Orientador: José Antônio Matthiesen / Banca: José Luiz Pinheiro Melges / Banca: Antonio Alves Dias / Resumo: As pontes mistas com vigas de madeira e tabuleiro de concreto, que constituem uma técnica já bastante estudada pelo meio acadêmico brasileiro, vêm ganhando cada vez mais espaço entre os projetistas e construtores de pontes em estradas vicinais do interior do Brasil. Entretanto, o vão dessas pontes é limitado pelo comprimento das peças de madeira, cujos valores máximos, em geral, ficam em torno de 6 metros para vigas serradas e 12 metros para vigas roliças. Neste contexto, a presente pesquisa propõe um novo sistema estrutural de pontes mistas para vencer vãos da ordem de 15 a 20 metros, constituído por vigas treliçadas de madeira que suportam a laje de concreto armado. O tabuleiro do sistema proposto pode ser executado utilizando, como pré-laje, painéis treliçados pré-moldados auto-portantes, evitando-se escoramentos e, conseqüentemente, reduzindo o tempo e os custos de construção. A laje final é solidarizada às treliças de madeira por intermédio de pinos metálicos de cisalhamento, que fazem com que ambos os materiais trabalhem solidariamente na resistência aos esforços solicitantes, buscando, portanto, a otimização do uso estrutural desses materiais. A principal abordagem desta pesquisa é experimental, com a construção e análise de um modelo físico reduzido na escala 1:4... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Timber-concrete composite structures - TCCS - constitute a technique well studied by the Brazilian academy and have been each time more present among the designers and constructors of bridges in secondary roads in the interior of Brazil. However, the span of these bridges is limited by the length of the timber beams, whose maximum values, in general, are around 6 meters for sawed beams and 12 meters for round beams. In this context, the present research suggests a new structural system of composite bridges, to overcome spans from 15 to 20 meters, built by trussed timber beams that support a reinforced concrete deck. The deck of the system can be executed using precast self-supported trussed panels, preventing props and, consequently, reducing time and costs of construction. The final slab is connected to the trussed beams by metallic shear bolts, which make that both the materials (timber and concrete) work together in the resistance to the requesting efforts, aiming the optimization of the structural use of these materials. This research was based on an experimental approach, with the construction and analysis of a reduced physical model in the scale 1:4, based on a bridge design classified as 30t with a free span of 16 meters. The model was instrumented with strain gauges and... (Complete abstract click electronic access below) / Mestre

Orientador: Nilson Tadeu Mascia / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Civil, Arquitetura e Urbanismo / Made available in DSpace on 2018-08-09T14:29:25Z (GMT). No. of bitstreams: 1 Forti_NadiaCazarimdaSilva_M.pdf: 2737779 bytes, checksum: ef0859d0c54102ccc7c7df3f3e38f2b0 (MD5) Previous issue date: 2004 / Resumo: O desenvolvimento tecnológico do projeto em estruturas de madeira permitiu melhorar o conhecimento de suas propriedades mecânicas e dos sistemas de conexões em estruturas. Estruturas mistas de madeira com concreto ou aço e os reforços do material com fibras de polímeros estruturais passaram a ser realidade. As estruturas mistas, constituídas por materiais de diferentes propriedades mecânicas associados, são uma solução alternativa às estruturas de uso corrente na construção civil. Essa medida busca obter redução de custos de construção, mantendo também a segurança estrutural, com um desempenho arquitetônico e ambiental vantajoso. A integração de uma estrutura mista deve-se, em geral, à eficiência do sistema de ligação, podendo ser do tipo rígido ou flexível. Esse sistema é responsável por transmitir a força de cisalhamento longitudinal na interface dos dois materiais combinados ao longo do comprimento da viga e também, impedir o desprendimento vertical dos mesmos. Esta pesquisa contribui para a análise do comportamento mecânico de vigas mistas de três maneiras: via programa de elementos finitos bidimensionais, via resolução analítica das equações de equilíbrio e via a equação do princípio dos trabalhos virtuais. A última abordagem foi concebida a partir de pesquisas de teoria das estruturas, expandindo seus conceitos para vigas mistas. A formulação proposta satisfaz as equações de equilíbrio mostrando-se consistente e seus resultados são condizentes com dados experimentais. Essa formulação pode ser facilmente integrada a códigos de elementos finitos requerendo apenas elementos unidimensionais / Abstract: The technologycal development of the design in wood structures has improved the knowledge of the material mechanical properties and the connection systems applied to structures. Composite structures of wood with concrete or steel and structural reinforcement using polymer fibers have become a reality. These structures, constituted by associating materials with different mechanical properties are an alternative solution for current using structures in civil construction. This arrangement aims at obtaining a reduction of construction costs also maintaing the structural safety with advantageous environmental and architectural performance. The integration of a composite structure is, in general, due to the efficiency of the connection system that can be rigid or flexible type. This system is responsible to transfer the longitudinal shear force on the interface of the associated materials along the beam length and to avoid the vertical detachment of them as well. This research contributes to the analysis of the mechanical performance of the composite beams in three ways: bidimensional finite element program, analytical solution of the equilibrium equations and virtual work principle equation via. The last approach was conceived from structural theory researches, expanding their concepts for composite beams. The proposal formulation fulfils the equilibrium equation showing to be consistent and the results fit with the experimental data. This formulation can be easily integrated to a finite element procedure requiring unidimensional elements only / Mestrado / Estruturas / Mestre em Engenharia Civil

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The purpose of this research is to investigate the structural efficiency of 8-node IsoTruss structures subject to uniaxial compression using numerical, dimensional, and optimization methods. The structures analyzed herein are based on graphite/epoxy specimens that were designed for light-weight space applications, and are approximately 10 ft. (3 m) long and 0.3 lb. (0.14 kg). The principal failure modes considered are material failure, global buckling, local buckling at the bay level, and longitudinal strut buckling. Studies were performed with the following objectives: to correlate finite element predictions with experimental and analytical methods; to derive analytical expressions to predict bay-level buckling; to characterize interrelations between design parameters and buckling behavior; to develop efficient optimization methods; and, to compare the structural efficiency of outer longitudinal configurations with inner longitudinal configurations. Finite element models were developed in ANSYS, validated with experimental data, and verified with traditional mechanics. Data produced from the finite element models were used to identify trends between non-dimensional Pi variables, derived with Buckingham's Pi Theorem. Analytical expressions were derived to predict bay-level buckling loads, and verified with dimensional analyses. Numerical and dimensional analyses were performed on IsoTruss structures with outer longitudinal members to compare the structural performance with inner longitudinal configurations. Analytical expressions were implemented in optimization studies to determine efficient and robust optimization techniques and optimize the inner and outer longitudinal configurations with respect to mass. Results indicate that the finite element predictions of axial stiffness and global buckling loads correlate with traditional mechanics equations, but overestimate the capacity demonstrated in previously published experimental results. The buckling modes predicted by finite element predictions correlate with traditional mechanics and experimental results, except when the local and global buckling loads coincide. The analytical expressions derived from mechanics to predict local buckling underestimate the constraining influence of the helical members, and therefore underestimate the local buckling capacity. The optimization analysis indicates that, in the specified design space, the structure with outer longitudinal members demonstrates a greater strength-to-weight ratio than the corresponding structure with inner longitudinal members by sustaining the same loading criteria with 10% less mass.

<div>Polymer matrices present in composite materials are prone to have time-dependent behavior very sensitive to changes in temperature. The modeling of thermoviscoelasticity is fundamental for capturing the performance of anisotropic viscoelastic materials subjected to both mechanical and thermal loads, or for manufacturing simulation of composites. In addition, improved plate/shell and beam models are required to efficiently design and simulate large anisotropic composite structures. Numerical models have been extensively used to capture the linear viscoelasticity in composites, which can be generalized in integral or differential forms. The hereditary integral constitutive form has been adopted by many researchers to be implemented into finite element codes, but its formulation is complex and time consuming as it is function of the time history. The differential formulation provides faster computation times, but its applicability has been limited to capture the behavior of three-dimensional thermoviscoelastic orthotropic materials.</div><div><br></div><div>This work extends mechanics of structure genome (MSG) to construct linear thermoviscoelastic solid, plate/shell and beam models for multiscale constitutive modeling of three-dimensional heterogeneous materials made of time and temperature dependent constituents. The formulation derives the transient strain energy based on integral formulation for thermorheologically simple materials subject to finite temperature changes. The reduced time parameter is introduced to relate the time-temperature dependency of the anisotropic material by means of master curves at reference conditions. The thermal expansion creep is treated as inherent material behavior. Exact three-dimensional thermoviscoelastic homogenization solutions are also formulated for laminates modeled as an equivalent, homogeneous, anisotropic solid. The new model is implemented in SwiftComp, a general-purpose multiscale constitutive modeling code based on MSG, to handle real heterogeneous materials with arbitrary microstructures, mesostructures or cross-sectional shapes.</div><div><br></div><div>Three-dimensional representative volume element (RVE) analyses and direct numerical simulations using a commercial finite element software are conducted to verify the accuracy of the MSG-based constitutive modeling. Additionally, MSG-based plate/shell results are validated against thin-ply high-strain composites experimental data showing good agreement. Numerical cases with uniform and nonuniform cross-sectional temperature distributions are studied. The results showed that unlike MSG, the RVE method exhibits limitations to properly capture the long-term behavior of effective coefficients of thermal expansion (CTEs) when time-dependent constituent CTEs are considered. The analyses of the homogenized properties also revealed that despite the heterogeneous nature of the composite material, from a multiscale analysis perspective, the temperature dependencies of the effective stiffness and thermal stress properties are governed by the same shift factor as the polymer matrix. This conclusion remains the same for MSG-based solid, plate/shell and beam models with uniform temperature distributions.</div>

Bio-composites are increasing in demand due to governmental incentives across the globe for both environmental and human health reasons. The ideal bio-composite is renewable, recyclable, available, and non-toxic. To properly engineer bio-composite products, the physical properties of the fiber as well as fiber/matrix interactions must be known. The problem lies in the fact that many suitable natural fibers are not currently available in a material form that may be easily worked with. This research investigates methods to process raw kenaf (hibiscus cannabinus) on a scale that allows researchers to make more consistent samples for testing. Though kenaf is highlighted, these processing methods may be applied to any natural fiber. The raw fibers are processed into kenaf chopped strand mats (KCSM) by adapting basic paper-making techniques. KCSM exhibit paper-like qualities and mechanical properties and provide a material of uniform thickness for use in composite parts. Also presented are a basic understanding of natural fiber constituents and effects of mechanical and co-mechanical treatments on those constituents. To test KCSM, samples are made for the ASTM D3039 tensile testing and for testing in a dynamic material analyzer (DMA). Both mechanically and chemo-mechanically processed samples are made for the purpose of comparison. Also, I-beam bridges are built with KCSM to demonstrate how KCSM may be used to create a structure. This is spurred on by the annual SAMPE bridge competition that includes special categories for natural fiber beams. The lay-up procedure is shown in detail to provide a framework that future competitors may use to build quality I-beams for this competition. The properties obtained by using the KCSM are competitive with other reported properties for kenaf-based composites. A kenaf I-beam demonstrates a strength-to-weight ratio that is 65% of a berglass I-beam built to the same dimensions. Trade-os of using KCSM are the random 2d-fiber orientation and brittle failure, which are not usually desirable in composite components. The chemically treated samples indicate a higher degree of crystallinity but demonstrate inferior mechanical properties when compared to the untreated samples.

Damage in composite material fabricated aerospace, aeronautical, mechanical, civil and offshore structures often results from factors such as fatigue, corrosion and accidents. Such damage when left unattended can grow at an alarming rate due to the singularity of the stress and strain in the vicinity of the damage. It can lead to increase in the vibration level, reduction in the load carrying capacity, deterioration in the normal performance of the component and even catastrophic failure. In most conditions, the service life of damaged components is extended with repair instead of immediate replacement. Effective repair of structural damage is therefore an important and practical topic. Repair can extend the service life and can be a cost efficient alternative to immediate replacement of the damaged component. Most conventional repair methods involve welding, riveting or mounting additional patches on the parent structure without removing the damaged portion. These methods tend to be passive and inflexible, faced with the limitations of adjusting the repair to the changes in external loads.Besides, in certain cases these methods may lead to additional damage to the structure. For example, the in-situ drilling required in some cases can cause damage to items such as hidden or exposed hydraulic lines and electrical cables. Welding or bonding patches can cause significant stress alterations and serious stress corrosion problems, apart from burdening the weight sensitive structures. Above all, effective repair applying conventional analytical methods hinges on calculation of the singularity of stress and strain in the vicinity of the damage, which is be a difficult as only approximate solutions are available. Thus, a need is felt to update the repair methods with the advancement in fields of materials, sensing and actuating. This can make the repair more effective and efficient than conventional repair methodology. Current research proposes the use of piezoelectric materials in repair of delaminated composite structures. A detailed mechanics analysis of the delaminated beams, subjected to concentrated static loads and axial compressive loads, is presented. The discontinuity of shear stresses induced at delamination tips due to bending of the beams, under action of concentrated static load and axially compressive load, is studied. This discontinuity of the shear stresses normally leads to the sliding mode of fracture of the beam structures. In order to ensure proper functioning of these beam structures, electromechanical characteristics of piezoelectric materials are employed for their repair. Numerical simulations are conducted to calculate the repair voltage to be applied to the piezoelectric patches to erase the discontinuity of horizontal shear stress at the delamination tips and thus, render the beam repaired. The variation of repair voltage with location and size of the delamination is considered. FE simulations are performed to validate the numerically calculated voltage values. The research presented serves to provide information on the design of piezoelectric materials for the repair of delaminated composite structures.

Composite sandwich structures are prevalent in engineering applications where high strength to weight ratios are critical. A composite sandwich includes the addition of a core material between two composite face sheets to increase ultimate stress in compression and bending loading cases. The performance of many composite sandwich structure configurations is well understood in the undamaged case. This analysis examines a type of damage, low velocity indentation, and determines the effect on mechanical behavior. The scope of the analysis includes manufacturing sandwich composite structures, creating indentation in the composite, and testing the sandwich composite structure. The mechanical behavior of the composite sandwich structures is characterized through ASTM C364 test standard for compressive strength and ASTM C393 standard test standard for flexural properties of sandwich constructions. The experiment is conducted with varied indentation depth, core materials, composite sandwich thickness, and composite face sheet thickness. The findings are compared to control specimens and used to determine the effect of indentation depth and create a relationship for the mechanical performance of indented sandwich composites.

The digital transformation of engineering design processes is essential for the aerospace industry to remain competitive in the global market. Multidisciplinary design optimization (MDO) frameworks play a crucial role in this transformation by integrating various engineering disciplines and enabling the optimization of complex spacecraft structures. Since the design team consists of multiple entities from different domains working together to build the final product, the design and analysis tools must be readily available and compatible. An integrated approach is required to handle the problem's complexity efficiently. Additionally, most aerospace structures are made from composite panels. It is challenging to optimize such panels as they require the satisfaction of constraints where the design ply thicknesses and orientations can only take discrete values prescribed by the manufacturers. Heuristics such as particle swarm or genetic algorithms are inefficient because they provide sub-optimal solutions when the number of design variables is large. They also are computationally expensive in handling the combinatorial nature of the problem. To overcome these challenges, this work proposes a two-fold solution that integrates multiple disciplines and efficiently optimizes composite spacecraft structures by building a rapid design framework. The proposed model-based design framework for spacecraft structures integrates commercially available software from Siemens packages such as NX and HEEDS and open-source Python libraries. The framework can handle multiple objectives, constraint non-linearities, and discrete design variables efficiently using a combination of black-box global optimization algorithms and Mixed Integer Programming (MIP)-based optimization techniques developed in this work. Lamination parameters and MIP are adopted to optimize composite panels efficiently. The framework integrates structural, thermal and acoustic analysis to optimize the spacecraft's overall performance while satisfying multiple design constraints. Its capabilities are demonstrated in optimizing a small spacecraft structure for required structural performance under various static and dynamic loading conditions when the spacecraft is inside the launch vehicle or operating in orbit. / Doctor of Philosophy / The design of new spacecraft takes several years and requires significant resources. The primary design objective is to minimize spacecraft mass/cost while satisfying the mission requirements. This is done by altering the structure's geometric and material properties. Most spacecraft panels are made from composite materials where the orientations of fiber paths and the thickness of the panel determine its strength and stiffness. Finding the best values for these parameters cannot be done efficiently using existing optimization algorithms, as several combinations of orientations can give a similar performance which can be subpar. In this dissertation, mathematical programming is adopted for fast evaluation of optimum panel properties, thereby saving a significant amount of resources compared to conventional techniques. Moreover, the requirements that govern the design process are handled one at a time in an organization. This leads to discrepancies in the various teams' designs that satisfy all requirements. A framework is built to integrate all requirements to account for their conflicting nature and quickly give the best possible spacecraft structural design configuration.

Composite materials, constructed from a combination of fibre and resin, have rapidly emerged as a high performance alternative to conventional materials for new constructions as well as strengthening and repair of existing structures. However, the use of such materials may be accompanied by various types of damages and failure modes, including delamination, debonding, fibre rupture, and matrix cracking. This thesis presents a new nondestructive evaluation (NDE) technique for damage detection in composite structures. The concept, based on detecting local dielectric permittivity variations, was employed to design capacitance sensors with high sensitivity to detect such damages. An analytical and 2D finite element models were used to assess the influence of the sensor geometrical parameters on the output signals and to optimize the sensor design. Concrete and wood specimens wrapped with glass-fibre composites containing pre-induced defects with different types and sizes were constructed and inspected. The sensors were also used to detect the delaminations and water intrusion defects in pultruded composite members. The principles behind the sensor operation were also applied to detect other damages in other structures; the capacitance sensors were designed and used to locate ungrouted cells in a concrete masonry wall. The proposed sensors, coupled with a commercially available portable capacitance meter, facilitate employing this technique in the field for rapid inspection of composite structures without the need for sophisticated data analyses that are usually required by other more expensive and time consuming NDE techniques. / Thesis / Master of Applied Science (MASc)