Use of composite steel construction with precast hollow core slabs is now popular in the UK, but the present knowledge in shear capacity of the headed shear studs for this type of composite construction is very limited. Currently, all the information is based on the results obtained from experimental push-off tests. A finite element model to simulate the behaviour of headed stud shear connection in composite beam with precast hollow core slabs is described. The model is based on finite element method and takes into account the linear and non-linear behaviour of all the materials. The model has been validated against the test results, for which the accuracy of the model used is demonstrated. Parametric studies showing the effect of the change in transverse gap size, transverse reinforcement diameter and in-situ concrete strength on the shear connection capacity are presented.

This paper presents a nonlinear 3-D finite element model for eccentrically loaded concrete encased steel composite columns. The columns were pin-ended subjected to an eccentric load acting along the major axis, with eccentricity varied from 0.125 to 0.375 of the overall depth (D) of the column sections. The model accounted for the inelastic behaviour of steel, concrete, longitudinal and transverse reinforcement bars as well as the effect of concrete confinement of the concrete encased steel composite columns. The interface between the steel section and concrete, the longitudinal and transverse reinforcement bars, and the reinforcement bars and concrete were also considered allowing the bond behaviour to be modelled and the different components to retain its profile during the deformation of the column. The initial overall geometric imperfection was carefully incorporated in the model. The finite element model has been validated against existing test results. The concrete strengths varied from normal to high strength (30¿110 MPa). The steel section yield stresses also varied from normal to high strength (275¿690 MPa). Furthermore, the variables that influence the eccentrically loaded composite column behaviour and strength comprising different eccentricities, different column dimensions, different structural steel sizes, different concrete strengths, and different structural steel yield stresses were investigated in a parametric study. Generally, it is shown that the effect on the composite column strength owing to the increase in structural steel yield stress is significant for eccentrically loaded columns with small eccentricity of 0.125D. On the other hand, for columns with higher eccentricity 0.375D, the effect on the composite column strength due to the increase in structural steel yield stress is significant for columns with concrete strengths lower than 70 MPa. The strength of composite columns obtained from the finite element analysis were compared with the design strengths calculated using the Eurocode 4 for composite columns. Generally, it is shown that the EC4 accurately predicted the eccentrically loaded composite columns, while overestimated the moment.

Yes / Elliptical Hollow Sections (EHSs) have been utilized in construction recently because of their visual appearance as well as the potential structural efficiency owing to the presence of the two principle axes. However, little information currently exists for the design of beam to elliptical column connections, which is an essential part of a building structure. Thus, to ensure the safe and economic application of EHSs, a new research project has been initiated. Rotation behaviour of simply bolted beam to concrete-filled elliptical steel column connections was investigated experimentally. Various joint types were considered and the benefits of adopting core concrete and stiffeners were highlighted. This paper covers the experimental studies and simulation of the connections using the ABAQUS standard solver. Comparisons of failure modes and moment vs. rotation relationships of the connections between numerical and experimental results were given. Good agreement has been obtained and the developed finite element model was therefore adopted to conduct a preliminary parametric study to explore the effect of critical parameters on the structural behaviour of beam to concrete-filled elliptical column connections.

No

Indiana University-Purdue University Indianapolis (IUPUI) / Cellular structural mechanics play a key role in homeostasis by transducing mechanical signals to regulate gene expression and by providing adaptive structural stability for the cell. The alteration of nuclear mechanics in various laminopathies and in natural aging can damage these key functions. Arterial endothelial cells appear to be especially vulnerable due to the importance of shear force mechanotransduction to structure and gene regulation as is made evident by the prominent role of atherosclerosis in Hutchinson-Gilford progeria syndrome (HGPS) and in natural aging. Computational models of cellular mechanics may provide a useful tool for exploring the structural hypothesis of laminopathy at the intracellular level. This thesis explores this topic by introducing the biological background of cellular mechanics and lamin proteins in arterial endothelial cells, investigating disease states related to aberrant lamin proteins, and exploring computational models of the cell structure. It then presents a finite element model designed specifically for investigation of nuclear shear forces in arterial endothelial cells. Model results demonstrate that changes in nuclear material properties consistent with those observed in progerin-expressing cells may result in substantial increases in stress concentrations on the nuclear membrane. This supports the hypothesis that progerin disrupts homeostatic regulation of gene expression in response to hemodynamic shear by altering the mechanical properties of the nucleus.

The heavy use of de-icing salts in the winter to accommodate heavy traffic has been the most detrimental cause of chloride-induced corrosion in Canadian reinforced concrete (RC) bridge infrastructure. In addition, the rise of greenhouse emissions and subsequent increase in the mean surface temperature have increased the potential risk of carbonation-induced corrosion. It is believed that the synergistic effect of multiple deteriorating mechanisms will accelerate the incidence of reinforcement corrosion in Canadian infrastructure. Over time, premature deterioration of RC bridges due to reinforcement corrosion leads to concrete cover cracking and spalling, loss of bond between reinforcement and concrete, and reduction in the structural capacity and ductility of the structure. There is limited research work that has examined the effect of corrosion on the structural performance of RC columns. This research has evaluated the axial and flexural capacity of corroded RC columns exposed to different levels and patterns of reinforcement corrosion. An experimental testing campaign of ten RC columns was conducted in two stages. During the first stage, eight columns were subjected to an accelerated corrosion regime by impressing a constant current for 137 days. In the second stage, all ten columns were subjected to an axial quasi-static load until failure. Five columns were loaded concentrically, while the remaining five were loaded eccentrically. The structural performance (residual strength, ductility, resilience, stiffness, toughness and failure mode) of the columns were analyzed from load-displacement curves of the entire and mid-span length of the columns. The experimental results show that corrosion of the ties directly affects the column's post-peak response even at low corrosion levels. Columns with corroded ties had a brittle failure, and the residual ductility and toughness were significantly reduced. On the other hand, longitudinal reinforcement corrosion primarily affects the residual strength of the columns, which is prominent at a medium level of corrosion. At high levels of both longitudinal and transverse reinforcement corrosion, the residual strength, ductility, and axial stiffness are significantly reduced. This is accompanied by a significant deterioration of the cover and local buckling of the longitudinal rebars, which is attributed to a significant reduction in the confinement pressure of the core concrete. A three-dimensional non-linear finite element model (3D-NLFEM) of the columns was developed using the finite element package DIANA (v.10.4) and validated with the experimental results. The effect of reinforcement corrosion on the structural response of columns was modelled as a change in the mechanical and geometrical properties of concrete and steel materials. This was achieved by integrating constitutive and deteriorating models into the 3D-NLFEM. The model accounts for the bond-slip behaviour between longitudinal bars and concrete (for eccentrically loaded columns), the confinement of the concrete core and strength reduction of the concrete cover, and the buckling potential of longitudinal reinforcement. The validated model was used to conduct a parametric analysis to investigate the effect of several influencing variables such as damage level and patterns and to explore scenarios beyond those tested in a laboratory setting. Finally, an analytical model based on sectional analysis was developed and compared with both the experimental and FEM results. The proposed analytical approach was developed by integrating deteriorating models and incorporating data collected from field investigation. Based on this evaluation, a practical analytical approach is proposed to estimate the nominal residual capacity of corroded columns considering the reduction in confinement effects, bond loss and potential buckling. The results from the experimental, numerical, and analytical studies correlate well. This work's outcome will contribute to a better understanding of the axial and flexural performance in terms of the ultimate capacity, post peak response and failure mode of RC columns affected by the reinforcement corrosion and static loading. Moreover, it provides a simplified analytical tool for practicing engineers to predict the axial and flexural capacity of deteriorated bridges vulnerable to reinforcement corrosion and increased traffic volume.

Medial osteoarthritis (OA) and lateral OA have distinct characteristic cartilage lesion locations and knee flexion angles associated with lesion development. These types of OA are suggested to be caused by loading when the knee is in extension and mid-range flexion, respectively. This project used subject-specific finite element (FE) models to investigate contact conditions within the extended and flexed knee. A method of creating subject-specific FE models by combining geometry (derived from magnetic resonance imaging scans) and load cases (calculated from motion analysis data) collected from the same subject was developed. This model creation method was validated by comparing experimentally-measured pressure data to contact data calculated by FE models. Models of normal knees in three subjects were created first. Models with larger subject-specific loads had larger displacements and higher stresses and contact pressures. Contact occurred over most of the articulating cartilage surfaces, both in areas of typical cartilage lesions and outside areas of typical cartilage lesions. Parameters in the normal models were then altered to reflect three mechanical changes hypothesized to lead to OA: increased loading, globally decreased cartilage stiffness, and locally decreased cartilage stiffness. Increased loading led to increased displacements, stresses, and contact pressures. Contact shifted anteriorly in the extended knee models to locations of typical medial OA cartilage lesions; contact remained stationary with elevated stress magnitudes in the flexed knee models. Globally decreasing cartilage stiffness had limited effects on contact results. Locally decreased cartilage stiffness led to locally increased displacement and strain and locally decreased stress and contact pressure. Contact again shifted anteriorly in the extended knee models. Potential mechanisms of OA initiation were then proposed. Increased weight or locally decreased cartilage stiffness increased strains within the cartilage. High strains can damage the cartilage matrix fibres, further decreasing cartilage stiffness and eventually leading to cartilage lesions and OA.

Most modern product development utilizes computational models. With increasing demands on reducing the product development lead-time, it becomes more important to improve the accuracy and efficiency of simulations. In addition, to improve product performance, a lot of products are designed to be lighter and more flexible, thus more prone to nonlinear behaviour. Linear finite element (FE) models, which still form the basis of numerical models used to represent mechanical structures, may not be able to predict structural behaviour with necessary accuracy when nonlinear effects are significant. Nonlinearities are often localized to joints or boundary conditions. Including nonlinear behaviour in FE-models introduces more sources of uncertainty and it is often necessary to calibrate the models with the use of experimental data. This research work presents a model calibration method that is suitable for mechanical systems with structural nonlinearities. The methodology concerns pre-test planning, parameterization, simulation methods, vibrational testing and optimization. The selection of parameters for the calibration requires physical insights together with analyses of the structure; the latter can be achieved by use of simulations. Traditional simulation methods may be computationally expensive when dealing with nonlinear systems; therefore an efficient fixed-step state-space based simulation method was developed. To gain knowledge of the accuracy of different simulation methods, the bias errors for the proposed method as well as other widespread simulation methods were studied and compared. The proposed method performs well in comparison to other simulation methods. To obtain precise estimates of the parameters, the test data should be informative of the parameters chosen and the parameters should be identifiable. Test data informativeness and parameter identifiability are coupled and they can be assessed by the Fisher information matrix (FIM). To optimize the informativeness of test data, a FIM based pre-test planning method was developed and a multi-sinusoidal excitation was designed. The steady-state responses at the side harmonics were shown to contain valuable information for model calibration of FE-models representing mechanical systems with structural nonlinearities. In this work, model calibration was made by minimizing the difference between predicted and measured multi-harmonic frequency response functions using an efficient optimization routine. The steady-state responses were calculated using the extended multi-harmonic balance method. When the parameters were calibrated, a k-fold cross validation was used to obtain parameter uncertainty. The proposed model calibration method was validated using two test-rigs, one with a geometrical nonlinearity and one with a clearance type of nonlinearity. To attain high quality data efficiently, the amplitude of the forcing harmonics was controlled at each frequency step by an off-line force feedback algorithm. The applied force was then measured and used in the numerical simulations of the responses. It was shown in the validation results that the predictions from the calibrated models agree well with the experimental results. In summary, the presented methodology concerns both theoretical and experimental aspects as it includes methods for pre-test planning, simulations, testing, calibration and validation. As such, this research work offers a complete framework and contributes to more effective and efficient analyses on mechanical systems with structural nonlinearities.

Atmospheric plasma sprayed (APS) thermal barrier coatings (TBCs) are commonly used for thermal protection of components in modern gas turbine application such as power generation, marine and aero engines. TBC is a duplex material system consisting of an insulating ceramic topcoat layer and an intermetallic bondcoat layer. TBC microstructures are highly heterogeneous, consisting of defects such as pores and cracks of different sizes which determine the coating's final thermal and mechanical properties, and the service lives of the coatings. Failure in APS TBCs is mainly associated with the thermo-mechanical stresses developing due to the thermally grown oxide (TGO) layer growth at the topcoat-bondcoat interface and thermal expansion mismatch during thermal cycling. The interface roughness has been shown to play a major role in the development of these induced stresses and lifetime of TBCs.The objective of this thesis work was two-fold for one purpose: to design an optimised TBC to be used for next generation gas turbines. The first objective was to investigate the relationships between coating microstructure and thermal-mechanical properties of topcoats, and to utilise these relationships to design an optimised morphology of the topcoat microstructure. The second objective was to investigate the relationships between topcoat-bondcoat interface roughness, TGO growth and lifetime of TBCs, and to utilise these relationships to design an optimal interface. Simulation technique was used to achieve these objectives. Important microstructural parameters influencing the performance of topcoats were identified and coatings with the feasible identified microstructural parameters were designed, modelled and experimentally verified. It was shown that large globular pores with connected cracks inherited within the topcoat microstructure significantly enhanced TBC performance. Real topcoat-bondcoat interface topographies were used to calculate the induced stresses and a diffusion based TGO growth model was developed to assess the lifetime. The modelling results were compared with existing theories published in previous works and experiments. It was shown that the modelling approach developed in this work could be used as a powerful tool to design new coatings and interfaces as well as to achieve high performance optimised morphologies.

This thesis is dedicated to the study of structural and petroleum geology problems. To this purpose, a frictional elastoplastic law based on the Van Eekelen criterion is formulated, which avoids the classical drawbacks of the Drücker Prager criterion. Also, a 2D automatic adaptive re-meshing algorithm is developed for complex multidomains configurations, in order to overcome the limitation of the Lagrangian mesh. Details of the hydromechanical formulation implemented in the LAGAMINE FE code in a large strain context are presented. Application cases (reproduction of sandbox simulation, study of a hydrocarbon trap) concentrate on the study of the strain localisation and potential fracturation using different criteria. In the first case, re-meshing technique allowed to reproduce successfully analogue experiment of thrusting propagation. In the second case, a detailed study based on different initial conditions has brought new insight to the reactivated origin of some faults and has allowed to obtain information on the potential fracturing of the hydrocarbon reservoir unit. As an academic case, the study of anorthosite diapirism is carried out, which confirms the validity of the petrological model of diapirism. Eventually, the hydromechanical coupling effects between a layered porous medium and a fault are illustrated on a simple case.