This research focuses on improvements and application of 1D finite elements for nonlinear dynamic analysis of reinforced concrete frames under extreme loadings. The concept of force interpolation is adopted for the element formulation and a solution scheme developed based on a total secant stiffness approach that provides good convergence characteristics. The geometrical nonlinearities including 2nd order P-Delta effects as well as catenary action are considered in the element formulation. It is shown that geometrical nonlinearities may have a significant effect on member (structure) response within extreme loading scenarios. In the analysis of structures subjected to extreme loadings, accurately modelling of the post peak response is vital and, in this respect, the objectivity of the solution with softening must be maintained. The softening of concrete under compression is taken into account, and the objectivity preserved, by adopting a nonlocal damage model for the compressive concrete. The capability of nonlocal flexibility-based formulation for capturing the post-peak response of reinforced concrete beam-columns is demonstrated by numerical examples. The 1D frame element model is extended for the modelling of 3D framed structures using a simplified torque-twist model that is developed to take account of interaction between normal and tangential forces at the section level. This simplified model can capture the variation of element torsional stiffness due to presence of axial force, bending moment and shear and is efficient and is shown to provide a reasonable degree of accuracy for the analysis of 3D reinforced concrete frames. The formulations and solution algorithms developed are tested for static and dynamic analysis of reinforced concrete framed structures with examples on impact analysis of beams, dynamic analysis of frames and progressive collapse assessment of frames taken from the literature. The verification shows that the formulation is very efficient and is capable of modelling of large scale framed structures, under extreme loads, quickly and with accuracy.

This research focuses on improvements and application of 1D finite elements for nonlinear dynamic analysis of reinforced concrete frames under extreme loadings. The concept of force interpolation is adopted for the element formulation and a solution scheme developed based on a total secant stiffness approach that provides good convergence characteristics. The geometrical nonlinearities including 2nd order P-Delta effects as well as catenary action are considered in the element formulation. It is shown that geometrical nonlinearities may have a significant effect on member (structure) response within extreme loading scenarios. In the analysis of structures subjected to extreme loadings, accurately modelling of the post peak response is vital and, in this respect, the objectivity of the solution with softening must be maintained. The softening of concrete under compression is taken into account, and the objectivity preserved, by adopting a nonlocal damage model for the compressive concrete. The capability of nonlocal flexibility-based formulation for capturing the post-peak response of reinforced concrete beam-columns is demonstrated by numerical examples. The 1D frame element model is extended for the modelling of 3D framed structures using a simplified torque-twist model that is developed to take account of interaction between normal and tangential forces at the section level. This simplified model can capture the variation of element torsional stiffness due to presence of axial force, bending moment and shear and is efficient and is shown to provide a reasonable degree of accuracy for the analysis of 3D reinforced concrete frames. The formulations and solution algorithms developed are tested for static and dynamic analysis of reinforced concrete framed structures with examples on impact analysis of beams, dynamic analysis of frames and progressive collapse assessment of frames taken from the literature. The verification shows that the formulation is very efficient and is capable of modelling of large scale framed structures, under extreme loads, quickly and with accuracy.

No description available.

This study presents an approach based on the floating frame of reference method to model complex three-dimensional bodies in a multibody system. Unlike most of the formulations based on the floating frame of reference method, which assume small or moderate deformations, the present formulation allows large elastic deformations within each frame by using the co-rotational form of the updated Lagrangian description of motion. The implicit integration scheme is based on the Generalized-alpha method, and kinematic joints are invoked in the formulation through the coordinate partitioning method. The resulting numerical scheme permits the usage of relatively large time steps even though the flexible bodies may experience large elastic deformations. A triangular element, based on the first order shear deformable theory, has been developed specifically for folded plate and shell structures. The plate element does not suffer from either shear or aspect-ratio locking under transverse and membrane bending, respectively. A stiffened plate element has been developed that combines a shear deformable plate with a Timoshenko beam. A solid element, that utilized the isoparametric formulation along with incompatible modes, and one-dimensional elements are also included in the element library. The tools developed in the present work are then utilized for detailed rotorcraft applications. As opposed to the conventional approach of using beam elements to represent the rotor blade, the current approach focuses on detailed modeling of the blade using plate and solid elements. A quasi-steady model based on lifting line theory is utilized to compute the aerodynamic loads on the rotor blade in order to demonstrate the capabilities of the proposed tool to model rotorcraft aeroelasticity.

A materially non-linear layered beam super element is developed for the analysis of RC beams and columns strengthened by externally bonded steel/FRP plates. The elasto-plastic behavior of RC member is incorporated by its internally generated or externally supplied moment-curvature diagram. The steel plate is assumed to be elasto-plastic and the FRP laminate is assumed to behave linearly elastic up to rupture. The thin epoxy layer between the RC member and the externally bonded lamina is simulated by a special interface element which allows for the changing failure modes from steel plate yielding/FRP plate rupture to separation of the bonded plates as a result of bond failure in the epoxy layer. An empirical failure criterion based on test results is used for the epoxy material of the interface. The most critical aspect of such applications in real life frame structures is the anchorage conditions at the member ends and junctions. This has direct influence on the success and the effectiveness of the application. Therefore, a special corner piece anchorage element is also considered in the formulation of the joint super element, which establishes the fixity and continuity conditions at the member ends and the joints.

The technology of haptics rendering has greatly enriched development in Multimedia applications, such as teleoperation, gaming, medical and etc., because it makes the virtual object touchable by the human operator(s) in real world. Human head stiffness rendering is significant in haptic interactive applications as it defines the degree of reality in physical interaction of a human avatar created in virtual environment. In a similar research, the haptic rendering approach has two main types: 1) Haptic Information Integration and 2) Deformation Simulation. However, the complexity in anatomic and geometric structure of a human head makes the rendering procedure challenging because of the issues of accuracy and efficiency. In this work, we propose a hybrid method to render the appropriate stiffness property onto a 3D head polygon mesh of an individual user by firstly studying human head's sophisticated deformation behaviour and then rendering such behaviour as the resultant stiffness property on the polygon mesh. The stiffness property is estimated from a semantically registered and shape-adapted skull template mesh as a reference and modeled from soft tissue's deformation behaviour in a nonlinear Finite Element Method (FEM) framework. To render the stiffness property, our method consists of different procedures, including 3D facial landmark detection, models semantic registration using Iterative Closest Point (ICP) technique, adaptive shape modification processed with a modified Weighted Free-Form Deformation (FFD) and FEM Simulation. After the stiffness property is rendered on a head polygon mesh, we perform a user study by inviting participants to experience the haptic feedback rendered from our results. According to the participants' feedback, the head polygon mesh's stiffness property is properly rendered as it satisfies their expectation.

A finite element model of fibre metal laminate (FML) fuselage was developed in order to evaluate its impact response under survivable crash event. To create a reliable crash finite element (FE) model of FML fuselage, a ‘building block approach’ is adapted. It involves a series of validation and verification tasks in order to establish reliable material and damage models, verified impact model with structural instability and large displacement and verified individual fuselage structure under crash event. This novel development methodology successfully produced an FE model to simulate crash of both aluminium alloy and FML fuselage under survivable crash event using ABAQUS/Explicit. On the other hand, this allows the author to have privilege to evaluate crashworthiness of fuselage that implements FML fuselage skin for the whole fuselage section for the first time in aircraft research field and industry. The FE models consist of a two station fuselage section with one meter longitudinal length which is based on commercial Boeing 737 aircraft. For FML fuselage, the classical aluminium alloy skin was replaced by GLARE grade 5-2/1. The impact response of both fuselages was compared to each other and the results were discussed in terms of energy dissipation, crushing distance, failure modes, failure mechanisms and acceleration response at floor-level. Overall, it was observed that FML fuselage responded similarly to aluminium alloy fuselage with some minor differences which conclusively gives great confidence to aircraft designer to use FML as fuselage skin for the whole fuselage section. In terms of crushing distance, FML fuselage skin contributed to the failure mechanisms of the fuselage section that lead to higher crushing distance than in aluminium alloy fuselage. The existence of various failure modes within FML caused slight differences from the aluminium fuselage in terms of deformation process and energy dissipation. These complex failure modes could potentially be manipulated to produce future aircraft structure with better crashworthiness performance.

Shear failure in concrete beams are often brittle in nature and potentially dangerous without adequatereinforcing measures. In design of concrete, it is commonly recommended to install transversalreinforcement along the shear span to induce a more ductile structural response, improving the shearcapacity all together and providing sufficient warning prior to collapse. However, it is more frequentlybeing assessed whether analogous performance can be achieved in fiber reinforced concrete beamswithout stirrups, and multiple attempts in literature confirm that it is possible. This alternative technologyintroduces need for better understanding of the modeling aspects of FRC in numerical simulations, as it isbecoming more common for engineers to resort to the finite element method in quality assurance ofstructures.In this thesis, the possibility of predicting shear failure numerically in simply supported fiber reinforcedconcrete beams with flexural bar reinforcement but without stirrups was investigated by means ofnonlinear finite element analysis, using the software package ATENA 2D Engineering. The ultimate aimwas to, as accurately as possible by means of numerical analyses on representative FE-models, replicatethe results from physical three-point-bending tests on simply supported FRC beams of various sizesperformed by Minelli et al. (2014). These beams were merely equipped with flexural reinforcement andexhibited shear failure.This thesis revolved around development and comparative assessment of material models for FRC basedon the smeared crack approach, adopting two different strategies: (1) The first strategy was to calibratematerial parameters based on results from 3PBT on notched FRC beams that were carried out prior totesting of the reinforced FRC beams, as reported by Minelli et al. (2014). Nonlinear finite element analysiswas used on representative FE-models for the notched 3PBT specimens, from which material parameterswere obtained iteratively by employing inverse analysis methods proposed by Červenka Consulting s.r.o.(2). The second strategy comprised of utilizing recommended constitutive relations from designrecommendations in SS812310 and RILEM TC 162-TDF. All of the constructed material models werefinally coupled with the FE-models that represented the beams with flexural reinforcement for evaluationof their performance based on their consistency with experiment data.It was found that the material models that were generated from inverse analysis in general would haveyielded successful predictions for the occurrence of shear failure in the reinforced FRC beams, providedthat the governing post-cracking residual tensile parameters were processed with respect to relevantassumptions as to describe uniaxial tensile behavior. However, although it was possible to utilize theproposed calibration method to replicate the load-displacement data for the notched 3PBT specimens withsufficient conformity, it was not possible to arrive at only one unique solution. Instead, multiple outcomescould be obtained based on the initial choice for the input value of the uniaxial tensile strength, leading tothe conclusion that experience and the engineering judgment of the user is of high importance whenadopting this method.Regarding the material models that were derived from constitutive relations in design recommendations,satisfactory estimates for the shear capacity could be obtained from the FE-models that were based onrecommendations by RILEM. The models that were based on SS812310, on the other hand, demonstratedover-stiff behavior and they were unable to provide accurate graphical visualizations of characteristicshear cracking, although the obtained load bearing capacity overall matched the experiment data in caseswhen size effects seemingly had a minor influence. An important observation from the comparison ofthese material models was that the initial drop in tensile strength during crack initiation within an elementis crucial in modeling of FRC, as it accounts for a more realistic behavior through a gradual transitionfrom aggregate bridging mechanisms of PC to the added fiber bridging mechanisms of FRC. Forsituations with high residual tensile strengths in relation to tensile strength at crack initiation, theguidelines in SS812310 become less practical for predicting shear failure by means of NLFEA.

No description available.

Non-ductile Reinforced Concrete Frames (RCF) with and without Unreinforced Masonry (URM) infills can be found in many places around the world including the Western United States, Eastern Europe, Asia and Latin America. These structures can have an unsatisfactory seismic performance which may even lead to collapse due to brittle failure modes. Furthermore, the effect of the infills on the seismic response of the structural system is not always accounted for in analysis and design. At present, there is no consensus on whether masonry infills are beneficial (by increasing the resistance of the system) or detrimental (by leading to brittle failure modes) for RCF construction. This study focuses on the development of a simplified modeling approach for non-ductile RCF with URMI that combines the simplicity of strut-and-tie models with the accuracy of Nonlinear Finite Element Analysis (NLFEA). Despite the fact that NLFEA procedures are the most advanced way to address the structural analysis of RCF with URM infills, their conceptual complexity and computational cost may hinder their widespread adoption as an analysis and design tool. At the same time, simplified methods, such as those based on the equivalent strut concept, may be overly crude and neglect essential aspects of the nonlinear response. To address the need for an adequately accurate, but computationally and conceptually efficient analysis method, this study establishes a novel method for planar RCF with URM infills subjected to lateral loads. The method, which is based on the Nonlinear Truss Analogy (NLTA) is shown to have an accuracy comparable to that of NLFEA. Specifically, the method is shown to adequately capture the strength and stiffness degradation and the damage patterns while entailing a reduced computational cost (compared to that of NLFEA). The proposed method is expected to bridge the gap between overly crude equivalent strut models and computationally expensive NLFEA. / Ph. D.