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131	Der Einfluss des Verankerungsniveaus und der Verankerungsmethodik von Rekonstruktionstechniken des vorderen Kreuzbandes mit "Hamstring"-Sehnen / eine biomechanische Studie unter zyklischer Belastung Scheffler, Sven 13 December 2002 (has links) Einleitung: Aufgrund der hohen Inzidenz der vorderen Kreuzbandverletzungen und der damit einhergehenden funktionellen Einschränkung besteht ein anhaltendes Interesse an der Verbesserung bestehender und Entwicklung neuer, besserer Techniken zur Rekonstruktion dieser Bandstruktur des Kniegelenkes. In dieser Studie wurde der Einfluss des Verankerungsniveaus (anatomisch vs. extrakortikal) und der Verankerungsart (direkt vs. indirekt) auf das mechanische Verhalten von drei exemplarischen, in der Klinik häufig angewandten Rekonstruktionstechniken, untersucht. Material & Methoden: An insgesamt 24 Kniegelenken humaner Spender mittleren Alters (40 Jahre) wurden drei Rekonstruktionstechniken (n=8 pro Gruppe) des VKB durchgeführt. Als Transplantat wurden jeweils humane Hamstringsehnen verwendet: 1.) HADBIO: anatomische und direkte Verankerung mit biodegradierbaren Interferenzschrauben, 2.) HADTIT: semi-anatomische und direkte Verankerung mit Titanschrauben, 3.) HEIButton: extrakortikale, indirekte Verankerung mit Faden-Button Verbindung. Alle rekonstruierten Kniegelenke wurden einer zyklischen, inkremental zunehmenden Belastung bis zum Versagen unterzogen. Es wurden die Parameter Konstruktsteifigkeit, absorbierte Energie, Transplantatauslenkung und Laxizitätszunahme bei Belastungen von 200, 300, 400 N, sowie die maximale Steifigkeit und Versagenskraft bestimmt. Ergebnis: Die anatomische und direkte Transplantatverankerung mit biodegradierbarer Interferenzschraube zeigt die vorteilhaftesten mechanischen Eigenschaften, während die extrakortikale und indirekte Verankerung die niedrigsten mechanischen Eigenschaften aufwies. Die tibiale Verankerungsseite ist bei Interferenzschraubenverankerung der Schwachpunkt, während die Fadenverbindungen bei der extrakortikalen Verankerungstechnik die Schwachstelle darstellten. Auch bei anatomischer und direkter Transplantatfixation findet ein nicht zu vernachlässigender permanenter Verankerungsverlust bei vergleichsweise geringer Versagenskraft statt, der vor allem auf der tibialen Verankerungsseite zu beobachten ist. Diskussion: Eine anatomische und direkte Transplantatverankerung ist von mechanischem Vorteil. Allerdings hängt die Konstruktsteifigkeit auch in erheblichem Maße vom Fixationsobjekt ab. Extrakortikale Fixationstechniken, die eine indirekte Faden-Knoten-Transplantatverbindung erfordern, unterliegen einer erheblichen nicht-reversiblen Lockerung unter zyklischer Belastung und sollten durch direkte Verankerungstechniken ersetzt werden. Aufgrund der permanenten Laxizitätszunahme auch in der anatomischen und direkten Interferenzschraubenverankerung, vor allem der tibialen Seite, sollte über Sicherungsverankerungen, so genannten Hybridfixationen nachgedacht werden, um die mechanischen Vorteile dieser Rekonstruktionsart voll zum Tragen bringen zu können. / Introduction: There is a continuous interest in the improvement and development of new techniques for the reconstruction of the anterior cruciate ligament (ACL) because of the high incidence of its injury and the resulting functional deficit. Purpose of this study was the impact of fixation level (anatomic vs. extracortical) and fixation method (direct vs. indirect) on the mechanical properties of three frequently used reconstruction techniques. Material & Methods: 24 human cadaveric knees with an average age of 40 years were used for simulation of three reconstruction techniques (n=8 per group). Human hamstring tendons were utilized as tendon grafts. 1.) HADBIO: anatomic and direct fixation with biodegradable interference screws, 2.) HADTIT: semi-anatomic and direct fixation with titanium interference screws, 3.) HEIButton: extracortical, indirect fixation with tape/button combination. All reconstructed knee joints underwent cyclic incremental loading until failure. Construct stiffness, absorbed energy, displacement and laxity increase were calculated at loads up to 200, 300, 400 N. Maximum stiffness and failure load were also recorded. Results: The anatomic and direct graft fixation with biodegradable interference screws provided the highest, while the combination of extracortical and indirect fixation showed the lowest mechanical properties. The tibial fixation site is the critical factor in interference screw fixation, while the tape/suture interfaces were the location of failure in the extracortical reconstructions. Even in the anatomic and direct reconstruction technique a considerable permanent loss of fixation, especially at the tibial fixation site and a comparably lower failure load were observed. Discussion: The combination of anatomic and direct fixation showed to be of mechanical benefit. However, construct stiffness seemed to be also affected by the fixation device. Extracortical fixation techniques, which require suture-tape/knot interfaces for graft fixation, undergo significant permanent loosening of fixation under cyclic loads and should be replaced by direct fixation techniques. Since a permanent laxity increase was still observed in the anatomic and direct interference screw reconstructions, especially on the tibial site, backup or so called hybrid fixations should be considered, which would allow to take full advantage of the mechanical improvements in these reconstruction techniques. vordere Kreuzband Rekonstruktionstechniken Biomechanische Eigenschaften zyklische Belastung Verankerungsniveau Verankerungsmethodik ACL reconstruction techniques mechanical properties cyclic loading fixation level fixation method 610 Medizin und Gesundheit 33 Medizin YK 3650 ddc:610
132	Experimental and numerical studies of masonry wall panels and timber frames of low-rise structures under seismic loadings in Indonesia Susila, Gede Adi January 2014 (has links) Indonesia is a developing country that suffers from earthquakes and windstorms and where at least 60% of houses are non-engineered structures, built by unskilled workers using masonry and timber. The non-engineered housing units developed in urban region are also vulnerable to seismic hazard due to the use of low quality of material and constructions method. Those structures are not resistant to extreme lateral loads or ground movement and their failure during an earthquake or storm can lead to significant loss of life. This thesis is concerned with the structural performance of Indonesian low-rise buildings made of masonry and timber under lateral seismic load. The research presented includes a survey of forms of building structure and experimental, analytical and numerical work to predict the behaviour of masonry wall and traditional timber frame buildings. Experimental testing of both masonry and timber have been carried out in Indonesia to establish the quality of materials and to provide material properties for numerical simulations. The experimental study found that the strength of Indonesia-Bali clay brick masonry are below the minimum standard required for masonry structures built in seismic regions, being at least 50% lower than the requirement specified in British Standard and Eurocode-6 (BS EN 1996-1-1:2005). In contrast, Indonesian timber materials meet the strength classes specified in British Standard/Eurocode- 5 (BS EN 338:2009) in the range of strength grade D35-40 and C35).Structural tests under monotonic and cyclic loading have been conducted on building components in Indonesia, to determine the load-displacement capacity of local hand-made masonry wall panels and timber frames in order to: (1) evaluate the performance of masonry and timber frame structure, (2) investigate the dynamic behaviour of both structures, (3) observe the effect of in-plane stiffness and ductility level, and (4) examine the anchoring joint at the base of timber frame that resists the overturning moment. From these tests, the structural ductility was found to be less than two which is below the requirement of the relevant guidelines from the Federal Emergency Management Agency, USA (FEMA-306). It was also observed that the lateral stiffness of masonry wall is much higher than the equivalent timber frame of the same height and length. The experimental value of stiffness of the masonry wall panel was found to be one-twelfth of the recommended values given in FEMA-356 and the Canadian Building code. The masonry wall provides relatively low displacement compared to the large displacement of the timber frame at the full capacity level of lateral load, with structural framing members of the latter remaining intact. The weak point of the timber frame is the mechanical joint and the capacity of slip joint governs the lateral load capacity of the whole frame. Detailed numerical models of the experimental specimens were setup in Abaqus using three-dimensional solid elements. Cohesive elements were used to simulate the mortar behaviour, exhibiting cracking and the associated physical separation of the elements. Appropriate contact definitions were used where relevant, especially for the timber frame joints. A range of available material plasticity models were reviewed: Drucker-Prager, Crystalline Plasticity, and Cohesive Damage model. It was found that the combination of Crystalline Plasticity model for the brick unit and timber, and the Cohesive Damage model for the mortar is capable of simulating the experimental load-displacement behaviour fairly accurately. The validated numerical models have been used to (1) predict the lateral load capacity, (2) determine the cracking load and patterns, (3) carry out a detailed parametric study by changing the geometric and material properties different to the experimental specimens. The numerical models were used to assess different strengthening measures such as using bamboo as reinforcement in the masonry walls for a complete single storey, and a two-storey houses including openings for doors and windows. The traditional footing of the timber structures was analysed using Abaqus and was found to be an excellent base isolation system which partly explains the survival of those structures in the past earthquakes. The experimental and numerical results have finally been used to develop a design guideline for new construction as well as recommendations for retrofitting of existing structures for improved performance under seismic lateral load. 624.1
133	Essais et modélisation du cisaillement cyclique sol-struture à grand nombre de cycles. Application aux pieux / Behaviour of soil-structure interfaces subjected to large number of cycles. Application to modeling of piles cyclically loaded Pra-ai, Suriyavut 28 February 2013 (has links) On présente tout d’abord une série d’essais de cisaillement direct 2D monotones et cycliques sur l’interface sable de Fontainebleau-plaque rugueuse et lisse, `a contrainte normale constante (CNL) et à rigidité normale imposée (CNS). Le but de ces essais est de simuler la situation mécanique le long de pieux soumis à un grand nombre de cycles d’origine environnementale ou anthropique. Ces cycles (typiquement 10000) de faible amplitude (10`a 40 kPa en terme de contrainte de cisaillement) ne sont pas cens´es produire de rupture prématurée. Ces tests incluent une série de cycles d’amplitudes (successives) variées. Le problème de la perte de sable entre la boite et la plaque est trait´e avec attention. Nous avons interprété l’effet de la position du ”centre des cycles” dans le plan de contraintes (variables cycliques moyennes) et de la densité initiale. Plusieurs facteurs tels que l’indice initial de densité (ID0), la contrainte normale cyclique moyenne (_n cm0), le niveau initial moyen de contrainte de cisaillement (_cm0), l’amplitude cyclique réduite (__) et la rigidité normale imposée (k qui dans cette thèse, va de 1000 `a 5000 kPa/mm), influencent les déplacements relatifs cycliques moyens normal ([u]cm) et tangentiel [w]cm) et sont pris en considération.On observe soit de la dilatance, soit de la contractance en accord avec l’état caractéristique développé par Luong. L’influence du chemin de contrainte (CNL ou CNS) est également analysée. Un modèle phénoménologique et analytique de comportement d’interface sur chemins cycliques CNL est propos´e. C’est également le cas pour le comportement monotone sur chemins oedométrique et CNL, la variable de mémoire unique étant la densité d’interface (sous contrainte) ou le déplacement relatif normal. Cette formulation permet de traiter, par incréments analytiques finis, les chemins comportant une variation d’amplitude cyclique, et les chemins CNS, ce qui introduit la notion de nombre de cycles équivalent. On notera que les chemins CNS sont toujours contractants. Ces essais sont utilisés pour aborder la simulation par éléments finis, avec le logiciel Plaxis, selon une approche de pseudo-viscoplasticité, le nombre de cycles tenant lieu de temps fictif. L’essai de cisaillement monotone`a la boite est modélisé en densités faible et forte, ainsi que deux essais de pieux modèles centrifugés, l’un en traction, l’autre en compression. Des recommandations sont proposées pour le calcul courant des pieux sous sollicitations cycliques. Cette thèse a été soutenue par l’ANR SOLCYP et le programme national ” recherches sur le comportement des pieux soumis à des sollicitations cycliques”. / A series of monotonic and cyclic 2D direct shear tests on sand (Fontainebleau)-rough/smoothmaterial interfaces under constant normal load (CNL) and constant normal stiffness (CNS)conditions are presented. The aim of these tests is to simulate the situation along the shaftof piles subjected to a large number of cycles due to environmental or anthropic loadings.These cycles (typically 104) are of small amplitude (10, 20 and 40 kPa in terms of shearstress) as the service loads are not supposed to produce an early failure. These tests in-clude the series of changing the cyclic amplitude in succession. The problem of loss of sandbetween the box and the rough plate, typical phenomenon in this type of test, receives aspecial attention. It is interesting to observe, according to the initial density, the positionof the ”center of cycles” in the stress plane (mean cyclic variables). Several factors such asinitial density (ID0), initial normal stress (_n cm0), level of initial mean cyclic stress ratio(_cm0), reduced cyclic amplitude (__) and imposed normal stiffness (in this thesis, k =1000, 2000 and 5000 kPa/mm) that influence the intensity of mean cyclic normal ([u]cm)and shear ([w]cm) displacements are considered. Along CNL paths either dilation or con-traction is exhibited, in agreement with the characteristic state developed by Luong. Theinfluence of the stress path (under constant normal stress or prescribed normal stiffness)is also highlighted. It should be highlighted that CNS paths are ever contractive. Themodel of monotonic interface behaviour under CNL and oedometer paths is fully analyt-ical and based on the rate-type framework with the normal relative displacement or theinterface density as unique memory parameter. While the analytical formulations for iden-tification are first proposed to describe the interface behaviour under cyclic CNL condition,the variation of cyclic amplitude and CNS condition are modeled by applying the analyticalformulations for validation using finite analytical increments and introducing the notion ofequivalent number of cycles. For numerical simulations by the FEM (Plaxis) these tests areinterpreted and formulated according to a pseudo visco-plastic framework, the number ofcycles being a fictitious time. The direct shear tests and two centrifuge pile tests (pull-outand compression) are also modeled. Recommendations are proposed for the calculation ofreal usual piles under cyclic loading. This thesis is one part of the national French project”ANR and National Program SOLCYP” (Research on behaviour of piles subjected to cyclicloading). Essais de cisaillement direct Interface sol granulaire-structure Chargement cy- clique Chemin cyclique moyen Grand nombre de petits cycles État caractéristique Pseudo- visco plasticité Direct shear tests Granular soil-structure interface Cyclic loading Mean cyclic path Large number of small cycles Characteristic state Pseudo visco-plasticity
134	Repair and Retrofit Strategies for Structural Concrete against Thermo-Mechanical Loadings Guruprasad, Y K January 2014 (has links) (PDF) Reinforced cement concrete (RCC) structures have become an important aspect in most of the buildings in our society around the world. Most of the multistoried reinforced concrete buildings house important institutions such as hospitals, schools, government establishments, defense establishments, business centers, sports stadiums, super markets and nuclear power plants. The cost of construction of such multistoried RCC structures is very high, and these structures need to be maintained and restored based on their functionality and importance using repair and retrofit strategies when these structures undergo damage. The steps involved in restoring RCC structures that have damages using repair / retrofit measures consists of identifying the source or cause of damage, assessment of the degree or extent of damage that has taken place using nondestructive techniques. Based on the assessment of degree of damage suitable repair / retrofit strategy using the appropriate repair material is applied to achieve the required load carrying capacity or strength. The present work involves assessing the efficacy of carbon fibre reinforced polymer (CFRP) based system applied on pre-damaged structural members to restore the member’s strength and stiffness through experimental investigations and finite element predictions. To validate the macrolevel properties of predamaged concrete micromechanical analysis, microscale studies and analytical investigations have been conducted. Plain and reinforced concrete test specimens: cylinders, square prisms and rectangular prisms having 25MPa and 35MPa cylinder compressive strengths pre-damaged due to mechanical (monotonic and cyclic loading) and thermal loading (exposure to different temperature and time durations) with applications of CFRP repair subjected to compression is investigated to study the behavior and enhancement in the compressive strength and stiffness after application of repair. Non destructive testing of thermally damaged concrete (exposed to different temperature and exposure time) is conducted using ultrasonic pulse velocity and tomography methods to understand the degradation in the strength and stiffness of thermally damaged concrete. The results of the non destructive testing helps in assessing the amount of repair that can be applied. To validate the macro scale behavior of thermally damaged concrete micro scale studies was performed adopting micro indentation, petrography, Raman spectroscopy, scanning electron miscroscopy (SEM) and Electron probe micro analysis (EPMA). During the event of a fire in RC structures which have been retrofitted. The high temperature caused due to fire tends to make the concrete to deteriorate and the repair material to delaminate. Loss of strength/ stiffness in concrete and delamination of the repair material in a retrofitted structural component in a structure causes instability which results in partial collapse or complete collapse of the structure. Thermal insulation of concrete and the repair material (CFRP) using geo-polymer mortar and simwool thermal fibre blanket exposed to high temperature and different exposure time are experimentally investigated. This is to evaluate the effectiveness of the thermal insulation in protecting epoxy based structural repair material(CFRP) from thermal damage and to minimize the delamination of the repair material when exposed to high temperatures. Slender columns when loaded eccentrically fail at a load much lesser than their actual load carrying capacity. In RC buildings where additional floors need to be added, in those situations slender columns which are already eccentrically loaded tend to get damaged or fail due to additional load which act on them. Therefore to restore such columns experimental and finite element investigations on reinforced concrete slender columns having 25MPa cylinder compressive strength subjected to eccentric monotonic compressive loading with applications of CFRP repair is studied to understand the behavior and the enhancement in load carrying capacity after application of repair. Experimental investigations are conducted to study fracture and fatigue properties of thermally damaged concrete geometrically similar notched plain and reinforced concrete beams having 25MPa cylinder compressive strength exposed to different combinations of temperature and durations with application of repair (CFRP). Nonlinear fracture parameters of thermally damaged concrete is computed which help in understanding the fracture behavior of thermally damaged concrete and application of repair. Effectiveness of CFRP repair and failure behaviour of these beams are studied when these thermally damaged notch concrete beams are subjected to monotonic and cyclic (fatigue) loading. Reinforced concrete slender beams when subjected to unexpected loads such as earthquakes get damaged. The increase in load carrying capacity and fatigue life of reinforced concrete slender beams having 25MPa cylinder compressive strength in flexure subjected to monotonic and cyclic loading with applications of CFRP repair is investigated using experimental and finite element investigations. Finite element analysis of concrete specimens pre-damaged due to mechanical (monotonic and cyclic loading) / thermal loading (exposure to different temperature and time durations) with applications of CFRP repair and assessment of amount of repair required is investigated. Analytical (empirical) models are developed to assess the mechanical properties of concrete (elastic moduli, compressive strength and split tensile strength) exposed to different temperatures and time durations. Nonlinear fracture parameters of geometrically similar plain concrete notch beams exposed to different temperature and time durations are determined. Fracture parameters (stress intensity factor) of thermally damaged plain and reinforced concrete notched beams with application of CFRP have been determined. Effect of size and shape of thermally damaged plain concrete compression members with application of CFRP wrap have been studied. Crack mouth opening displacements (CMOD), strains and crack lengths of thermally damaged plain concrete (PC) notched beams using digital image correlation has also been determined. Thermo-Mechanical Loadings Structural Concrete Reinforced Cement Concrete Structures Concrete - Structural Analysis Reinforced Concrete Concrete - Analysis Carbon Fiber Reinforced Polymer Concrete - Finite Element Analysis Plain Concrete Concrete Structures Reinforced Cement Concrete (RCC) CFRP Repair Cyclic Loading High Temperature on Concrete Civil Engineering
135	Rehabilitation of Exterior RC Beam-Column Joints using Web-Bonded FRP Sheets Mahini, Seyed Saeid Unknown Date (has links) In a Reinforced Concrete (RC) building subjected to lateral loads such as earthquake and wind pressure, the beam to column joints constitute one of the critical regions, especially the exterior ones, and they must be designed and detailed to dissipate large amounts of energy without a significant loss of, strength, stiffness and ductility. This would be achieved when the beam-column joints are designed in such a way that the plastic hinges form at a distance away from the column face and the joint region remain elastic. In existing frames, an easy and practical way to implement this behaviour following the accepted design philosophy of the strong-column weak-beam concept is the use a Fibre Reinforced Plastic (FRP) retrofitting system. In the case of damaged buildings, this can be achieved through a FRP repairing system. In the experimental part of this study, seven scaled down exterior subassemblies were tested under monotonic or cyclic loads. All specimens were designed following the strong-column weak-beam principal. The three categories selected for this investigation included the FRP-repaired and FRP-retrofitted specimens under monotonic loads and FRP-retrofitted specimen under cyclic loads. All repairing/retrofitting was performed using a new technique called a web-bonded FRP system, which was developed for the first time in the current study. On the basis of test results, it was concluded that the FRP repairing/retrofitting system can restore/upgrade the integrity of the joint, keeping/upgrading its strength, stiffness and ductility, and shifting the plastic hinges from the column face toward the beam in such a way that the joint remains elastic. In the analytical part of this study, a closed-form solution was developed in order to predict the physical behaviour of the repaired/retrofitted specimens. Firstly, an analytical model was developed to calculate the ultimate moment capacity of the web-bonded FRP sections considering two failure modes, FRP rupture and tension failure, followed by an extended formulation for estimating the beam-tip displacement. Based on the analytical model and the extended formulation, failure mechanisms of the test specimens were implemented into a computer program to facilitate the calculations. All seven subassemblies were analysed using this program, and the results were found to be in good agreement with those obtained from experimental study. Design curves were also developed to be used by practicing engineers. In the numerical part of this study, all specimens were analysed by a nonlinear finite element method using ANSYS software. Numerical analysis was performed for three purposes: to calculate the first yield load of the specimens in order to manage the tests; to investigate the ability of the web-bonded FRP system to relocate the plastic hinge from the column face toward the beam; and to calibrate and confirm the results obtained from the experiments. It was concluded that numerical analysis using ANSYS could be considered as a practical tool in the design of the web-bonded FRP beam-column joints. Reinforced concrete Reinforcement Bar strong-column weak-beam principal Exterior Beam-Column Joints Core Small scale modelling Experimental Test set-up Control Plain specimen Rehabilitation Retrofitting retrofitted Repair Repaired Repairing Strengthening Controlling Relocating Plastic hinge Pre-cracking Cracking Crushing Post-cracking Crack Cracked Penetration Damaged Pre-cracked Web-Bonded Wrapping De-bonding Fibre Reinforced Plastic FRP Sheets Composite Confinement Monotonic loads Cyclic loading Loads Displacement control Load control Regime Phase Loading sequence Procedure Available ductility factor Curvature ductility factor Ultimate First yield Flexural yielding Strength Moment Stiffness Failure mechanism Modes Sudden Brittle failure Measured beam-tip displacement Deflection Numerical analysis ANSYS Solid65 Solid45 Link8 Non-linear Finite Element (FE) Convergence criteria Analytical Closed from FRP rupture tension failure Compression failure Minimum thickness Maximum thickness Compressive Tensile Steel Ratio Design charts Effective Moment of Inertia Compatibility Strain Stress
136	Verifikace nelineárních materiálových modelů betonu / Verification of nonlinear material models of concrete Král, Petr January 2015 (has links) Diploma thesis is focused on the description of the parameters of nonlinear material models of concrete, which are implemented in a computational system LS-DYNA, interacting with performance of nonlinear test calculations in system LS-DYNA on selected problems, which are formed mainly by simulations of tests of mechanical and physical properties of concrete in uniaxial compressive and tensile on cylinders with applying different boundary conditions and by simulation of bending slab, with subsequent comparison of some results of test calculations with results of the experiment. The thesis includes creation of appropriate geometric models of selected problems, meshing of these geometric models, description of parameters and application of nonlinear material models of concrete on selected problems, application of loads and boundary conditions on selected problems and performance of nonlinear calculations in a computational system LS-DYNA. Evaluation of results is made on the basis of stress-strain diagrams and load-displacement diagrams based on nonlinear calculations taking into account strain rate effects and on the basis of hysteresis curves based on nonlinear calculations in case of application of cyclic loading on selected problems. Verification of nonlinear material models of concrete is made on the basis of comparison of some results of test calculations with results obtained from the experiment.

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