O trabalho analisa as forças atuantes no contraventamento de treliças triangulares de coberturas de madeira por meio de modelos numéricos computacionais. Os modelos foram confeccionados no sistema de análise estrutural Strap e consideram o funcionamento do contraventamento na estrutura tridimensional. Os valores máximos das forças obtidas nos modelos tridimensionais foram comparados aos valores mínimos indicados pelo método de estimativa da NBR 7190 (1997), este, baseado na instabilidade lateral do elemento contraventado. Os valores dos modelos tridimensionais também foram comparados aos métodos do Eurocode 5, da norma sul-africana SABS 0163 e aos valores propostos por Underwood (2000), por apresentarem formulação semelhante ao da NBR 7190 (1997). Os modelos representam galpões usuais na prática, com dimensões variando de 12 a 24 metros de vão; 24 a 96 metros de comprimento; 3, 4 e 6 metros de altura do pilar. Foram analisados para os tipos de treliça Howe e Pratt, para as classes de madeira C30 e C50 e para os tipos de telhas fibrocimento, metálicas e cerâmicas, materiais mais utilizados no Brasil. Os resultados mostram que as forças atuantes no contraventamento dos modelos tridimensionais são superiores aos valores obtidos pelo método da NBR 7190 (1997) e que valores obtidos pelos métodos propostos pelo Eurocode 5 e por Underwood (2000) apresentam-se mais seguros diante do funcionamento global da estrutura. / This work analyzes the forces acting on the bracing bars of triangular timber trusses by computational numerical models. The models are produced in the system of structural analysis Strap and consider the operation of bracing in the three-dimensional structure. The maximum forces obtained in the three-dimensional models are compared to the minimum values indicated by the estimation method of the NBR 7190 (1997), which is based on the lateral instability of the braced element. The values of three-dimensional models are also compared to the methods of Eurocode 5, the South African standard SABS 0163 and the values proposed by Underwood (2000). The models represent sheds with usual dimensions ranging from 12 to 24 meters wide, 24 to 96 feet long, and pillar 3, 4 and 6 meters tall. Are analyzed the Pratt and Howe types of truss, the timber classes C30 and C50 and the types of tiles: cement, metal and ceramics, materials most used in Brazil. The results show that the forces acting on the bracing of the three-dimensional models are greater than those obtained by the NBR 7190 (1997) and values obtained by methods proposed by the Eurocode 5 and Underwood (2000) provides more insurance on the overall functioning structure.

Este trabalho apresenta o estudo teórico e experimental do comportamento de placas ortótropas treliçadas protendidas transversalmente, sendo as ligações das barras das treliças com conector de chapas com dentes estampados (CDE), para aplicação em pontes de madeira observando as principais características do sistema como: avaliação do elemento estrutural e do modelo estrutural para verificação dos deslocamentos da placa. Para esta finalidade foram determinadas as propriedades dos materiais, elementos estruturais e níveis de protensão da placa. A avaliação das propriedades elásticas da placa foi realizada utilizando dois modelos numéricos, sendo um baseado no método dos elementos finitos e o segundo em séries de Levy-Nadai. A aferição do modelo proposto foi realizado com o ensaio de um protótipo em escala real. Os resultados indicaram que a placa tem um ótimo comportamento para a utilização em pontes apresentando elevada rigidez e baixo consumo de madeira, e que os modelos propostos apresentaram-se consistentes para aplicação nos sistemas de placas ortótropas treliçadas com ligações de chapas com dentes estampados / This work aim to the theoretical and experimental study of the behaviour of orthotropic stress-laminated truss plate for timber bridges construction. To this purpose the material properties, structural elements, conections and prestress level were analysed. Two numeric models were used in order to avaliate the plate elastic properties, based on the finite elements analysis method and in Levy-Nadai series. The theorical model calibration was made with the results obtained in a full-scale prototype. The results indicated that the plate behavior was efficiency for the use in bridges with high stiffness and wood low consumption, and that the proposed numeric models was consistent for application in ortrotropic stress-laminated truss plate systems with metal-plate-connected

A norma brasileira para projeto de estruturas de madeira foi revisada recentemente para considerar critérios de dimensionamento baseados no método dos estados limites. Com isto ocorreu uma alteração fundamental no processo de dimensionamento de elementos estruturais de madeira. O objetivo deste trabalho é identificar os aspectos pertinentes do processo de dimensionamento de estruturas treliçadas industrializadas de madeira para telhados, e desenvolver um software para determinar as solicitações de cálculo e verificação dos estados limites últimos e de utilização de elementos estruturais (barras de tesouras, ligações entre barras de tesouras por conectores metálicos com dentes estampados (CDE), terças e caibros) baseadas na norma NBR 7190 - Projeto de Estruturas de Madeira da Associação Brasileira de Normas Técnicas (1997). / The brazilian code for design of timber structures were recently revised to consider the concepts of limit states design. There was a fundamental alteration in the process for design of wooden structures. The aim of this study is the identification of the pertinent aspects of the design process for industrialized trussed timber structures for roofing, and the development of a software for structural analysis and design of structural members (truss members, metal plate connected joints, purlins and rafters) based on the standard NBR 7190 - Projeto de Estruturas de Madeira - Associação Brasileira de Normas Técnicas (1997).

<p> A research programme is presented for the analytical. evaluation of the deflections of Vierendeel trusses comprised of semi-rigid connections under panel feint loadings. The semi-rigid connections are made of two unequal width square ESS members welded at right angles. As the flexibility of the joints increases when the width ratio is less than 1.0, the joints are unable to develop the moment capacity of the web member and excessive deflections limit functional capability of the truss. Hence, several types of joint reinforcement are recommended. A yield line method is attempted to estimate the strength capacity of the joint with and without reinforcements. In addition, a plate analysis forms the basis for estimating elastic joint stiffness for evaluating anticipated deflections at mid span. </p> / Thesis / Master of Engineering (MEngr)

A method for the incorporation of continuum modeling in the optimization of large discrete structures is presented. The use of a continuum model facilitates decomposition of optimization problems and augments the scope and applicability of the multilevel decomposition method. This new concept is demonstrated by the optimization of slender, multi-bay, beam-like trusses with large numbers of members. An algorithm for the continuum model optimization of the truss is developed and tested against a traditional algorithm that might be used to solve the problem. Data are presented that reflect the advantages of the continuum model method over the traditional in the areas of computational efficiency and robustness. Additionally, design results for the beam-like truss are presented. / Master of Science

The probabilistic approach to design optimization has received increased attention in the last two decades. It is widely recognized that such an approach should lead to designs that make better use of the resources than designs obtained with the classical deterministic approach by distributing safety onto the different components and/or failure modes of a system in an optimal manner. However, probabilistic models rely on a number of assumptions regarding the magnitude of the uncertainties, their distributions, correlations, etc. In addition, modelling errors and approximate reliability calculations (first order methods for example) introduce uncertainty in the predicted system reliability. Because of these inaccuracies, it is not clear if a design obtained from probabilistic optimization will really be more reliable than a design based on deterministic optimization. The objective of this work is to provide a partial answer to this question through laboratory experiments — such experimental validation is not currently available in the literature. A cantilevered truss structure is used as a test case. First, the uncertainties in stiffness and mass properties of the truss elements are evaluated from a large number of measurements. The transmitted scatter in the natural frequencies of the truss is computed and compared to experimental estimates obtained from measurements on 6 realizations of the structure. The experimental results are in reasonable agreement with the predictions, although the magnitude of the transmitted scatter is extremely small. The truss is then equipped with passive viscoelastic tuned dampers for vibration control. The controlled structure is optimized by selecting locations for the dampers and for tuning masses added to the truss. The objective is to satisfy upper limits on the acceleration at given points on the truss for a specified excitation. The properties of the dampers are the primary sources of uncertainties. Two optimal designs are obtained from deterministic and probabilistic optimizations; the deterministic approach maximizes safety margins while the probability of failure (i.e. exceeding the acceleration limit) is minimized in the probabilistic approach. The optimizations are performed with genetic algorithms. The predicted probability of failure of the optimum probabilistic design is less than half that of the deterministic optimum. Finally, optimal deterministic and probabilistic designs are compared in the laboratory. Because small differences in failure rates between two designs are not measurable with a reasonable number of tests, we use anti-optimization to identify a design problem that maximizes the contrast in probability of failure between the two approaches. The anti-optimization is also performed with a genetic algorithm. For the problem identified by the anti-optimization, the probability of failure of the optimum probabilistic design is 25 times smaller than that of the deterministic design. The rates of failure are then measured by testing 29 realizations of each optimum design. The results agree well with the predictions and confirm the larger reliability of the probabilistic design. However, the probabilistic optimum is shown to be very sensitive to modelling errors. This sensitivity can be reduced by including the modelling errors as additional uncertainties in the probabilistic formulation. / Ph. D.

Two prominent continuum mechanics based incremental nonlinear finite element formulations are reviewed. An introduction to different material response measures suitable for nonlinear analysis, in addition to an overview of the Total and Updated Lagrangian reference frames, serve as the starting point for this review. The two nonlinear formulations are specialized for use with a geometrically nonlinear plane truss finite element. The truss formulations are then implemented into separate geometrically nonlinear finite element codes. Numerical comparisons of five test structures are carried out using ABAQUS and both programs. ABAQUS serves as the bench-mark by which the solution accuracy of the two programs is judged. / Master of Science / incomplete_metadata

The neutral point of a truss-column joint can be determined very easily, using the thrust stiffnesses. Once the neutral point is determined the moment and thrust distribution about the neutral point may be performed quite rapidly, since the thrusts and moments converge more rapidly about the neutral point than about the joint. The actual process of distribution of moments and thrusts follows the pattern outlined by Professor D.H. Pletta in his <u>Notes on Statically Indeterminate Structures</u>⁷. / Master of Science

Metal plate splice joints with gaps between butting pieces of lumber were tested in compression to evaluate the effect of gap size on joint serviceability performance. The current design methodology for compression splice joints was also evaluated. Specimens representing floor and roof trusses, with 16 and 20 gauge plates of staggered and aligned tooth configurations were tested for each of two gap sizes. Generally, 20 gauge plates and 16 gauge plates with 1/8” gaps buckled under compression loads while 16 gauge plates with 1/16" maximum gap did not buckle before the gap closed; rather, the gap closed primarily due to slippage between the teeth and the wood. 16 gauge plates generally outperformed 20 gauge plates based on serviceability performance of the test compression splice joints. Furthermore, gap size had less of an influence on joints with 16 gauge plates than on joints with 20 gauge plates. The current practice of sizing plates for compression splices to withstand one-half of the calculated chord force could not be physically confirmed using the study joint serviceability criteria. The test results indicate that basing allowable plate ratings on a per area basis derived from tension tests is misleading. / Master of Science

This study presents analytical and experimental procedures and design tools for the control of flexible structure vibrations using a cantilevered adaptive truss. A specific six-actuator, octahedral-octahedral truss effects the control of different flexible structures. These structures could represent space structures or robotic manipulators or a variety of other flexible structures where unwanted structural vibration could reduce the performance of the system. Three of these structures; a slender beam, a single curved beam, and two curved beams are controlled both in simulation and with an experimental test article. The test article, comprised of the flexible structure, the adaptive truss, and the actuators shows excellent agreement between simulated and experimental responses to initial conditions in both open-loop and (LQR) closed-loop control. As a example of the ability of the truss to control the slender beam, a first mode simulated frequency of 3.11Hz (3.09Hz experimental) and damping ratio of 0.0044 (0.0044) are controlled to produce a 3.20Hz (3.14Hz) frequency and a damping ratio of 0.2876 (0.2746). This 6000% increase in damping without a significant change in the modal frequency shows the potential of the adaptive truss in vibration control. The agreement between simulated and experimental data shows the validity of the modeling and experimental procedures. From the information gained, conclusions are drawn about the uses of an adaptive truss in the control of flexible structure vibrations. / Ph. D.