the Friedrichs extension of S. This establishes the Krein extension as a natural object in elasticity theory (in analogy to the Friedrichs extension, which found natural applications in quantum mechanics, elasticity, etc.) (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Global and local linear buckling behavior of a chiral cellular structurePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2005A. Spadoni Abstract This paper investigates the flat-wise compression behavior of an innovative cellular structure configuration. The considered layout has a hexagonal chiral geometry featuring cylinders, or nodes, joined by ligaments, or ribs. The resulting assembly is characterized by a number of interesting properties that can be exploited for the design of alternative honeycombs or cellular topologies to be used in sandwich construction. The flat-wise strength of the chiral geometry is investigated through classical analytical formulas for the linear buckling of thin plates and shells and a bifurcation analysis performed on a Finite Element model. The analytical expressions predict the global buckling behavior and the resulting critical loads, and can be directly compared with the results obtained from the Finite Element analysis. In addition, the Finite Element model predicts local buckling modes, which should be considered to evaluate the possible development of localized plasticity. A sensitivity study is performed to evaluate the influence of the geometry of the chiral structure on its buckling strength. The study shows that the considered topology can offer great design flexibility, whereby several parameters can be selected and modified to improve the flat-wise performance. The comparison with traditional, hexagonal centro-symmetric structural configurations concludes the paper and demonstrates the enhanced performance and the potentials of chiral noncentro-symmetric designs. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Sorption behavior in polymers above Tg: Relations between mechanical properties and swelling in limonenePOLYMER ENGINEERING & SCIENCE, Issue 9 2005J.E. Ritums The sorption behavior of two highly swelling "rubbery" polymers, natural rubber and polyethylene, has been studied. The polymers are in many aspects very different. Yet, when the solute mass uptake, in this case limonene, is plotted as a function of the square root of time, both polymers show similar "sigmoidal"-types of curves. This triggered the research to determine what mechanisms were responsible for the observed similarities and if the degree in sigmoidal behavior and swelling anisotropy could be easily assessed explicitly by any mechanical parameter. It was found that their degrees of swelling anisotropy, described by a solute-surface-concentration relaxation time, could be explained by their relative bulk moduli. It was assumed that the ratio in bulk modulus at zero pressure, determined from compression measurements, could represent the ratio in expansion bulk modulus during swelling. However, the prediction in swelling anisotropy during sorption using the ratio in bulk modulus was slightly less successful when the swelling anisotropy was quantified as the relative ratio of sheet thickness to cross-sectional area side length. It should be noted that the ratio in uniaxial tensile modulus between polyethylene and natural rubber was several orders of magnitude higher than their ratio in swelling anisotropy. The natural rubber sheet became saddle-shaped during limonene sorption and collapsed into a flat shape when the saturation concentration was approached. During desorption, the sheet went from flat to cup-shaped and then flat again at the end of desorption. The saddle and cup shapes occurred in both square and round sheets. These shapes are believed to be a consequence of buckling and deformation due to instabilities in the stress state of the sheet. This was, in turn, explained by the normally existing local variation in cross-link density. POLYM. ENG. SCI., 45:1194,1202, 2005. © 2005 Society of Plastics Engineers [source] Cadaveric and Engineering Analysis of the Septal L-Strut,THE LARYNGOSCOPE, Issue 11 2007Ted Mau MD Abstract Objectives: To identify patterns of failure of the L-strut, to identify elements of the nasal framework that support the L-strut, and to investigate the effect of altering L-strut design on its stability. Study Design: Laboratory study with human cadaveric heads and computational modeling. Methods: Directional forces were applied to cadaveric L-struts and patterns of failure with incremental force were noted. Computational modeling using the finite element method (FEM) was employed to determine quantitatively the effect of various modifications on the stability of the L-strut. Results: The L-strut was found to respond to frontal force initially by buckling. This buckling was reversible until the force exceeded a certain threshold when the L-strut broke at the bony-cartilaginous junction. The threshold force varied depending on the length of the overlap with the bony vault. Intact mucoperichondrium provided significant stability. Modeling with FEM showed that the preservation of a triangular piece of cartilage at the dorsal anchor of a narrowed L-strut can offset some of the loss in mechanical stability. Conclusions: Intrinsic elasticity of the septal cartilage, the mucoperichondrial flap, and overlap with the bony vault all contribute to the stability of the L-strut, which is enhanced by preserving a small segment of cartilage at the bony-cartilaginous junction of the dorsal L-strut. [source] The effect on outcome of peribulbar anaesthesia in conjunction with general anesthesia for vitreoretinal surgeryANAESTHESIA, Issue 3 2010A. M. Ghali Summary The purpose of this study was to evaluate peri-operative outcome after vitreoretinal surgery when peribulbar anaesthesia is combined with general anaesthesia. Sixty adult patients undergoing elective primary retinal detachment surgery with scleral buckling or an encircling procedure received either peribulbar anaesthesia in conjunction with general anaesthesia or general anaesthesia alone. For peribulbar anaesthesia a single percutaneous injection of 5,7 ml of local anaesthetic solution (0.75% ropivacaine with hyaluronidase 15 iu.ml,1) was used. The incidence of intra-operative oculocardiac reflex and surgical bleeding interfering with the surgical field, postoperative pain and analgesia requirements, and postoperative nausea and vomiting were recorded. In the block group there was a lower incidence of oculocardiac reflex and surgical bleeding intra-operatively. Patients in the block group also had better postoperative analgesia and a lower incidence of postoperative nausea and vomiting compared with the group without a block. The use of peribulbar anaesthesia in conjunction with general anesthesia was superior to general anaesthesia alone for vitreoretinal surgery with scleral buckling. [source] Planung und Bauausführung des Al-Sadd Stadions in Doha, KatarBAUTECHNIK, Issue 6 2005Geschäftsführender Gesellschafter Richard Stroetmann Dr.-Ing. Das Stadion des Al-Sadd Sports Club, dem renommiertesten Fußballklub des Emirats Katar, wurde in einem Zeitraum von rund 14 Monaten renoviert und in großen Teil en durch einen Neubau ersetzt. Der Beitrag berichtet über Besonderheiten bei der Planung und Bauausführung dieses Projekts. Auf die Stabilitätsberechnung des bogenförmigen Dachtragwerks wird detailliert eingegangen. Design and construction of the Al-Sadd Stadium in Doha, Qatar. The stadium of Al-Sadd Sports Club, which is the most famous soccer club of the state of Qatar, has recently been upgraded and in large parts been reconstructed from scratch within a period of 14 months. The paper describes some specific features of the design and the construction of this project. The issue of lateral torsional buckling of the curved roof structure and the respective calculations are addressed in detail. [source] Zur maßgebenden Verkehrslaststellung bei SchrägseilbrückenBAUTECHNIK, Issue 4 2004Harald Unterweger ao. Als Grundlage der Bemessung erfordert die Systemberechnung im Brükkenbau auch die Auffindung der ungünstigsten Verkehrslaststellung für jeden betrachteten Brückenquerschnitt. Insbesondere beim Fahrbahnbalken von Schrägseilbrücken ergibt sich die Gesamtbeanspruchung aus einem komplexen Zusammenwirken aus Normalkräften, Querkräften und Biegemomenten. In der Praxis erfolgt üblicherweise eine Selektion jener Verkehrslaststellungen, die eine der Teil beanspruchungen am Querschnitt (meist ausgedrückt durch Schnittkräfte) maximieren, wodurch jedoch für die nachfolgend betrachteten Stahl- bzw. Verbundbrücken nicht immer die höchsten Beanspruchungen entstehen. Einleitend erfolgt die Darstellung eines einfachen und anschaulichen Verfahrens, um , unabhängig von der Komplexität der Grenzzustandsfunktion, die auch das Beulen des Hauptträgerstegs beinhalten kann , die ungünstigste Verkehrslaststellung am Querschnitt zu finden. Dies stellt eine Verallgemeinerung des in [1] vorgestellten Verfahrens dar. Der Hauptteil beinhaltet ein Anwendungsbeispiel einer Schrägseilbrücke mit Verbundquerschnitt, wobei zwei repräsentative Fahrbahnquerschnitte näher untersucht werden. Einerseits werden die Gesamtbeanspruchungen der konventionellen und der genauen Vorgehensweise anhand von Einflußlinien erläutert, und andererseits lassen sich daraus Hinweise für die Praxis ableiten. Die dargestellte ingenieurmäßige Vorgehensweise kann alle Arten der Einwirkungen beinhalten und ist grundsätzlich auch auf andere Bauwerke sowie Baustoffe (z. B. Stahlbeton) direkt anwendbar. Appropriate traffic load cases for steel and composite cable , stayed bridges. A significant problem in the global analysis of bridge structures is to find the most unfavourable position of the traffic loads for each cross-section. In practice usually those traffic load cases are chosen which maximise one part of stresses at the cross-section (often expressed in form of internal forces). First of all a simple method is presented to find out the most unfavourable traffic load position, also applicable for complex interaction formulae including web buckling. Secondly an example of a cable-stayed bridge is analysed. For two significant sections of the bridge deck the results are presented. The stresses due to the conventional practical procedure are compared with the more accurate ones. The behaviour is explained by the corresponding influence lines. Based on these results some proposals for practical work are given. The presented procedure is also applicable to other types of construction works and materials (e.g. reinforced concrete). [source] | |||||||||||||||||||