Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2004. / Includes bibliographical references. Also available in electronic version. Access restricted to campus users.

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references (leaves 206-211). Also available on the Internet.

The finite element method is applied in conjunction with Reissner's mixed variational principle to the investigation of two-dimensional elastic contact problems. The versatility of the mixed principle in incorporating boundary conditions pertinent to the contact problem is demonstrated. Contact conditions are modelled by appropriate manipulations of boundary variables. In cases where the contact region is independent of the applied loading, an iterative procedure is used to establish the sliding and adhering portions in the contact region. Numerical results for displacements and stresses are independently confirmed by the finite element analysis in conjunction with the minimum potential energy principle. In cases where the contact region is a function of the applied loading, or progressive contact, an incremental formulation is employed to describe the discretized contact stages. In the example of a frictionless contact between a long cylinder and a rigid base, good confirmation is obtained from Hertz's analytical solution. Criteria for taking one contact stage to another are also outlined for frictional progressive contact. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

A micro mechanical finite element model to compute the overall instantaneous stiffness of fiber-reinforced composites in elastic-plastic response is presented. The model is applicable to a periodic diamond array of elastic circular fibers embedded in an elastoplastic matrix subjected to a plane stress loading. This model enforces symmetry and anti-symmetry conditions isolating the smallest unit cell and should greatly increase the speed of doing "built-inn micromechanics within a larger finite element program because of the small number of degrees of freedom (12 to 14 d.o.f.). The matrix plastic behavior is modeled using the endochronic theory without a yield surface. Various off-axis elastoplastic characteristics predicted by the mini grid for a boron/aluminum composite are presented. Comparison with experimental data and a fine grid finite element solution shows very good agreement and demonstrates the effectiveness of the mini model presented. / Master of Science

Call number: LD2668 .T4 1979 E43 / Master of Science

This dissertation investigates the distributed damage effect on Progressive Collapse of structures highlighted by applications on the nonlinear static and dynamic behavior of buildings, and contributes to the theoretical development of the Variability Response Function concept and its applicability extension in two-dimensional elasticity stochastic problems. Part I of this dissertation focuses on the recently emerging research field of Progressive Collapse of structures. The alternate load path method has so far dominated the field of progressive collapse of structures; in order to assess the resilience of structural systems, the concept of the removal of a key element is utilized as a means of damage introduction to the system. Recent studies have indicated that the complete column loss notion is unrealistic and unable to describe a real extreme loading event, e.g. a blast, that will introduce damage to more than one elements in its vicinity. This dissertation presents a new partial distributed damage method (PDDM) for steel moment frames, by utilizing powerful finite element computational tools that are able to capture loss of stability phenomena. Through the application of a damage index δj and the investigation of damage propagation, it is shown that the introduction of partial damage in the system can significantly modify the collapse mechanisms and overall affect the response of the structure. Subsequently, Part I elaborates on the distributed column damage effect on Progressive Collapse vulnerability in steel buildings exposed to an external blast event. Recent terrorist attacks on civil engineering infrastructure around the world have initiated extensive research on progressive collapse analysis of multi-story buildings subjected to blast loading. The widely accepted alternate load path method is a threat-independent method that is able to assess the response of a structure in case of extreme hazard loads, without the consideration of the actual loads occurring. Such simplification offers great advantages but at the same time fails to incorporate the role of a wider damaged area into the collapse modes of structures. To this end, the investigation of damage distribution on adjacent structural members induced by blast loads is considered critical for the evaluation of structural robustness against abnormal loads that may initiate progressive collapse. This dissertation presents detailed 3D nonlinear finite element dynamic analyses of steel frame buildings in order to examine the spatially distributed response and damage to frame members along the building exterior facing an external blast. A methodology to assess the progressive collapse vulnerability is also proposed, which includes four consecutive steps to simulate the loading event sequence. Three case studies of steel buildings with different structural systems serve as examples for the application of the proposed methodology. A high-rise (20-story) building is firstly subjected to a blast load scenario, while the complex 3D system results in the heavily impacted region are compared with individual column responses (SDOF) obtained from a simplified analytical approach consistent with current design recommendations. Parameters affecting the spatially distributed pressure and response quantities are identified, and the sensitivity of the damage results to the spatial variation of these parameters is established for the case of the 20-story building. Subsequently, two typical mid-rise (10-story) office steel buildings with identical floor plan layout but different lateral load resisting systems are examined; one including perimeter moment resisting frames (MRFs) and one including interior reinforced concrete (RC) rigid core. It is shown that MRFs offer a substantial increase in robustness against blast events, and the role of interior gravity columns identified as the `weakest links'\ of the structural framing is discussed. Part II of this dissertation focuses on the development of Variability Response Functions for apparent material properties in 2D elasticity stochastic problems. The material properties of a wide range of structural mechanics problems are often characterized by random spatial fluctuations. Calculation of apparent properties of such randomly heterogeneous materials is an important procedure, yet no general method besides Monte Carlo simulation exists for evaluating the stochastic variability of these apparent properties for structures smaller than the representative volume element (RVE). In this direction, the concept of Variability Response Function (VRF) has been proposed as a means to capture the effect of stochastic spectral characteristics of uncertain system parameters modeled by homogeneous stochastic fields on the uncertain response of structural systems, without the need for computationally expensive Monte Carlo simulations. Recent studies have formally proved the existence of VRF for apparent properties for statically determinate linear beams through elastic strain energy equivalence of the heterogeneous and equivalent homogeneous bodies, while a Monte-Carlo based methodology for the generalization of the VRF concept to statically indeterminate beams has been recently developed. In this dissertation, the VRF methodology of apparent properties is extended to two-dimensional elasticity stochastic problems discretized on a finite element domain, in order to analytically formulate a VRF that is independent of the marginal distribution and spectral density function of the underlying random heterogeneous material property field (it depends only on the boundary conditions and deterministic structural configuration). Representative examples that illustrate the approach include two-dimensional plane stress problems and underline the dependence of the VRFs on scale, shape and aspect ratio of the finite elements.

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"November 1967." / Includes bibliographical references / 2 v. : ill., plates ; 1967 / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Civil Engineering, 1968

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