The introduction of carbon-fibre reinforced plastics in loadbearing automotive structures provides a great potential toreduce vehicle weight and fuel consumption. To enable themanufacture and assembly of composite structural parts,reliable and cost-effective joining technologies must bedeveloped. This thesis addresses several aspects of joining andload introduction in carbon-fibre reinforced plastics based onnon-crimp fabric reinforcement. The bearing strength of carbon fibre/epoxy laminates wasinvestigated considering the effects of bolt-hole clearance.The laminate failure modes and ultimate bearing strength werefound to be significantly dependent upon the laminate stackingsequence, geometry and lateral clamping load. Significantreduction in bearing strength at 4% hole deformation was foundfor both pin-loaded and clamped laminates. The ultimatestrength of the joints was found to be independent of theinitial bolt-hole clearance. The behaviour of hybrid (bolted/bonded) joints wasinvestigated both numerically and experimentally. Athree-dimensional non-linear finite element model was developedto predict the load transfer distribution in the joints. Theeffect of the joint geometry and adhesive material propertieson the load transfer was determined through a parameter study.An experimental investigation was undertaken to determine thestrength, failure mechanisms and fatigue life of hybrid joints.The joints were shown to have greater strength, stiffness andfatigue life in comparison to adhesive bonded joints. However,the benefits were only observed in joint designs which allowedfor load sharing between the adhesive and the bolt. The effect of the environment on the durability of bondedand hybrid joints was investigated. The strength and fatiguelife of the joints was found to decrease significantly withincreased ageing time. Hybrid joints demonstrated increasedfatigue life in comparison to adhesive bonded joints afterageing in a cyclic freeze/thaw environment. The strength and failure mechanisms of composite laminatessubject to localised transverse loading were investigatedconsidering the effect of the specimen size, stacking sequenceand material system. Damage was found to initiate in thelaminates at low load levels, typically 20-30% of the ultimatefailure load. The dominant initial failure mode wasintralaminar shear failure, which occurred in sub-surfaceplies. Two different macromechanical failure modes wereidentified, fastener pull-through failure and global collapseof the laminate. The damage patterns and ultimate failure modewere found to depend upon the laminate stacking sequence andresin system. Finite element analysis was used to analyse thestress distribution within the laminates and predict first-plyfailure. Keywords:Composite, laminate, bearing strength,joining, load introduction, hybrid joint, finite elementanalysis, mechanical testing.

<p>The introduction of carbon-fibre reinforced plastics in loadbearing automotive structures provides a great potential toreduce vehicle weight and fuel consumption. To enable themanufacture and assembly of composite structural parts,reliable and cost-effective joining technologies must bedeveloped. This thesis addresses several aspects of joining andload introduction in carbon-fibre reinforced plastics based onnon-crimp fabric reinforcement.</p><p>The bearing strength of carbon fibre/epoxy laminates wasinvestigated considering the effects of bolt-hole clearance.The laminate failure modes and ultimate bearing strength werefound to be significantly dependent upon the laminate stackingsequence, geometry and lateral clamping load. Significantreduction in bearing strength at 4% hole deformation was foundfor both pin-loaded and clamped laminates. The ultimatestrength of the joints was found to be independent of theinitial bolt-hole clearance.</p><p>The behaviour of hybrid (bolted/bonded) joints wasinvestigated both numerically and experimentally. Athree-dimensional non-linear finite element model was developedto predict the load transfer distribution in the joints. Theeffect of the joint geometry and adhesive material propertieson the load transfer was determined through a parameter study.An experimental investigation was undertaken to determine thestrength, failure mechanisms and fatigue life of hybrid joints.The joints were shown to have greater strength, stiffness andfatigue life in comparison to adhesive bonded joints. However,the benefits were only observed in joint designs which allowedfor load sharing between the adhesive and the bolt.</p><p>The effect of the environment on the durability of bondedand hybrid joints was investigated. The strength and fatiguelife of the joints was found to decrease significantly withincreased ageing time. Hybrid joints demonstrated increasedfatigue life in comparison to adhesive bonded joints afterageing in a cyclic freeze/thaw environment.</p><p>The strength and failure mechanisms of composite laminatessubject to localised transverse loading were investigatedconsidering the effect of the specimen size, stacking sequenceand material system. Damage was found to initiate in thelaminates at low load levels, typically 20-30% of the ultimatefailure load. The dominant initial failure mode wasintralaminar shear failure, which occurred in sub-surfaceplies. Two different macromechanical failure modes wereidentified, fastener pull-through failure and global collapseof the laminate. The damage patterns and ultimate failure modewere found to depend upon the laminate stacking sequence andresin system. Finite element analysis was used to analyse thestress distribution within the laminates and predict first-plyfailure.</p><p><b>Keywords:</b>Composite, laminate, bearing strength,joining, load introduction, hybrid joint, finite elementanalysis, mechanical testing.</p>

Concrete-Filled Steel Tubular (CFST) columns are increasingly being used because of their many advantages, including high strength, high ductility, and higher fire resistance than conventional steel or concrete columns of the same size. In order to maximise the advantages of CFST column, composite action of the column should be ensured. In realistic structures, the load is not directly applied to the entire CFST column section and is introduced from the beam-column connection. Simple shear connections, which are usually preferred in constructions, are only connected to the external face of the steel tube and there is an issue about how this load is introduced to the concrete core, through the bond at the steel/concrete interface. There are fundamental errors in the load introduction mechanism assumed in various current design methods. Furthermore, based on this erroneous load introduction mechanism, construction methods, such as placing shear connectors inside the steel tube or using through-column plates, are recommended to ensure complete load introduction. However, these methods are either impractical or uneconomical. The aim of this project, therefore, is to develop a thorough understanding of the load introduction mechanism and to use the new insights to assess design implications, for both ambient temperature and fire safety design. The research has been conducted through physical testing, extensive numerical modelling and detailed analytical derivations. A series of new load introduction tests, in which square CFST columns are loaded through simple fin plate connections, are carried out. These tests are designed to investigate the effects of changing column lengths below and above the connection, the effectiveness of using shear connectors inside the steel tube below the connection (according to Eurocode 4) and using a cap plate on the column top for load introduction into the concrete core. The test results indicate that the connection load is introduced to the concrete core through the column length above and within the connection or the cap plate on top of the column. This is different from the currently assumed mechanism of load introduction which assumes that load introduction occurs from underneath the connection. Below the connection, there is transfer of forces from the steel tube to the concrete core, but the total force in the column remains unchanged. Consequently, using shear connectors below the connection is ineffective in increasing CFST column strength, as has been demonstrated by the tests. The physical tests are supplemented by an extensive numerical parametric study to check whether the conclusions are applicable to different design conditions and to provide data for development of a new design method. The parameters include: section geometry (square, circular, and rectangular), position of load application to CFST column, dimensions of the square column cross-section, steel tube thickness, connection length, column length above the connection, column length below the connection, and maximum bond stress at the steel-concrete interface. The numerical simulation results confirm the experimental observations. Furthermore, the numerical simulation results indicate that the entire column length and the entire perimeter of the steel-concrete interface above and within the connection are engaged in load introduction. Based on the experimental and numerical simulation results, a simple calculation method has been proposed to calculate the column cross-section resistance under compression. According to this equation, the concrete compression resistance to the composite column is the minimum of the plastic resistance or the bond strength within and above the connection. This gives rise to a “concrete strength reduction factor” to account for incomplete load introduction, being the ratio of the load introduced to the concrete core through the interface bond to the concrete plastic resistance. Based on the new load introduction calculation method and using representative values of column dimensions and concrete cylinder strength, it has been demonstrated that complete load introduction can be achieved in almost all practical arrangements of concrete-filled tubular construction. For slender CFST column design, this concrete strength reduction factor should also be used to calculate the CFST column cross-section flexural stiffness. For a CFST column under combined axial compression and bending, the concrete strength reduction factor should be used when calculating the compression force, but should be ignored when calculating the bending resistance because composite action is not necessary for bending of the CFST column. The new load introduction mechanism induces additional compression in the concrete core and possible tension in the steel tube above the connection. Therefore, the concrete core of the column above the connection in multi-storey construction should be designed to resist the additional compression force. For the steel tube, in ambient temperature design, the steel contribution ratio (steel section resistance/plastic resistance of composite cross-section) of the top floor column should be at least 0.25. For fire resistance design, the steel contribution ratio of the top floor columns, those on the floor below the top floor, and those two floors below the top floor, should not be less than 0.5, 0.33, and 0.25 respectively.

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Die Präsentation stellt kurz die Grundlagen der Berechnung von Schraubenverbindungen in Anlehnung an die VDI-Richtlinie 2230 Teil 1 dar. Auch die vier FEM-Modellklassen, die die VDI 2230 Teil 2 (Entwurf) zur Berechnung von Mehrschraubenverbindungen vorschlägt, werden behandelt, und die in Creo Simulate vorhandenen Softwarefeatures zu deren Umsetzung vorgestellt. Es folgt eine Darstellung, was bei der Linearisierung von Schraubenverbindungen zur vereinfachten Berechnung zu beachten ist, und wieso bei der Berechnung im FEM-System dann nicht notwendigerweise eine Vorspannung benötigt wird. Ausführlich wird das neue Schraubenfeature in Creo Simulate betrachtet, das eine weitgehend automatisierte Modellierung und Berechnung von Standardverschraubungen erlaubt. Weitere Features, wie die neuen Vorspannelemente, werden erläutert, sowie auch die Grenzen der Software aufgezeigt. Abschließend werden zwei anspruchsvolle Anwendungsbeispiele vorgestellt: Eine zentrisch belastete Verschraubung mit Berücksichtigung von Elasto-Plastizität und einer komplexen Lasthistorie (Anziehen durch Anzugsmoment, Setzeffekte, Entfall des Torsionsmomentes durch das Anziehen, Betriebskraft) sowie eine exzentrisch belastete Verschraubung, die wegen eines relativ dünnen Flansches starke Biegezusatzbeanspruchungen erfährt. / The presentation shows the foundations of bolt analysis according to VDI-guideline 2230 part 1. In addition, the four FEM model classes proposed in VDI 2230 part 2 (draft) are described, as well as the features available in Creo Simulate to realize these model classes. Next, the presentation shows the requirements for linearizing bolted connections, and why in a FEM analysis with a linearized connection no preload is necessary. The new fastener feature introduced in Creo Simulate is explained in detail. This feature allows the automated modeling and analysis of bolted connections having standard geometry. Further software features, like pretension elements, as well as the current software limitations are shown. Finally, two advanced application examples are shown: A centrically loaded bolted connection taking into account elasto-plasticity and a complex load history (tightening torque, embedding, removal of tightening stress, operational load), and an eccentrically loaded flange connection, which is subjected to high additional bending loads because the flange is relatively thin.

Die Präsentation stellt kurz die Grundlagen der Berechnung von Schraubenverbindungen in Anlehnung an die VDI-Richtlinie 2230 Teil 1 dar. Auch die vier FEM-Modellklassen, die die VDI 2230 Teil 2 (Entwurf) zur Berechnung von Mehrschraubenverbindungen vorschlägt, werden behandelt, und die in Creo Simulate vorhandenen Softwarefeatures zu deren Umsetzung vorgestellt. Es folgt eine Darstellung, was bei der Linearisierung von Schraubenverbindungen zur vereinfachten Berechnung zu beachten ist, und wieso bei der Berechnung im FEM-System dann nicht notwendigerweise eine Vorspannung benötigt wird. Ausführlich wird das neue Schraubenfeature in Creo Simulate betrachtet, das eine weitgehend automatisierte Modellierung und Berechnung von Standardverschraubungen erlaubt. Weitere Features, wie die neuen Vorspannelemente, werden erläutert, sowie auch die Grenzen der Software aufgezeigt. Abschließend werden zwei anspruchsvolle Anwendungsbeispiele vorgestellt: Eine zentrisch belastete Verschraubung mit Berücksichtigung von Elasto-Plastizität und einer komplexen Lasthistorie (Anziehen durch Anzugsmoment, Setzeffekte, Entfall des Torsionsmomentes durch das Anziehen, Betriebskraft) sowie eine exzentrisch belastete Verschraubung, die wegen eines relativ dünnen Flansches starke Biegezusatzbeanspruchungen erfährt. / The presentation shows the foundations of bolt analysis according to VDI-guideline 2230 part 1. In addition, the four FEM model classes proposed in VDI 2230 part 2 (draft) are described, as well as the features available in Creo Simulate to realize these model classes. Next, the presentation shows the requirements for linearizing bolted connections, and why in a FEM analysis with a linearized connection no preload is necessary. The new fastener feature introduced in Creo Simulate is explained in detail. This feature allows the automated modeling and analysis of bolted connections having standard geometry. Further software features, like pretension elements, as well as the current software limitations are shown. Finally, two advanced application examples are shown: A centrically loaded bolted connection taking into account elasto-plasticity and a complex load history (tightening torque, embedding, removal of tightening stress, operational load), and an eccentrically loaded flange connection, which is subjected to high additional bending loads because the flange is relatively thin.