Variable Geometry Trusses (VGT’s) can be used as the fundamental building blocks in constructing long-chain, high degree-of-freedom manipulators. This thesis focuses on the kinematics of two such manipulators. It also illustrates how the concept of shape control can be applied to simplify the computational aspects of controlling these devices. To serve as examples, algorithms are developed for the control of both a thirty degree of freedom planar manipulator and a sixty degree-of-freedom spatial manipulator. Based on a review of the literature, this work appears to be the first attempt to develop real-time, position control strategies for such highly-dexterous manipulators. / Master of Science / incomplete_metadata

The purpose of this thesis is to develop a formal methodology for determining the loads occurring in the members of an adaptive truss due to both gravity and acceleration. This force analysis can be used as the basis for a design code which will provide truss member dimensions and actuator characteristics. Three different truss structures are considered. The first is a planar, triangular truss consisting of one actuated member and two fixed length members. The second structure is a spatial, double-octahedral truss with three active members and eighteen fixed length members. The third structure is a truss consisting of several double-octahedral bays connected together as a chain. For each structure, the active link motion is first simulated and the position, velocity, and acceleration history of each of the member connecting points is calculated. The dynamic equations of motion for each member are developed and combined to form a system of equations describing the motion of the entire truss. These equations are then solved to find the forces occurring at each node. Once the forces are determined, the internal forces in each member can be found, and the resulting stresses are calculated. The members are also checked for buckling using Euler buckling theory. The stress calculations are checked against experimental values and show good agreement for both static only and static and dynamic loading. / Master of Science

The modified Riks/Wempner method was examined for elastic, geometrically nonlinear space trusses. A computer program, RWCNR, was developed using the Riks/Wempner algorithm. The study includes an examination of three trusses, of which two exhibit bifurcation. A method of branching onto secondary equilibrium paths was studied, and the computer program incorporates this concept. This method of branching was found to work well provided the intersection of the fundamental and secondary equilibrium paths is good. The computer program was found to be very useful and reliable. It successfully traced fundamental equilibrium paths, located critical points (load levels), and branched onto secondary equilibrium paths. The modified Riks/Wempner method was found to be a very reliable method of obtaining equilibrium paths up to, and beyond, limit points, and it could branch onto secondary equilibrium paths. / Master of Science

A procedure for analyzing a two and three dimensional truss-rigid-frame with elope deflection method is investigated in this thesis. In the first few chapters of this thesis the elope deflection equations for solving the trussed-rigid-frame problem were derived. The point of great importance in deriving slope deflection equations is that the imaginary plates or bars are added at separated domains or parts. Because of the existence of imaginary plates or bars the whole trussed-rigid-frame can be regarded as the rigid beam frame. The equations for determining the coefficients for the equivalent slope deflection equations of the separate domains can be formulated by applying the Castigliano’s theorems. The reactions and the stresses in every member of the trusses can be calculated after the reactions at the “joints” have been determined. In the last few chapters an illustrative example is given. Its solutions are checked with the solutions obtained by applying Castigliano's theorem to the whole frame. This proves that it is possible to analyze the trussed-rigid-frame by using the procedure mentioned in this thesis. The advantage in using this method is that the whole structure may be separated into domains when the number of members increases to such an extent that the capacity of a computer is exceeded. / Master of Science

Before the method of moment and thrust distribution can be applied to trussed bents, certain constants must be determined. These constants can be obtained without too much difficulty as has been shown. Once these bent constants are known, the moment and thrust distribution may then be performed about an equivalent joint. For Fink type trussed bents the location of this equivalent joint is dependent upon either of two assumptions which make use of the Spagnuolo column and the Maugh equivalent column. The actual process of the distribution of the thrusts and moments follows the pattern developed by Professor Cross. Care must be taken however in carrying out the procedure to be certain of including all the effects that accompany the balancing process. / Master of Science

The purpose of this study is to investigate the static and dynamic stability of an elastic truss model. The truss model· is subjected, separately, to static loads, dynamic step loads, and dynamic impulse loads. For each loading, the results are presented in the form of stability boundaries and displacement criteria. For the static loading, the stable equilibrium displacement fields are determined by minimizing the energy of the model. The type of failure, limit or bifurcation, and the critical load magnitudes, are determined based on plots of load-frequency curves. For the dynamic loadings, the magnitudes of the critical load are based on the criterion presented by Budiansky and Roth. The stability boundaries for the static loading and the dynamic step loading are compared. It is found that the static critical load values are three to seven times the magnitude of the dynamic step critical loads. It is found that the truss model shows a local and global failure for a certain class of loading. The magnitudes of the critical loads for local instability are significantly less than the magnitudes of the critical loads for global instability when the loading is symmetric or near symmetric. It is found that the critical load magnitudes for a symmetric loading are much larger than for an asymmetric loading. Constant displacement curves (based on displacement constraints for the truss model) are also presented. These results are helpful in indicating loading configurations to which the response of the truss model is sensitive. / M.S.

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

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.

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).

Stability analysis of truss chords loaded by a combination of axial and lateral forces is studied. A simple model based on beam-column theory is proposed and analyzed. The continuous truss chord is replaced by a beam column loaded by end moments replacing the effect of adjacent members. The solution yields deflections and moments allowing one to compute the stress at any point of the truss chord. Analytical and numerical solutions are applied to an example of a wood truss with a continuous top chord. The numerical solution for the deformations converges rapidly. Non-converging results indicate instability. A new design procedure for wood truss chords subjected to possible buckling is proposed. The procedure is based on the analysis of a beam-column model and a mechanics of materials approach. / Graduation date: 1994